1. 1
CAST IRON
HANDBOOK
IIF Center, 335 Rajdanga Main Road, Kolkata - 700 107
Ph.: 033 2442 4489 / 6825 / 7385, 4063 0074, Fax : 033 2442 4491
E-mail : cet@indianfoundry.org
The Institute of Indian Foundrymen
Compiled by :
IIF JAMSHEDPUR CHAPTER
Edited by :
Mr. Gautam Banerjee
2.
3. 3
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, 37
Malleable & Ductile Iron
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 61
Defects in Iron Castings, Their Causes and Remedies
10. National and International Standards 69
11. Important Tables and Figures 85
12. Glossary of Terms 112
4.
5. 5
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.
6.
7. 7
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
Percent%
Type of
Iron
Carbon Silicon Manganese Sulphur Phosphorous
Unalloyed
white
1.80-3.60 0.50-1.90 0.25-0.80 0.060-0.20 0.060-0.20
Malleable 2.20-2.90 0.90-1.90 0.15-0.20 0.020-0.20 0.020-0.20
Grey 2.50-4.00 1.00-3.00 0.20-1.00 0.020-0.25 0.020-1.00
Ductile 3.00-4.00 1.80-2.80 0.10-1.00 0.010-0.030 0.010-1.00
Compacted
Graphite
2.50-4.00 1.00-3.00 0.20-1.00 0.010-0.030 0.010-1.00
8. 8
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-Fe3
C-Si ternary equilibrium diagram sectioned at 2%
(Fig-2.1) and Fe-Fe3
C 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.
9. 9
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
12. 12
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 Allioying elements
Structure
V Cr Mo Cu Ni Sn
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
13. 13
13
Table - 3.2
Effects of alloy Addition on the Increase of
Tensile Strength of Pearlitic Grey Iron
Element % Addition Increase UTS
(N/mn
2
)
Copper 1 25-30
Nickel 1 15-25
Chromium 0.40 30-50
Molybdenum 0.25 25-30
Vanadium 0.20 25-35
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.
upto 0.40% - 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.
CAUTION : CHILL INDUCING PROPENSITY HIGH.
6. Nickel - Similar to copper.
14. 14
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.
Examples :
(a) 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 - Copperservestocounteractthechillformation
+ 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.
15. 15
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.
16. 16
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
(o
C) = 738 + 18 Si 1.75
........... (1)
t1
(o
C) = 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 (o
C) ........... (4)
tc’ = 1145 - 10Si - 30 P + 30 Cr (o
C) ........... (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)
17. 17
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 fluctuationslike 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 0
C/hr. Now, during heating, the temperature is higher by
about 330
C and the lower limit is taken to be approximately 7000
C.
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 - +280
C
P - +2200
C
Mn - - 1300
C
Ni - - 250
C
Theeutectiodtranformationtemperaturerangeaffectsthestructureandpropertiesof
cast irons, significantly. The generally accepted values of the eutectoid transformation
ranges in the case of different cast irons during heating are given below (0
C) :
18. 18
Grey iron - 750 - 850
Malleable iron - 730 - 790
S. G. iron - 750 - 850
During cooling these temperatures are lower by 35-50o
C
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
D. N. = ........... (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 :
D. N. = ........... (4)
Simplifying,
D. N. = ........... (5)
(C —CE)
(Cc —CE)
C - 2.01 + 0.15 Si
4.26 - 0.3 Si - 2.01 + 0.15 Si
C + 0.15 Si - 2.01
2.25 - 0.15 Si
19. 19
Actual carbon content
Eutectic carbon content
C
4.26 - 0.3 (Si + p)
For quick, practical assessment one can use the following equation
D. N. =
= ........... (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.
20. 20
Table - 3.7
Relative Effect of Elements on
Properties of C.I.
Element Max. content, Increase in %
% transverse strength
Cr 0.5-1.0 4-6
Mo 0.75-1.0 12-15
W 2.0-3.0 20-30
V 0.3-0.5 6-7
Ti 0.10-0.15 2-5
Ni 1.5-2.5 3-7
Cu 2.0-3.0 4-8
Sn 0.05-0.12 3-5
Recommended Ratios :
Cr:Ni = 1:3 to 3:1
Ni:Mo = 4:1 or 3:1, rarely 2:1
Cr:V or Cr:Mo = 1:1
Table - 3.8
Classification of Elements in Cast Iron
Group Elements Effect on as-Cast Effect on I and II
structure of metallic stage grtaphitization
matrix
1. a. Cr, Mo, V, Mg, Stabilize pearlite and Inhibit
Te, B, O, N, H cementite. Increase graphitization
chilling tendency.
b. Mn, 1.0% above
the qtty. reqd.
to balance S.
c. At relatively
high concentration
Ti, Zr
21. 21
Group Elements Effect on as-Cast Effect on I and II
structure of metallic stage grtaphitization
matrix
2. Si, C, Al Graphitize and ferri- Promote both
tize stages.
