In this presentation the maximum information collected and covered very fully and deeply about metallurgical study of cast irons by M.M.RAFIK.

1. C.U.Shah College of Engineering &
Technology, Wadhwan city.
Prepared by :
MEMAN MAHAMMADRAFIK J.

2.  Cast iron is made when pig iron is re-
melted in small cupola furnaces (similar to the
blast furnace in design and operation) and
poured into molds to make castings. Cast Iron
is generally defined as an alloy of Iron with
greater than 2% Carbon, and usually with
more than 0.1% Silicon.
 Silicon and other alloying elements may
considerably change the maximum solubility of
Carbon in Austenite. Thus certain alloys can
solidify with a eutectic structure having less
than 2% Carbon.

3.  Cast iron has its earliest origins in China between
700 and 800 B.C.
 Until this period ancient furnaces could not reach
sufficiently high temperatures.
 The use of this newly discovered form of iron
varied from simple tools to a complex chain
suspension bridge erected approximately 56 A.D.
 Cast iron was not produced in mass quantity until
fourteenth centaury A.D.

4.  In 1325 A.D. water driven bellows were introduced
which allowed for a greater draft to be fed to the
pit, thus increasing temperatures.
 The next significant development in cast iron was
the first use of coke in 1730 by an English founder
named Darby.
 Coke could be used more efficiently than coal, thus
lowering the cost and time necessary to yield a
final product.

5.  This discovery, with stronger and more efficient
cast iron alloys being produced, led to larger scale
production of cast irons with varying properties.
 Due to this revolution, better casts were available
for more versatile roles, such as James Watt's first
steam engine, constructed in 1794.
 In 1810, Swedish chemist Bergelius, and German
physicist Stromeyer discovered that by adding
Silicon to the furnace, along with scrap and pig
iron, consistently stronger cast iron is produced.

6.  In 1885 Turner added
ferrosilicon to white iron
to produce stronger gray
iron castings.
 In the later 20th century
the major use of cast
irons consisted of pipes,
thermal containment
units, and certain
machine or building
entities which were
necessary to absorb
continuous vibrations.

7.  White Iron: large amount of
carbide phases in the form of
flakes, surrounded by a matrix
of either Pearlite or Martensite.
The result of metastable
solidification. Has a white
crystalline fracture surface
because fracture occurs along
the iron carbide plates.
Considerable strength,
insignificant ductility.
 Gray Iron: Graphite flakes
surrounded by a matrix of
either Pearlite or a-Ferrite.
Exhibits gray fracture surface
due to fracture occurring along
Graphite plates. The product of
a stable solidification.
Considerable strength,
insignificant ductility.
Microstructure of White Cast Iron
Microstructure of Gray Cast Iron

8.  Ductile (Nodular) Iron:
Graphite nodules surrounded by
a matrix of either a-Ferrite,
Bainite, or Austenite. Exhibits
substantial ductility in its as cast
form.
 Malleable Iron: cast as White
Iron, then malleabilized, or heat
treated, to impart ductility.
Consists of tempered Graphite
in an a-Ferrite or Pearlite
matrix.
Microstructure of Ductile Iron
Microstructure of Malleable Iron

9.  Chilled Iron: White Iron that has been produced by quenching
through the solidification temperature range.
 Mottled Iron: Solidifying at a rate with extremes between those for
chilled and gray irons, thus exhibiting micro-structural and
metallurgical characteristics of both.
 Compacted Graphite Cast Iron: consists of a microstructure similar to
that of Gray Iron, except that the Graphite cells are coarser and more
rounded. Namely, it consists of a microstructure having both
characteristics of Gray and Ductile Irons.
 High-Alloy Graphitic Irons: produced with microstructures consisting
of both flake and nodule structures. Mainly utilized for applications
requiring a combination of high strength and corrosion resistance.

