US2215740A - Alloy cast iron - Google Patents

Description

Patented Sept. 24, 1940 UNITED STATES] ALLOY CAST IRON Clarence H. Lorig, Columbus, Ohio, a'ssignor to Battelle Memorial Institute, Columbus, Ohio, a

corporation of Ohio No Drawing. Application May 4, 1938,

Serial No. 206,021

3 Claims.

This invention relates to an alloy cast iron.

It has to do, more particularly, with an alloy cast iron which is particularly suitable for sand castings in which the cast structure is either marten- 5 sitic or austenitic and for use in making chilled castings, although it is not necessarily limited thereto.

For many purposes for which sand-cast alloyed iron castings are employed, it is desirable that the 0 iron show strong tendencies to form martensite or austenite in the as-cast state. Such tendencies are important in irons specifically designed for heat treatment and for wear resistance. For other purposes for which chilled castings are emplayed, it is desirable that the castings have a 'hardchilled surface free from blemishes and which will take on a good polish. It is also desirable for the chilled portion to extend from the surface into the casting for a depth suflicient to produce a wearing surface which will have reasonable life with repeated dressings but not so deep as to cause the castings, as a whole, to be mechanically weak and brittle, The degree of polish on castings of the type in question and their resistance to roughemng are determined not only by the hardness but also by the fineness of grain in the chilled structure. To resist breakage, the merging of the chill with the core of the casting should be gradual so that there 'is no distinct line of demarcation between the various zones. The core itself should'be strong and tough.-

In the prior art of making chilledcastings, considerable difficulty has been encountered in producing castings with very hard, fine grain chilled zones that grade gradually into strong, tough core materials without a distinct line of demarcation between the various zones. Efforts to raise 40 the hardness of the chill by producing a martensitic matrix have resulted in the use of combinations of molybdenum-manganese, manganesenickel, nickel-chromium, nickel-chromium-molybdenum and nickel-chromium molybdenum- 45 manganese besides'relatively high percentages of either manganese or nickel in the cast irons. As the chill on cast iron is composed essentially of 50 per cent carbide and 50 per cent matrix, the carbide having a Brinell hardness of about 800,

50 the-conversion of the matrix from relatively soft pearlite to very hard martensite has increased the hardnes of the chill considerably. On alloying, as stated above, surface hardnesses of 6'75 Brinell have been obtained. The grain structure 55 of the chill, however, is not essentially refined by the use of these combinations of alloying elements.

The some combination of elements, i. e., high nickel, high manganese, manganese-molybdenum, manganese-nickel, nickel-chromium, nickel chromium molybdenum, nickel-chromiummoiybdenum-manganese,- and others has been used for sand-cast unchilled castings to produce martensitic, and sometimes, by using sufiicient quantities of the alloying elements, austenitic l0 matrices in the iron. In the prior art, the amount of alloying element or elements required for producing martensitic or austenitic structures made the irons very expensive, however.

One of the objects of this invention is the provision of an alloy cast iron wherein the structure after sand-casting is martensitic or austenitic and is particularly suitable for resisting wear and for responding to heat treatment.

Another object of this invention is the provi- 20 sion of an alloy cast iron which may be used for producing a chilled casting wherein the chilled zone possesses great hardness, strength, and

. toughness and shades of]? gradually and without a distinct line of. demarcation into a tough wear- 25 resistant secondary chill and core.

Another object of this invention is the provision of an alloy cast iron which may be used for producing a chilled casting, the chilled zone of which has a more refined grain structure than 30 hitherto possible in the prior art so that it may be given a more highly polished surface of greater hardness and toughness than previously possible.

Another object of this invention is the provision of a fine grain chilled casting whose matrix is essentially martensite, martensite-sorbite, or austenite, or mixtures of these constituents.

A further object of this invention is the provision of a heat-treatable gray cast iron whose matrix after sand casting is essentially martensite. martensite-sorbite, or austenite, or mixtures of these constituents.

Other objects and advantages of my invention will become apparent from the following description and claims.

I have found that copper in cast iron alloys having substantial amounts of manganese and molybdenum vary materially aids in the retention of martensitic and austenitic matrices, makes the alloys particularly responsive to heat treatment and, when the alloy is used for making chilled castings, refines the structure of the chill and permits the chill to grade off into the core without showing a distinct line of demarca- 66 but in amounts not exceeding a total of 4 per cent.

In chilled castings, it is well known that carbon has little effect on the depth of chili, though high carbon contents give chills of greater hardness, and that silicon is the dominating element with respect to control of depth of chill, the chill depth varying inversely with the silicon content.

. The silicon content for chilled casting producit should not be used in excess.

