US2355059A - Production of cast iron - Google Patents

Description

Patented Aug. 8, 1944 UNITED STATES "PATENT, OFFICE PRODUCTION OF CAST IRON John T. Eash, Westfield, N. 1., as signor to The International Nickel Company, Inc., New York, N. Y., a corporation of Delaware No Drawing. Application October 14, 1943, Serial No. 506,262

11 Claims coma-13o) The present invention relates to an addition alloy and more particularly to an addition alloy for use in producing cast iron.

Cast irons containing low carbon and/or sili-- con for the section size involved and/or containing appreciable amounts of carbide stabilizing elements and cast irons produced under conditions of rapid freezing tend to becomeance to scufling. The cast iron may exhibit the dendritic structure near the surface and some distance below the surface or may exhibit the dendritic structure throughout the entire cross section. The dendritie graphite structure also tends to result in poor machinability, strength and toughness and low growth resistance, etc. The production of machinetools, gears, automotive and engine castings, cylinder heads, cylinders, pistons, piston rings, pumps, valves, etc, has presented particular problems. The production of cast iron piston rings, which are made of, relatively high carboncast iron but are cast in rather small section sizes, illustrates some of the defects and problems encountered in the production of cast iron products. The production of piston rings is but one of the many examples that could be cited. Piston rings, especially for airplane engines, must-possess a special combination of properties. They must possess high mechanical properties and must exhibit resistance to scuffing properties in order to obtain satisfactory wear resistance. Furthermore as the piston ring blanks are cast individually and then machined to proper size it is essential that they possess adequate machinability and be substantially free from hard spots which interfere with machining and which rapidly decrease the life of the cutting tool. In producing the rough piston rings, i. e., the piston ring blanks, it is im-- vantages connected with the use of prior inoc-- portant that the method employed yield a product having the desired hardness and that it neither raise nor lower the hardness excessively. Methods for producing piston rings have possessed the disadvantage of tending to produce hard spots, internal defects, pn holes, internal slag particles, white edges, low strength, excessively decreased hardness, an fopen iron, dendritic graphite, substantial amounts of primary or fine ferrite associated with dendritic graphite, low scuffing resistance, and/or other disadvantages. In some proposed methods various 1noculants and addition alloys were used but it was found that in overcoming one defect these inoculants and addition alloys produced another defect or shortcoming. Thus, treating the relatively high carbon cast iron used for piston rings with an addition of ferro-silicon in sufilcient amounts. to produce an inoculating effect tended to produce kish on the melt and to yield an open iron having excessively reduced hardness. Calcium silicide additions had a similar effect. Additions of an alloy. containing about 6% silicon and 92% nickel in amounts sufficientto have an inoculating effect raised the hardness excessively. Additions in quantities sufiicient to completely inoculate cast iron. i. e., in quantities suflicient to secure the proper graphite structure, of an alloy containing about 20% silicon, 33% chromium, 15% manganese,

2.5% carbon, 1% calcium and balance iron, or an alloy containing about 25% to 50% chromium, 10% to 25% silicon, 5% to 15% manganese, 0.2% to 2% or more calcium, often with about 0.2% to 2% titanium, and balance ,iron plus small amounts of minor constituents such as carbon, etc., e. g., an alloy containing about 40% chromium, 15% silicon, 10% manganese, 1% titanium, 0.5% calcium and balance iron, tended to produce white edges. about 755% silicon, 7.5% manganese, 7% Znconium, 0.5% aluminum, and balance iron tended to produce pin holes and internal slag particles and yielded a piston ring having lower hardness than desired. An addition agent of silicon and graphite produced kish on the melt and yielded a product having lower hardness than desired. Additions of term-silicon containing aluminum had the same effect and also tended to produce pin holes. Because of the disadulants and addition alloys, most'commercial producers of piston rings avoided the use of any inoculant or ladle addition alloy. The commercial methods used to produce piston rings suffered from the disadvantage that inconsistent results were obtained. Sometimes the method yielded good results and at other times yielded unsatisfactory results, for example, hard spots, dendritic graphite, fine free ferrite, etc. Generally, un-

satisfactory results were associated with a den- 'dritic., structure. In order to minimize these defects, some piston rings have been chromium- An' alloy containing plated. In actual tests conducted on commercially produced machined piston rings, it was trusion. The galling is often evidenced by deep pitting and scoring.