10.  Most common alloying element of Cast
Irons is Silicon for various reasons,
which include the manipulation of
temperatures required to achieve desired
microstructures.
 example: Increases the stability of
solidification of Graphite phases.
Decreases the stability of the
solidification of Fe3C. Eutectic and
eutectoid temperatures change from
single values to temperature ranges.
Eutectic and eutectoid compositions are
affected.
 %C + 1/3%Si = 4.3
 Carbon Equivalent  CE: a measure
of the equivalency of Carbon coupled
with other alloying elements to that of
just Carbon. An easier basis for
classifying the properties of a mult ialloy
material.
 %C + 1/3%Si = CE [1]
 (hypoeutectic) < CE = 4.3 <
(hypereutectic)
 With the addition of Phosphorus
 CE = %C + 1/3(%P + %Si) [2]

11.  Graphite structure is a factored crystal bounded by low index
planes.
 Growth occurs along (ı0ī0) & (000ı) planes (direction A & C).
Unstable growth occurs along direction A, giving the Graphite
microstructure rough, poorly defined, edges in certain areas.
 When grown from the solidification of liquid Iron Carbon alloys,
Graphite takes on a layer structure. Among each layer covalent
chemical bonds with strengths between (4.19E5 - 5E5)J/mol exist.
Between layers weaker bonds exist on the order of (4.19E3 -
8.37E3)J/mol.
 The structure of the Graphite depends on the chemical
composition, the ratio of temperature gradient to growth rate, and
the cooling rate. Such structures are:
 a) Flake or Plate Graphite
 b) Compacted vermicular Graphite
 c) Coral Graphite
 d) Spheroidal Graphite

12.  A wide variety of compounds and certain metals have been
claimed to serve as either inoculants or nuclei for Flake Graphite
growth. (Silicon dioxide, silicates, sulfides, boron nitride,
carbides, sodium, potassium, calcium, etc.)
 Two methods of growth.
 The nucleation of Flake Graphite Iron occurs mainly on silicon
dioxide particles.
 Salt like carbides containing the ion Carbon are used as
inoculants. Such carbides include NaHC2 & KHC2 from Group
I, CaC2, SrC2, BaC2 from group II, and YC2 & LaC2 from
group III.

13.  The solidification of a sample is
represented mathematically by
the relationship.
 dQ/dt = VCp dT/dt [3]
 where V is the volume of the
sample,  is the density, Cp is the
heat capacity, and dT/dt is the
cooling rate of the liquid. dT/dt is
the slope of the cooling curve
before solidification begins.
 When the liquid cools below
the liquidus temperature, crystals
nucleate and begin to grow. The
rate is thus reexpressed as:
 dQ/dt = (VCp +
Hdƒ/dT)dT/dt [4]
 where H is the heat of
solidification and dƒ/dT is the
volume fraction of solid formed at
a changing temperature.

14.  White Cast Irons contain
Chromium to prevent formation of
Graphite upon solidification and to
ensure stability of the carbide
phase. Usually, Nickel,
Molybdenum, and/or Copper are
alloyed to prevent to the formation
of Pearlite when a matrix of
Martensite is desired.
 Fall into three major groups:
 Nickel Chromium White Irons:
containing 3-5%Ni, 1-4%Cr.
Identified by the name Ni-Hard 1-4
 The chromium-molybdenum
irons (high chromium irons): 11-
23%Cr, 3%Mo, and sometimes
additionally alloyed w/ Ni or Cu.
 25-28%Cr White Irons:
contain other alloying additions of
Molybdenum and/or Nickel up to
1.5%

15.  Produced for more than 50 years, effective materials for crushing and grinding in industry.
 Consists of Martensite matrix, with Nickel alloyed at 3-5% in order to suppress
transformation of Austenite to Pearlite.
 Chromium usually included between 1.4-4% to ensure Carbon phase solidifies to Carbide,
not Graphite. (Counteracts the Graphitizing effect of Ni)
 Abrasion resistance (usually desired property of this material) increases with Carbon content,
but toughness decreases.
 Various grades class I Type A abrasion resistant; class I type B toughness
 Applications: Because of low cost, used primarily in mining applications as ball mill liners and
grinding balls.
 Class I, type A (max abrasion resistance) ash pipes, slurry pumps, roll heads, Muller tires,
augers, coke crusher segments, and brick molds.
 Class I type B (more strength and exerting moderate impact) crusher plates, crusher
concaves, and pulverizer pegs.
 Class I, type C (designed for single purpose of grinding aggregate) sand cast and chill cast
Class I, type D (higher strength and toughness) pump volutes handling abrasive slurries and
coal pulverizers.