0.01 up to 0.25 per cent, and phosphorus, from tion is, therefore, held to a low value seldom exceeding 2.00 per cent. Onthe other hand, substantially higher silicon contents are required for gray iron castings in order to avoid the formation of chili. In the latter case, the silicon content may be as high as per cent, although normally silicon contents between 1 and 3 per cent are preferred. V

The use of 1 to 5 per cent of .copper requires some consideration of its effect on the depth of chili and on the degree of graphitization, as it is a mild graphit' ng element and is capable of replacing par of the silicon in that capacity. The manganese" and molybdenum are mild carbidecrming elements and counteract the graphitizing effect of the copper to some extent. The depth of chill in chilled castings may, therefore, be controlled by proportioning the silicon to the copper, manganese, and molybdenum contents or .by employing small amounts of strong carbideforming elements, such as chromium and vanadium, when adjustments in silicon contents are impractical, as for example, when the silicon content is so low that it is undesirable to reduce it further.

In the alloys which I preferably use, the elements phosphorus and sulphur occur within the usual percentage ranges for cast iron alloys. While sulphur is sometimes used to control chill depth in some compositions, in this case the high manganese content tends to destroy the chilling tendencies of sulphur. It is, therefore, unnecessary'to maintain the sulphur content so closely within narrow limits for chill control. However, the sulphur content should not be too great inasmuch as sulphur is detrimental to strength. Phosphorus adds fluidity to the molten metal. butas it increases the brittleness of the castings, Sulphur, from 0.01 up to 1.00 per cent, may be used without departing from my invention.

1 The important alloying elements in mycast ir'on alloy are copper, manganese, and molybuseful in producing extreme hardness in the chill of chilled castings and toughness and strength in the core. With the alloys I have made, I have found that 2 per cent copper or more is required to develop martensitic structures to an appreci-' able entent in heavy sections of sand castings and to substantially refine the grain of chilled castings. continues with increased copper content, and the use of high percentages of copper is limited only by the fact that the solubility of copper in the alloy cast iron is readily exceeded, causing particles of nearly pure copper to form. These particles are soft and my experimentsto date indicate that they become of sumcient size at 5 per cent copper to be noticeable to the extent of interfering with the smoothness of ground and polished chilled surfaces and with the uniformity of surface hardness.

The effect of copper on grain refinement and chill hardness was demonstrated on an iron whose composition was 3.60 per cent carbon, 3.0 per cent manganese, 0.60 per cent silicon, 0.10 per cent phosphorus, 0.05 per cent sulphur, 0.50 per cent molybdenum, and 0.50 per cent chromium, the latter being used to increase the depth of chill. To this cast iron was added 1.0, 2.0, 3.0 and 4.0 per cent copper with results as follows:

Brinell Copper. T of crystals in Casting Per cent gained surface 53 3 0 Coarse columnar 529 1 ...do 553 2 do 608 3 Moderately column 613 4 Fine columnar 616 .of polish, and strength, I have found copper to be an important element in my alloy cast iron when used for chilled castings.

The stabilizing of sorbitic-martensitic, martensitic, or austenitic matrices in my alloy cast iron is accomplished by employing manganese and molybdenum, which are augmented by the copper. Various proportions of these elements stabilize the different matrices, in general, sorbite-martensite forming with-the alloying elements toward the very low side of the range,

martensite forming in the intermediate range, and austenite forming toward the upper side of the range of alloy contents. Of course, difierent proportions of the elements may be used to produce equivalent stabilizing effects, for the stability of a structure depends on the relative proportions of each element, the composition of the base metal, the rate at which the casting cools in the mold, and the size of the casting. I have found, however, on investigating sand-cast irons ranging in composition from 1 to 3 per cent of manganese, 1.5 to 4 per cent of copper, 0 to 1.0 per cent of molybdenum, which were cast into sections x x 1 x 1%", and 3" x 3", as well .as into transverse bars, that martensite was stabilized even in the larger sections with as little as 1.50 per cent manganese,

3.0 per cent copper, and 0.50 per cent molybdenum. An iron with 3.08 per cent carbon, 1.88 per cent silicon, 0.12 per cent phosphorus, 0.03 per cent sulphur, 1.46 per cent manganese, 3.05 per cent copper, and 0.50 per cent molybdenum Grain refinement in chilled castings had Brinell hardness values in the tour sizes of sections cast in sand molds as follows:

Size of Brinell Section hardness tructure 2 601 whm x I V 77 Gray. 1%:1 415 1),, 3 x 3 454 Do.

