Artigo Gray Iron

8/3/2019 Artigo Gray Iron

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Gray Iron-A Unique Engineering Material

By

D. E. Krause, Executive Director - 1940-1973

(The Gray Iron Research Institute, Inc.)

The Iron Casting Research Institute

REFERENCE: Krause, D. E., "Gray Iron-A Unique Engineering Material" Gray,

Ductile, and Malleable Iron Castings-Current Capabilities, ASTM STP 455,

American Society for Testing and Materials, Philadelphia, 1969, pp. 3-28.

ABSTRACT: Gray iron is the most versatile of all foundry metals. The high carbon

content is responsible for ease of melting and casting in the foundry and for ease of

machining in subsequent manufacturing. The low degree or absence of shrinkage

and high fluidity provide maximum freedom of design for the engineer. By suitable

adjustment in composition and selection of casting method, tensile strength can be

varied from less than 20,000 psi to over 60,000 psi and hardness from 100 to 300

BHN in the as-cast condition. By subsequent heat treatment, the hardness can be

increased to H Rc 60.

If the service life of a gray iron part is considered to be too short, the design of the

casting should be carefully reviewed before specifying a higher strength and

hardness grade of iron. An unnecessary increase in strength and hardness may

increase the cost of the casting as well as increase the cost of machining through

lower machining rates. Although the relationship between Brinell hardness and

tensile strength for gray iron is not constant, data are shown which will allow use of

the Brinell hardness test to estimate the minimum tensile strength of the iron in a

casting.

KEY WORDS: gray iron castings, casting design, foundry methods, ductile iron

castings, malleable iron castings, metals, tests, evaluation

Preface:

September 7, 1990

To: All readers of report on Gray Iron by D.E Krause


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While this brief technical paper, originally presented in 1969, is still one of the best

summaries of gray iron metallurgy and properties, we call your attention to one

item on which recent research and foundry experience has shed more light. This

is the matter of manganese and sulfur effects.

In contrast to the traditional view of these elemental effects noted herein, work in

the 1980's confirms that in many cases manganese levels beyond that amount

combined with sulfur (about 1.7 times the sulfur level) tend to reduce strength and

hardness via promotion of more ferrite. However, low levels too close to this 1.7

"balanced ratio" tend to promote high and more erratic hardness and/or carbides.

Consequently, for most applications the optimum operating level for manganese

appears to be about (1.7 x % Sulfur), + 0.3% to 0.5%. For example, for an iron

with 0.10% Sulfur, the optimum range for Manganese would be 0.47% to 0.67%.Running toward the low end of the range would normally maintain higher

hardness and tensile strength while running toward the high end would decrease

both. This effect is also influenced by other metallurgical conditions peculiar to

each base iron so that the optimum range needs to be determined for each

particular melting operation.

We hope this clarification will be informative and useful to both casting producers

and users.

William F. Shaw, Executive Director, Iron Casting Research Institute

Gray iron is one of the oldest cast ferrous products. In spite of competition from

newer materials and their energetic promotion, gray iron is still used for those

applications where its properties have proved it to be the most suitable material

available. Next to wrought steel, gray iron is the most widely used metallic

material for engineering purposes. For 1967, production of gray iron castings was

over 14 million tons, or about two and one-half times the volume of all other types

of castings combined. There are several reasons for its popularity and widespread

use. It has a number of desirable characteristics not possessed by any other

metal and yet is among the cheapest of ferrous materials available to the

engineer. Gray iron castings are readily available in nearly all industrial areas and

can be produced in foundries representing comparatively modest investments. It

is the purpose of this paper to bring to your attention the characteristics of gray

iron which make the material so useful.


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Gray iron is one of the most easily cast of all metals in the foundry. It has the

lowest pouring temperature of the ferrous metals, which is reflected in its high

fluidity and its ability to be cast into intricate shapes. As a result of a peculiarity

during final stages of solidification, it has very low and, in some cases, no liquid to

solid shrinkage so that sound castings are readily obtainable. For the majority of

applications, gray iron is used in its as-cast condition, thus simplifying production.

Gray iron has excellent machining qualities producing easily disposed of chips

and yielding a surface with excellent wear characteristics. The resistance of gray

iron to scoring and galling with proper matrix and graphite structure is universally

recognized.

Gray iron castings can be produced by virtually any well-known foundry process.

Surprisingly enough, in spite of gray iron being an old material and widely used in

engineering construction, the metallurgy of the material has not been clearly

understood until comparatively recent times. The mechanical properties of gray

iron are not only determined by composition but also greatly influenced by foundry

practice, particularly cooling rate in the casting. All of the carbon in gray iron, other

than that combined with iron to form pearlite in the matrix, is present as graphite in

the form of flakes of varying size and shape. It is the presence of these flakes

formed on solidification which characterize gray iron. The presence of these flakes

also imparts most of the desirable properties to gray iron.

Metallurgy of Gray Iron

MacKenzie [1] in his 1944 Howe Memorial Lecture referred to cast iron as "steel

plus graphite." Although this simple definition still applies, the properties of gray

iron are affected by the amount of graphite present as well as the shape, size, and

distribution of the graphite flakes. Although the matrix resembles steel, the silicon

content is generally higher than for cast steels, and the higher silicon content

together with cooling rate influences the amount of carbon in the matrix. Gray iron

belongs to a family of high-carbon silicon alloys which include malleable and

nodular irons. With the exception of magnesium or other nodularizing elements in

nodular iron, it is possible through variations in melting and foundry practice to

produce all three materials from the same composition. In spite of the widespread

use of gray iron, the metallurgy of it is not clearly understood by many users and

even producers of the material. One of the first and most complete discussions of

the mechanism of solidification of cast irons was presented in 1946 by Boyles [2].

Detailed discussions of the metallurgy of gray iron may be found in readily

available handbooks [3-7]. The most recent review of cast iron metallurgy and the


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formation of graphite is one by Wieser et al [8]. To avoid unnecessary duplication of

information, only the more essential features of the metallurgy of gray iron will be

discussed here.

Composition

Gray iron is commercially produced over a wide range of compositions. Foundries

meeting the same specifications may use different compositions to take

advantage of lower cost raw materials locally available and the general nature of

the type of castings produced in the foundry. For these reasons, inclusion of

chemical composition in purchase specifications for castings should be avoided

unless essential to the application. The range of compositions which one may find

in gray iron castings is as follows: total carbon, 2.75 to 4.00 percent; silicon, 0.75

to 3.00 percent; manganese, 0.25 to 1.50 percent; sulfur, 0.02 to 0.20 percent;phosphorus, 0.02 to 0.75 percent. One or more of the following alloying elements

may be present in varying amounts: molybdenum, copper, nickel, vanadium,

titanium, tin, antimony, and chromium. Nitrogen is generally present in the range

of 20 to 92 ppm.

