US2885284A - Ferrous alloy - Google Patents

Description

1959 w. MOORE 2,885,284

FERROUS ALLOY Filed Aug. 15, 1957 2 Sheets-Sheet 2 INVENTOR.

) WILLIAM H. MOORE WW 5 Wm? ATTQRNEYS United States Patent il FERROUS ALLOY William H. Moore, New Rochelle, N.Y., assignor to Meehanite Metals Corporation Application August 13, 1957, Serial No. 677,916

8 Claims. (Cl. 75-124) The present invention relates to a unique ferrous alloy having improved and unusual combinations of properties, particularly in the direction of improved wear resistance and heat resistance.

In the field of abrasive Wear, ordinary cast iron may be used successfully where the impract in service is not severe. Such cast iron, particularly white cast iron, is resistant to abrasive wear because of the presence of extremely hard carbides in the matrix of the cast iron. Unfortunately, however, these carbides are normally massive and impart a degree of brittleness to the cast iron which considerably limits its usefulness.

While some advances have been made in alloying the cast iron so as to improve its toughness while still retaining the hardness, no one has proposed a generally satisfactory method of positive control of both the carbides and the matrix structure of the cast iron, so as to render it both hard and tough.

Improvement in toughness in white irons has usually been obtained by lowering the carbon content, so as to reduce the quantity of massive carbides that are present in the matrix structure. This also lowers the hardness and wear resistance.

Certain steels, namely, austenitic steels and other alloy steels, are often used for abrasive resistance, particularly where toughness is a prime requisite. They have the advantage of being very tough, but are free from carbides which are so important for good wearing qualities. Austenitic steels owe their resistant qualities to their ability to work harden under the action of pounding impact in service.

The present invention is based on the discovery that the austenitising tendency of manganese may be utilized in cast irons to provide the product advantages of austenitic steels with those of white cast irons. In the ferrous alloy of the invention, manganese and aluminum are added to the melt in conjunction, so as to provide a complete family of cast irons ranging from white to gray, with the matrix ranging from fully austenitic through martensitic to pearlitic.

It is an object of this invention to provide a ferrous alloy of improved wear resistance.

It is another object to provide a ferrous alloy of improved heat resistance.

It is another object to provide a ferrous alloy of nonmagnetic qualities being either white or gray, according to service requirements.

Other objects and advantages of the present invention will be apparent to those skilled in the art from the following description, taken in conjunction with the drawings in which:

Figure 1 is a drawing showing the types of structures obtained with various combinations of the alloying ingredients of this invention.

Figure 2 is a reproduction of a photomicrograph taken at a magnification of 400 diameters and showing the etched structure in the as cast condition of an alloy produced in accordance with the present invention.

Figure 3 is a reproduction of a photornicrograph taken at a magnification of 600 diameters and showing the etched structure in the quenched condition of an alloy in accordance with the present invention.

Figure 4 is a reproduction of a photornicrograph taken at a magnification of 600 diameters and showing the etched structure in the quenched condition of an alloy in accordance with the present invention.

Figure 5 is a reproduction of a photomicrograph taken at a magnification of 400 diameters, showing the etched structure in the as cast condition of an alloy containing the special elements of this invention.

Figure 6 is a reproduction of a photomicrograph taken at a magnification of 400 diameters, showing the etched structure in the quenched condition of an alloy containing the special elements of this invention.

The present invention provides a novel ferrous product containing at least about 50% iron, carbon and silicon within the cast iron range and at least 1 /2% manganese and at least 1% aluminum. Free carbon may be in the form of graphite or in the form of carbides. For increased hardness, the carbon is preferably predominant in the form of carbides, but for increased toughness the carbon is predominantly in the form of graphite. The proportion of carbide or graphite present may be adjusted according to the service performance desired.

The ferrous matrix may be pearlite, ferrite, martensite, austenite, bainite or other acicular transformation constituents, tempered martensite, sorbite, etc., or the known combinations thereof. These structures may be obtained in the as cast condition or by heat treatment, but in any case, the presence of the alloying combination of this invention viz. manganese and aluminum, enables the desired matrix structure to be obtained more readily than when this combination is absent.

The use of manganese as an alloying element in cast iron is old in the art. In ordinary cast irons the manganese content is usually below 1% and is rarely more than 1 /2 It has been found that cast irons containing more than 1% manganese, are subject to many founding difficulties, particularly gas holes, pinholes, gas tears and the like. In addition to this, manganese in large amounts is a carbide stabilizer and may lead to poor machining characteristics. Martensitic cast irons have been produced using manganese contents in excess of 2% and nickel as an additional alloying agent. Because of the expense of these alloy additions and because of the aforementioned founding difiiculties, these irons have not found wide acceptance in industry. When manganese is used as a single alloying element in cast iron, approximately 10% is required before the cast iron becomes austenitic. In the process of this invention no useful purpose is served by having the magnese content above 15%.

