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CAST IRON HANDBOOK Compiled by : IIF JAMSHEDPUR CHAPTER Edited by : Mr. Gautam Banerjee
The Institute of Indian Foundrymen IIF Center, 335 Rajdanga Main Road, Kolkata - 700 107 Ph.: 033 2442 4489 / 6825 / 7385, 4063 0074, Fax : 033 2442 4491 E-mail : [email protected] 1
Contents Chapter
Page
1.
Family of Cast Iron : An Overview
7
2.
The Iron-Carbon-Silicon System
8
3.
Alloying Elements in Cast Irons
12
4.
Special Cast Irons
26
5.
Effect of Trace Elements in Grey, Malleable & Ductile Iron
37
6.
Molten Metal Processing : Techniques & Control
42
7.
Heat Treatment of Iron Castings
49
8.
Reclamation of Iron Castings
54
9.
Scrap Diagnosis Chart for Some Coomon Defects in Iron Castings, Their Causes and Remedies
61
10. National and International Standards
69
11. Important Tables and Figures
85
12. Glossary of Terms
112
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Forward This handbook, is shape and content, is intended to be a ready reference for practising foundryment. The focus is on metallurgical aspects. In view of the bewildering wealth of information available on metallurgy of cast iron, it lays no claim to be encyclopaedic. The topics compiled herein are based not only in literature survey but our experience too.
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CHAPTER - 1 FAMILY OF CAST IRON : AN OVERVIEW Metallurgically cast iron is an alloy of iron, carbon, and silicon containing manganese, sulphur and phosphorus as impurities, small in quantity but having appreciable influence on properties.
Classification : (Ref. Table -1.1) There are five grades of unalloyed cast iron and their typical compositions are given Table-I, the sixth grade of cast iron consists of alloyed cast iron and they have a wide range in base composition and also contain major quantities of alloying elements.
Table-1.1 Typical Compositions of Unalloyed Cast Irons Type of Iron Unalloyed white Malleable Grey Ductile Compacted Graphite
Percent%
Carbon
Silicon
Manganese
Sulphur
Phosphorous
1.80-3.60
0.50-1.90
0.25-0.80
0.060-0.20
0.060-0.20
2.20-2.90 2.50-4.00 3.00-4.00 2.50-4.00
0.90-1.90 1.00-3.00 1.80-2.80 1.00-3.00
0.15-0.20 0.20-1.00 0.10-1.00 0.20-1.00
0.020-0.20 0.020-0.25 0.010-0.030 0.010-0.030
0.020-0.20 0.020-1.00 0.010-1.00 0.010-1.00
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CHAPTER - 2 THE IRON-CARBON-SILICON SYSTEM Cast irons, with their higher carbon and silicon contents compared to steels (Fe-C-Alloys) are considered as ternary Fe-C-Si alloys. A comparison of the Fe-Fe3C-Si ternary equilibrium diagram sectioned at 2% (Fig-2.1) and Fe-Fe3C binary diagram (Fig-2.2) indicates the following effects of silicon :
i) The eutectoid and eutectic compositions, and the maximum solubility of carbon in austenite are significantly altered. Thus the carbon content of pearlite in cast irons is less than that in steels.
ii) The eutectioid and eutectic reactions occur over a range of temperatures and at a higher temperature than in the Fe-C alloys.
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The temperature range over which these transformations occur is a function of the silicon content and increases with the silicon content. The metallurgy of cast iron (Fe-C alloys) in fact is usually confined to iron-ironcarbide metastable system, the former can occur either in the metastable system or the stable iron-graphite system, or in both. Effect of common elements present in cast iron and their influence on the microstructure, cell size, rate of growth, atomic bond etc. are shown in Tables 2.1 & 2.3
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CHAPTER - 3 ALLOYING ELEMENTS IN CAST IRONS This Chapter covers low levels of alloy addtions in grey and nodular irons. Purpose : 1.
In irons for ambient temperature service : improvement in tensile strength, hardness or wear resistance.
2.
In irons for elevated temperature service : Improvement in creep resistance, oxidation performance, microstructural stability and thermal fatigue.
Table - 3.1 Effects of Alloying Elements On Grey Iron Approximate Structure
Allioying elements
V
Cr
Mo
Cu
Ni
Chill
2
1
0.30
-0.40
-0.30
Cell
+
+
+
Ferrite Hardening
1.80
1.10
1.70
1.15
0.90
1.2
Pearlitisation
1
2
-1
1
0.2
12
Hardenability
3
3
19
8
19
12
Sn
Optimum Level of Alloy Additions : 1. Tin
- around 0.1%
-
Suppresses free fertite and a minimum harness of 190-200 Brinell is maintained.
2. Copper
- about 10%
-
Similar effects as (1) plus increase in tensile strength.
3. Chromium -
-
Being highly chill inducing, additions are to be carefully controled.
-
Increases hardenss and tensile strength, supresses ferrite, stabilizes pearlite at elevated temperatues to a certain degree.
4. Molybdenum -
Upto 0.50% most effective for increasing tensile strength.
5. Vanadium - upto 0.20%
Increases tensile strength.
upto 0.40%
-
CAUTION : CHILL INDUCING PROPENSITY HIGH. 6. Nickel
-
Similar to copper.
Table - 3.2 Effects of alloy Addition on the Increase of Tensile Strength of Pearlitic Grey Iron Element % Addition
Increase UTS (N/mn2)
Copper
1
25-30
Nickel
1
15-25
Chromium
0.40
30-50
Molybdenum
0.25
25-30
Vanadium
0.20
25-35
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Alloy Combination : Logic 1.
A synergy may exist in which the combined effect is much greater than that of the individual elements resulting in a smaller and less expensive total addition.
2.
One element may be added to counteract the detrimental effects of another such as the use of a graphitizing element to compensate for the chill promoting influence of a carbide former.
(a)
Examples : 0.20 to 0.50% Cr - Hardness achieved 240 HB. + Tensile strength increased 0.25 to 0.60% Mo by over 80N/mm2.
(b)
1.0 to 1.50% Cu - Copper serves to counter act the chill formation + tendency of chromium whilst maintaining a Cr or Cr + Mo high hardness and tensile strength.
Table - 3.3 Desirable Elevated Temperature Properties & Alloys Properties
Alloys
Creep Resistance
Mo
Pearlite Stability
Cr, Sn, Mo, Cu.
Oxidation Resistance
Cr
Thermal Fatigue Resistance
High C, Mo, V
Nodular Irons :
Alloying Nodular Irons for Ambient Temperature Service : normally copper, rickel, molybedenum and tin are the only alloy elements used. 14
Table - 3.5 Ferritic Elevated Temperature Nodular Irons
Type
Alloys
Oxidation Resistance
4-6% Si, < 6% Al
Structural Stability
3-6% Si, < 6% Al
Strength
0.40-2% Mo
Thermal Fatigue Resistance
0.4% Mo
Alloying Nodular Irons for Elevated Temperature Service : For the structural stability in long term elevated temperature service the matrix structure should be ferritic and as such the field of alloying elements is restricted to silicon, molybdenum, aluminium and nickel only. Aluminium, due to its pinhole and inclusion characteristics and nickel due to its cost are not very popular.
15
Influence of Alloying Elements on Various Factors The effect of various elements, especially, in presence of one another, on structure and properties of cast iron is quite complex. However, some approximate predictions can be made and one can come across various formulae : (1) tu (oC) = 738 + 18 Si 1.75
........... (1)
t1 (oC) = 738 + 5 Si 2
........... (2)
Where, tu and t1 = upper and lower limits of eutectoid transformation temperature. Liquidus temperature tL = 1670 - 124 (C-P/2+Si/4)
........... (3)
Eutectic temperatures tc = 1152 + 7.5 Si - 30 P - 2 Cr (oC)
........... (4)
tc’ = 1145 - 10Si - 30 P + 30 Cr (oC)
........... (5)
Solidification interval ∆t = 518 - 124 (C + 0.3 Si + 0.26 P)
........... (6)
∆t = 525 - 124 (C + 0.17 Si + 0.26 P) ........... (7) Eutectoid temperatures tu= 738 + 35 Si + 200 P + 8 Cr - 20 Ni - 35 (Mn - 1.75) - 10 Cu
........... (8)
t1= 723 + 25 Si + 200 P + 8 Cr - 30 Ni - 35 (Mn - 1.75) - 10 Cu
........... (8)
Carbon content in the eutectic Cc = 4.26 - 0.3 (Si + P) - 0.4S + 0.03 (%) Mn - 0.07 Ni - 0.05 Cr
........... (10)
Cc = 4.3 - 0.3 (Si + P) - 0.4S + 0.03 (%) Mn - 0.07 Ni - 0.05 Cr
........... (11)
16
Carbon content in the eutectoid Cs = 0.68 - 0.15 Si - 0.05 (Ni+Cr+Mn-1.7S) % ........... (12) Cs’ = 0.80 - 0.11 Si - 0.05 (Ni+Cr+Min-1.7S) ........... (13) Carbon content in saturated austenite CE = 2.01 - 0.15 Si-0.3P + 0.04 (Mn-1.7S) -0.09 Ni - 0.07 Cr.
........... (14)
CE = 2.03 - 0.11 Si-0.3P + 0.04 (Mn-1.7S) 0.09 Ni - 0.07 Cr.
........... (15)
Where tc’, ∆t’, ts’ etc. are the respective characteristics for the metastable system and, likewise, tc, ∆t, ts etc. signify the stable system. These formulae are based upon the normal general engineering grade compositions. Also, it needs to be clarified that the formulae assume equilibrium conditions and do not take into account the common production fluctuations like the actual superheating temperatures, cooling rates etc. which would also affect these relationships. To illustrate this, according to J. E. Rehder, ts= 722+37 Si+220 P-37 Mn-0.28v, where, V = cooling rate in 0C/hr. Now, during heating, the temperature is higher by about 330 C and the lower limit is taken to be approximately 7000C. For more accurate calculations, it needs to be borne in mind that for each 1% increase, the influence of various elements on ts is as follows :
Si
-
+280C
P
-
+2200C
Mn -
- 1300C
Ni
- 250C
-
The eutectiod tranformation temperature range affects the structure and properties of cast irons, significantly. The generally accepted values of the eutectoid transformation ranges in the case of different cast irons during heating are given below (0C) :
17
Grey iron Malleable iron S. G. iron
- - -
750 - 730 - 750 -
850 790 850
During cooling these temperatures are lower by 35-50oC
Carbon Equivalent Carbon equivalent of cast iron is another important indicator of its founding and mechanical properties. It its simplest form it is expressed thus : C. E. = C + 0.3 (Si + P)
........... (1)
For liquidus arrest the formula used is; C.E. = C + Si/ 4 + P/2
........... (2)
It is interesting to note that the latter formula is also valid for estimation of the fuidity of the metal. The C.E. value (1) is used to calculate the Degree of Normality which is given by
(C —CE) D. N. = (Cc —CE)
........... (3)
Where, C = Carbon content of the cast ion CE = Carbon content of saturated austenite Cc = Carbon content of the eutectic It can also be expressed as :
C - 2.01 + 0.15 Si D. N. = ........... (4) 4.26 - 0.3 Si - 2.01 + 0.15 Si
Simplifying,
C + 0.15 Si - 2.01 D. N. = 2.25 - 0.15 Si
........... (5)
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For quick, practical assessment one can use the following equation Actual carbon content D. N. = Eutectic carbon content
C = 4.26 - 0.3 (Si + p)
........... (6)
For more accurate estimation of the carbon equivalent the following relationship can be used in the case of irons of normal compositions : C. E. =
C+0.3 (Si+P) - 0.03 Mn + 0.4S +0.07 Ni + 0.05 Cr + 0.074 Cu + 0.25 Al
However at higher levels of concentration the coefficients would be higher.