The concentration of some elements may exceed the limits shown above, but

generally the ranges are less than shown.

Carbon is by far the most important element in gray iron. With the exception of the

carbon in the pearlite of the matrix, the carbon is present as graphite. The graphite

is present in flake form and as such greatly reduces the tensile strength of the

matrix. It is possible to produce all grades of iron of ASTM Specification for Gray

Iron Castings (A 48-64) by merely adjusting the carbon and silicon content of the

iron. It would be impossible to produce gray iron without an appropriate amount of

silicon being present. The addition of silicon reduces the solubility of carbon in iron

and also decreases the carbon content of the eutectic. The eutectic of iron andcarbon is about 4.3 percent. The addition of each 1.00 percent silicon reduces the

amount of carbon in the eutectic by 0.33 percent. Since carbon and silicon are the

two principal elements in gray iron, the combined effect of these elements in the

form of percent carbon plus 1/s percent silicon is termed carbon equivalent (CE).

Gray irons having a carbon equivalent value of less than 4.3 percent are

designated hypoeutectic irons, and those with more than 4.3 percent carbon

equivalent are called hypereutectic irons. For hypoeutectic irons in the automotive

and allied industries, each 0.10 percent increase in carbon equivalent valuedecreases the tensile strength by about 2700 psi.


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If the cooling or solidification rate is too great for the carbon equivalent value

selected. the iron may freeze in the iron-iron carbide metastable system rather

than the stable iron-graphite system, which results in hard or chilled edges on

castings. The carbon equivalent value may be varied by changing either or both

the carbon and silicon content. Increasing the silicon content has a greater effect

on reduction of hard edges than increasing the carbon content to the same carbon

equivalent value. Silicon has other effects than changing the carbon content of the

eutectic. Increasing the silicon content decreases the carbon content of the

pearlite and raises the transformation temperature of ferrite plus pearlite to

austenite. This influence of silicon on the critical ranges has been discussed by

Rehder [9].

The most common range for manganese in gray iron is from 0.55 to 0.75 percent.

Increasing the manganese content tends to promote the formation of pearlite

while cooling through the critical range. It is necessary to recognize that only that

portion of the manganese not combined with sulfur is effective. Virtually, all of the

sulfur in gray iron is present as manganese sulfide, and the manganese

necessary for this purpose is 1.7 times the sulfur content. Manganese is often

raised beyond 1.00 percent, but in some types of green sand castings pinholes

may be encountered.

Sulfur is seldom intentionally added to gray iron and usually comes from the coke

in the cupola melting process. Up to 0.15 percent, sulfur tends to promote the

formation of Type A graphite. Somewhere beyond about 0.17 percent, sulfur may

lead to the formation of blowholes in green sand castings. The majority of

foundries maintain sulfur content below 0.15 percent with 0.09 to 0.12 percent

being a common range for cupola melted irons. Collaud and Thieme [10 ] report that,

if the sulfur is decreased to a very low value together with low phosphorus and

silicon, tougher irons will result and have been designated as "TG," or tough

graphite irons.

The phosphorus content of most high-production gray iron castings is less than

0.15 percent with the current trend toward more steel in the furnace charge;

phosphorus contents below 0.10 percent are common. Phosphorus generally

occurs as an iron iron-phosphide eutectic, although in some of the higher- carbon

irons, the ternary eutectic of iron iron-phosphide iron-carbide may form. This

eutectic will be found in the eutectic cell boundaries, and beyond 0.20 percent

phosphorus a decrease in machinability may be encountered. Phosphorus

contents over 0.10 percent are undesirable in the lower-carbon equivalent irons


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used for engine heads and blocks and other applications requiring pressure

tightness. For increased resistance to wear, phosphorus is often increased to 0.50

percent and above as in automotive piston rings. At this level, phosphorus also

improves the fluidity of the iron and increases the stiffness of the final casting.

Copper and nickel behave in a similar manner in cast iron. They strengthen the

matrix and decrease the tendency to form hard edges on castings. Since they are

mild graphitizers, they are often substituted for some of the silicon in gray iron. An

austenitic gray iron may be obtained by raising the nickel content to about 15

percent together with about 6 percent copper, or to 20 percent without copper as

shown in ASTM Specification for Austenitic Gray Iron Castings (A 436-63).

Chromium is generally present in amounts below 0.10 percent as a residual

element carried over from the charge materials. Chromium is often added toimprove hardness and strength of gray iron, and for this purpose the chromium

level is raised to 0.20 to 0.35 percent. Beyond this range, it is necessary to add a

graphitizer to avoid the formation of carbides and hard edges. Chromium

improves the elevated temperature properties of gray iron.

One of the most widely used alloying elements for the purpose of increasing the

strength is molybdenum. It is added in amounts of 0.20 to 0.75 percent, although

the most common range is 0.35 to 0.55 percent. Best results are obtained whenthe phosphorus content is below 0.10 percent, since molybdenum forms a

complex eutectic with phosphorus and thus reduces its alloying effect.

Molybdenum is widely used for improving the elevated temperature properties of

gray iron. Since the modulus of elasticity of molybdenum is quite high,

molybdenum additions to gray iron increase its modulus of elasticity.

Vanadium has an effect on gray iron similar to molybdenum, but the concentration

must be limited to less than 0.15 percent if carbides are to be avoided. Even insuch small amounts, vanadium has a beneficial effect on the elevated

temperature properties of gray iron.

The beneficial effect of relatively small additions of tin (less than 0.10 percent) on

the stability of pearlite in gray iron has been reported by Davis et al [11 ]. The results

of extensive use of tin in automotive engines has been reported by Tache and

Cage [12 ]. Its use is particularly helpful in complex castings wherein some sections

cool rather slowly through the Ar 3 temperature interval. It has been found thatadditions of up to 0.05 percent antimony have a similar effect. In larger amounts,


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these elements tend to reduce the toughness and impact strength of gray iron,

and good supervision over their use is necessary.

Although most gray irons contain some titanium and the effect of titanium on the

mechanical properties has been investigated many times, it is only recently that

Sissener and Eriksson [13] have reported the effect of titanium reduced from a

titanium containing slag in an electric arc furnace. With titanium contents of 0.15

to 0.20 percent, the graphite flakes tend to occur as Type D graphite rather than

predominantly Type A, which is generally considered desirable. They found that

for irons with carbon equivalent of less than about 3.9 percent, the addition of

titanium tends to lower tensile strength. but, for the higher carbon equivalent irons,

tensile strength is improved. Increasing the titanium content of gray iron from

about 0.05 to 0.14 percent through the use of a titanium bearing pig iron increased

the strength of a hypereutectic iron in an ASTM Specification A 48 test bar A (7/8

in. diameter) from 22,000 to 34,000 psi. Further work is being done with titanium

additions.