Aluminum is not regarded as a common alloying element in cast iron, but it has found frequent use in certain special cast irons. Small quantities of aluminum, i.e., up to about 0.5%, have been used as a grapihtizing addition and larger quantities, such as 5% or more, have been used with or without chromium to provide a special heat resistant cast iron. Quantities of aluminum in the order of about 5% have a very embrittling influence on cast iron. In the process of this invention no useful purpose is served by having the aluminum content above 5%.

It has been pointed out that manganese is a carbie stabilizer and the addition of manganese in excess of 2% to an ordinary cast iron tends to produce massive carbides which may be objectionable. Aluminum, on the other hand is a graphitizer and when used in conjunction with manganese, effectively prevents the formation of massive carbides. This invention is based on the discovery that aluminum in excess of 1% when added to a cast iron containing manganese in excess of 1 /2 provides a new and improved ferrous alloy having properties not found in cast iron, where aluminum is used with low manganese contents or where high manganese is used without aluminum.

For the manufacture of a gray cast iron having relatively few carbides present, it is necessary to keep the aluminum content at a value sufficient to overcome the carbide forming propensity of manganese. The exact amount of aluminum required to prevent free carbides will, of course, depend on the combination of other elements in the cast iron. In the process of this invention it is preferred to keep the manganese and aluminum in a ratio of approximately /6 to 1% parts of aluminum to one part of manganese for a gray iron. This ratio applies to aluminum contents below 5% because above this amount aluminum itself will act in the capacity of a carbide former.

For the manufacture of a white cast iron having relatively little free graphite present, it is necessary to keep the aluminum content at a value low enough to allow manganese to exert its carbide forming propensity or high enough for aluminum itself to form carbides. The exact ratio of aluminum to manganese will vary, according to the concentration of other elements in the cast iron. In the process of this invention it is preferred to keep the manganese and aluminum in a ratio of approximately two to four parts of manganese to one part of aluminum for a white iron.

Those skilled in the art will readily see that any degree of carbide formation or graphite formation is possible by varying the ratio of aluminum to manganese and/or by altering the combination of other elements present in the cast iron in accordance with accepted cast iron practice.

It has been found that any common alloying element used in cast iron may also be used along with the manganese and aluminum content of this invention. Thus, chromium, vanadium, molybdenum, copper, nickel and cobalt may be used quite effectively and other elements such as calcium, cerium, magnesium, lithium, sodium, potassium, bismuth and titanium may also be present as trace amounts or in amounts sutficient to produce an effect. For example, magnesium and other nodularizing agents may be utilized in the process of this inventron in amount sufiicient to render all graphitic carbon 1n the nodular and spherulitic form. The elements total carbon, silicon, sulphur and phosphorus, are present in the amounts normally obtained in cast irons and are varied in the manner known to those skilled in the art.

The aluminum and manganese content of this invention may be introduced into the cast iron by any of the methods known to those skilled in the art. The product of the invention may be prepared from cast iron melted in the cupola, the electric furnace, the air furnace, or any other type of melting unit. The electric furnace and the basic lined cupola are the preferred melting units, because in both of these it is possible to melt with a relatively low loss of manganese on melting. This has economic advantages and also results in a cleaner molten metal, less likely to contain oxide dross.

While high manganese metal melted in the acid cupola is usually contaminated with gas holes, it has been found that the product of this invention is relatively free from these gas holes. It is thought that this freedom from gas is due to the degasifying influence of aluminum. As both aluminum and manganese are relatively inexpensive alloying elements, readily available at all times, the present invention has made possible the manufacture of cast iron of unusual properties on a very sound economical basis.

The greater part of the aluminum required in the composition of this invention is preferably added as a ladle addition after the cast iron has been melted. It has been found that this method of addition gives the best recovery from the addition. Pure aluminum in ingot or shot form may be used. When the aluminum is added in the melted condition, it is particularly effective in that the aluminum dross formed is at a minimum. Alloys of alu' minum and manganese and other aluminum alloys may be used, it being understood that the element associated with the aluminum is desired in the final cast iron composition.