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Table - 3.7 Relative Effect of Elements on Properties of C.I. Element Cr Mo W V Ti Ni Cu Sn
Max. content, %
Increase in % transverse strength
0.5-1.0 0.75-1.0 2.0-3.0 0.3-0.5 0.10-0.15 1.5-2.5 2.0-3.0 0.05-0.12
4-6 12-15 20-30 6-7 2-5 3-7 4-8 3-5
= = =
1:3 to 3:1 4:1 or 3:1, rarely 2:1 1:1
Recommended Ratios : Cr:Ni Ni:Mo Cr:V or Cr:Mo
Table - 3.8 Classification of Elements in Cast Iron Group Elements
Effect on as-Cast structure of metallic matrix
Effect on I and II stage grtaphitization
1. a. Cr, Mo, V, Mg, Te, B, O, N, H
Stabilize pearlite and cementite. Increase chilling tendency.
Inhibit graphitization
b.
Mn, 1.0% above the qtty. reqd. to balance S.
c.
At relatively high concentration Ti, Zr 20
Group Elements
Effect on as-Cast structure of metallic matrix
Effect on I and II stage grtaphitization
2. Si, C, Al
Graphitize and ferri- tize
Promote both stages.
3. Ni, Cu Graphitize and stabi- lize pearlite
Promote I stage but inhibit II stage graphitization
4. Ti, Zr
In small quantities, graphitize & inoculate
Promote I stage
5.
Pearlitizes
Inhibits II stage
Mn. upto 1.0% over that reqd. to balance S, Sn
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Table - 3.10 Effect of Alloying Elements Element
% in Pearl Chill Iron
Cr 0.15-1 V 0.15-0.5 Mn 0.3-1.25 Mo 0.3-1.0 Cu 0.5-2.0 C Si Al Ni 0.1-3.0 Ti 0.05-0.1 Zr 0.1-0.3
Graphite Refinement
++ ++ + + - — — — – – –
Refines ++ + +++ 0 (approx) Coarsens -do-doRefines +++ Ref. 0 (approx)
Cc pearlite
Matrix
++
Refines pearl & hardens
++
-do-
++
-do-
+
Refines & strengthens
-
Hardness
—
Ferritizes & softnes
—
-do-
—
-do-
- & Stabilizes at eutectoid
Refines pearlite and hardens
–
Ferrities & softens
-do-
23
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Table - 3.13 Effect of Some Elements on Properties of Cast Iron C
1% C increases solidification shrinkage by 0.25% 1% graphite decreases shrinkage by 0.24%
Mn 1% increase in Mn. increases the BHN by 15. P
1% increase in P increases the BHN by 10
Cu 1% increase in Cu increases the T.S. by 10-15%. Iron containing Cu and with 350 BHN has the same machinability as ordinary cast iron with 240 BHN. Ni 1% Ni increases the T.S. by 10% Cr 1% Cr increases BHN by 80-100 and T.S. by 20% Mo 1% Mo increases T.S. by 40% (P must be 0.12) Al 1/3 to 1/2 as strong as Si w.r.t. graphitization
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CHAPTER - 4 SPECIAL CAST IRONS The special cast irons described in this chapter are high alloy irons and austempered ductile irons. High Alloy Irons : High alloy irons, in view of their chemistry, are those in which the alloy contents is more than three percent. In this group of irons are included high alloy grey, white and ductile irons. Malleable irons are not heavily alloyed because alloying interferes with the mallablizing process. The high alloy irons are classified below under three kinds of service conditions : 1.
Corrosive Service :
a) b)
2.
Elevated Temerature Service :
a) b) c) d)
3.
Abrasive Condition :
a) b) c)
1.
Corrosive Service :
a)
Nickel alloyed irons (Ni-resist) High silicon irons.
Nickel alloyed irons (Ni-resist) High silicon irons Aluminium alloyed iron High chromium white iron
Nicel-chromium white irons (Ni-hard) High chromium white irons Moly-chromium white irons
Nickel Alloyed Irons : These irons derive their excellent resistance to corrosion from the presence of nickel in the range of 13.5 to 36%, to chromium in the
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range of 1.8 to 6%, and in some, to copper contents in the range of 5.5 to 7.5 (see table 4.1 & 4.2).
b)
2.
High Silicon Irons : These irons owe their corrosion resistance to the presence of silicon in the range of 14.2 to 14.75% (see table 4.3). The high silicon irons have poor machinability due to their high hardness.
Elevated Temperature Service :
These irons must satisfy three major conditions :
•
should resist deformation and fracture at service load at the highest temperature to which they will be subjected during application.
•
should resist oxidation by the ambient atmosphere in the temperature range of application.
•
should be structurally stable in the temperature range of application.
3.
Typical compositions, mechanical properties and applications of the four kinds of high alloy irons for elevated temperature are given in Table 4.4.
Abrasive Condition :
The predominant carbides in the microstructure of high alloy white cast irons makes them specially suitable for abrasion resistant applications. The matrix structure is developed by adjusting the alloy content and/ or heat treatment to have the necessary balance between abrasion resistance and repeated impact loading.
The compositions, mechanical requirements and applications of these irons are detailed in Table 4.5 and Table 4.6.
A type D white iron made to Ni-hard 4 specification confirms to the following specification :
C - 2.8 to 3.2% Si - 1.5 to 2.0% Mn - 0.4 to 0.7% Cr - 7.5 to 9.0% Ni - 5.5 to 6.5% For maximum wear resistance type D iron is usually heat treated as given below :
27
Castings are heated to 7500C and held at that temperature for 8 hours followed by air cooling. Complex shaped castings with varying cross section are heated to 5500C for 4 hours and air cooled to room temperature. This is foollowed by holding for 16 hours at 4500C and air cooling. The heat treated castings have a tensile strength in the range of 520 to 550 MPa (75,000 to 80,000 psi) and hardness of 600 to 800 BHN. All Ni-hard castings are stress relived at 200 to 2300C for 4 hours before placing it in service.
Austempered Ductile Iron :
Austempered ductile irons are alloyed nodular irons with an excellent combination of strength and ductility.
Alloy combinations :
1. 2.
0.3% Mo + 1.5% Ni or 0.5% Mo + 1.4% Cu
Austempering Treatment : See figs 4.1 & 4.2
28
Mechanical Properties :
Y.S N/mm2
U.T.S. N/mm2
%E
BHN
750-1250
900-1500
2-8
285/360
Advantages over forged steel :
a.
b. c. d. e. f. g. h.
Application :
Gears and other dynamically loaded castings.
Excellent machinability, longer tool life and increased machining speeds. Higher quality finish on machined surfaces. Excellent resistance to scoring and wear. Higher damping capacity and therefore quiter operation. Shorter heat treatment cycle. Less machining required. A 10% savings in weight. A lower energy requirement from molten to finished component.
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35
36
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CHAPTER - 6 MOLTEN METAL PROCESSING : TECHNIQUES & CONTROL Consistency of machinability, structure, soundness and mechanical properties of castings are all affected by metal composition and melting and treatment techniques. This chapter discusses the important aspects of metal control and treatment techniques required to minimize metallurgical variations so that consistently high quality castings can be produced. The production of casting of high metallurgical quality and consistency requires the control of three fundamental components
- - -
metal composition-main and trace elements, the degree of nucleation, and the pouring temperature.
These three components of melt quality are affected by many individual factors which also require close and careful control. Fig. 6.1 indicates the important aspects of molten-metal production and treatment processes and the necessary features of control. Metal composition
-
Basemetal, alloying elements trace elements.
Raw Material control
-
Specification, quality verification, storage.
Charge make up
-
Specify charge balance, weighing facilities.
Furnace Control
-
Type of furnace and its controls.
Melting & Holding
-
Desulphurize, carburize, temperature control chill test chemical analysis.
S. G. Iron
Grey Iron
Inoculation, pouring temperature Nodulzarizing Pour treatment Temperature control, nodularizing agent addition, treatment check (Metallographically and/or ultrasonically) Fig. 6.1 Factors in the control of metal production. 42
Efects of Metal Composition on Quality : The final composition, both the main elements and those present at trace levels, need to be adequately controlled, since the level of individual elements and the interrelation between certain elements can have important effects on both material properties and quality of castings. The main effects of the various alloying elements are given in Chapter 3. Control of the five basic elements-carbon, silicon, manganese, sulphur and phosphorus; can be achieved easily by the judicious use of raw materials of known composition, by the understanding and control of the possible variations that can arise during the melting and treatment processes, and by reaction to the results of rapid analysis and shop floor testing. Raw Material Control Acquisition of raw material and its control should involve the preparation of specifications, selection of suppliers, testing of the material on delivery, storage of materials in marked locations and maintenance of regular and detailed records. Raw material control is a basic element affecting the final casting quality. Table 6.1 gives the common raw materials and their effect on quality due to lack of control. Charge make-up A basic requirement in metal production and its quality control is the charge calculation and any changes should be carried out only after proper calculations taking into account the raw material composition and expected recoveries from the various furnace additions. For consistent quality in production reliable weighing facilities must be available for the main charge materials and additives. Effect of furnace type The effects of the use of cupola or electric melting are given in Table 6.2 Post melting treatment Carburization, desulphurization and inoculation are a few of the useful molten metal treatment processes in use which have a profound effect on quality. 43
Desulphurization a)
In grey iron sulphur levels less than 0.1 percent reduce the dross forming tendency and leads to the reduction in subsurface blowholes.
b)
In the production of SG iron, sulphur levels less than .024% prior to magnesium treatment reduces costs and minimizes dross related problems.
c)
It can be done in ladles and agitation can be carried out by mechanical stirring or gas injection through a porous plug.
d)
Maximum efficiency of desulphurization is maintained at higher temperatures (1500-15000C).
e)
The pressure and time of gas flow should be essentially controlled.
Table 6.1 Effect of Raw Material Quality on Castings. Raw Material
Effects
Steel Scrap
-
Contamination of the metal with lead, chromium and aluminium will lead to cracking in castings, chiling tendency and increased hardness and pinholing tendency.
Cast Iron
-
Contaminatin as above.
Scrap
-
Improper grade wise segregation may result in off specification metal.
Pig Iron
-
Variable composition and no chemical checking may result in shrinkage defects. off-specification and soft metal.
Ferro alloys Inoculants -
Large size may result in machinability problems, hard spots and tool breakage.
Raw Materials
-
Effects
Carburizers
-
Incorrect meterial due to lack of proper indentification mark can result in off specification metal w.r.t. composition and properties.
44
Poor quality material will result in increased nitrogen & aluminium content leading to fissure defects and pinholes.
Table 6.2 Effect of furnace type
Cupola Electric Melting
1. Inconsistent blast rate, resulting from fluctuating demands for liquid metal causes a significant variation in metal quality w.r.t. temperature, carbon pick up & silicon losses. 2. A high steel scrap charge results in losses of trace elements and hence, a less pure charge can be employed.
The loss of trace elements is significantly reduced and hence cleaner & purer charge material will have to be used.
3. Unless there is a wide variation in the base composition, the degree of nucleation remains constant.
The degree of nucleation can be significantly reduced due to increased super heating and holding time. Trimming additions on the other hand, increases nucleation.
4. It is important to have provision for metal mixing. 5. Rapid change in the grade of base iron is possible due to carburization. Carburization a)
High purity carburizers are essential when substantial carburization is carried out to keep the sulphur content at low elevels.
b)
Less pure carburizers such as coke is suited to grey iron production. High percentage additions lead to nitrogen pick up which causes nitrogen fissure defects. 45
c)
High carbon recovery is favoured at high temperature and bath agitation.
d)
Carburizer particles between 1-5mm. should be preferable used to ensure rapid carbon pick up.
e)
Carburizers should be stored in dry condition lest there is hydrogen pick up.