Normally. nitrogen is not considered as an alloying element and generally occurs

in gray iron as a result of having been in the charge materials. Morrogh [14 ] has

reported that at higher nitrogen levels the graphite flakes become shorter and the

strength of the iron is improved. Gray irons usually contain between 20 and 92

ppm (0.002 to 0.008 percent) nitrogen. If the nitrogen approaches or exceeds 100

ppm, unsoundness may be experienced if the titanium content is insufficient to

combine with the nitrogen.

Effect of Section Size on Structure

All cast metals are said to be section sensitive. As the section size increases. the

solidification rate decreases with an accompanying increase in grain size and

subsequent decrease in tensile strength. The effect of freezing rate on strengthand hardness is more pronounced in gray iron than for other cast metals. This is a

result of the mechanism of solidification. For a hypoeutectic iron, the first phase to

separate on cooling is austenite in the form of dendrites at the liquidus

temperature. As cooling progresses, the austenite dendrites grow, and the

remaining liquid becomes enriched in carbon until the eutectic composition of 4.3

percent carbon equivalent is reached. This occurs at a temperature of

approximately 2092F depending on the silicon cont ent. At this temperature,

eutectic austenite and graphite in the form of flakes are deposited simultaneously.


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The austenite-graphite deposition occurs at a number of centers or nuclei, and

these grow in size until all of the liquid is gone creating a cell-type structure.

During this period of cell growth, the phosphorus is rejected toward the cell

boundaries and freezes as a eutectic at about 1792F. The presence of the

phosphorus in the cell boundaries makes it possible to clearly reveal them by

etching with Stead's reagent. It has been demonstrated that the graphite flakes

grow only within the boundaries of a cell and are interconnected. The cell size is

dependent on the degree of nucleation of the iron and the freezing rate. It will vary

from about 500 to as high as 25,000 cells per square inch.

Since graphite has a much lower density than iron, the normal contraction which

will occur when the iron changes from liquid to solid is completely compensated

for by the formation of graphite. For ASTM Designation A 48, Class 30B iron,

shrinkage is virtually absent so that sound castings are readily produced providing

the mold has adequate rigidity. The graphite structure seen in gray iron has been

completely established by the time the iron is solidified. Upon further cooling,

some additional carbon is deposited on the graphite flakes until the Ar3

temperature is reached. As a result of the high silicon content of gray iron, the

transformation of austenite to pearlite and ferrite does not occur at a fixed

temperature but takes place over a temperature range termed the "pearlite

interval" and is explained fully by Boyles[15]. Since the presence of silicon makes

iron carbide unstable, the proportion of ferrite and pearlite in the matrix after

transformation is completed will depend on the cooling rate through this

temperature range. For heavy sections and high silicon contents, the matrix can

be completely ferritic.

The graphite flake type, form, and size can be defined by following the procedure

described in ASTM Method for Evaluating the Microstructure of Graphite in Iron

Castings (A 247-67). Since graphite is a relatively soft material, special care

needs to be exercised in the preparation of a specimen for metallographic

examination. If improperly done, the true shape of the graphite may be obscured

by distorted metal that flowed over the graphite. It is only after several etching and

polishing operations that a true representation of the graphite will be revealed.

Casting Processes

Several molding processes are used to produce gray iron castings. Some of these

have a marked influence on the structure and properties of the resulting casting.The selection of a particular process depends on a number of factors, and the


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design of the casting has much to do with it. The processes using sand as the

mold media have a somewhat similar effect on the rate of solidification of the

casting, while the permanent mold process has a very marked effect on structure

and properties.

Green sand molding is frequently the most economical method of producing

castings. Until the introduction of high-pressure molding and very rigid flask

equipment, dimensional accuracy has not been as good as can be obtained from

shell molding. If green sand molds are not sufficiently hard or strong, some mold

wall movement may take place during solidification, and shrinkage defects

develop. Although castings up to 1000 lb or more can be made in green sand, it

generally is used for medium to small size castings. For the larger castings, the

mold surfaces are sometimes sprayed with a blacking mix and skin dried to

produce a cleaner surface on the casting. This procedure is often used on engine

blocks.

To withstand the higher ferrostatic pressures developed in pouring larger castings;

dry sand molds are often used. In some cases, the same sand as used for green

sand molding is employed, although it is common practice to add another binder

to increase the dry strength.

The shell molding process is also used for making cores which are used in othertypes of molds besides shell molds. Its principal advantage is derived from the

ability to harden the mold or core in contact with a heated metal pattern, thus

improving the accuracy with which a core or mold can be made. In addition to the

improved accuracy, a much cleaner casting is produced than by any other high-

production process. Although the techniques and binders for hot box and the

newest cold box processes differ from those used for the shell molding process,

the principle is similar in that the core is hardened while in contact with the

pattern.

Centrifugal casting of iron in water-cooled metal molds is widely used by the cast

iron pipe industry as well as for some other applications. With sand or other

refractory lining of the metal molds, the process is used for making large cylinder

liners.

For some types of castings, the permanent mold process is a very satisfactory

one, and its capabilities have been described by Frye[16]. Since the cooling orfreezing rate of iron cast into permanent molds is quite high, the thinner sections

of the casting will have cementite. To remove the cementite the castings must be


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annealed, and it is universal practice to anneal all castings. The most economical

composition of the iron for permanent mold castings is hypereutectic. This type of

iron expands on solidification, and, because the molds are very rigid, the pressure

developed by separation of the graphite during freezing of the eutectic ensures a

pressure tight casting. Since the graphite occurs predominantly as Type D with

very small flakes, permanent mold castings are capable of taking a very fine

finish. For this reason, it finds extensive use in making valve plates for

refrigeration compressors. The process is also ideally suited for such components

as automotive brake cylinders and hydraulic valve bodies. Although the

predominantly Type D graphite structure in permanent mold castings with a matrix

of ferrite have much higher strength than sand castings of comparable graphite

content, the structure is not considered ideal for applications with borderline

lubrication. The castings perform very well, however, when operating in an oil

bath.

Unless some special properties are desired and are obtained only with a particular

casting process, the one generally selected yields castings at the lowest cost for

the finished part.

Casting Design

There are a number of requirements which must be met before the design of acasting can be considered completely satisfactory. In some respects, the design

of a casting for gray iron is somewhat simpler than for any other foundry metal in

that solidification shrinkage is at a minimum and for the softer grades is absent

altogether. With few exceptions, little concern needs to be given to the problem of

feeding metal to heavier sections. Patternmakers shrinkage is also low. The low

shrinkage characteristics contribute to freedom from hot tears encountered with

some of the other foundry metals. These factors afford the engineer greater

freedom of design.