Another method of adding aluminum, is to add solid aluminum chunks mixed with aluminum powder and a metallic oxide such as iron oxide or manganese oxide. Such a mixture is exothermic and will generate large quantities of heat, thereby resulting in an effective addition and improving the fluidity of the cast iron.

It has been found that the cast iron of this invention has normal founding characteristics from the standpoint of fluidity, castability, shrinkage and etc. Where the iron is white, it behaves in a manner common to white cast irons and where it is gray, it behaves in a manner common to gray cast irons.

As the aluminum content of the iron increases, it appears more sluggish, but this is due to the formation of an oxide coating on the surface of the metal. Where the oxide coating is likely to be severe, it is advisable to gate the molds, so that there is a minimum of turbulence during pouring.

The process of this invention is best illustrated by a series of examples.

These examples are in the most part related to the type of structure produced in the cast iron. Those skilled in the art can readily see the type of service performance to be expected and the mechanical properties attendant with any given structure.

Table No. 1 sets forth the composition of a series of typical cast irons of this invention, along with the structures obtained in casting sections of approximately 1"2". White irons have the excess carbon present predominantly as carbides, mottled irons have substantial proportions of graphite and carbide present, whereas gray irons have the excess carbon present predominantly as graphite.

TABLE NO. 1

Matrix structure of various manganese-aluminum cast ir0nselements in percent by weight Mn Structure Si Al White: Austenlte-Martensitc. Mottled: Austenite-Martenslte. Mottled: Austenite.

Gray: Bainite-Pearlite. Mottled: Austenite-Bainite. Gray): Pearlite.

o. White: Bainite1 earlite. Mottled: Bainite.

Mottled: PearliteBainite. Gray: Austenite.

Gray: Austenite-Marteusite. Gray: Martensite-Bainite. White: Martensite-Pearlite. Gray: Bainite-Pearlite. Gray: Pearlite.

Gray: Austenite.

Chromium and vanadium are particularly useful in conjunction with the aluminum and manganese of this invention in the production of white and mottled cast irons having superior wear characteristics. Vanadium appears to promote a tougher matrix with less massive carbides. A few typical wear resisting irons containing chromium and vanadium are shown in Table No.

TABLE N0. 2

Wear resistant manganese-aluminum cast irons containing chromium or vanadium Brinell 'I.G Si Mn A1 Or V Hardness The combined effect of manganese and aluminum or the structure of cast iron may be seen from Figure 1, which has been produced by examining a number of melts produced according to this invention. This diagram is very useful from a practical standpoint as it readily indicates the composition combination necessary for a given structure.

If the composition of an alloy falls in zone 1 bounded by the lines RB, BA and the vertical reference coordinate between A and R, it will consist essentially of pearlite with carbides in the matrix.

In zone 2, bounded by the lines AB, BC, CH, HE and EA, it will consist of pearlite with bainite.

In zone 3, bounded by the lines HC, CD, DG, GI and 1H, it will consist of austenite with bainite.

in zone 4, bounded by the lines GD, DF, and FG, it will consist of austenite.

In zone 5, bounded by the lines FP, PK, K], II, IG and GF, it will consist of austenite and carbides.

In zone 6, bounded by the lines LN, NJ, JK, KS, and the horizontal reference coordinate between S and L, it will consist of carbide and pearlite.

In zone 7, bounded by the lines EH, HI, I], IN, and NE, it will consist of bainite and carbide.

In zone 8, bounded by the lines AE, EN, NL, the horizontal reference coordinate between zero and L and vertical reference coordinate between zero and A, it will consist of pearlite.

Alloys falling within any of the zones indicated in Figure 1 may contain some proportion of free graphite, depending, among other factors, on the composition balance and the rate of cooling. Figure 1 is merely meant to be a general guide for the manganese and aluminum contents for various types of structures. The position of the various lines dividing the diagram of the different zones can vary, according to the compositional balance of the other constituents of the cast iron and according to other factors well known to those skilled in the art.

The cast iron of this invention is particularly susceptible to all types of heat treatment known to those skilled in the art. The as cast pearlite or bainitic structure may readily be converted to an austenitic structure by quenching from a temperature of about l600 F.-1900 F., depending on the composition balance of the iron. With certain composition balance it is possible to obtain an austenitic structure by quenching from still lower temperatures.

The austenitic product of the invention may be precipitation hardened by heating to a temperature of about 900 F.-l200 F. For certain composition balances, a heating temperature above or below this range may also be effective. The ability of manganese-aluminum cast iron to be hardened by heating makes it a very versatile engineering material. Thus, it is possible to cast soft and machinable or quench for softness and follow the machining operation by a simple heating without any significant dimensional change.