Alloy additions a)
Ferro alloys or pure metals can be added to a duplexing furnace or to a ladle to increase alloying elements in the metal.
b)
The composition of the additives and expected recovery should be taken into account before any additions.
c)
The weights of the metal to be treated and the alloy should be accurately known.
d)
Lumpy forms (pieces greater than 25mm) is to be in the primary melting unit and granular material (less than 6 mm) should be used for ladle additions.
e)
Undissolved particles in castings should be avoided by the control of metal temperature and agitation of the metal.
f)
Ladle additions should not exceed 2.0 percent.
Inoculation a)
To enhance the structure and properties of castings mostly ferrosilicon or graphite based inoculants are used in the production of grey and ductile cast iron. (see table 6.3)
b)
Pure ferrosilicon is not an effective inoculant and hence, silicon based inoculants should contain one or more minor elements like aluminium, cerium, barium etc.
c)
Graphite of cystalline form is an excellent inoculant.
d)
For ladle inculation, the inoculant should be sized in the range 3-8 mm. and for metal stream inoculation it should be less than 1.5 mm.
e)
They should be stored in a dry area to prevent hydrogen pick up and should be easily identifiable.
f)
The inoculating effect is maximum immediately after the treatment and it 46
fades with time and hence, the inoculated metal should be poured as quickly as possible. Nodularization
By magnesium treatment, Mg is introduced through nodularizers like Ni Mg, Fe mg, Cu Mg, Fe Si Mg, pure Mg, Mag Coke. Table 6.3 Effect of Inoculation Type of Iron
Grey Iron
Metallurigical Effect
Effect on Quality
- Promotes type A graphite Improves hardness and tensile formation strength. - Increases eutectic cell count Uniform properties throughout the casting - Reduces formation chilled edges.
of Improves machinability and increases tool life
- Excessive inoculation is Increases propensity detrimental shrinkage and porosity Ductile Iron
to
- Increases nodularity and Improves machinability ferrite in as cast iron - Reduces carbide
Increases ductility
strength
and
- Excessive inoculation is Pinhole formation may take detrimental and may give place. high aluminium. Adversely affects mechanical properties.
47
Metal Handling and On-line Controls : Ladle practice a)
Lining material should be high quality refractory with fusion point in excess of 14500C.
b)
Ladle lining condition should be properly maintained and ladle spouts kept clean.
c)
Temperature losses should be minimized by the use of insulating covers.
d)
Ladle should always be preheated prior to use.
Temperature control a)
The pouring temperature is one of the most important control parameters for obtaining defect free castings. High temperature pouring can result in porosity, swollen castings, core distortion and metal penetration.
b)
Every casting has an optimum pouring temperture range. This should be determined and maintained.
Chill test This test is a reliable indicator of the chilling propensity of cast iron and is detailed in speficiation A 367 in the 1974 book of ASTM standards. The moulds are made in well baked resin or oil bonded core sand with an AFS fineness ranging from 70 to 100. Chill plates against which the specimen are cast is mostly made of cast iron with fairly fine finish. Thermal analysis It is used for the determination of total cabon, silicon contents and carbon equivalent values in cast irons. The accuracy depends on the precise phosphorus value used in calculating the carbon equivalent which is given by the relation.
CE1 = Tc% + Si% / 4 + P% / 2
Spectroscopic analysis Rapid analysis based on optical emission or X-ray fluorescence aids in accurate compositional control.
48
CHAPTER - 7 HEAT TREATMENT OF IRON CASTINGS This chapter outlines the heat treatment of grey iron, nodular iron as well as the malleablizing cycles for the diffrent grades of malleable iron. 1.
Grey Iron castings normally are used in as cast state. Stress relieving is done before machining in case of castings with very close machined dimensional tolerance, susceptible to distortion after machining.
Normalizing is resorted to only when the castings are soft or have chilled edges, or residual carbides in welded areas. Typical Cycle : 9200C - 30 mins. to 120 mins., depending on section size - air cool.
2.
Nodular iron may be heat treated for one of the following reasons :
a) to produce matrix structures necessary to give the speficied machnical properties for the different grades of nodular iron.
b) to graphitise carbides which may be present as a result of poor inoculation, incorrect composition or segregation in the HAZ of welds.
c) to improve the surface wear and/or friction characteristics.
d) to improve machinability
e) to effect stress relief.
Annealing Foundries which do not make as cast grades of ferritic nodular iron resort to annealing to ferritize the matrix. Typical cycle : 9200C-2 hours-furnace cool to 5000C then air cool. Normalising The major objective is to obtain uniform mechanical properties. Usually castings with high hardness and residual carbides are subjected to this treatment to improve machinability without compromising the mechanical properties. The following two heat treatment cycles are most popular :
49
a) Normalise - 9200C, 2 hours - Air cool Temper - 6800 to 7100C, 2 to 4 hours.
b) Step Normlize - 9200C, 2 hours furnace cool to 8000C - hold for 30 mints. - furnace cool to 5000C - hold for 30 mins.
Hardening & Tempering
The main objective of this treatment is for improved wear resistance.
Typical Cycle - 9200C, 2 hours -oil quench Temper - 6800 to 7100C - 2 to 4 hours.
Stress Relieving
Same as in grey iron
3.
Malleable iron -
See : Table 7.1 Figs. 7.1, 7.2, 7.3 Table 7.1 Malleable Iron : Chemical Composition
%
Pearlitic
Ferritic
C
2.30/2.40
2.30/2.40
Si
1.30/1.50
1.30/1.50
Mn
0.40 max.
0.35 max.
P
0.06 Max.
0.06
S 0.06 Max.
To balance Mn (% Mn=1.75 × %S + 0.15) if necessary through addition of iron sulphide.
For ferritic grades only
Al
0.01-.015
50
Ladle addition :
Bi B
.01/.015 .001/.0015
N.B. a) Bismuth addition : - Ensures, complete white structure. - High carbon equivalent iron can be produced. - Helps in reducing FSG/SSG. (Treatment temperature 0C - 1480/1500). b) Boron addition : - Reduces FSG/SSG by better nucleation.
51
52
53
CHAPTER - 8 RECLAMATION OF IRON CASTINGS General : Iron castings having foundry defects like surface blowholes, inclusions, cracks, misruns or castings damaged during machining for example, over-machined; can be successfully and economically reclaimed. The preconditions, however, are the defects, are accessible and not extensive compared to the size of the castings. The various methods for such reclamation of iron castings are : 1.
Fusion Welding
a) Metal Arc
b) Gas (Oxy - Acetylene)
2.
Low Heat Input Welding
3.
Brazing
4.
Soldering
5.
Cold Welding
1.
Fusion Welding :
Because of high carbon content cast irons are difficult to weld. Rapid solidification after welding may lead to the formation of hard and brittle carbides in the fusion zone and martensite and/or bainite in the heat affected zone of the base iron, making the iron crack prone and difficult to machine. However, these problems can be circumvented through the use of proper welding techniques and electrodes.
Weld preparation : -
Any contaminants such as slag, rust, paint, oxide, and and oil should be removed.
-
The castings skin must also be removed by grinding/machining.
-
The grooves and cavities should be shaped to allowe ease of access and manipulation of the welding torch or electrode (Fig 8.1)
-
Chipping, machining or grinding are the accepted methods for weld 54
preparation. Flame or arc gouging methods are not recommended as considerable hardening of the iron adjacent to the seared surface takes place due to the formation of undersirable martensitic/or bainitic structure. Even preheating does not help.
55
Table 8.1 Electrodes for the Welding of Cast Irons
Class of Electrode
1. Ferritic
Details
Low hydrogen carbon steel electrodes suitable for noncritical jobs.
Preheating temperture-3500C.
2. Nickel based
Most suitable for coping with the dilution in cast iron welding. The carbon in the weldmetal is present as free graphite, on cooling, this increases the volume of weldmetal thus reducing shrinkage stresses. The weld metal remains ductile and machinable.
2a) Pure Nickel Type
% Ni>92
Deposits the softest i.e. the easiest machinable weldmetal. Thin sections of grey iron can be welded. In high phosphorus/sulfur irons the deposits are crack-prone.
The tensile strength of the weldmetal maybe low or some nodular iron welding.
% Ni - 55, % Fe - 45
2b) Nickel Iron Type
Most versatile cast iron electrode. Less sensitive to solidification cracking, hence recommended for high phosphorus grades. Tensile strength of deposit being close to nodular iron quite suitable for nodular iron welding.
% Ni - 70, % Cu - 30
2c) Monel Type
Strength of deposit intermediate between nickel and nickel-iron type electrodes. The weldmetal is sensitive to iron pick up. This sometimes leads to cracks in the weldmetal along the fusion line. As a result, the use of this type is decreasing. 56
Table 8.2 Typical Chemistry and Mechanical Properties of Nickel-based Electrodes Main Composition % Classification U.T.S.
H.V. (N/mn2)
Pure Nickel C-1.0, Ni 93
AWS ENi Cl DIN B573 ENi G2
390
170
Nickel Iron C-0.7, Ni 57 Fe: Balance
AWS ENi FeCl DIN B573 ENiF eG2
550
190
Nickel C-1.0, Ni.63 Copper Type Cu Balance
AWS ENi CuB* DIN B573 ENi Cu G2
450
180
*Nearest Preheating Preheating reduces the temperature differential throughout the casting and reduces the rate of cooling after welding. The overall effect being reduction in the tendency of carbide precipitation in the fusion zone, martensite in the heat affected zone and residual stresses in the casting. Preheating the entire casting : in a furnace Localised preheating : low intensity gas burners (oxy-acetylene torch), resistance heaters. Type of Iron
Preheat Temp 0 C
a)
Grey Iron
325
b)
Pearlitic Malleable Iron
-do-
c)
Pearlitic Nodular Iron
-do-
d)
Ferritic Malleable Iron
-do-
e)
Ferritic Nodular Iron
-do57
Post Heating Stress relieving : heating to 6000C followed by uniform cooling. Note : In case residual carbides be present in amounts and locations detrimental to machinability or mechanical properties the welded castings should be normalized. a)
Arc Welding-Electrodes :
See Tables 8.1 & 8.2 b)
Gas Welding :
Applications In the reclamation of defective castings (both large and small) specifically when the weldzone is required to have mechanical properties and corrosion resistance matching as closely as possible to those of the component. Filler Rods : Diameter of the filler rod : d = s/2 +1 Where d = diameter of filler rod in mm. s = thickness of parent metal in mm. Chemical composition 1.
For Welding grey iron High silicon iron (%Si around 3.50)
2.
For Welding nodular iron Normal magnesium treated nodular iron.
Fluxes : 1.
Calcined borax.
2.
A mixture of 50% borax, 47% sodium bicarbonate and 3% silica.
2.
Low Heat Input Welding :
This process combines the advantages of the low heat input of brazing, with strength and homogeneous joints obtained by fusion welding of the parent metal. The base metal is not brought to fusion temperature; thereby; eliminating formation of carbide structure. The bond is obtained through surface alloying whereby a 58
nonfusion filler rod tins the base metal and also interalloys by diffusion in a nrarrow zone at the filler alloy base metal interface. In case of arc welding low heat input is realised by a shorter arc, shorter welding time and lower intensity of current. No preheating of the job is required. The hot weld joint is quenched by water to avoid slow cooling through 7100C which leads to cracking. Chemical Composition of Electrodes :
Preliminary layer - High silicon cast iron electrode (% Si around 3.20)
Final layer - 99.7% nickel electrode.
Amperage Required : For 10 SWG electrode 65 to 70 Amps compared to 120 Amps for conventional electrodes. 3.