Although a casting must be designed to withstand the loads imposed on it, there

are many instances where deflection under load is of primary consideration to

ensure proper alignment of components under load. There are a number of

handbooks which contain information helpful to the design engineer[17-19]. The

appearance of many castings suggests, however, that the designer has been

unduly influenced by the characteristics of flat plates and other wrought shapes. It

appears he is unable or incapable of utilizing tapered sections, long radius fillets,and variable thickness sections which are easily obtained in a casting. Instead of


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a clean design, the casting is a conglomeration of plates, ribs, bosses, and small

radii. Because of the low level of elongation values for gray iron, the only

satisfactory method of determining stress levels in a casting under load is through

the use of SR-4 strain gages. Without proper stress analysis, the first tendency is

to "beef" up the section in which failure has occurred. Grotto[20] has shown that

such an approach does not result in the best design and often makes the

condition worse.

The molding method must be decided upon before a final casting design can be

achieved. If the casting has internal cores, they must have some means of

support and these must be provided for in the design. In using molding methods

capable of greater control over dimensional accuracy, it is often possible to reduce

section thickness. As the section thickness is decreased and the cooling rate

accordingly accelerated, the strength per unit of cross-sectional area increases. In

general, a 50 percent reduction in casting section results in somewhat less than a

40 percent reduction in section strength. If the castings have complex core

assemblies, such as are found in diesel engine cylinder heads, provision must be

made to get the sand out of the cored passages and to allow inspection.

With an increasing trend toward higher machining speeds and metal removal

rates, thought must be given to the manner in which the casting is held during the

machining operation so that high chucking pressures do not distort the part.

Furthermore, the design should include readily maintained locating points. An

ingate should not be placed at a locating point because, in grinding the connection

in the finishing operation, some variation in the amount of metal removed can be

expected.

The mechanical properties of gray iron are dependent on cooling rate. Some care

needs to be exercised in avoiding extreme ranges in section thickness, or hard

edges will be found at the extremities of the thin sections and too low hardness in

the heavy sections. It may be desirable to increase the thickness of the lightest

sections to avoid this condition. Sometimes a bead along the outer edges of a

flange may be helpful. lf the casting is to be used in an application where vibration

is a problem, consideration needs to be given to the damping capacity of the

casting. Although gray iron has quite a high damping capacity, casting design to

avoid resonance should also be considered. Small appendages on castings

should be avoided or strengthened to avoid undue breakage in the handling,

finishing, and shot blasting operations. Although the subject of casting design has


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received much attention during the past 10 years, a great deal more needs to be

done in the field of gray iron casting design.

Mechanical Properties of Gray Iron

Properties of principal interest to the designer and user of castings are: resistanceto wear; hardness; strength; and, in many cases, modulus of elasticity. Some of

the relationships between these properties are quite different for gray iron as

compared with steel. The variable relation between hardness and tensile strength

in gray iron appears to confuse the engineer when most of his experience may

have been with other metals.

The excellent performance of gray iron in applications involving sliding surfaces,

such as machine tool ways, cylinder bores, and piston rings, is well known. Theperformance in internal combustion engines and machine tools is remarkable

when one considers the ease of machining gray iron. Gray iron is also known for

its resistance to galling and seizing. Many explanations have been given for this

behavior, such as the lubricating effect of the graphite flakes and retention of oil in

the graphite areas. This is very likely true, but it is also possible that the graphite

flakes allow some minor accommodation of the pearlite matrix at areas of contact

between mating surfaces. It is seldom possible to obtain perfect fits, and,

ordinarily, high spots in mating metal surfaces may result in high unit pressurescausing seizing.

The Brinell hardness test is the one most frequently used for gray iron, and,

whenever possible, the 10-mm ball and 3000-kg load is preferred. If the section

thickness or area to be tested will not withstand the 3000-kg load, a 1500-kg load

is frequently used. The hardness values obtained with the lower load may differ

appreciably from those obtained with the higher load, and this possibility is pointed

out in ASTM Test for Brinell Hardness of Metallic Materials (E 10-66). For grayiron, the difference in hardness values may be as great as 35 BHN, and, if a

difference exists, it is always lower for the lower load. Since in most cases the

Brinell hardness test can be considered a nondestructive test, Brinell hardness is

used as an indication of machinability, resistance to wear, and tensile strength.

For light sections, such as piston rings and other light castings having a small

graphite size, the Rockwell hardness test is often satisfactory.

The Brinell hardness test is actually a specialized compression test and measuresthe combined effect of matrix hardness, graphite configuration, and volume of

graphite. The Brinell hardness of gray iron with an entirely pearlitic matrix may


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vary from as low as 148 to over 277 depending on the fineness of the pearlite and

to a greater extent on the volume of graphite present. Over this range of

hardness, the actual hardness of the pearlite may vary from about 241 to over 400

Knoop hardness as determined by microhardness measurements.

Virtually, all specifications and standards for gray iron classify it by tensile

strength. The tensile strength of gray iron for a given cooling rate or section size is

very much dependent on the amount of graphite in the iron. The carbon equivalent

value for the iron will give a close approximation to the amount of graphite

present. The tensile strength is also very much influenced by cooling rate,

particularly through the eutectic solidification interval, and is generally related to

section size. In recognition of the effect of section size on strength, ASTM

Specification A 48 not only classifies the iron by strength but also requires

selection of the size of the test bar in which the strength is to be obtained.

The majority of purchasers of gray iron castings rely on the Brinell hardness test

to determine if the casting meets specifications. The variable relation between

Brinell hardness and tensile strength for gray iron is confusing to materials

engineers, who are accustomed to the fixed relation of Brinell hardness to tensile

strength for wrought steel of about 492. For gray iron, the ratio will vary from as

low as 140 for low-strength irons to over 250 for gray irons having a tensile

strength of over 60,000 psi. In recognition of the wide use of the Brinell hardness

test for estimating the strength of the iron in the casting, Division 9 of the Iron and

Steel Technical Committee (ISTC) of the Society of Automotive Engineers is in the

process of revising SAE J431 a. Gray iron for automotive castings, in which gray

iron castings meet various strength levels, will be specified by a minimum Brinell

hardness.

There have been numerous papers dealing with the subject of the correlation of

Brinell hardness with tensile strength. Probably the most extensive report was that

prepared by MacKenzie[21] from data obtained for the "Impact Report" for ASTM

Committee A-3 (now A-4). The report by him was widely published and showed

considerable scatter. He felt that some of the scatter could have been a result of

the manner in which the Brinell hardness measurements were made. When he

selected data taken from the shoulders of the tension test specimens, the

correlation was very much better.

Many users and particularly engineers are critical of cast metal propertiesobtained from test bars. The situation for gray iron is very much different from that


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of the other cast metals. Whereas the other ferrous metals, particularly steel and

nodular iron, use test bars with an unusually high ratio of riser to test bar quite

unlike the relation used for a commercial casting, test bars for gray iron are quite

simple castings and gated very much like commercial castings. This can be done

since there is either very little shrinkage or none in gray iron. Careful

investigations have shown that if the test bar has the same thermal history as the

section in the casting under consideration, hardness and tensile strength will be

similar. In a casting with varying section sizes, the properties in the casting will

only be the same where solidification and cooling rates are the same. It is possible

to predict the tensile strength in other parts of the casting if the Brinell hardness is

determined.