The ability to harden under heating is also very useful where the cast iron is used at elevated temperatures under conditions where it is required to have wear resistance. A typical example would be in a hot forming die.

The austenitic cast iron of this invention also has the ability to work-harden during use. This type of hardening is well known to those skilled in the art and is one of the chief reasons for the excellent wear characteristics of a material such as austenitic manganese steel.

When white iron or mottled iron containing manganese and aluminum according to the teachings of this invention, is heated to and then quenched from temperatures about 1600 F., it is considerably toughened. This improvement in toughness is due to spherodizing of carbides and austenitizing of the matrix. This facility is extremely useful where good wear resistance under severe impact is required in service.

The behavior of manganese-aluminum cast iron under heat treatment is best illustrated by a series of examples. A 1%" diameter bar Was cast from a melt having the following composition:

Total carbon 3.12 Silicon 1.34 Manganese 2.68 Aluminum 2.35

In the as cast" condition a portion of this bar was martensitic and is shown in Figure 2. The hardness of this sample was BHN 420. A second portion of this bar was heated to 1850 F. and was quenched in oil from this temperature. The structure of the quenched piece was austenitic and is shown in Figure 3. This piece had a hardness of BHN 230.

A third portion of this bar was quenched from 1850 F. and was then reheated to 1000 F. The structure of this quenched and drawn piece was martensitic and is shown in Figure 4. This piece had a hardness of BHN 450.

In another example, a test bar was cast from a melt having the following composition:

The as cast structure of this bar was mottled with a pearlitic matrix. This is shown in Figure 5. The random distribution of these carbides is a characteristic of this type of composition balance. The as cast hardness was BHN 411.

A portion of this bar was heated to 1500 F. and was quenched from this temperature. This treatment resulted in a structure consisting of spheroidized carbides in an austenitic matrix. The structure of this piece is shown in Figure 6. The hardness after this treatment was BHN 387. The piece thus heat treated exhibited an unusual degree of toughness.

It has been found that any cast iron of this invention responds to the types of heat treatment described, as well as to all types of treatment practiced by those skilled in the art. The temperatures required to achieve any effect will vary according to the composition balance of the iron, and can be determined quite readily by conducting a series of simple laboratory tests. These types of tests are well known to those skilled in the art.

The novel structure and physical properties of the cast iron of this invention makes it a useful product in industrial applications, where severe service conditions often make other common cast irons useless. Where the manganese-aluminum cast iron is gray, it may be produced to as cast tensile strengths ranging from as low as 25,000 p.s.i. to as high as 100,000 p.s.i. by varying the composition in a manner common to ordinary cast irons. When the composition is such as to produce an acicular matrix, the strength is usually in excess of 60,000 p.s.i. and when the composition is such as to render the graphite nodular or spheroidal, the strength is usually in excess of 80,000 p.s.1.

The service characteristics of manganese-aluminum cast irons may be illustrated by a series of tests and examples.

A number of materials were tested by rotating test bars made from the materials in abrasive silicon carbide particles at a high rate of speed. Among these materials was a test bar No. made from the cast iron of this invention and having the following composition:

Total carbon 3.14 Silicon 1 .42 Manganese 4.60 Aluminum 2.20 Chromium 1 .85 Vanadium 0.52

The results of these tests are expressed in a comparative manner where the cold rolled medium carbon steel has a wear factor of 100, and are tabulated in Table 3:

TABLE NO. 3

Abrasive wear tests on ferrous materials rotated in bath of silicon carbide Test Bar No. Type of Material Comparative Wear Factor Cold Rolled Medium Carbon Steel 100 Gray Cast Iron 90 White Cast Iron 66 Martensitic White Cast Iron 42 lllanganese-Aluminum Cast Iron- 25 Spherulitic Graphite Cast Iron 84 Heat Treated Cast Iron 75 Austenitie Manganese Steel. 55

Table No. 3 clearly indicates the excellent wear properties of the cast iron produced according to the teachings of this invention.

A number of materials were tested for heat resistance by immersing test bars made from these materials into a furnace maintained at 1650 F. for a period of 300 hours. After this period of time, the test bars were measured for dimensional changes and weight changes. The results of these tests are shown in Table No. 4. Among these results is that on Test Bar No. 4, made from the cast iron of this invention and having the following composition:

Austenitic Cast; Iron Ferritic Silicon Cast Iron It has also been found that the austenitic cast iron of this invention has an excellent corrosion resistance. It resists the rusting action of the atmosphere extremely well, probably because of a thin surface coating of oxide that is always present and which is more pronounced in compositions having an aluminum content above 3.0%. The manganese-aluminum cast irons are also resistant to certain acids, alkalies' and chemicals and for this reason, castings of this novel material may be used extensively in chemical and allied industries.