Brazing :
Finds very limited application in salvaging of iron castings. The process is carried out above 4250C but below the melting point of iron, therefore, a carbide structure cannot be formed. Alloys & Fluxes for Brazing :
Universally used brazing alloys : Silver based.
Alloys : 35 to 90% silver, alloyed with copper and zinc. Other alloying elements added -cadmium, nickel, manganese, tin, lithium. Fluxes :
Type
Flouride
Form Powder Liquid Paste (most polular)
59
4.
Soldering :
This process too has limited application in this field. Soldering is carried out at temperatures below 4250C.
Typical Composition :
5.
Solder
% Sn 35
% Pb 30
Flux
% Zn 35 Zn cl2
Cold Welding :
The name itself is suggestive of the metallurgical advantags of the process. However, to date it finds restricted applications : a)
Minor cosmetic repairs :
Material :
2 part system -
* *
Metallic filler in powder or paste form. Polymer based cold setting hardner.
Method : A mix of filler plus hardener of right consistency is prepared. Then the defect is filled up with this paste by pressing and smearing. Dressed after drying. Defects on machined surfaces can also be rectified by this method. Final finishing is done by either grinding or machining. b)
Sealing of microporosity :
Material :
One or two component liquid cold curing polymeric system.
Method : Brushed on the affected area of the casting, the one component system as such, the two component system sequentially. After application cold cured for 24 to 48 hours.
60
61
62
63
64
65
66
67
68
CHAPTER - 10 NATIONAL AND INTERNATIONAL STANDARDS Grey Cast Iron :
INDIA IS : 210 - 1978
Grade
Tensile Strength MPa (N/mm2) min.
B.H.N
FG 150
150
130-180
FG 200
200
160-220
FG 220
220
180-220
FG 260
260
180-220
FG 300
300
180-230
FG 350
350
207-241
FG 400
400
207-270
On 30 mm f test bar. INTERNATIONAL ORGANIZATION FOR STANDARDIZATION ISO R185 1961 Grade
Dia. of as-Cast test bar
mm
Tensile Strength Rm’ min
kgf/ mm2
tonf/ in2
lbf/ in2
10
30-32
10
6.3
14 200
15
30-32
15
9.3
21 300
20
30-32
20
12.7
28 400
25
30-32
25
15.9
35 600
30
30-32
30
19.0
42 700
35
30-32
35
22.2
49 800
40
30-32
40
25.5
56 900
69
UNITED KINGDOM BS 1450 : 1977 Grade
Dia. of as-Cast test bar
Tensile Strength Rm’ min
mm
N/mm2
150
30-32
150
180
30-32
180
220
30-32
220
260
30-32
260
300
30-32
300
350
30-32
350
400
30-32
400
WEST GERMANY DIN 1691 : 1964 Grade
Dia. of as-Cast test bar
Tensile Strength Rm’ min
mm
Kp/mm2
GG10
30
10
GG15
13
23
20
18
30
15
45
11
GG20
13
28
20
23
30
20
45
16
70
Grade
Dia. of as-Cast test bar
Tensile Strength Rm’ min
mm
Kp/mm2
GG25
13
33
20
28
30
25
45
21
GG 30
20
33
30
30
45
26
GG35
20
38
30
35
45
31
GG40
30
40
45
36
GG12*
30
12
GG14
30
14
GG22
30
22
GG26
30
26
*The grades shown in italics are from DIN 1691 : 1949, now superseded by DIN 1691:1964. They are given in DIN 1691:1964 and are still accepted until further notice.
71
USA ANSI / ASTM A 48-76 Nominal section Grade thickness
Nominal dia. of as-cast test-bar
mm mm 20A
6-12
22.4
B
13-25
30.5
C
26-50
50.8
S
50
Tensile Strength Rm’ min
MPa N/mm2
ksi*
138
20
172
25
207
30
241
35
276
40
Bar S
25A
6-12
22.4
B
13-25
30.5
C
26-50
50.8
S
50
Bar S
30A
6-12
22.4
B
13-25
30.5
C
26-50
50.8
S
50
Bar S
35A
6-12
22.4
B
13-25
30.5
C
26-50
50.8
S
50
Bar S
40A
6-12
22.4
B
13-25
30.5
C
26-50
50.8
S
50
Bar S
72
Nominal section Grade thickness
Nominal dia. of as-cast test-bar
mm mm 45A
6-12
22.4
B
13-25
30.5
C
26-50
50.8
S
50 6-12
22.4
B
13-25
30.5
C
26-50
50.8
S
50 6-12
22.4
B
13-25
30.5
C
26-50
50.8
S
50 6-12
22.4
B
13-25
30.5
C
26-50
50.8
S
50
1 kilo pound = 1000 pound
310
45
345
50
379
55
414
60
Bar S
60A
ksi*
Bar S
55A
Ksi - kilo pounds per square inch;
MPa N/mm2
Bar S
50A
*
Tensile Strength Rm’ min
Bar S
all dimensions of test bar S shall be agreed upon between the manufacturer and the purchaser.
73
74
75
76
77
USA ANSI/ASTM A159-77 SAE J431c (1975) (Automotive grey iron castings) Grade
Hardness, HB
G1800
187-max
G2500
170-229
G3000
187-241
G3500
207-255
G4000
217-269
G2500a
170-229
G3500b
207-255
G3500c
207-255
These irons are specified on hardness and microstructure.
78
79
80
81
82
83
USA SAE J434B* (Automotive ductile iron casting : 1970)
Hardness
Structure
Grade D4018
HB 170mx.
Ferrite
D4512 156-217
Ferrite & Pearlite
D5506 187-255
Ferrite & Pearlite
D7003 DQ&T**
241-302
Pearlite
—
Martensite
*These irons are primarily specified on hardness and structure. The mechanical properties are given for information only. **Quenched and tempered grade; hardness to be agreed between supplier and purchaser.
84
CHAPTER - 11 IMPORTANT TABLES AND FIGURES Tabloe 11.1 Temperature Converstions Albert Sauveur type of table. Look up reading in middle column : if in degrees Centigrade, read Fahrenheit equivalent in right hand column; if in degrees Fahrenheit, read Centigrade equivalent in left hand column. Values as printed in Bethlehem Alloy Steels.: C. F.
C. F.
-273 -268 -262 -257 -251 -246 -240 -234 -229 -223 -218 -212 -207 -201 -196 -190 -184 -179 -173 -169 -168 -162 -157 -151 -146 -140
-134 -129 -123 -118 -112 -107 -101 -96 -90 -84 -79 -73 -68 -62 -57 -51 -46 -40 -34 -29 -23 -17.8 -17.2 -16.7 -16.1 -15.6
-459.4 -450 -440 -430 -420 -410 -400 -390 -380 -370 -360 -350 -340 -330 -320 -310 -300 -290 -280 -273 -270 -260 -250 -240 -230 -220
-459.4 -454 -436 -418 -400 -382 -364 85
-210 -200 -190 -180 -170 -160 -150 -140 -130 -120 -110 -100 -90 -80 -70 -60 -50 -40 -30 -20 -10 0 1 2 3 4
-346 -328 -310 -292 -274 -256 -238 -220 -202 -184 -166 -148 -130 -112 -94 -76 -58 -40 -22 -4 14 32 33.8 35.6 37.4 39.2
C. F.
C. F.
-15.0 -14.4 -13.9 -13.3 -12.8 -12.2 -11.7 -11.1 -10.6 -10.0 -9.4 -8.9 -8.3 -7.8 -7.2 -6.7 -6.1 -5.6 -5.0 -4.4 -3.9 -3.3 -2.8 -2.2 -1.7 -1.1 -0.6 0.0 0.6 1.1 1.7 2.2 2.8 3.3 3.9 4.4 5.0 5.6
6.1 6.7 7.2 7.8 8.3 8.9 9.4 10.0 10.6 11.1 11.7 12.2 12.8 13.3 13.7 14.4 15.0 15.6 16.1 16.7 17.2 17.8 18.3 18.9 19.4 20.0 20.6 21.1 21.7 22.2 22.8 23.3 23.9 24.4 25.0 25.6 26.1 26.7
5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42
41.0 42.8 44.6 46.4 48.2 50.0 51.8 53.6 55.4 57.2 59.0 60.8 62.6 64.4 66.2 68.0 69.8 71.6 73.4 75.2 77.0 78.8 80.6 82.4 84.2 86.2 87.8 89.6 91.4 93.2 95.0 96.8 98.6 100.4 102.2 104.0 105.8 107.6 86
43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80
109.4 11.2 113.0 114.8 116.6 118.4 120.2 122.0 123.8 125.4 127.4 129.2 131.0 132.8 134.6 136.4 138.2 140.0 141.8 143.6 145.4 147.2 149.0 150.8 152.6 154.4 156.2 158.0 159.8 161.6 163.4 165.2 167.0 168.8 170.6 172.4 174.2 176.0
C. F.
C. F.
27.2 27.8 28.3 28.9 29.4 30.0 30.6 31.1 31.7 32.2 32.8 33.3 33.9 34.4 35.0 35.6 36.1 36.7 37.2 38 43 49 54 60 66 71 77 82 88 93 99 100 104 110 116 121 127 132
138 143 149 154 160 166 171 177 182 188 193 199 204 210 216 221 227 232 238 243 249 254 260 266 271 277 282 288 293 299 304 310 316 321 327 332 338 343
81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 110 120 130 140 150 160 170 180 190 200 210 212 220 230 240 250 260 270
177.8 179.6 181.4 183.2 185.0 186.8 188.6 190.4 192.2 194.0 195.8 197.6 199.4 201.2 203.0 204.8 206.6 208.4 210.2 212 230 248 266 284 302 320 338 356 374 390 410 413.6 428 446 464 482 500 518 87
280 290 300 310 320 330 340 350 360 370 380 390 400 410 420 430 440 450 460 470 480 490 500 510 520 530 540 550 560 570 580 590 600 610 620 630 640 650
536 554 572 590 608 626 644 662 680 698 716 734 752 770 788 806 824 842 860 878 896 914 932 950 968 986 1004 1022 1040 1058 1076 1094 1112 1130 1148 1166 1184 1202
C. F.
C. F.
349 354 360 366 371 377 382 388 393 399 404 410 416 421 427 432 438 443 449 454 460 466 471 477 482 488 493 499 504 510 516 521 527 532 538 543 549 554
560 566 571 577 582 588 593 599 604 610 616 621 627 632 638 643 649 654 660 666 671 677 682 688 693 699 704 710 716 721 727 732 738 743 749 754 760 766
660 670 680 690 700 710 720 730 740 750 760 770 780 790 800 810 820 830 840 850 860 870 880 890 900 910 920 930 940 950 960 970 980 990 1000 1010 1020 1030
1120 1238 1256 1274 1292 1310 1328 1346 1364 1382 1400 1418 1436 1454 1472 1490 1508 1526 1544 1562 1580 1598 1616 1634 1652 1670 1688 1706 1724 1742 1760 1778 1796 1814 1832 1850 1868 1886 88
1040 4050 1060 1070 1080 1090 1100 1110 1120 1130 1140 1150 1160 1170 1180 1190 1200 1210 1220 1230 1240 1250 1260 1270 1280 1290 1300 1310 1320 1330 1340 1350 1360 1370 1380 1390 1400 1410
1904 1922 1940 1958 1976 1994 2012 2030 2048 2066 2084 2102 2120 2138 2156 2174 2192 2210 2228 2246 2264 2282 2300 2318 2336 2354 2372 2390 2408 2426 2444 2462 2480 2498 2516 2534 2552 2570