Since it was easier to evaluate the effect of section size and composition of gray

iron in cylindrical castings, this was done in three foundries from 150 ladles of

regular production iron cast into bars from s/s to 6 in. diameter. The molds were

similar to those used for commercial castings. The sizes of the bars were as

follows:

Although the castings were made under normal production conditions, all phases

of the operations were observed more thoroughly than usual. All testing was done

in a research laboratory with properly calibrated equipment and with qualified

operators. Dimensions of tension test specimens conformed to ASTM

Specification A 48. The tension test specimens were machined from the center of

the casting for all sizes and, in addition, were machined from a position about 3/4

in. from the outside for the 4 and 6-in castings.

Diameter, in. Length, in.

5/8 8

7/8 15

1.2 21

2 & 3 10

4 6

6 18


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The tension test specimens had a reduced section diameter of 0.75 in., with the

exception of the test specimen from the 7/8-in. casting which had a diameter of0.5 in. in the reduced section. Brinell hardness tests were made with a 3000-kg

load and 10-mm ball. The hardness measurements were taken on a cross section

of the casting corresponding with the position from which the tension test

specimen was taken.

Foundry F normally produces light to medium weight castings, such as small

compressor heads and bodies, air conditioning component castings, valve and

pressure regular bodies, manifolds, and other types of automotive castings.Since section sizes seldom exceed 1 in., the testing is confined to 7/8 and 1.2-in.

bars. Some of the irons are alloyed with one or more of the elements (copper,

chromium, and molybdenum) in small to moderate amounts. The data are shown

in Fig. 1. The proposed minimum Brinell hardness being considered by the SAE

Division 9 ISTC Committee is also shown. With only two exceptions, the values

are all above the line.

Foundry S is a jobbing foundry specializing in truck and marine diesel and

gasoline engine blocks and heads together with related items, such as flywheels,

manifolds, transmission cases, and clutch housings. Since heavier sections than


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in Foundry F are being made, test bar castings up to 4 in. diameter are cast. The

data obtained are shown in Fig. 2. The alloyed irons are at a higher strength level.

Note that test specimens cut from near the outer surface of the 4-in.-diameter bars

show a higher strength for a given hardness than test specimens machined from

the center of the 4-in. bars. This is generally a result of a larger graphite flake size

in the center of the bar. Also, note that all of the values are above the SAE line.

Foundry W produces medium to heavy castings for large gas line compressors,

engines, pumps, flywheels, and related items with sections up to 4 in. The

complete range of test bar sizes are cast at this foundry. The data obtained are

shown in Fig. 3. The scatter in values becomes somewhat larger at the higherstrength levels. Note that the inoculated irons are higher in strength than the base

iron bars, which accounts for the increase in range of tensile strengths for a given

hardness. Some of the tensile strength values falling below the SAE line are from

the center of the 6-in.-diameter sections and have a rather large graphite flake

size.


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Some casting users specify a minimum tensile strength at some designated

location in the casting. This is particularly true for such castings as hydraulic pump

bodies, high-duty diesel engine cylinders, pistons and heads, and other highlystressed castings. Data obtained from production castings are shown in Fig. 4.

Also shown on this figure for comparison are data obtained from tension test

specimens cut from annealed permanent mold castings. These castings will be

hypereutectic in composition with Type D graphite and a ferritic matrix. These

irons have a higher strength for a given hardness than irons cast in sand.


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Curves showing the minimum Brinell hardness for a given tensile strength for the

irons reported, together with MacKenzie's and Caine's data, are shown in Fig. 5.

The curves are in fair agreement except for the minimum values reported by

MacKenzie. It is possible that the irons for Foundries F, S, and W had a higher

concentration of residual alloying elements, which would tend to keep the matrix

pearlitic with accordingly higher strength.


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It is sometimes necessary to machine tension test specimens with a reduced

section of 0.357 in. diameter from a casting, since the casting shape does notallow making a larger size specimen. Some casting users have raised the

question of the reliability of the smaller specimens. Over a period of years, several

size specimens have been taken from the same casting, and it has been found

that, if machining is carefully done, the results are reliable. The data in Fig. 6 are

representative and have been obtained from a small automotive clutch plate. The

hardness and tensile strength data for this casting show that a 5/8-in. plate has a

similar cooling rate to a 1.2-in. test bar.


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In trying to predict tensile strength in a casting from Brinell hardness, there are

more factors involved than mere section thickness. For sections from which heat

flow during cooling is unimpeded, a very good hardness-tensile strength

relationship can be established. For more complex castings, such as diesel

engine cylinder heads having many cored passages, the cooling pattern may be

complicated. The section within the head may freeze fairly rapidly, but, after the

eutectic temperature interval is passed, there is a heat build up, and the section

may cool more like a simple section two to four times as thick. For such cases, a

correlation needs to be worked out for each type of casting.

Steel shows a rather minor influence of tensile strength and hardness on the

modulus of elasticity, since it is mostly in the range of 29,000,000 to 30,000,000

psi. For gray iron, the modulus of elasticity not only varies with tensile strength but

also with the stress level. As a result of these factors, the modulus of elasticity will

vary from around 12,000,000 psi for a very soft iron to over 20,000,000 psi for a

high strength iron. The stress-strain curve for gray iron in tension is almost a

curved line from the origin. This has been reported by many investigators, and

Morrogh[14], in reporting some work by Gilbert, suggests that the curve is a result

of some volume changes in the spaces occupied by the graphite. They have also

shown that some microcracking takes place between flakes. Some investigators

have used resonant frequency measurements and also sound velocity

measurements which are dependent on modulus of elasticity to predict tensile

strength.


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In machine tool and other applications where maximum stiffness of a structure is

desired, a high modulus of elasticity is desirable. There are other applications,

notably those involving thermal fatigue for which a low modulus of elasticity is

wanted to minimize the increase in stress levels associated with expansion

resulting from temperature increases under operating conditions. High-duty brake

drums are an example of this type of situation. It has been found that a rather

high-carbon iron (3.60 to 3.92 percent) will give better service than a lower carbon

iron. The higher-carbon irons nearly always have a lower modulus of elasticity.

Unfortunately. the tensile strength tends to be low with such high-carbon irons.

and it becomes necessary to add an alloy to strengthen the matrix.

Materials engineers often look on percent elongation as obtained from tension test

specimens as a measure of the ductility of the material. With this concept. gray

iron would not be considered ductile.