3. Ni, Cu Graphitize and stabi- Promote I stage
lize pearlite but inhibit II stage
graphitization
4. Ti, Zr In small quantities, Promote I stage
graphitize
inoculate
5. Mn. upto 1.0% Pearlitizes Inhibits II stage
over that reqd.
to balance S, Sn
25. 25
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
26. 26
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) Nickel alloyed irons (Ni-resist)
b) High silicon irons.
2. Elevated Temerature Service :
a) Nickel alloyed irons (Ni-resist)
b) High silicon irons
c) Aluminium alloyed iron
d) High chromium white iron
3. Abrasive Condition :
a) Nicel-chromium white irons (Ni-hard)
b) High chromium white irons
c) Moly-chromium white irons
1. Corrosive Service :
a) 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
27. 27
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) 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.
2. 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.
Typical compositions, mechanical properties and applications of the
four kinds of high alloy irons for elevated temperature are given in
Table 4.4.
3. 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 :
28. 28
Castings are heated to 7500
C and held at that temperature for 8
hours followed by air cooling. Complex shaped castings with varying
cross section are heated to 5500
C for 4 hours and air cooled to room
temperature. This is foollowed by holding for 16 hours at 4500
C 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 2300
C 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. 0.3% Mo + 1.5% Ni or
2. 0.5% Mo + 1.4% Cu
Austempering Treatment : See figs 4.1 4.2
29. 29
Advantages over forged steel :
a. Excellent machinability, longer tool life and increased machining
speeds.
b. Higher quality finish on machined surfaces.
c. Excellent resistance to scoring and wear.
d. Higher damping capacity and therefore quiter operation.
e. Shorter heat treatment cycle.
f. Less machining required.
g. A 10% savings in weight.
h. A lower energy requirement from molten to finished component.
Application :
Gears and other dynamically loaded castings.
Mechanical Properties :
Y.S U.T.S. %E BHN
N/mm2
N/mm2
750-1250 900-1500 2-8 285/360
42. 42
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
Raw Material control
Charge make up
Furnace Control
Melting Holding
Nodulzarizing
treatment -
Temperature control, nodularizing agent addition, treatment check
(Metallographically and/or ultrasonically)
Fig. 6.1
Factors in the control of metal production.
Pour
S. G. Iron Grey Iron
-
-
-
-
-
-
Basemetal, alloying elements trace elements.
Specification, quality verification, storage.
Specify charge balance, weighing facilities.
Type of furnace and its controls.
Desulphurize, carburize, temperature control chill
test chemical analysis.
Inoculation, pouring temperature
43. 43
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.
44. 44
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
(1500-15000
C).
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.
45. 45
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.
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.
3. Unless there is a wide variation in
the base composition, the degree of
nucleation remains constant.
4. It is important to have provision for
metal mixing.
5. Rapid change in the grade of base iron
is possible due to carburization.
The loss of trace elements is
significantly reduced and hence
cleaner purer charge material will
have to be used.
The degree of nucleation can
be significantly reduced due to
increased super heating and holding
time. Trimming additions on the
other hand, increases nucleation.
Poor quality material will result in increased
nitrogen aluminium content leading to fissure
defects and pinholes.
Table 6.2
Effect of furnace type
46. 46
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) Pureferrosiliconisnotaneffectiveinoculantandhence,siliconbasedinoculants
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
47. 47
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
Ductile Iron
Metallurigical Effect
- Promotes type A graphite
formation
- Increases eutectic cell count
- Reduces formation of
chilled edges.
- Excessive inoculation is
detrimental
- Increases nodularity and
ferrite in as cast iron
- Reduces carbide
- Excessive inoculation is
detrimental and may give
high aluminium.
Effect on Quality
Improves hardness and tensile
strength.
Uniform properties through-
out the casting
Improves machinability and
increases tool life
Increases propensity to
shrinkage and porosity
Improves machinability
Increases strength and
ductility
Pinhole formation may take
place.
Adversely affects mechanical
properties.
48. 48
Metal Handling and On-line Controls :
Ladle practice
a) Lining material should be high quality refractory with fusion point in excess
of 14500
C.