0 I tendency to be martensitic with both copper and manganese under 3 per cent, while manganese and molybdenum alone showed no tendency to be martensitic with manganese below 2.5 per cent and molybdenum below 0.5 per cent. Chromium 5 was found to inhibit the formation of martensite to some extent, but its eflect can be offset by increased percentages of one or more of the three principal alloying elements. Chromium is desirable in some instances to improve the wear liquid. Properties of the iron after heat treatment were as follows:

Transverse Dciiec- Tensile Heat treatment strength, tion, Strength, pounds inches lie/sq. in.

1,600 F. cooled in iurnace.-.. 2, 730 0. 28 44, 000 1,000 F. for 2 hours, cooled in furnace 2,760 .25 53,500

After quenching in oil from 1600 degrees and drawing at 500 degrees F., the hardness was again raised to 3'75 Brinell.

Thus, by heat treatment the iron can be made machinable, and by suitable control and with simple heat-treating practice considerable variations in tensile strength and hardness of the iron are effected.

The stabilizing of 'sorbitic-martensitic, martensitic, or austenitic matrices in thechill and core of chilled castings is also dependent on the relative proportions of manganese, molybdenum, and copper, and the following table lists a number of irons cast into a given size chilled mold for the purpose of showing the stabilizing effects of the three elements, These effects were observed from the trend in hardness of the chill with variations in manganese, copper, and molybdenum contents, and from micrographs.

Composition, per cent Cash Brinell mg hardness Carsmcon Manga- Molyb- Cop- Chro Vana of chill bon nese denum per mium dium 3030 3. 2) 0. 60 2. 0 0. 3 4. 0 467 3034.. 3. 0. 60 1. 5 1. 0 4. 562 3031.- 3. 20 0. 50 2. 5 i 0.3 4. 0 463 3110.- 3. 00 0. 60 3. 0 0. 3 4. 0 594 3111.- 3. 00 0.60 3. 0 0. 5 4. 0 584 3113.- 3. 00 0. 60 3. 0 1. 0 4. 0 619 3115... 3. 60 0. 60 3. 0 0. 5 4. 0 642 3116..- 3. 60 0. 00 2. 5 l. 0 4. 0 642 3354..- 3. 60 0. 60 4. 0 0. 5 4. 0 616 3355... 3. 60 0.60 5.0 0. 5 4. 0 017 3352.. 2. 80 0. 00 3. 0 0. 5 4. 0 587 3350.. 3. 60 0. 20 3. 0 0. 5 4. 0 617 3353.- 3. 60 0. 00 3. 0 0. 5 4.0 590 3678.-. 3. 60 0. 60 10. 0 l. 0 5. 0 518 3079.. 3. 00 0. 60 7. 0 1. 0 4. 0 523 3600... 3. 00 0. 60 7. 0 2. 0 4. 0 527 3681.. 1. 80 1. 10. 0 l. 0 3. 0 318 3682.. 2. 50 0. 00 7. 0 l. 0 4. 0 378 I resistance of 'the iron. Austenitic structures can be obtained in sand castings when the manganese content is above about 5.per cent, the copper content is above 2 per cent, and the molybdenum content is from 0.25 to 2 per cent. The austenitic structures are non-magnetic.

An alloy cast iron containing from 1.7 to 4.0 per cent carbon, 0.1 to 5.0 per cent silicon, 1.2 to 5 per cent manganese, 1.0 to 5.0 per cent copper, 0.1 to 2.0 per cent molybdenum, up to 0.25 per cent sulphur, up to 1.0 per cent phosphorus, with or without an element from the group'consisting of chromium, nickel and vanadium, and the balance substantially iron, will have a martensitic structure and a Brinell hardness when chilled in excess of 475.

, Transverse bars of the iron used to illustrate the hardness of the various cast sections were too hard to machine. Simple heat treatments, such as furnace cooling from 1600 degrees 1". or furnace cooling after 2 hours at 1000 degrees F'., lowered the hardness to 212 and 298 Brinell, respectively, in which conditions the iron was machinable. The iron can again be hardened after machining by heating to a temperature above the critical and quenching in air or in a The matrix of the chills in the lower-hardness, lower-alloy range was sorbitic, but with increased hardness and alloy content it.changed to a mixture of sorbite and martensit'e, and finally became full martensitic at hardness in the vicinity of 600 Brinell and above. The matrix of the chill in alloys containing 7 per cent or more of manganese was austenitic, causing the Brinell hardness to again decrease. Thus the whole range of structures from sorbitic to martensitic, and finally to austenitic, may be obtained within the composition limits of my invention.