Nevertheless. gray iron in the form of commercial castings will satisfactorily

withstand a considerable amount of moderate shock loading. With careful control

of melting practice and selection of raw materials, Collaud and Thieme[10] have

reported irons with 2.4 percent elongation at fracture under load and by ferritizing

such an iron have obtained 5.4 percent elongation. Gray irons of the same tensile

strength may show differences of 50 percent in regard to breaking energy

absorbed in shock loading. Although gray iron is said not to be notch sensitive,

this is most likely a result of being fairly well saturated with notches in the form of

graphite flakes so that the presence of another notch does not materially affect the

behavior on impact.

Heat Treatment of Gray Iron

Although the majority of gray iron castings are used in the as-cast condition, gray

iron is heat treated for a variety of reasons, such as to relieve residual stresses,improve machinability, increase the hardness of the surface either through

induction or flame hardening, or harden the entire section through an oil quench

and draw treatment. Recommended practice for such heat treatments and the

results obtained will be found in handbooks dealing with cast iron, particularly,

ASM Metals Handbook22]. The graphite structure cannot be changed by heat

treatment. although the graphite may increase in volume if a pearlitic iron is

completely ferritized, in which case, the graphite is usually deposited on the flakes

originally present. The matrix however is quite responsive to heat treatment justas in the case of steel.


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Stress relief heat treatments are generally made in the temperature range of 1000

to 1100F. Below 950F the relief of stresses proce eds rather slowly, while at

temperatures above 1100F, some loss of strength ma y be experienced

particularly in unalloyed, ASTM Designation A 48. Class 35B irons and softer.

Stress relief heat treatments may be given to improve the dimensional stability of

machined castings and are required for pressure containing parts operating at

over 450F and up to 650F made to ASTM Specificati ons for Gray Iron Castings

for Pressure-Containing Parts for Temperatures up to 650F (A 278-64). Heating

and cooling rates for such a heat treatment are generally limited to 400 F/h per

inch of thickness. This is particularly important on heating as the residual stresses

in the casting may be increased as a result of thermal expansion of various parts

of the casting.

Smaller castings such as refrigeration compressor parts are often stress relief

annealed to maintain very close operating clearances in the finished compressor.

If difficulties are being encountered with residual stresses in the finished machined

parts, it is desirable to evaluate the internal stress level after each machining

operation. Castings sometimes have a lower level of internal stresses as they

come from a shell molding operation than at any other time in the process. Such

castings given stress relief annealing treatments and then subsequently run

through a shot or grit blasting operation will show an increase in stress level. In

stress relief annealing of large castings, it is desirable to affix thermocouples onto

the casting to see that temperature differences do not become too great. A casting

can be broken in heating unless precautions are taken.

A cast iron table 4 ft wide and 6 ft long cracked during the stress relief heat

treatment. Although the furnace control thermocouple showed a uniform heating

rate within recommended limits, thermocouples at various locations on the casting

showed temperature differences of 300F. Another ta ble of the same design was

arranged outside the furnace with thermocouples and strain gages so that the

temperature difference could be reproduced. It was found that for this temperature

difference tensile stresses of 9200 psi in critical areas were reached.

Annealing for improved machinability is carried out in two temperature ranges. If

the principal purpose is merely to reduce hardness to some lower level and no

carbides are present, temperatures of 1250 to 1450F are generally employed

depending on how much reduction in hardness is desired. If the castings have

cementite or carbides, it is necessary to heat to a 1650 to 1725F range to break

down such carbides.


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Gray iron can successfully be hardened by either flame or induction heating. The

matrix of the iron should be pearlitic. It is also desirable to keep silicon at the

lowest feasible level, generally below l.75 percent. As the silicon content of gray

iron is raised, not only is the Ac3 temperature increased, but a two-phase field of

ferrite and austenite is encountered. Satisfactory hardness will not be obtained

when the iron is heated in this temperature range. The higher austenitizing

temperatures required for the higher-silicon irons also increase the possibility of

cracking during the quenching cycle. It is customary to specify the desired

hardness in terms of Rockwell hardness, C scale, although the hardness

measurements were made with a scleroscope. Direct measurement with a

Rockwell hardness test using the C scale is not satisfactory as the presence of the

graphite flakes in the hard matrix results in spalling or crushing around the

indenter giving low values.

For parts such as cylinder liners, through hardening by austenitizing and oil

quenching followed by a draw to yield the desired hardness greatly improves the

performance of the liner. There are many applications for which this type of heat

treatment is more suitable than flame or induction hardening.

Machining of Gray Iron

Of the widely used ferrous materials for construction purposes, gray iron for agiven hardness level is one of the most readily machinable. Gray iron is free

cutting in that the chips are small and easily removed from the cutting area.

Furthermore, there is little difficulty with the chips marring the finished surface.

The free cutting behavior is a result of the randomly distributed graphite flakes

which interrupt the continuity of the matrix. Although gray iron is very successfully

machined without coolants, they may be found necessary if high machining rates

and close tolerances are desired. The coolant not only helps in chip removal but

also controls the temperature of the casting, which is necessary for close

tolerance work.

In spite of the good machinability of gray iron, various machining problems are

encountered such as hard edges, reduced tool life, inability to obtain a

satisfactorily smooth surface, and difficulty with maintaining the desired

dimensional tolerances. Some of these problems are a result of selection of the

wrong grade of iron, shortcomings in design of the casting, or incorrect machining

procedures. Recommended tooling, speeds, feeds, and depths of cut for gray ironof various strength classifications and for various types of machining operations


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are readily found in a number of handbooks [3, 5, 23, 24] and will not be

discussed here.

Since many castings are purchased to meet ASTM Specification A 48, hardness

will vary for a given strength class specified. Castings consistently near the top

hardness limit may require a reduction in surface cutting speed to obtain

satisfactory tool life as compared with castings near the lower hardness limit. Iron

of normal composition for the type of casting produced may solidify with a mottled

or chilled iron structure if a critical cooling rate is exceeded. Such a condition may

result from a fin on the casting, or, if the casting has a wide range in section sizes,

the foundry may resort to unusually heavy alloy additions to keep the hardness up

in the heavy section, which will result in the iron being too hard for the lighter

sections. Encountering such hard areas very often results in breakage of the tool

or sufficient damage to the cutting edge to interfere with subsequent satisfactory

machining operations. Sometimes the design of the casting can be modified to

avoid the formation of chilled edges, or foundry practice can be modified by

relocation of the gates or using flowoffs of various types to slow down the

solidification rate of the problem area. Through proper use of inoculants, the

foundry can appreciably reduce the incidence of hard edges. Walz [25] points out

that the foundry during inspection can check for freedom from hard edges by

means of a fairly simple file test and thus avoid damaging an expensive tool. With

proper quality control and inspection procedures, the incidence of hard and chilled

edges and bosses should be negligible.