The product of this inventionmay be magnetic or nonmagnetic, according to the composition balance. This confers very useful electrical characteristics to castings made from manganese-aluminum cast irons. The magnetic properties of the material are also an extremely useful guide in the process of manufacture, particularly during heat treatment for austenetizing. Certain of the composition balances used in the process of this invention are characterized by a very high magnetic retentivity.

No theory is advanced to account for the novel product that results from alloying a cast iron with manganese and aluminum, according to the process of this invention. It is thought that the graphitizing potential of aluminum sets up in opposition to the carbide impelling potential of manganese, so as to enable positive control of carbon condition in the cast iron and obtain full benefit of both these alloying elements on the equilibrium transformation points during solidification of the melt. Regardless of the exact mechanism of the invention, it has been discovered that the presence of both aluminum and manganese in the amounts contemplated by the invention result in a cast iron having a novel structure and physical properties not possible when either manganese or aluminum is absent.

Although the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention, as those skilled in the art will readily understand.

Such variations and modifications, apparent to those skilled in the art, are considered to be within the purview and scope of the invention and the appended claims.

What is claimed is:

1. As a new article of manufacture a cast iron containing free graphite in a matrix of bainite, said cast iron being further characterized by having an aluminum content in the range of 1% to 5% and a manganese content in the range of 1 /2% to 15%, said aluminum and said manganese together being proportioned so as to fall above the line AENJK as shown in Figure l.

2. As a new article of manufacture a cast iron containing free graphite in a matrix of austenite, said cast iron being further characterized by having an aluminum content in the range of 1% to 5% and a manganese content in the range of 1 /2% to 15%, said aluminum and said manganese together being proportioned so as to fall above the line CHI] K as shown in Figure 1.

3. As a new article of manufacture a cast iron containing free graphite in a matrix of austenite and bainite, said cast iron being further characterized by having an aluminum content and a manganese content, said aluminum and said manganese together being proportioned so as to fall Within the lines bounded by the point CHIGD as shown in Figure 1.

4. As a new article of manufacture a cast iron containing free graphite an a matrix of bainite and pearlite, said cast iron being further characterized by having an aluminum content in the range of 1% to 5% and a manganese content in the range of 1%% to 15%, said aluminum and said manganese together being proportioned so as to fall above the line AENJK as shown in Figure 1.

5. As a new article of manufacture a white cast iron containing free carbides in a matrix of bainite, said cast iron being further characterized by having an aluminum content in the range of 1% to 5% and a manganese content in the range of 1 /2 to 15 said aluminum and said manganese together being proportioned so as to fall above the line AENJK as shown in Figure l.

6. As a new article of manufacture a white cast iron containing free carbides in a matrix of austenite, said cast iron being further characterized by having an aluminum content in the range of 1% to 5% and a manganese content in the range of 1% to 15%, said aluminum and said manganese together being proportioned so as to fall above the line CHIJK as shown in Figure 1.

7. As a new article of manufacture a white cast iron containing free carbides in a matrix of austenite and bainite, said cast iron being further characterized by having an aluminum content and a manganese content, said aluminum and said mangaese together beig proportioned so as to fall within the lines bounded by the points CHIGD as shown in Figure 1.

8. As a new article of manufacture a white cast iron containing free carbides in a matrix of bainite and pearlite, said cast iron being further characterized by having an aluminum content in the range of 1% to 5% and a manganese content in the range of 195% to 15%, said aluminum and said manganese together being proportioned so as to fall above the line AENJK as shown in Figure 1.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Hurst: Journal of the Iron and Steel Institute, vol. 135,

15 1937, No. 1, pages 255P-267P. Published by the Iron and Steel Institute, London, England.

Claims (1)

1. AS A NEW ARTICLE OF MFANAFACTURE A CAST IRON CONTAINING FREE GRAPHITE IN A MATRIX OF BAINITE, SAID CAST IRON BEING FURTHER CHARACTERIZED BY HAVING AN ALUMINIUM CONTENT IN THE RANGE OF 1% TO 5% AND A MANGANESE CONTENT IN THE RANGE OF 11/2% TO 15%, SAID ALUMINIUM AND SAID MANAGANESE TOGETHER BEING PORPORTIONED SO AS TO FALL ABOVE THE LINE AENJK AS SHOWN IN FIGURE 1.

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