C. F.
C. F.
771 777 782 788 793 799 804 810 816 821 827 832 838 843 849 854 860 866 871 877 882 888 893 899 904 910 916 921 927 932 938 943 949 954 960 966 971 977
982 988 993 999 1004 1010 1016 1021 1027 1032 1038 1043 1049 1054 1060 1066 1071 1077 1082 1088 1093 1099 1104 1110 1116 1121 1127 1132 1138 1143 1149 1154 1160 1166 1171 1177 1182 1188
1420 1430 1440 1450 1460 1470 1480 1490 1500 1510 1520 1530 1540 1550 1560 1570 1580 1590 1600 1610 1620 1630 1140 1650 1660 1670 1680 1690 1700 1710 1720 1730 1740 1750 1760 1770 1780 1790
2588 2606 2624 2642 2660 2678 2696 2714 2732 2750 2768 2786 2804 2822 2840 2858 2876 2894 2912 2930 2948 2966 2984 3002 3020 3038 3056 3074 3092 3110 3128 3146 3164 3182 3200 3218 3236 3254 89
1800 1810 1820 1830 1840 1850 1860 1870 1880 1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010 2020 2030 2040 2050 2060 2070 2080 2090 2100 2110 2120 2130 2140 2150 2160 2170
3272 3290 3308 3326 3344 3362 3380 3398 3416 3434 3452 3470 3488 3506 3524 3542 3560 3578 3596 3614 3632 3650 3668 3686 3704 3722 3740 3758 3776 3794 3812 3830 3848 3866 3884 3902 3920 3938
C. F.
C. F.
1193 1199 1204 1210 1216 1221 1227 1232 1238 1243 1249 1254 1260 1266 1271 1277 1282 1288 1293 1299 1304 1310 1316 1321 1327 1332 1338 1343 1349 1354 1360 1366 1371 1377 1382 1388 1393 1399
1404 1410 1416 1421 1427 1432 1438 1443 1449 1454 1460 1466 1471 1477 1482 1488 1493 1499 1504 1510 1516 1521 1527 1532 1538 1543 1549 1554 1560 1566 1571 1577 1582 1588 1593 1599 1604 1610
2180 2190 2200 2210 2220 2230 2240 2250 2260 2270 2280 2290 2300 2310 2320 2330 2340 2350 2360 2370 2380 2390 0400 0410 2420 2430 2440 2450 2460 2470 2480 2490 2500 2510 2520 2530 2540 2550
3956 3974 3992 4010 4028 4046 4064 4082 4100 4118 4136 4154 4172 4190 4208 4226 4244 4262 4280 4298 4316 4334 4352 4370 4388 4406 4424 4442 4460 4478 4496 4514 4532 4450 4568 4586 4604 4622 90
2560 2570 2580 2590 2600 2610 2620 2630 2640 2650 2660 2670 2680 2690 2700 2710 2720 2730 2740 2750 2760 2770 2780 2790 2800 2810 2820 2830 2840 2850 2860 2870 2880 2890 2900 2910 2920 2930
4640 4658 4676 4694 4712 4730 4748 4766 4784 4802 4820 4838 4856 4874 4892 4910 4928 4946 4964 4982 5000 5018 5036 5054 5072 5090 5108 5126 5144 5162 5180 5198 5216 5234 5252 5270 5288 5306
C. F.
C. F.
1616 1621 1627 1632
1638 1643 1649
2940 2950 2960 2970
5324 5342 5360 5378
2980 2990 3000
5396 5414 5432
Table 11.2 Density of Different Types of Cast Iron White Grey Malleable C.I SG Iron C.I C.I Black Heart White Ferritic Pearlitic Ferrtic Pearl Heart 7.4-7.75 6.9-7.4
7.2-7.3 7.3-7.45 7.3-7.77
7.02-7.2
7.35
Table 11.3 Relationship between Tensile Strength and Density of Grey Cast Iron T.S. Desity
kg/mm2 g/cm3
14
17
20
23
28
32
38
6.8-7.1 7.0-7.1 7.2-7.3 7.25-7.4 7.3-7.4 7.3-7.4 7.4-7.6
91
Table 11.4 Density of Cast Irons
gm/c.c
1. Liquid cast iron (at liquidus temp)
6.23
2. High C ferritic grey iron
6.8
3. Med. -C, ferr+pearl. grey iron
7.05
4. Low -C, pearl. grey iron
7.28-7.4
5. White iron unalloyed
7.6-7.8
6. High-Si, grey (Silal)
6.8-7.2
7. High gr, white
7.3-7.5
8. High Al., grey
5.5-6.4
9. High Ni, aust., grey (Ni-resist)
7.4-7.6
10. Nicrosilal, aust
7.2-7.4
11. Ni. Cr., white nihard
7.6-7.8
12. High-Mo, white
7.6-7.9
13. High-C, ductile, ferritic
7.1
14. High C., ductile, pearlitic
7.15
15. High Si., ductile, ferritic
7.1
16. High Ni, ductile, aust (Ni, resist)
7.4
17. Pure iron
7.87
92
Table 11.5 Specific Gravity and Melting Point of Casting Alloys Alloy
Sp. Gravity
Melting Point, 0C
1.
Open grained high Carbon
2.
Close grained low carbon C.I. 7.35
1130-1250
3.
White Cast Iron
1180-1220
4.
Ferritic blackheart M malleable
6.95
7.3-7.75 7.1-7.3
5. Pearlitic blackheart M 7.3-7.45 6. Whiteheart Malleable 7.3-7.7
1180-1220
7.
S.G. Ion (Ferritic)
7.0-7.2
8.
S. G. Iron (Pearlitic)
7.25-7.35
9.
Liquid cast ion (at solidification temp.)
6.23
10.
Carbon Steel
11.
High alloy steel
12.
Pure iron
13.
Aluminium silicon
2.5-2.6
640-650
14.
Leaded bronze
8.9-9.7
1020-1040
15.
Tin bronze
8.6-8.9
1010-1040
7.8-7.85
1400-1525
7.5-8.1
1450-1500
7.87
93
1535
Alloy
Sp. Gravity
Melting Point, 0C
16.
Brass
8.6-8.70
950-1050
17.
Aluminium bronze
7.3-7.6
1040-1060
18.
Manganese bronze
7.7-8.0
1060-1080
19.
Silicon bronze
8.2-8.4
1040-1050
Table 11.6 Bulk Density (Wt., Kg/litre) of Some Materials
Material
Wt. in Kg/litre
Powdered clay
1.00
Bentonite
1.00
Quartzite (dry)
1.50
Quartzite (wet)
1.25
Oil
0.92
Dextrine
0.75
Molasses
1.35
Graphite
0.80
Coke (powdered)
0.85
Coal dust
0.70
Charcoal powder
0.45
Tar
0.92
Saw Dust
0.27
94
Table 11.7 Properties of Microstructural Consituents of Cast Iron Structural Component
Sp. Gravity
Graphite
2.3
Phosphide eutectic
7.32
Ferrite
7.87
Acicular Ferrite
Tensile str. Kg/mm2
Hardness BHN
Elong. d %
35-45
110-130
15-25
3-5
600-900
230-260
Cementite
7.82
Austenite Pearlite (unalloyed)
7.8
Spheroidized pearlite
7.8
80-100
Sorbite Martensite
200 200-230
6
160-190
120-140
240-280
7.63
Table 11.8 Segregation of Elements in Cast Iron Analysis from
Si
Mn
P
Cr
Ni
Cu
Average content in metal
1.40
0.94 0.11
0.32
0.19 0.14
Eutectic cell boundaries
1.14
0.56
Tr.
0.32
0.13
—
In phosphide eutectic
0.25
2.37 9.02
3.82
0.05
—
95
Table 11.9 Effect of Common Elements on Graphite and Eutectic Cells
C
Si
Mn
S
P
Graphitization during crystallization
+
+
–
–
+
Graphitization during eutectoid transfn.
+
+
–
–
–
Formation of interdendritic graphite
–
0
+
+
–
Graphite flake size
+
0
–
–
+
Eutectic cells
+
0
0
–
–
Probability of effect on graphite through change of interval Tstable -TMetastable
–
+
?
+
?
Number of nuclei
+
–
–
–
+
Rate of grwoth of nuclei
–
+
?
+
?
Bond energy between atoms (ions)
+
+
+
?
–
Table 11.10 Composition of Cast Iron for Machine Tool Castings Composition, % X-Section, mm
T.C.
Si
Mn
200-250
2.9
1.2
1.1
100-200
3.0
1.4
1.0
”
0.2
0.4
37-100
3.1
1.6
1.0
”
0.2
—
18-37
3.2
1.8
0.8
”
0.4
—
18
3.3
2.2
0.8
”
0.6
—
96
S
P
Mo
0.1 (max) 0.1
0.4
Table 11.11 Relationship between Tensile Strength and Brinell Harness for Various Microstructures and Compositions Carbon Equivalent, %
3.45-3.65
Ration, Ten. Str. + BHN 210 and over
Microstructure
Smallest cell, normal graphite.
190-210
Small cell, normal graphite.
180-190
Medium cell, some type D graphite.
170-180
Large cell, some type D-medium
cell, completely type D.
160-170
Large cell, partial type D graphite.
160 and below
3.65-3.85
Large cell, complete type D graphite.
190-210
Small cell, normal graphite.
180-190
Medium cell, normal grahite
or small cell, partial type D.
Medium cell, with partial type
170-180
D Graphite
Large cell, type D graphite or free
160-170
ferrite.
190-210
Medium cell, normal graphite.
180-190
Medium cell, large normal graphite.
170-180
Medium or large cell, some type D.
160-170
Large cell, type D graphite.
160 or below
Free ferrite, type D graphite.
3.85-4.20
97
Table 11.12 The Influence of Notches on the Tensile Strength of Two Grey Irons
Type of Test
Iron A
Iron B
Smooth 0.798” dia. bar...
41,000
48,600
Notched Tensile Strength, psi 450 V-Notch of 0.331” root dia. in a0.564” dia. test bar...
34,100
44,100
Stress Concentration Factor...
1.20
1.10
Grooved Tensile Strength, psi 0.1” groove of 0.331” bose dio. in a .564” dio. test bar...
34,300
44,700
Stress Concentration FActor...
1.20
1.09
Tensile Strength, psi
1 inch=25.4 mm 1000 psi = 6.8947 N/mm2
Table 11.13 Gases in Cast Iron General levels of nitrogen, hydrogen and oxygen in cast iron are as follows :
Nitrogen Hydrogen Oxygen
(15-140) (0.5-3) (4-100)
× × ×
The gas content is measure as
i) ii) iii)
CC/100 g of metal ; per cent ; Parts per million. (ppm) 98
10-4% 10-4% 10-4%
Their mutual relationship are as follows : = 0.00125% 1 CC/100 g. of N2 = 12.5 ppm 1 CC/100 g. of H2
= =
0.00009% 0.9 ppm
1 CC/100 g. of O2
= =
0.00143% 14.3 ppm
Solubility of gases in molten cast iron : Nitrogen Log [n%] = -100/T=0.86-0.06 [Si+S] -0.24 C -0.15 P + 0.015 Mn + 0.03 Cr Hydrogen For the normal compositions and temperatures and at atmospheric pressure : [H] CC/100g = 25 - 3.5 C - 2Si + 10 Mn - 3 Cr. However, in hypereutectic cast irons, carbon increases the solubility of H2 due to adsorption on graphite. Osygen Log [%0] = -2975/T - 1.06 -log[%C] + 0.19 [%C] - 0.5 log [% Si] Like in the case of hydrogen, the solubility of oxygen in hypereutectic irons also increases due to adsorption.
99
100
101
102
103
104
105
106
107
108
109
110
111
GLOSSARY OF TERMS Acicular Structure :
A microstructure characterized by needleshaped constituents.