In chilled castings diiferent proportions of manganese and molybdenum may be used to produce equivalent stabilizing effects as it is shown. The lower manganese content irons require more molybdenum to obtain martcnsite than the high manganese content irons. I prefer, however, to use manganese contents above 3.0 per cent, for .at lower manganese contents the irons are more susceptible to grinding cracks and are not as tough. In that case the molybdenum content may be under 1 per cent to obtain martensite in the matrix of the chill. The increase in toughness of the chill with manganese content appears to result from the retention of increased amounts of austenite in the matrix; Substantial'amounts of austenite are obtained in both the chill and the gray iron core with manganese contents above 5 per cent. Austenite in the core of the castings makes them more resistant to breakage. The hardness 'of the chill decreases as the amount of austenite increases. However, the austenite transforms to martensite on slight deformation as aresult of the well known work-hardening effect.

Molybdenum contents from 1 to 2 per cent in the higher manganese containing irons are helpful but appear to be of no material advantage, and I prefer to maintain the molybdenum content below 1 per cent in these irons.

Since the speed of cooling and cast thickness affect the formation of martensite and the retention of austenite, these factors must be taken into account in proportio'ning the manganese and molybdenum and to some extent the copper. Nickel may be used as a supplementary element, particularly in very large castings or to retain austenite, as it has a powerful influence on the stability of martensite and on the retention of austenite. The combined content of nickel, chromium'and vanadium which may be found in the castings is limited to a maximum of 4 per cent.

Neither manganese nor molybdenum was found to influence the grain structure of chilled surfaces to any extent, and essentially all refine ment was obtained through the use of copper.

It should .be understood that it is within the scope of my invention to provide a casting wherein the structure is either essentially martensitic or essentially austenitic; Various combinations may be produced by alteration of the percentages of the elements in the alloy within the ranges set forth in the appended claims, or variations of both the combinations and the rate of cooling. Thus, the matrix of the chill of chilled castings may be partially martensitic and partially austenitic if desired, while the core may be either austenitic, martensitic or sorbitic or a mixture of austenite and martensite or sorbite-martensite.

It will be seen from the above that I have provided a novel type of alloy cast iron which is particularly suitable for use in producing heattreatable and wear-resistant sand castings and chilled castings. Because of the use of copper in the alloy, it is possible to obtain a greater grain refinement in chilled castings than hitherto possible. As a result of this, I am able to obtain a chilled casting in which the surface on the chilled zone has a higher degree of polish and has a greater resistance to roughenlng. This makes quantity of the alloy particularly suitable for use in producing chilled cast'iron, rolls suitable for hot and cold forming of strip, sheets, and other articles of ferrous and non-ferrous metals. The alloy may also be used for producing other articles such as chilled cast iron wheels, balls for ball mills, crusher hammers, crusher liners and rolls, mold boards, and plow shares. In the sand-cast condition it may be used for various types of wearresistant castings such as plates and shells for ball mills, cylinder sleeves, cam shafts, and pump parts. Likewise, my use of copper as one component of an alloy containing manganese and molybdenum permits of the use of less manganese or less molybdenum to obtain martensitic or austenitic structures. Moreover, by proper regulation of the various factors, as indicated above, I am able to obtain a chill on castings wherein the matrix is at least partially martensitic with consequent hardness and toughness and a core which is either partially austenitic or partially sorbitic with consequent toughness and strength.

Although in the preceding description in order to bring out a number of the advantages of my alloy cast iron I have described it as being particularly suitable for use in producing heattreatable wear-resistant castings and chilled castings, it is to be understood that my alloy is not necessarily limited to use in producing such castings. It is capable of other uses.

Having thus described my invention, what I claim is:

1. An iron base casting-alloy containing more than 2 per cent and up to 5 percent copper, 1.7 to 4.0 per cent carbon, 0.1 to 5.0 per cent silicon, 1.2 to 10 per cent manganese, 0.1'to 2.0 per cent molybdenum, up to 0.25 per cent sulfur, up to 1.0 per cent phosphorus, from a trace to a total 4.0 per cent of at least one element of a group consisting of chromium, nickel and vanadium, and the balance iron with incidental impurities, said alloy having a fine grain structure essentially due to the said copper, having a martensitic or austenitic structure, and being further characterized by the ability to form, upon chill-casting, a fine grained hard white iron surface which grades without sharp demarcation into a tough strong core.

2. The alloy of claim 1, wherein the manganese is present in an amount from 1.2 to 5.0 per cent and the alloy is characterized by a martensitic structure.

3. The alloy of claim 1, wherein the manganese is present in an amount from 5.0 to 10.0 per cent and the alloy is characterized by an austenitic 1 structure.

CLARENCE H. LORIG.