17.  Excellent abrasion resistance. Provide the best combination
of toughness and abrasion resistance among White Cast
Irons. The tradeoff is between wear resistance and
toughness.
 Two types: the hard, discontinuous, X7C3 eutectic
Carbides present in the microstructure
 the softer, more continuous, X3C present in Irons
containing less Chromium.
 Usually produced by hypoeutectic compositions.
 For Abrasion Resistance: 11-23%Cr, 3.5%Mo. Usually
supplied as cast with an Austenitic or Austenitic-Martensitic
matrix, or heat treated with a martensitic matrix.
Considered the hardest of all grades of White Cast Iron.
 For Corrosion Resistance: 26-28%Cr 1.6-2.0%C. Provide
the max Cr content in the matrix for room temperature.
Fully austenitic matrix provides the best resistance to
corrosion in this alloy, but with a decrease in abrasion
resistance.
 For High-Temperature Service: Often used for high
temperature applications because of castability and cost.
Alloyed with between 12-39% Cr at temperatures up to
1040˚C for scaling resistance Cr causes the formation of a Cr
rich oxide film at high temperatures. Fall into three
categories depending on the Matrix: Martensitic irons
alloyed with 12-28%Cr; Ferritic Irons alloyed w/ 30-
34%Cr; Austenitic irons that contain 15 - 30% Cr with 10-
15%Ni to stabilize the Austenite phase. Applications include
recuperator tubes, breaker bars and trays in sinter furnaces,
other furnace parts, glass bottle molds, and valve seats for
combustion engines.

18.  Gray Cast Irons contain silicon, in addition to carbon, as a
primary alloy. Amounts of manganese are also added to
yield the desired microstructure. Generally the graphite
exists in the form of flakes, which are surrounded by an a-
ferrite or Pearlite matrix. Most Gray Irons are hypoeutectic,
meaning they have carbon equivalence (C.E.) of less than 4.3.
 Gray cast irons are comparatively weak and brittle in tension
due to its microstructure; the graphite flakes have tips which
serve as points of stress concentration. Strength and ductility
are much higher under compression loads.

19.  Graphite morphology and matrix characteristics affect the physical and
mechanical properties of gray cast iron. Large graphite flakes produce good
dampening capacity, dimensional stability, resistance to thermal shock and
ease of machining. While on the other hand, small flakes result in higher
tensile strength, high modulus of elasticity, resistance to crazing and smooth
machined surfaces.
 Mechanical Properties can also be controlled through heat treatment of the
gray cast iron. For example, as quenched gray cast iron is brittle. If
tempering is accomplished after quenching, the strength and toughness can
be improved, but hardness decreases. The tensile strength after tempering
can be from 35-45% greater than the as-cast strength and the toughness can
approach the as-cast level.

20.  The chemical analysis of gray iron can be broken into three main categories;
 The main elements: These are Carbon, Silicon, and Iron. Gray cast irons
typically contain 3.0-3.5% carbon, with silicon levels varying from 1.8-2.4%.
 The minor elements: Phosphorus and the two related elements, manganese
and sulfur. Phosphorus is found in all gray irons, although rarely added
intentionally, it does increase the fluidity of iron to some extent. High levels
promotes shrinkage porosity, while very low levels can increase metal
penetration into a mold. Thus, most castings are produced with 0.02-0.10% P.
Sulfur plays a significant role in nucleation of graphite in gray iron, with
optimum benefit at 0.05-0.12% sulfur levels. It is also important to note that
sulfur levels need to be balanced with manganese to promote formation of
manganese sulfides.
 The trace elements: Many other elements are utilized in limited amounts to
affect the nature and properties of gray iron. Although some are not
intentional, they do have a measurable affect on the gray cast iron. Some
promote Pearlite, such as tin, while others compact graphite and increase
strength, such as nitrogen.