Acid Refractory : Siliceous ceramic materials of a high melting temperature, such as silica brick used for metallurgical furnace linings. Age Hardening : The gradual hardening of a metal caused by precipitation of a constituent from a supersaturated solid solution. Aggregated Flake Graphite :
See compacted graphite.
Allotropy : The property, shown by certain elements, of being capable of existence in more than one form, due to differences in the arrangements of atoms or molecules. Alloys : A substance having metallic properties and composed of two or more chemical elements of which at least one is metal. Alloying Elements : Chemical elements constituting an alloy, usually limited to elements added to modify the properties of the base metal. Alpha iron : The magnetic form of iron that is stable below the critical temperature (9060C for pure iron) and characterized by a body-centered cubic cystal strucrture. Annealing : Generally a heat treatment to soften metals, for iron and steel, consists of heating above the critical temperature followed by slow cooling usually in the furnace.
112
Anode :
The positive electrode in an electrolytic cell.
Arc Furnace : A furnace in which metal is melted either directly by an electric arc between an electode and the work or indirectly by an arc between two electrodes ajacent to the metal. As-Cast Condition :
Casting as remove from the mould, without subsequent heat treatment.
Atmosphere (protective) : In metallurgical practice the gases sourrounding the work in a furnace or other high-temperature apparatus. The character of the atmosphere varies with the work being carried out and, in nature, may be oxidizing, reducing or neutral. Austempering : A heat treatment process that consists of quenching a ferrous alloy from a temperature above the critical range into a medium having a rate of heat abstraction (usually molten salt) sufficiently high to prevent the formation of high temperature transformation products, and in maintaining the alloy, until transformation is complete, at a temperature below that of pearlite and above that of martensile formation. Austenite : Solid solution of cementite, or iron carbide, in gamma iron, which is nonmagnetic and characterized by a face centered cubic crystal structure. Austenitic Iron : Iron containing alloying elements such as nickel in sufficient quantity to render substantially austenitic structure at ordinary temperatures. Bainite : A constituent in the microstructure of cast iron or steel, formed by the transformation of austenite below the pearlitic and above the martensitic transformation temperature. 113
Blackheart Malleable :
See malleable iron.
Blast Furnace : In ferrous metallurgy, a shaft furnace is supplied with a hot air blast and used for producing pig iron by smelting iron in a continuous operation. The raw materials (iron ore, coke, and limestone) are charged at the top, and the molten pig iron and slag which collect at the bottom, are tapped out at intervals. Brazing : Joining metals by fusion of non-ferrous alloys that have melting points above 0 425 C but lower that those of the metals being joined. Brinell Hardness : The value of hardness of a metal determined by measuring the diamter of the impression made by a ball of given diameter applied under a known load. Values are expressed in Brinell hardness numbers (BHN). British Thermal Unit (BTU) : The quantity of heat required to raise the temperature of ‘onelb’. of water 0 1 Fat or near its points of maximum density; a unit of heat measurement. Bull’s Eye Structure : The occurrence of a ferrite border around the graphite in the microstructure of ductile iron. The balance of matrix is usually pearlitic. Carbide :
A compound of carbon with one or more metallic elements.
Carbon Equivalent :
A relation between carbon, Silicon, and phosphorous in cast irons.
C.E. = % TC + % Si + %P 3 Carbonaceous : Said of matter, or a material that contains carbon in any or all of its several allotropic forms.
114
Carbonitriding :
Introducing carbon and nitrogen into solid iron by heat treating.
Carburizing : The diffusion of carbon into solid iron by heat treatment in a carbon rich atmosphere. Case Hardening : A process of hardening a ferrous alloy so that the surface layer or case is made substantially harder than the interior or core. Induction hardening and flame hardening are most commonly used for iron casting. Cast Iron :
A generic term for the family or highcarbon-silicon-iron casting alloys.
Castability : A complex conbination of liquid-metal properties and solidification characteristics which promotes accurate and sound final castings. Cathode :
The negative electrode in an electrolytic cell.
Cementite : A very hard, intermetallic compound of iron and carbon, usually containing other carbide-forming elements. (Loosely referred to as iron carbide or Fe3 C). Centerline Shrinkage :
Shrinkage or porosity occuring along the central plane or axis of a cast part.
Charge :
i)
The material placed in a melting furnace.
ii)
Casting placed in a heat treating furnace.
Charpy Test : A pendulum type of impact test in which a specimen, supported at both ends as a simple beam, is broken by the impact of the swinging pendulum. The energy absorbed in breaking the specimen as determined by the decreased rise of the pendulum, is a measure of the impact strength of the metal. 115
Chill Test : A small test casting that is fractured to indicate the carbide stability of the iron. Chilled Iron : Cast iron that is poured into a metal mould or against a mould insert so as to cause rapid solidification which often tends to produce a white iron structure in the casting. Coercive Force : The magnetizing force that must be applied in the direction opposite to that of the previous magnetizing force in order to remove residual magnetism, thus, an indicator of retained strength. Coining : A press metal working operation which establishes accurate dimensions of flat surfaces or depresion under predominantly compressive loading. Cold Work : Plastic deformation of a metal which substantially increases the strength and hardness. Columnar Structure : A coarse structure of parallel columns of grains, which is caused by highly directional solidification resulting from sharp thermal gradients. Combined Carbon : Carbon in iron which is combined chemically with other elements not in the free state as graphite or temper carbon. The difference between the total carbon and the graphite carbon analyses. Compacted Graphite Iron : Cast iron in which the graphite is in the form of interconnected flakes with blunt edges. Its properties are intermediate between grey iron and ductile iron.
116
Compression Yield Strength : The maximum stress that a material can withstand under compression without sustaining unit plastic deformation beyond a predetermined unit. Conductivity (Thermal) : The ability of heat to flow through a material as measure in heat units per unit time per unit of cross-sectinonal area per unit of length for a given temperature differential. (Electrical) The ability of a material to conduct electricity. The reciprocal of resistivity. Constitutent : A physically-distinct, mechanically-separable entity in the microstructure of a metallic system. Continuous Castings : A process for forming a bar of constant crosssection directly from molten metal by gradually withdrawing the bar form a die as the metal flowing into the die solidifies. Cooling Curve : A curve showing the relationship between time and temperature during the cooling of a metal sample. Since most phase changes involve evolution or absorption of heat, there may be abrupt changes in the slope of the curve. Cooling Stresses : Stesses developed during cooling by uneven contraction of metal, generally due to non-uniform cooling. Coupon : An extra peice of metal, either cast separately or attached to a casting, used to determine the analysis or properties of the metal. Cracking Strip :
A fin added to a casting to prevent hot tears and cracks.
117
Creep : The flow or plastic deformation of metals held for long periods of time at stresses lower than the normal yield strength. Critical Temperature : Temperature at which metal changes phase. In usual iron alloys, the temperature at which alpha iron transforms to gamma iron or vice versa. Actually, a temperature range for cast irons. Crucible : A pot or receptacle made of refractory materials such as high temperature resisting alloys, graphite, alundum, magnesia, or silicon, carbide, bonded with clay or carbon, and used in melting for fusion or metals. Crystal : A physically homogeneous solid in which the atoms, ions or molecules are arranged in a tridimensional, repetitive pattern. Crystalline Fracture : A brittle fracture of metal, showing definite crystal faces on the fractured surface. Cupola : A vertically cylindrical furnace for melting metal, in direct contact with coke as fuel, by forcing air under pressure through openings near its base. Curie Temperature :
The temperature at which a material, on heating, ceases to be ferromagnetic.
Current Density :
The current per unit area of a conductor or an electrode.
Cyaniding : Introducing carbon and nitrogen into solid iron by heat treating above the temperature at which austenite above the temperature at which austenite begins to form in contact with molten cyanide salt of suitable composition.
118
Damping Capacity : Ability of a metal to absorb vibration changing the mechanical energy into heat. Decarburization : Loss of carbon from the surface of a ferrous alloy, as aresult of heating in a medium containing oxygen that reacts with the carbon. Deflection : The maximum displacement in inches, before rupture, at the centre of the arbitration test bar in the transverse strength test for grey iron. Deformation :
Change in dimensions, as the result of an applied stress.
De Lavaued Process :
A centrifugual process employed chiefly for making cast iron pipe.
Delta Iron : The body-centered cubic crystal form of iron, which is stable from 13990C to the melting point. Dendrite :
A tree-like shape of solidified metal.
Density : The mass per unit volume of a substance, usually expressed in grams per cubic centemetre or in pounds per cubic foot. Desulfurizing: Removal of sulphur from molten metal by reaction with a suitable slag or a chemical such of a chemical such as soda ash. Die Casting: A castiong process in which the molten the molten metal is forced under pressure into a metal mould cavity. 119
Diffusion: The process by which atoms migrate as a result of their random thermal motion, usually in the direction from regions of high concentration towards regions of low concentration, to achieve homogenity of the solution, which may be either a liquid, a soil, or a gas. Directional Properties (Directionality) : Anisotropic relationship of mechanical and physical properties with respect to the direction or axis in which they are observed. Directional Solidification : The solidification of molten metal in a castiing in such a manner that liquid feed metal is always available for that portion that is just solidifying. Ductile Iron : Cast iron containing graphite in a spherulitic form also called nodular iron, spherulitic iron, spherulitic iron, or S.G. Iron. Duplexing :
Melting in one furnace and superheating and refining in another.
Eddy Current : Those currents that are induced in a body of a conducting mass by a variation of magnetic flux. Eddy Current Loss :
Energy lost as heat due to eddy currents.
Elastic Deformation : Temporary changes in dimensions caused by stress. The material returns to the original dimensions after removal of the stress. Elastic Limit :
Maximum stress that a material will withstand without parmanent deformation.
120
Electrical Resistance : The resistance of a material to transmission of electrical energy. It is measured by the resistance of a body of the substance of unit cross-section and unit length, and at a specified temperature. Electrode : In electro-metallurgy, a conductor belonging to the class of metallic conductors, but not necessarily a metal, through which electric current enters and leaves arc furnaces or electrolytic baths. In welding or arc applications, the two conductors between which the arc forms. Electron Beam Welding : A welding process in which heat is produced in metal by inpingement of a concentrated beam of high velocity electrons. Elecroslag Welding : An electric welding process in which the filler metal is melted and deposited under a blanket of molten slag. Elongation : Amount of permanent extension in the vicinity of the fractures in the tensile test, usually expressedd as a percentage of original gauge length, such as 25 percent in two inches. Embrittlement :
Loss of ductility.
Endurance Limit : A limition stress below which the metal will withstand, without rupture, an indefinitely large number of cycles of stress. Endurance Ratio : The ratio of endurance limit to ultimate strength. Endurance ratio equals endurance limit divided by ultimate strength.
121
Etching : In metallography, the process of revealing structural details by preferential attack of reagents on a metal surface. Eutectic : (1) Isothermal reversible reaction of a liquid that forms two different solid phases (in a binary alloy system) during cooling. (2) The alloy composition that freezes at constant temperature, undergoing the eutectic reaction completely. (3) The alloy structure of two (or more) solid phases formed from the liquid eutectically. Eutectic Alloy : In an alloy system, the composition at which two descending liquidus curves in a binary system, or three descending liquidus surfaces in a ternary system, meet at a point. Thus such an alloy has a lower melting point than neighbouring compositions. Eulectic Temperature : The lowest melting temperature in a series of mixture of two of more components. Eutectoid : An eutectoid is the lowest transformation temperatures at which a solid solution transforms into two solid phases. Eutectoid Reaction : Isothermal reversible reaction of a silid that forms two new solid phases (in a binary alloy aystem) during cooling. As with eutectic, the word eutectoid can also refer to an alloy composition or structure associated with the reaction. Extensometer :
An instrument for measuring deformation in a material while it is under stress.