The sudden failure of a cutter was not always a result of encountering mottled or

chilled iron. An investigation of failure of a large, inserted tooth face milling cutter

disclosed that a heavy, decarburized, layer of ferrite was responsible for the

failure. The castings had been annealed to a low hardness level of 121 BHN

maximum, and in so doing a thick ferrite layer devoid of graphite was produced.

This material was very tough rather than hard, but it stalled the cutter with

resulting chipping of carbide teeth.

Since such a decarburized surface is free of graphite flakes, a shiny and bright

finish will give the impression that it is hard. Inadequate cleaning of the casting or

the presence of burned in sand can cause premature failure of the tool. Zlatin [26]

reported that if such a condition is encountered, it may be necessary to reduce

machining rates to half of those used for subsequent cuts if satisfactory tool life is

to be obtained.


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A machined surface defect sometimes encountered in cylinder bores, ways and

slides of machine tools, and other surfaces requiring a low rms finish is referred to

as a pitted or open grain surface. An iron of too high a carbon content for the

section involved and which generally has long graphite flakes may result in

particles of the iron being torn out during rough machining, thus leaving

insufficient stock for finish machining. Lamb [27] states that a minimum of 0.010

in. should be left for a finish cut if a smooth surface is wanted. If graphite flakes

are too large, difficulty with ragged threads will be experienced in cutting threads

and "breakout" at the edges of castings, such as the bores in hydraulic spool-type

valve bodies, may occur. Although too high a carbon content can produce this

type of surface defect, dull tools and too heavy cuts prior to the finish cut or

honing operation will produce a similar defect. Field and Kahles[28] discuss

factors which affect the quality of the machined surface and emphasize the

importance of sharp cutting tools.

As a result of the demand for ever closer tolerances for the machined casting,

problems with maintaining dimensions become more frequent. Some of these may

result from residual stresses in the casting, some from variations in hardness and

the amount of finished stock to be removed, and others from shortcomings in the

machining operation. Whenever out-of round bores and difficulty with maintaining

flatness of machined parts are encountered, residual stresses in the casting are

suspected of being the cause. Depending upon the design, the determination of

the direction and level of residual stresses in a casting may be complicated and

usually requires destruction of the casting. For simple, cylindrical parts, the

presence of residual stresses can sometimes be detected by merely making saw

cuts in the casting and measuring the change in width of the cut. For more

complex castings or for more exact measurement of residual stresses, it is

necessary to resort to the use of SR-4 strain gages. Some trial and error approach

to the proper location of the gages on a casting is generally required. Although aresidual stress evaluation of a casting after final machining may show such

stresses to be responsible for the distortion, it does not necessarily follow that

these stresses were in the original casting. Severe stresses can be introduced by

various machining operations. The use of a too hard wheel on a surface grinding

operation can introduce surface stresses.

ln addition to internal stresses, either residual or introduced during the machining

operation, difficulty with maintaining critical dimensions can arise from other

sources. If the casting is subjected to clamping pressures which distort the casting

in the holding fixture while being machined, difficulties with holding dimensions


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can be expected. Since the modulus of elasticity of a 30,000 psi tensile strength

gray iron is approximately half of that of steel, the same clamping pressure on a

part of the same wall thickness will double the distortion of the gray iron casting as

compared with steel.

If machining is done without a coolant, the casting will heat up while being

machined. A bearing housing with a 2-1/2 in.-diameter bore and a 3/8 in. wall will

expand about 0.0005 in. with a temperature increase of 25F, it was found that a

variation of 1/32 in. in diameter of the bore of the casting with a normal 3/32-in.

stock removal would result in a 25F variation in temperature of the casting. If the

tool setting is based on measurements of the casting as it comes off the lathe,

final bore diameters at room temperature will vary over a range of 0.0005 in.

Although there are differences in the rigidity of machine tools, some deflectionalways occurs. For the same bearing housing casting mentioned above, it was

found that variations in Brinell hardness affected the finished bore diameter. The

machine shop had previously classified finished bores into three size ranges. It

was thought that this gaging operation could be eliminated by reducing machining

tolerances to "0.00025 in. on a 2.5 to 3.0-in.-diameter bore. The castings were

machined dry on a single spindle automatic lathe. Two cuts were taken, and the

rough and finish tools were mounted in tandem on the same carrier. The operator

was asked to set the machine to obtain the correct dimension and told not to

change the setting regardless of bore diameter. Both the operator and inspector

grouped castings by bore diameters being undersize, within range, and oversize.

Specimens from the three groups were subjected to intensive examination and

one of the factors appeared to be hardness as shown in Fig. 7.


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If relatively thin-walled castings are not centered properly in the machining fixture,

more stock will be removed from one side than the other and a distorted bore may

be expected.

The Future for Gray Iron

The properties of gray iron castings are almost as much dependent on foundry

practice as they are on the metallurgy of the material. During the past 10 years,

great progress has been made toward better dimensional control of castings, and

there has been a trend toward thinner sections. This trend will continue, and the

introduction of new inoculants with small amounts of such elements as cerium,

calcium, barium, and strontium has proved effective in obtaining the desired

properties in the lighter sections. De Sy[29] described the behavior of oxygen in

iron and its relation to inoculation practice.

The development and extensive use of a procedure to indicate the carbon

equivalent value of the molten iron at the melting furnace is described by

Redshaw and Payne[30] and by Kasch[31]. This test enables the foundryman to

control the composition of the iron within narrower limits and thus ensures more

uniform properties of the castings.


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The addition of small amounts of tin was instrumental in improving the properties

of gray iron in the heavier sections without creating hardness problems in the

lighter sections.

Although Brinell hardness is still a much used and useful test for evaluating the

strength of gray iron, Walter [32] described a method involving resonant frequency

measurements to predict engineering properties of gray iron. Abar et al[33]

described results obtained from a similar test. Carter[34] reported the use of an

eddy current tester as a rapid inspection tool to predict properties in gray iron

castings.

Barto et al[35] described results with die casting iron of gray iron composition

which should have specialized applications. Experimental work has shown that

certain types of mold surface treatments will allow casting of much thinnersections than previously thought possible.

The complex metallurgy of gray iron and the effect of rather small amounts of

minor elements in iron on the solidification characteristics of gray iron has

attracted the attention of a number of metallurgists. Morrogh[36] has discussed

the need for a better understanding of gray iron metallurgy. Bates and Wallace[37]

have shown the effect of small amounts of trace elements in gray iron and have

investigated means of minimizing the undesirable effects of these elements.

There is a need to develop mold materials or mold surface treatments to either

eliminate or minimize the shot and grit blasting operation, which is costly and apt

to introduce residual stresses in castings. The condition becomes worse as

casting sections become thinner.

The improved properties obtained with high-purity raw materials in making gray

iron should stimulate further investigations particularly in regard to obtaininggreater toughness. There is a need for a grade of iron between conventional gray

iron and nodular iron providing it can be made with the same ease as gray iron.