21.  As a liquid, Ductile Iron has a high fluidity, excellent castability,
but high surface tension. Thus, sands and molding equipment
must provide molds of high density and good heat transfer.
 Solidification of Ductile Cast Iron usually occurs with no
appreciable shrinkage or expansion due to the expansion of the
graphite nodules counteracting the shrinkage of the Iron matrix.
Thus, risers (reservoirs in mold that feed molten metal into the
cavity to compensate for a decrease in volume) are rarely used.
 Require less compensation for shrinkage. (Designers
compensate for shrinkage by casting molds that are larger than
necessary.)
 Most Ductile Irons used as cast. Heat treating (except for
austempering) decreases fatigue properties. Example: Holding at
the subcritical temperature (705˚C) for ≈ 4 hours improves fatigue
resistance. While heating above 790˚C followed by either an air or
oil quench, or ferritizing by heating to 900˚C and slow cooling
reduces fatigue strength and fatigue resistance in most warm
environments.
 Austempered Ductile Iron has been considered for most
applications in recent years due to its combination of desirable
properties. A matrix of Bainitic Ferrite and stabilized Austenite
with Graphite nodules embedded. Applications include: Gears,
wear resistant parts, High-fatigue strength applications, High-
impact strength applications, automotive crankshafts, Chain
sprockets, Refrigeration compressor crankshafts, Universal joints,
Chain links, and Dolly wheels.

22.  Effect of composition on properties:
 Carbon: During solidification, Carbon
precipitates to Graphite, which offsets
shrinkage. Amount necessary to achieve
this: %C + 1/7%Si ≥ 3.9% Also, Carbon
contents greater than this amount
decrease fatigue strength.
 Silicon: Graphitizing agent. Increasing
amount of Silicon also increases amount
of Ferrite. Increases strength and
hardness of this Ferrite and reduces
impact resistance. Also, provides high
temperature oxidation resistance. For
applications of high temperature, such as
turbocharger housings, Silicon contents
of between 3.75% and 4.25% are required.
 Manganese: Acts as a Pearlite
stabilizer and increases strength, but
decreases ductility and machinability.
 Nickel: Increases strength by
promoting formation of fine Pearlite.
Increases hardenibility.
 Copper: Used to form Pearlite upon
solidification with high strength and good
toughness and machinability.
 Molybdenum: Used to stabilize
structures at high temperatures.

23.  Effects of microstructure on properties:
 Graphite nodules cause the Iron to be both
strong and ductile (more so than gray Cast
Iron). Approaches the characteristics of Steel
(Tensile strengths between 400 and 480 MPa
Ductility between 15 and 20%. The smaller
and more numerous the nodules the higher
the tensile properties of the material. If
some minor alterations are made to the
microstructure compacted graphite Iron may
be achieved, namely, between 5 and 20% of
the graphite is of the shpeoridial form, the
rest being of a compacted blunt, vermicular
form. This material has better thermal
transfer characteristics and fewer tendencies
for porosity.
 The % nodularity, a measure of the amount of
graphite in the nodular form, corresponds
with the characteristics of this material.
%nodularity is measured by resonant
frequency or ultrasonic velocity
measurements.

24.  ASTM system for designating various Ductile Iron
grades incorporates numbers indicating Tensile
Strength in ksi, yield strength in ksi, and elongation
in percent. For example A 536 grade 80-60-03 = (80
ksi|552 MPa) min tensile strength, (60ksi|414MPa)
min yield strength, 3 % elongation.

26.  Stress Relieving: 540 - 595˚C reduces warping
and distortion during subsequent machining.
 Annealing: Full feritizing Annealing used to
remove carbides and stabilized Pearlite, heat to
900˚C, holding long enough to dissolve
carbides, then cooling at a rate of 85˚C/h to
705˚C, and still air cooling to room
temperature. Also improves low temperature
fracture resistance but reduces fatigue
strength.
 Normalizing, Quenching, and Tempering:
heated to 900˚C, held for 3 hours (allowing
1h/25mm or 1h/in of cross section to reach that
temperature). The air blasted or oil quenched.
Followed by tempering between 540 - 675˚C.
Used to achieve grade 100-70-03. Hardness’s
as high as 255HB, increase short time fatigue
strength, decreases fatigue life. Increases
tensile and yield strengths at the expense of
ductility.
 Autempering: Used to achieve Austempered
Ductile Iron, requires two stages. Stage 1:
heating to and holding at 900˚C. Stage 2:
quenching and isothermally holding at the
required austetempering temperature, usually
in a salt bath. austempering temperatures
shown in figure below.