Fatigue Fracture : The gradual propagation of a crack across a section due to cyclic stresses within the elastic limit. Fatigue Limit : Maximum stress that a metal will withstand without failure for a specified large number of cycle of stress. Usuaally synonymous with endurance limit. 122
Fatigue Ratio : The ratio of fatigue limit or fatigue strength a N cycles to the static tensile strength. Fatigue Strength : The maximum stress which a material can sustan, for a given number of stress cycles without fracture. Ferrite : An essentially carbon-free solid solution in which alpha iron is the solvent, and which is characterised by a body-centered cubic crystal structure. Ferro-Alloy : An alloy of certain elements with iron used to add these elements to molten metal. Ferrous :
Metallic materials in which the principal-component is iron.
File Hard :
Metal that is hard enough so that a new common file will not cut it.
File Hardness : The hardness of metal generally at an edge as determind by whether a file of an established hardness will bite into the metal. First stage Graphitization : The first phase of the annealing cycle in which all massive carbides are decomposed and equilibrium is established between austenite and carbon for the particular holding temperature. Flake Graphite : Graphite carbon, in the form of platelets, occuring in the microstructure of grey cast iron. Flame hardening :
Process of hardening a casting surface by heating it above the transformation 123
range with a high temperature flame followed by rapid cooling. Fluidity : The ability of moten metal to flow readily as measured by the length of a stadard spiral casting. Flux : A material of mixture of materials which causes other compounds with which it comes in contact to fuse at a temperature lower than their normal fusion temperature. Fog Quenching : A method of quenching in which a fine vapor or mist is used as the quenching medium Forehearth : A refractory-lined container, located near the taphole of a melting furnace, used to store, mix or treat the molten metal. Free Ferrite : That range of temperature between liquidus and solidus temperatures where molten and solid constituents coexist. Freezing Range : That range of temperature between liquidus and solidus temperatures where molten and solid constitutents coexist. Galvanizing :
The coating of iron or steel with zinc.
Galvanizing Embrittlement : The embrittlement of susceptible iron by having been rapidly cooled from about 8500 F (4500 C) as is and in galvanizing Gamma Iron : The non-magnetic form of iron, stable above the transformation temperature, characterized by a facecentered cubic crystal structure. 124
Gauss :
The electromagnetic unit of magnetic flux density.
Grain Growth :
An increase in the grain size of metal by a reduction in the number of grains.
Graphite :
One of the crystal forms of carbon; also the uncombined carbon in cast irons.
Graphitization : At elevated temperature, the precipitaion of graphite in solid iron as a result of the decomposition of iron carbide in corrosion. Graphitizer : Any material which increases the tendency of iron carbide to break down into iron and graphite. Graphitizing Anneal : A heating and cooling process by which the combined carbon in cast iron or steel is transformed, wholly or partly, to graphitic or free carbon. Grey Iron : Cast iron which contains a relatively large percentage of the carbon present in the form of flake graphite. The metal has grey fracture. Growth, Cast Iron : Permanet increase in dimensions of cast iron resulting from repeated or prolonged heating at temperatures over 900 F. This growth is due to 1) graphitization of carbides, and 2) internal oxidation. Hardenability : In a ferrous alloy, the property that determines the depth and distribution of hardness induced by quenching. Hardness :
The property of a substance determined by its ability to resist abrasion or 125
indentation by another substance. For metals, hardness is usually defined on terms of the size of an impression made by a standard indenter. (Brinell, Rockwell, Vickers etc). Heat : The entire period of operation of a continuous melting furnace such as a cupola from light-up to finish of melting. One cycle of operation in a batch melting furnace. Also the total metal from one such operation. Heat Treatment : A combination of heationg, holding, and cooling operations applied to a metal or alloy in the solid state in a manner which will produce desired properties. Heterogeneous Structure :
A micro structure containig more then one phase.
Hooke’s Law :
Stress is proportional to strain within the elastic range.
Hot Spots : Localized areas of a mould or casting where higher tempertures are reacher or where high temperature is maintained for an extended period of time. Hot Tear : Surface discontinuity or fracture caused by either external loads of internal stresses or a combination of both action on a casting during solidification and subsequent contraction at temperatures near the milting point. Hypereutectic Alloy :
An alloy containing more than the eutectic amounts of the solutes.
Hysteresis : The energy that is converted to heat in an elastic or magnetic energizing and de-energizing cycle. Impact Resistance :
The resistance of a material to breaking by loading or stressing at high rates. 126
Impact Strength : The energy absorbed in fracturing a standard specimen (notched or unnotched) by a blow from a pendulum in one of several standard impact tests. Impact Test : A test to determine the energy absorbed in fracturing a test bar at high velocity. See Izod Test; Charpy Test. Impact Transition Temperature :
That temperature below which agiven metal will display brittle inpact fracture.
Impregnation : The treatnent of defective castings with a sealing medium to stop pressure leaks in porous areas. Mediums used include sillicate of soda, drying oils with or without styrenes, plastics , and proprietary compounds. Inclusions : Non-metallic particles, such as oxides, sulphides or silicates that are held within solid metal. Induction Furnace : An alternation current electric furnace in which the primary conductor is coiled and generates a secondary current by eletromagnetic induction which heats the metal charge. Induction Hardening : Process od hardening the surface of a casting by heating it above the transformation range by electrical induction, followed by rapid cooling. Inoculant : Materials which, when added to molten metal, modify the structure, and thereby change the physical and mechanical properties to a degree not explained on the basis of the change in composition resultiong from their use. Intergranular Corrosion :
Corrosion in a metal taking place preferentially along the grain boundaries.
127
Internal Shirinkage : A void or network of voids within a casting caused by inadaquate feeding of that section during solidification. Internal Stresses : A system of balanced forces exisiting within a part when not subjected to a working load. These stresses are frequently caused by the differential contraction between parts of a casting as cools. Inverse Chill : The condition in a casting section where the interior is mottled or white, while the other sections are grey iron. Also known as Revers Chill, Internal Chill and Inverted Chill. Investment Process : The coating of an expendable patten with a ceramic material so that it forms the surface of the mould that contacts the moten metal when the pattern is removed and the mold is poured. Isothermal Transformation : The process of transforming austenite in a ferrous alloy to ferrite or ferritecarbide aggregate at any constant temperture below the critical temperature. Isotropic :
Having equal physical and or mechanical properties in all directions.
Izod Test : A pendulum-type impact test in which the specimen is supported at one end as a cantilever beam; the energy required to break off the free end is used as a measure of impact strength. Keel Block : A standard specimen for testing relatively high shrinkage ferrous alloys. A rectangular block with a smaller rectangular bar attached accross the bottom and resembling the keel of a boat. Kerf :
The space resulting from material removal in cutting. 128
Kish :
Free graphite which separates from molten hypreutectic iron.
Knoop Hardness : Microhardness determined from the resistance of metal to indentation by a pyramidal dimond indentor having edge angles of 1720 30’ and 1300 making a rhombohedral inpression with one long and one short diagonal. Ladle : Metal receptacle frequently linked with refractories used for transporting and pouring molten metal. Lamellar :
Plate-like.
Lamellar Structure : A constituent microstructure composed of an intimate mixture of platelets of two phases, typically resulting from an eutectoid reaction. The structure of pearlite in the iron-carbon system. Ledeburite :
Cementite-austenitte eutectic structure.
Liquid Contraction :
Shrinkage occuring in metal in the liquid state as it cools.
Liquidus : A line on a binary phase diagram, or a surface on a ternary phase diagram, representing the temperatures at which freezing begins during cooling, or melting ends during heating under equilibrium conditions. Macrograph :
A photographic reproduction of any object that has been magnified not more
than ten diameters. Macroscopic : Visible either with the naked eye or under low magnification (upto ten diameteres). 129
Macro structure :
Structure of metals as releaved by macroscopic examination.
Magnetic Hysteresis : The property of a magnetic material by virtue of which the magnetic induction for a given magentizing force depends upon the previous conditions of magnetization. Magnetic Hysteresis Loss : For a specified cycle of magnetizing force, the energy converted into heat as a result of magnetic hysteresis when the magnetic induction is cyclic. Magnetic Induction (Flux Density) : The magnetic analogue of current density in electrical conductor. The unit is the gruss. Magnetic Particle Inspection : The use of magnetic particles as a dry powder or in a liquid suspension to indicate discontinuities in a surface when it has been magnetized so that the particles adhere to the surface at the discontinuity. Magnetic Permeability : Magnetic permeability of a substnced is the ratio of the magnetic induction in the substance to the magnetizing field to which it is subjected; the magnetic analogue of electrical conductivety in the electrical circuit. Malleable Iron : Cast iron containing graphite in the from of modules of temper carbon. It is cast as white iron and the graphite is precipitated during the subsequent heat treatment. Manganese Sulfide : A compound of manganeses and sulfur that appers in the microstructure of iron as a small, medium grey, non-metallic inclusion. It may have a geometric shape. Martempering :
The process of quenching iron or steel from above the critical tempertures in 130
a bath at a temperture in or slightly above the upper portion of the temperature range of martensite formation, and holding in the bath until the temperature throughour the piece is substantially uniform. The piece is then allowed to cool in air through the temperature range of martensile formation. Martensite : In iron or steel a very hard micro-constituent with an acicular (needle-like) apperance; produced in heat treating by quenching or with alloys. Matrix : The principal phase in microstructure in which another constituent,such as graphite, is embedded or enclosed. Mechanical Properties : Those properties of a material that reveal the elastic and inelastic reaction when force is applied, or that involve the relationship between stress and strain; for example, the modulus of elasticity, tensile strength, and fatigue limit. These properties have often been designated as physical properties but the term mechanical properties is preferred. Melting Zone :
Portion of the cupola above the tuyeres in which the charge melts.
Metallography : Study or science of structures of metals and alloys, particularly visual examination by means of the microscope. Metallurgy : Science and art of extracting metals from their ores, refining them and preparing them for final use. Microhardness :
The hardness of microconsituents of a material.
Microporosity : Extremely fine porosity caused in castings by solidification shrinkage or gas evolution. 131
Micro-Shrinkage : Fine porosity or tiny cavities, of the order of a fraction of a millimetre in size, with irregular outlines. Microstructure : The structure of polished and etched metal and alloy specimens as revealed by the microscope at magnifications over ten diameters. Modulus of Elasticity : The ratio of tensile stress to the corresponding strain within the limit of elasticity of a material. Modulus of Resilience : The amount of energy absorbed when one cubic inch of material is stressed to its elastic limit. The modulus of resilience is porportional to the area under the elastic portion of the stress-strain diagram. Materials having modulus of resilience are capable of withstanding higher impact without damage. Modulus of Rupture : The ulitmate strength or the breaking load per unit area of a specimen tested in torsion or in bending (flexure). In tension it is the tensile strength. Mottled Cast Iron : A mixture of grey iron and white iron of variable proportions. The fracture has a mottled (speckled) appearance. NDT(Nil-Ductility Transition)
Same as Impact Transition Temperature.
Ni-Hard : The common trade name for nickel, chromium, alloyed white irons that have a martensitic martix as-cast. Ni-Resist :
The common trade name for high nickel content alloy grey and ductile irons.
132
Nitriding : A process of shallow case hardening in which a ferrous alloy, ussually of a special composition, is heated in an atmosphere of ammonia, or in contact with nitrogenous material, to produce surface hardening by formation of nitrides, without quenching. Nodular Graphite : Graphite in the nodular form as opposed to flake form. Nodular graphite is characteristic of malleable iron. The graphite of modular or ductile oron is spherulitic in form, but called nodular. Nodular Iron :
See ductile iron.