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.
49. 49
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 : 9200
C - 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 : 9200
C-2 hours-furnace cool to 5000
C 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 :
50. 50
a) Normalise - 9200
C, 2 hours - Air cool
Temper - 6800
to 7100
C, 2 to 4 hours.
b) Step Normlize - 9200
C, 2 hours furnace cool to 8000
C - hold for 30 mints.
- furnace cool to 5000
C - hold for 30 mins.
Hardening Tempering
The main objective of this treatment is for improved wear resistance.
Typical Cycle - 9200
C, 2 hours -oil quench Temper - 6800
to 7100
C - 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.
Al 0.01-.015 For ferritic grades only
51. 51
Ladle addition :
Bi .01/.015
B .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 0
C - 1480/1500).
b) Boron addition :
- Reduces FSG/SSG by better nucleation.
54. 54
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
55. 55
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.
56. 56
Table 8.1
Electrodes for the Welding of Cast Irons
Class of Electrode Details
1. Ferritic Low hydrogen carbon steel electrodes
suitable for noncritical jobs.
Preheating temperture-3500
C.
2. Nickel based Most suitable for coping with the dilution in
castironwelding.Thecarbonintheweldmetal
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 % Ni92
Depositsthesoftesti.e.theeasiestmachinable
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.
2b) Nickel Iron Type % Ni - 55, % Fe - 45
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.
2c) Monel Type % Ni - 70, % Cu - 30
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.
57. 57
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 390 170
DIN B573
ENi G2
Nickel Iron C-0.7, Ni 57 AWS ENi FeCl 550 190
Fe: Balance DIN B573
ENiF eG2
Nickel C-1.0, Ni.63 AWS ENi CuB* 450 180
Copper Type Cu Balance DIN B573
ENi Cu G2
*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 -do-
58. 58
Post Heating
Stress relieving : heating to 6000
C 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
59. 59
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 7100
C 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 4250
C 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 Form
Flouride Powder
Liquid
Paste (most polular)
60. 60
4. Soldering :
This process too has limited application in this field. Soldering is carried out
at temperatures below 4250
C.
Typical Composition :
Solder Flux
% Sn % Pb % Zn
35 30 35 Zn cl2
5. 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.
69. 69
CHAPTER - 10
NATIONAL AND INTERNATIONAL
STANDARDS
Grey Cast Iron :
INDIA IS : 210 - 1978
Grade Tensile Strength B.H.N
MPa (N/mm2
) min.
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 Tensile Strength
test bar Rm’
min
mm kgf/ tonf/ lbf/
mm2
in2
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
70. 70
UNITED KINGDOM BS 1450 : 1977
Grade Dia. of as-Cast Tensile Strength
test bar 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 Tensile Strength
test bar 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
71. 71
Grade Dia. of as-Cast Tensile Strength
test bar 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.
72. 72
USA ANSI / ASTM A 48-76
Nominal Nominal Tensile Strength
section dia. of Rm’
min
Grade thickness as-cast
test-bar
mm mm MPa
N/mm2
ksi*
20A 6-12 22.4 138 20
B 13-25 30.5
C 26-50 50.8
S 6 or 50 Bar S
25A 6-12 22.4 172 25
B 13-25 30.5
C 26-50 50.8
S 6 or 50 Bar S
30A 6-12 22.4 207 30
B 13-25 30.5
C 26-50 50.8
S 6 or 50 Bar S
35A 6-12 22.4 241 35
B 13-25 30.5
C 26-50 50.8
S 6 or 50 Bar S
40A 6-12 22.4 276 40
B 13-25 30.5
C 26-50 50.8
S 6 or 50 Bar S
73. 73
Nominal Nominal Tensile Strength
section dia. of Rm’
min
Grade thickness as-cast
test-bar
mm mm MPa
N/mm2
ksi*
45A 6-12 22.4 310 45
B 13-25 30.5
C 26-50 50.8
S 6 or 50 Bar S
50A 6-12 22.4 345 50
B 13-25 30.5
C 26-50 50.8
S 6 or 50 Bar S
55A 6-12 22.4 379 55
B 13-25 30.5
C 26-50 50.8
S 6 or 50 Bar S
60A 6-12 22.4 414 60
B 13-25 30.5
C 26-50 50.8
S 6 or 50 Bar S
* Ksi - kilo pounds per square inch;
1 kilo pound = 1000 pound
all dimensions of test bar S shall be agreed upon between the manufacturer
and the purchaser.