27.  Used for a variety of applications, specifically those requiring strength
and toughness along with good machinability and low cost. Casting,
rather than mechanical fabrication (such as welding), allows the user
to optimize the properties of the material, combine several castings into
a desired configuration, and realize the economic advantages inherent
in casting.
 Microstructure is consistent; machinability is low due to casting
forming the desired shape; porosity is predictable and remains in the
thermal center.
 Ductile Iron can be austempered to high tensile strength, fatigue
strength, toughness, and wear resistance. Lower density
 Ductile Iron seems to work in applications where theories suggest it
should not.
 Ductile Iron shipments exceeded 4 million in 95.
 Cast Iron pipe make up to 44% of those shipments.
 29% used for automobiles and light trucks (economic advantages
and high reliability)
 Other important applications are: Papermaking machinery; Farm
equipment; Construction machinery and equipment; Power
transmission components (gears); Oilfield equipment.

28.  Type of Iron with Graphite in the form of irregularly shaped nodules.
 Produced by first casting the Iron as a White Iron, then heat treating to
transform the Carbide into Graphite.
 Categorized into 3 categories: Ferritic, Pearlitic, and Martensitic Malleable
Cast Iron.
 Two types of Ferritic: Blackheart (top) and Whiteheart (not produced in US)
 Posses’ considerable ductility and toughness due to the combination of nodular
graphite and low carbon matrix. Often a choice between Malleable and Ductile
Iron for some applications, decided by economic constraints.
 Solidification of white Iron throughout a section is essential in producing
Malleable Iron, thus, applications of large cross section are usually Ductile Irons.
 Usually capable in section thickness between 1.5-100mm (1/16 4 in) and 30g
(1oz) - 180 kg (400lb)
 Preferred in the following applications: This section casting; parts that are to
be pieced, coined, or cold worked; parts requiring max machinability; parts that
must retain good impact resistance at low temp; parts requiring wear resistance.

29.  Consists of rosette nodules of graphite.
 Derived by control annealing of a cast of white Iron. During
annealing cycle, Carbon, whether in Carbide form or as a micro
constituent in Pearlite, is converted to a form of Graphite known as
temper Carbon.
 opt Iron 1st stage 3.5h at 940˚C(1720), Irons w/ lower Si count or
less opt nodule counts require approx 20h.
 Ferritic:
 stage 2 opt cooled to between 740 & 760(1360-1400) in 1-6h.
Then cooled at a rate of 3-11/h(5-20/h) ; Carbon dissolved in
Austenite is converted to Graphite and deposited on existing
particles of tempered Carbon.
 ferritic malleable Irons require a two stage annealing cycle. first:
converts primary carbides to temper Carbon. Second: converts
Carbon dissolved in Austenite at the first-stage annealing
temperature to temper Carbon and Ferrite.
 Consists of temper Carbon in a matrix of Ferrite. Contain a slight
amount of controlled Iron.
 Pearlitic:
 1st stage identical to that of Ferrite. Casting is slowly cooled to
approx 870˚C. When the combined Carbon content of the
Austenite is reduced to about .75% the castings are air cooled.
Usually air blasted to avoid the formation of ferrite around the
temper Carbon particles. Then, the castings are tempered to specs.
 Nodule Count: Low nodule count mechanical properties reduced
from opt. and second stage annealing time is unnecessarily long.
Excessive nodule leads to low hardenibility and nonuniform
tempering. 80-150 nodules/mm² of a photomicrograph magnified at
100x.

30.  Microstructure consists of temper Carbon in Matrix of Ferrite. No Flake
and no combined Carbon. Usually contain between 2.00-2.70%
Graphite. Si and Mg reduce the elongation and increase the strength of
the Ferrite.
 Mechanical properties: tensile prop: Lower than Pearlitic and
Martensitic.
 fatigue limit
 mod of Elasticity: approx 170GPa(25E6) in tension, 150-170GPa(22E6
25E6)compression, 65-75GPa Tor(9.5E6 11E6)
 Fracture Toughness
 Corrosion resistance: corrosion resistance increased by addition of Cu;
such as chain links. Can be galvanized to provide additional protection.