Normalizing : A heat treatment in which ferrous alloys are geated to a suitable temperature above the tensformation range and cooled in still air to room temperature. Notch Sensitivity : The reduction in the impact, endurance, or static strength of a metal that is caused by the presence of stress concentration as a result of scratches, pits, or other stess raisers on the surface, usually expressed as the ratio of the notched to the unnotched strength. Nuclei : Sites at which a new phase can be instigated. In iron, places where graphite can start forming. Oersted :
The electromagnetic unti of magnetizing force.
Oil Quenching : A ferrous material that has sufficient hardenability to satisfactorily hardened by quenching in oil.
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Open Grain Structure : A machined or fractured surface that appears coarse grained with visible grain separations, may be due to large graphite flakes or shrinkage. Pearlite : Lamellar aggregate (alternate plates) of ferrite and cementite in the microstructure of iron and steel. Peatlitic Malleable : An iron-silicon-carbon alloy, cast white and heat treated under controlled condition in such a manner that part of the carbon is present as nodules of graphite and the remainder is intentionally retained in the combined from. The combined carbon appears as spheroids, pearlite lamellae, or tempered martensite products. Phase :
A physically homogeneous entity occuring in a metallic system.
Phase Diagram : A graphical representation of the equilibrium temperature and composition limits of phase fields and phase reactions in an alloy system. Physical Properties : Properties, other than mechanical properties, that pertain to the physics of a material. Pickle :
To clean metal surfaces by chemical or electrochemical means.
Pig Iron : The crude product of the blast furnace where ore is reduced into iron and from which it is cast into small bars (pigs). Plasma Arc Welding : A welding process in which the heat from an arc is transferred to the work by a stream of ionized inert gas which also shields the weld.
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Plasticity : The property of a substance to be moulded or deformed (permanently) into a desired shape or form without rupture. Poisson’s Ratio : The absolute value of the ratio of transverse strain to the corresponding axial strain in a body subjected to uniaxial stress. Post Heating : Heating welded mtal immidiately after welding for tempering, stress relieving or providing a controlled rate of cooling to minimize formation of a hard or brittle structure. Primary Carbides : Iron carbide in the microstructure of cast iron that was formed during solidification. Primary Graphite :
Graphite that is formed in iron during its soldification.
Progressive Hardening : Flame, induction, or laser heating of a surface of a ferrous material by a traveling heating and quenching fixture. The heat imput and rate of travel are controlled so as obtain the desired metal temperture for quenching. Proof Stress :
The stress that will cause a specified small permanent set in a metal.
Proportional Limit : The greatest stress that the material is capable of sustraining without a deviation from the law of proportionality of stress to strain (Hooke’s Law). PSI :
Pounds per square inch.
Pyrometer :
A device for measuring indicating and/or recording temperature. 135
Quench Hardening : Process of hardening a ferrous alloy of suitable composition by heating within or above the transformation range and cooling at a rate sufficient to increase the hardness substantially. The process usually involves the formation of martensite. Quenching :
A process of inducing rapid cooling from an elevated temperature.
RMS Value : A term pertaining to the measured height of asperities constituting the roughness of a mechanical surface (See Surface Fininsh). Radiography : A non-destructive method of integral exemination in which metal objects are exposed to a beam of X-ray of gamma radiation. Differences in thickmess, density, or absorption, caused by internal defects either on a fluorescent screen or on photographic film placed behing the object. Reduction in Area : The difference between, the original cross-sectional area of a tensile, the piece and that of the smallest area at the point of fracture, Usually stated as percentage of the original area. Remnent Magnetism (Residual Induction) : The magnetic induction remaining in a magnetized material when the magnetizing force has been removed. Residual Stress : A stress that is a member of a balancing stress couple existing within a free body to generate the stress. Resilience :
The energy stored in a material when strained elastically.
Resistivity : The resistance of a material to the transmission of electrical energy. It is measured by the resistance of a body of the material of unit cross-section and unit length. 136
Rock well Hardness : The relative hardness value of a metal determined by measuring the depth of pentration of a steel ball (i.e. in dia, for B Scale) or a diamond point (C Scale) with controlled loading, the depth obrained with a minor and a major loading. Scleroscope Hardness Test : A hardness test in which the loss in kinetic energy of a falling metal ‘tup’, absorbed by indentation upon inpact of the tup on the metal being tested, is indicated by the height of rebound. Scrap :
a) Defective casting, b) Metal to be remelted.
Second Stage Graphitization : The second phase of the annealing cycie of malleableiron in which the last quantities of carbon, remaining after first stage graphitization. are precipitated as graphite on the modules formed during first-stage graphitization. Selective Hardening :
Obtaining desired degrees of hardness in different area of a casting.
S.G.Iron :
See dudtile iron.
Shear strength : Maximum shear stress that a material is capable of withstanding without failure. Shrinkage :
Decrease in volume of the metal as it solidifies
Silal :
An alloy grey iron containing 5 to 7% silicon.
Slag : A product resulting from the action of a flux on the oxidized non-metallic constituents of molten metals. May also be produced by oxidation of the molten 137
bath, ash from the fuel, erosion of the refractories, and floating of non-mentallics in the charge. Solid Contraction : Shirnkage occurring in metal in the solid state as it cool from solidifying temperture. Solidification Shrinkage :
The decrease in volume accompanying the freezing of a molten metal.
Solidus : A line on a phase diagam representing the temperature at which freezing ends on cooling, or melting begins on heating. Specific Damping Capacity :
The percent of decrease in vibrational amplitude per cycle. A material property.
Specific Heat : The quantity of heat required to produce a unit change in the temperature of a unit mass. Spheroidization (Spheroidizing Heat Treatment) : A long annealing at a temperature below but near the critical point, causing the cementite to spherodize. Spheroidized Cementite : A microstructure in which iron carbide occurs as small spheres in a ferritic matrix. Spheroidized Pearlite : A matrix microstructure that results from tempering pearlite at a sub-critical temperature. Sphertulitic Graphite : Graphite occuring in highly compact spherical or nearly spherical form with a radial internal structure. Characteristic of ductile iron. 138
Spin Hardening : The hardening of a surface on a ferrous material by rotating it while it is being heated so as to obtain more uniform heating for quenching. Spot Hardening : Localized hardening on a ferrous material by heating with flame, induction, or laser without motion and thin quenching. Streadite :
A hard phosphorus-rich microconstituent.
Stabillizer : Any substance that increasees the tendency of carbon to remain as iron carbide, i.e.retards graphitization. Strain : 1) The change per unit of length in any material as a result of stress. Strain in measured in inches per inch of length. 2) A casting defect, an out-of-shape castion due to distortion of the mold. Stress :
The intensity of force, force per unit area as pounds per square inch (psi)
Stress Concentraion Factor : When a stress concetration or notch is present on a part, the stress concentrainon factor is the ratio of the maximum normal stress at the notch to the momial stress in the part in the part if the notch were not present. Stress-corrosion Cracking : Spontaneous failure of metals by cracking under combined conditions of corrosion and stress, either residual or applied. Stress Raisers : Factors such as sharp changes in contour or surface defects, which concentrate stresses locally.
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Stress Relieving :
A subcritical heat treatment to reduce residual stresses.
Stress, Resedual : Stresses set up as a result of a non-uniform plastic deformation or the unequal cooling of a casting. Stress-Rupture : The fracture of a material after carrying a sustained load for an extended period of time usually at an elevated temperture. Supercooling : Lowering by rapid cooling the temperature at which a phase trensformation would normally occur in an alloy under equlibrium conditions. Superheating : Raising the temperature of molten metal above the normal melting temperture for more complete refining, greater fluidity, and other reasons. Supersalurated : Metastable solution in which the dissolved material exceeds the amount the solvent can hold in normal equilibrium at the temperature and under the other conditions that prevail. Temper Carbon : Graphite carbon that comes out of solution, usually in the form of nodules, during the annealing of malleable iron. Tempering : A heat treatment consisting of reheating quench-hardened or mormalized iron to a temperature below the transformation range, and holding for sufficient time to produce the desired properties. Tensile Strength : The mazimum load in tension which a material will withstand prior to fracture. It is calculated from the maximum load applied during the tensile test diveded by the original cross-sectional area of the sample. 140
Test Lug : A small projection on a casting that may be fractured to test the ductility of the metal in the piece without destroying the casting itself. Thermal Analysis : A method of determining transformations in a metal by noting the temperatures at which thermal arrests occur. Thermal Conductivity : The property of matter by which heat energy is transmitted. For engineering purposes it is measured by the amount of heat trasmitted by a given section over a given length under a known temperature difference in a unit of time,i.e. Cal/cm2/ cm/0C/sec. Trermal Contraction : The decrease in linear dimensions of a material accompanying a dectease in temperature. Thermal Expansion: The increase in linear dimensions of a material accompanying an increase in temperature. Thermal stresses :
Stress in metal, resulting from non-uniform distributions of temperature.
Thermal Welding : The wilding of metal parts with molten metal Which was heated by the chemical reaction of metallic oxides and powdered aluminium. Thermocouple : A device for measuring temperatures by the use of two dissimilar metals in contact, the junction of these metals gives rise to measurable elecrtical potential which varies with the temperature of the junction. Thermocouples are used to operate temperature indicators or heat controls. Torsion Strength :
The shearing stress limit for a body when loaded by twisting. 141
Torsional Modulus : In a torsion test, the ratio of the shear stress to the unit displacement caused by it in the elastic range. Toughness : Ability of a material to absorb energy without failure. May be expressed as the total area under the stress-strain curve. Tranformation Temperature Range : A range in temeprature in which a change in phase occurs. For iron about 0 1400 to 15000 F. (depending upon silicon content). Undercooled : The tranformation of material below its normal transformation temperature as a aresult of rapid cooling and insufficient nuclei for the new phase. It can result in a structure that is different from normal. Vermicular Graphite :
See compacted graphite.
Vickers Hardness : An indetation hardness test employing a 1360 diamond pyramid indentor and variable loads enabling the use of one hardness for all ranges of hardness. White Iron : Irons possessing white fractures because all or susbtantially all of the carbon is in the combined form. Whiteheart Malleable :
An European type of malleable iron.
Work Hardening : Hardness developed in metal as a result of mechanical working, particularly cold working.
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Yield Point : The load per unit of original cross-section at which a marked increase in defromation occurs without increase in load. Yield Strength : The stress at which a material exhibits a speicified limit of permanent strain; often the maximum unit load with a 0.2% deviation from a proportional stress-strain relation.
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BIBLIOGRAPHY
1.
Iron Casting Handbook, Edited by Walton & Opar, Published by Iron Casting Society Inc.
2.
Malleable Iron Castings, Malleable Founders Society-Cleveland, Ohio.
3.
Ductile Iron, Stephen I. Karsay.
4.
Use of Allying Elements in Cast Irons, W. Fairhurst and K. Rohrig, FoundryTrade Journal-International, Decemebr ‘81.
5.
The Effect of some Trace Elements in Cast Iron, M. J. Fallon, Indian Foundry Journal June ‘80.
6.
The Heat Treatment of S. G. Iron, G. J. Cox, The Metallurigst and Material Technologist, November ‘80.
7.
Welding S. G. Iron, The International Nickel Company (Mond) Ltd. 1962.
8.
Modern Casting July ‘84.
9.
Welding of Cast Irons with Coated Electrodes, The International Nickel Company (Mond) Ltd.
10. Pearlitic, Malleable Cast Iron, Dr. U. K. Bhattacharya. 11. “Eutectic” Low Heat Input Metal Joining Process-Papers presented in seminar organised at Jamshedpur in 1972 by Larsen & Toubro Ltd. 12. Foseco Foundryman’s Handbook. 13. I S, I S O, B S, D I N, A S T M Standards. 14. Production of Machine Tool Castings, British Foundryman, 1963, No. 9, 418425, Discussion 425-426.
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