84. 84
USA SAE J434B*
(Automotive ductile iron casting : 1970)
Hardness Structure
Grade
HB
D4018 170mx. Ferrite
D4512 156-217 Ferrite
Pearlite
D5506 187-255 Ferrite
Pearlite
D7003 241-302 Pearlite
DQT** — 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.
85. 85
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.
-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
-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
-459.4
-454
-436
-418
-400
-382
-364
-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.
91. 91
C. F.
1616
1621
1627
1632
1638
1643
1649
2940
2950
2960
2970
2980
2990
3000
5324
5342
5360
5378
5396
5414
5432
C. F.
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. kg/mm2
14 17 20 23 28 32 38
Desity g/cm3
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
92. 92
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
93. 93
Table 11.5
Specific Gravity and Melting Point of
Casting Alloys
Alloy Sp. Melting
Gravity Point, 0
C
1. Open grained high
Carbon 6.95
2. Close grained low 1130-1250
carbon C.I. 7.35
3. White Cast Iron 7.3-7.75 1180-1220
4. Ferritic blackheart M 7.1-7.3
malleable
5. Pearlitic blackheart M 7.3-7.45
1180-1220
6. Whiteheart Malleable 7.3-7.7
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 7.8-7.85 1400-1525
11. High alloy steel 7.5-8.1 1450-1500
12. Pure iron 7.87 1535
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
94. 94
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
Alloy Sp. Melting
Gravity Point, 0
C
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
95. 95
Table 11.7
Properties of Microstructural Consituents of Cast Iron
Structural Component Sp. Tensile str. Hardness Elong. d %
Gravity Kg/mm2
BHN
Graphite 2.3
Phosphide eutectic 7.32
Ferrite 7.87 35-45 110-130 15-25
Acicular Ferrite 230-260
Cementite 7.82 3-5 600-900
Austenite 200
Pearlite (unalloyed) 7.8 80-100 200-230 6
Spheroidized pearlite 7.8 160-190
Sorbite 120-140 240-280
Martensite 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 —
96. 96
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 S P Mo
200-250 2.9 1.2 1.1 0.1 (max) 0.1 0.4
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 —
97. 97
Table 11.11
Relationship between Tensile Strength and Brinell Harness for
Various Microstructures and Compositions
Carbon Ration,
Equivalent, % Ten. Str. + BHN Microstructure
3.45-3.65 210 and over 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 Large cell, complete type D graphite.
3.65-3.85 190-210 Small cell, normal graphite.
180-190 Medium cell, normal grahite
or small cell, partial type D.
170-180 Medium cell, with partial type
D Graphite
160-170 Large cell, type D graphite or free
ferrite.
3.85-4.20 190-210 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.
98. 98
Table 11.12
The Influence of Notches on the Tensile
Strength of Two Grey Irons
Type of Test Iron A Iron B
Tensile Strength, psi
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
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 (15-140) × 10-4
%
Hydrogen (0.5-3) × 10-4
%
Oxygen (4-100) × 10-4
%
The gas content is measure as
i) CC/100 g of metal ;
ii) per cent ;
iii) Parts per million. (ppm)
99. 99
Their mutual relationship are as follows :
1 CC/100 g. of N2
= 0.00125%
= 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.
112. 112
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 (9060
C
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.
113. 113
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
transformationproducts,andinmaintainingthealloy,untiltransformationiscomplete,
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 non-
magnetic 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.
114. 114
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
4250
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
10
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.
115. 115
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.
116. 116
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.
117. 117
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.
118. 118
Creep :
The flow or plastic deformation of metals held for long periods of time at
stresses lower than the normal yield strength.
Critical Temperature :
Temperatureatwhichmetalchangesphase.Inusualironalloys,thetemperature
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.
119. 119
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 13990
C 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.
120. 120
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.
121. 121
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 :
Inelectro-metallurgy,aconductorbelongingtotheclassof metallicconductors,
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.
122. 122
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.
123. 123
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
124. 124
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.
125. 125
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
126. 126
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.
127. 127
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.
128. 128
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 ferrite-
carbide 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.
129. 129
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).
130. 130
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
131. 131
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.
132. 132
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.
133. 133
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.
134. 134
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.
135. 135
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.
136. 136
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.
137. 137
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
138. 138
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.
139. 139
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.
140. 140
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.
141. 141
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 :
Amethodof determiningtransformationsinametalbynotingthetemperatures
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/0
C/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.
142. 142
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
14000
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.
143. 143
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.