31.  Can be produced with a wide variety of properties,
depending on heat treatment, alloying, and melting
practices.
 Lower strength produced by air cooling and
casting after first stage anneal, stronger liquid
quench after first stage anneal.
 mechanical properties: vary in a substantially
linear relationship with Birnell Hardness. > 207 HB
properties of air quenched & tempered pearlitic =
oil-quenched and tempered martensitic. This is due
to the fact that both treatments yield a coarsening
of matrix carbides and partial second stage
graphitization.
 Oil quenched pearlitic has finer Pearlite, thus
having more strength and being harder, as high as
321HB. Air quenched 255HB.
 tensile properties
 Compressive strength seldom determined because
failure almost never occurs in the manner.
Compressive yield strengths slightly higher than
tensile due to decreased influence of graphite
nodules and delayed onset of plastic deformation.
 Shear and Torsional Strength: 80% of tensile
strength for ferritic, 70-90%for pearlitic.
 Modulus Elasticity in Tension pearlitic 176-
193GPa(25.5E6 28.0Eg psi)
 Fracture Toughness
 fatigue limits: tempered pearlitic 40-50% of tensile
strength, temp martensitic 35-40%
 Excellent wear resistance due to structure.

32.  Essential parts in trains,
frames, suspensions, and
wheels.
 differential cases,
bearing caps, steering-gear
housings, spring hangers,
universal-joint yokes,
automatic transmission
parts, rocker arms, disc
brake calipers, wheel hubs,
etc.
 a) Driveline yokes,
 b) Connecting rods,
 c) Diesel pumps,
 d) Steering-gear housing.

33.  Possible to identify and classify a sample of
unknown cast iron.
 Identification can be accomplished through the use
of many known mechanical, chemical and
structural properties of the cast iron alloys.
 As part of our research, we attempted to examine
and identify separate cast iron samples of
unknown composition.

34.  We obtained two samples
of what was initially
perceived to be cast iron.
The first being a cooking
pot, and the second a 90°
pipe fitting.
 Both samples were cut,
mounted and polished in
a bakelite round, for
microstructure
examination.
 Followed by a Rockwell
hardness test of each
specimen.

35.  The microstructure analysis was accomplished
after polishing and etching (utilizing a 3% nitric
acid solution in ethanol) to reveal the grains.
 Initially it was believed that both samples were
cast irons, and although the 90° pipe fitting
appears to be cast iron, the microstructure of the
pot handle yielded a different conclusion.

36.  The two micrographs are shown above, the 90° pipe fitting on
the left, and the cooking pot handle on the right.
 The Rockwell hardness was also measured for both samples,
yielding a hardness of 157 HRB for the fitting, and 120 HRB for
the pot handle.

37.  Upon analysis of the microstructures, it became
apparent that the cooking pot does not conform
to any common form of cast iron.
 Although the handle fractured in a manner very
similar to that of cast iron, the microstructure
shows little resemblance to those of cast iron.
 Although further analysis would be required, one
possibility is a cast steel material. This would
account for the similarity of its fracture to that of
cast iron.

38.  The 90° fitting shows indications
of a dark graphite surrounded
by lighter colored matrix. The
graphite appears to be in the
form of dark rosettes, while the
matrix is a lighter color.
 Upon comparison to the known
structure of different types of
cast irons, it can be seen that the
microstructure of malleable iron
most closely matches our
sample.
 To the right is a side-by-side
comparison, with our sample on
the top, and a known Malleable
microstructure on the bottom.
Pipe Sample (150X mag)
Malleable Iron (150X mag)

39.  Cast Iron and historical significance:
 Used throughout history since its discovery, stepping stone to the
development of modern technology (First Steam Engine)
 Types of Cast Irons and microstructure:
 Grays, Whites, Ductile, Malleable
 Applications:
 Automotive, Industrial, Household, Aeronautical, & Construction
 Sample Analysis and Comparison for identification and Classification:
 Capability to analyze and compare microstructures to determine Cast
Iron Type. And Hardness measurements to identify heat treatment.