The large investments in gray iron foundries during the past few years is an

indication that gray iron will be considered a valuable engineering material for

some time to come.

References:


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[1] MacKenzie. J. T., "Gray Iron-Steel plus Graphite," Foundry, Vol. 72, No. 8, Aug. 1944, pp.

86-88,154; No. 9, Sept. 1944, pp. 70-72; No. 10, Oct.1944, pp. 86-88.

[2] Boyles, Alfred, The Structure of Cast Iron, American Society for Metals, Metals Park. OH,

1947.

[3] Gray Iron Castings Handbook, Gray and Ductile Iron Founder's Society, Cleveland, OH,

1958.

[4] ASM Metals Handbook, 8th ed., Vol. I . American Society for Metals, Metals Park, Ohio,

1961, pp. 349-365.

[5] Angus, H. T., Physical and Engineering Properties of Cast Iron, The British Cast Iron

Research Assn., Birmingham, England. 1960.

[6] Cast Metals Handbook. American Foundrymen's Society. Des Plaines, IL, 1957.

[7] Typical Microstructures of Cast Metals. 2nd ed.. The Institute of British Foundrymen,

London, 1966.

[8]

Wieser, P. F., Bates. C. E., and Wallace. J. F., "Mechanism of Graphite Formation in Iron-Silicon-Carbon Alloys" Malleable Founders Society, Cleveland, Ohio, I967.

[9] Rehder, J. E., "The Critical Temperature Range in Cast Irons", Transactions, American

Foundrymen's Society, Vol. 73, 1965. pp. 473-487.

[10] Collaud, A. and Thieme. J. C., "Toughness of Flake-Graphite Cast Iron as an Index of

Quality, and New Methods for Improving the Toughness, [11] Davis. J. A., Krause, D. E.,

Lownie, H. W., Jr., "Tin as an Alloy in Gray Cast Iron," Transactions, American Foundrymen'sSociety, Vol. 65, 1957, pp. 592-597.

[12] Tache. A. J. and Cage, R. M., "Tin-Alloying Speeds Production of Gray-Iron Cylinder

Blocks." Journal, Society of Automotive Engineers, Vol. 73. No. 1, Jan. 1965, pp. 66-69.

[13] Sissener, John and Eriksson, John, "The Influence of Titanium Reduced from Titanium

Oxide Containing Slags on the Mechanical Properties of Cast Iron, Proceedings, 34th

International Foundry Congress; Paper No. 1, Editions Techniques des Industries de la

Fonderie, Paris,1967.


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[14] Morrogh, H., "The Status of the Metallurgy of Cast Irons," Journal of the Iron and Steel

Institute, Jan. 1968, pp. 1-10.

[15] Boyles, Alfred. "The Pearlite Interval in Gray Cast Iron," Transactions, American

Foundrymen's Society, Vol. 48, 1940, pp. 531-573.

[16] Frye, G. R., "Permanent Mold Process as Applied to Production of Gray Iron Castings,"

Modern Castings, Vol. 54, No. 4, Oct. 1968, pp. 52-55.

[17] Caine, J. B., Design of Ferrous Castings. American Foundrymen's Society, Des Plaines,

Ill., 1963.

[18] A Practical Guide to the Design of Gray Iron Castings for Engineering Purposes, The

Council of Ironfoundry Associations London,1960.

[19] Casting Design Handbook, American Society for Metals, Metals Park, Ohio, 1962.

[20] Grotto, L. A., "Engine Castings Development by Experimental Stress Analysis,"

Transactions, American Foundrymen's Society, Vol. 69,1961, pp. 636-645.

[21] MacKenzie, J. T., "Brinell Hardness of Gray Cast Iron-Its Relation to Other Properties,"

Foundry, Vol. 74, No. 10, Oct. I946, pp. 88-93; pp. 191-194.

[22] ASM Metals Handbook, 8th ed., Vol. 2, American Society for Metals, Metals Park Ohio,

1964. pp. 203-213.

[23] ASM Metals Handbook, 8th ed., Vol. 3, American Society for Metals, Metals Park, Ohio.

1967.

[24] Machining Data Handbook, Metcut Research Associates, Inc., Cincinnati, Ohio, 1966.

[25] Walz, W., "Today's Engineering Designs Create a Challenge to Foundry Cast Metals

Industry," Transactions, American Foundrymen's Society, Vol. 72,1964, pp. 914-922.

[26] Zlatin, Norman, "The Machinability of an Unalloyed and an Alloyed Gray Iron," Gray and

Ductile Iron News, March 1965. pp. 5-14.


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[27] Lamb, A. D., "Material and Technique Factors in the Machining of Iron Castings, Gray and

Ductile Iron News, Part I, April 1967, pp. 5-13; Part II, May 1967, pp. 11-20.

[28] Field, M. and Kahles, J. F., "Factors Influencing Machined Finish of Gray Iron, Gray and

Ductile Iron News, April 1966. pp. 5-23.

[29] De Sy, A., "Oxygen. Oxides. Superheating and Graphite Nucleation in Cast Iron,"

Transactions, American Foundrymen's Society. Vol. 75. 1967. pp. 161-172.

[30] Redshaw, A. A., Payne, C. A., and Hoskins. J. A., "Gray Cast Iron Control by Cooling

Curve Techniques, Transactions. American Foundrymen's Society, Vol. 70. 1962, pp. 89-96.

[31] Kasch, F. E., "Carbon Equivalent by Cooling Curves-A Rapid and Practical Test,"

Transactions, American Foundrymen's Society, Vol. 71 , 1963. pp. 266-274.

[32] Walter, G. H., "Correlation of Structure Characteristics and Resonant Frequency

Measurements with the Engineering Properties of Gray Iron," Publication 650519, Society of

Automotive Engineers, 1965.

[33] Abar, J. W., Cellitti, R. A., and Spengler, A. F., "The Use of Sonics to Predict the

Mechanical Properties of Gray Iron, Transactions, American Foundrymen's Society, Vol. 74,1966, pp. 7-I2.

[34] Carter, K. D., "Non-Destructive Eddy Current Testing of Gray Iron, Gray and Ductile Iron

News, Feb. 1966. pp. 8-10.

[35] Barto, R. L., Hurd, D. T., and Stoltenberg, J. P., "The Pressure Die Casting of Iron and

Steels." Transactions. American Foundrymen's Society, Vol. 75, 1967, pp. 181 - 192.

[36] Morrogh, H., "Progress and Problems in the Understanding of Cast Irons," Transactions,

American Foundrymen's Society, Vol. 70, 1962. pp. 449-458.

[37] Bates, C. E. and Wallace. J. F.. "Effects and Neutralization of Trace Elements in Gray,

Ductile and Malleable Iron," Transactions, American Foundrymen's Society, Vol. 75. 1967,

pp. 815-846.

Artigo Gray Iron

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