- The foregoing illustrates, by reference to the production of cast iron piston rings, some of the. defects and problems encountered in producing cast iron products. The production of machine tool beds and frames or automotive and engine castings, including pistons, cylinders, cylinder heads, cylinder blocks, etc., or high strength gears or pumps or valves or numerous other cast ironproducts likewise exhibited various defects and difficulties which are overcome by the invention described hereinafter. It is to be understood that the present invention is not limited to the illustrative examples cited herein butv is broadly applicable to the treatment of cast iron to improve the properties of the product. Thus, machine tool beds made of cast iron produced without a late addition of an alloy-tendedto have hard spots which detrimentally affected the machining of the beds and tended to have a detrimental dendritic graphite structure, usually in association with fine free ferrite, which resulted in scufiing and galling on the wearing surface where the cast iron was subjected to sliding contact with another metal part. Such a cast iron may contain about 3% carbon and 2% silicon. The defects encountered. in the production of machine tool beds and other cast iron products have been recognized and discussed in the literature,

for example in F. J. Dost's article on Making better machine tool castings" published in Mechanical Engineering, May, 1940, pages 365 et seq. and the discussion of said article published in Mechanical Engineering, March, 1941, pages 226 to 229.

As another example, the production of a Diesel engine piston, having ring grooves chilled to eliminate leakage, resulted in an unmachinable product when produced without a late addition of an .not detrimentally affect the strength and other desired properties. Attempts to produce a ma- .chinable chilled groove piston having high strength by additions of prior known alloys were not satisfactory. Thus, late additions of ferrosilicon did not reduce the chill sufliciently to consistently yield a machinable piston. Sometimes the cast iron was machinable and sometimes it was not machinable, although in both instances the cast ironv might. have the same hardness. Late additions of an alloy containing about 6% silicon and balance mainly nickel, or of an alloy falling within the range of about 25% to chromium, 10% to 25% silicon, 5% to 15% manganese, 0.2% to 2% calcium, often also containing about 0.2% to 2% titanium, and balance mainly iron, likewise did not reduce the chill sufficiently. A late addition of an alloy containing about 75% silicon, 7.5% manganese, 7% zirconium, 0.5% aluminum and balance iron reduced the chill but at the same time markedly reduced the strength of the cast iron compared to those treated by the previously mentioned alloys. Furthermore, the use of ferro-silicon produced a product which tended to exhibit pin holes or gas holes. Additions of the alloy containing 75% silicon, 7.5% manganese, 7% zirconium, 0.5% aluminum and balance iron had a similar effect and, in addition, tended to result in scumming. In view of the shortcomings of the prior addition alloys, a demand existed for a suitable alloy to be used as a late addition in producing cast iron pistons. A suitable cast iron .for pistons might contain about 2.9% to 3.3% carbon, 1.6% to 2.2% silicon, 0.9% to 1.8% nickel, and 0.5% to 0.8% molybdenum.

The foregoing examples also illustrate some of the defects and/or shortcomings of prior known alloys when used as a late addition to cast iron. These prior alloys possess various undesirable features such as causing hardening, or alternatively, excessive softening and weakening or decreased strength. Scumming, pin-holing, hard spots, white edges, and/or the production of kish, are some of the other defects associated with the use of prior alloys.

Many of the commonly used inoculants and addition alloys had high melting points which were also undesirable characteristics. For example, the 50% grade of ferro-silicon melts at about 2250 F.; the 85% grade of ferro-silicon melts at about 2450 FL; silicon carbide melts above 2600 F.; and commercial calcium silicide melts at about 2100 F. These inoculants and addition alloys, particularly calcium silicide, do not have as high a solution rate in the molten iron as desired.

I have discovered that the foregoing and other difiiculties may be avoided and that high quality cast iron can be produced consistently by a simple and efficient method involving the use of a novel addition alloy that produces an inoculating effect on cast iron.

It is an object of the present invention to provide a novel addition alloy.

It is another object of the invention to provide a novelladle addition alloy containing special proportions of nickel, silicon and calcium which is particularly suitable for producing high quality cast iron.

It is a further object of the invention to provide a method of consistently producing cast iron having high mechanical properties and substantially free from the defects normally associated with the use of prior art inoculants and addition alloys, said process involving the use of a novel addition alloy.

Th invention also contemplates a method of consistently controlling the microstructure of cast iron to obtain a structure substantially devoid of areas'containing fine dendritic graphite associated with fine free ferrite, said method involv ing the use of a novel addition alloy.

Other objects and advantages of the invention will become apparent to those skilled in the art from the following description.

The present invention provides novel alloys particularly'adapted for use as addition alloys to cast iron and the like for reducing chill and producing random graphite distribution without detrimenproperties. The alloys provided by the invention ass-5,059

contain about 27% to 50% silicon, a small but effective amount, say 0.07%, to 1% calcium, a small amount-up to 20% iron and the balance substantially all nickel. In general, the composition of the alloys will fall within the ranges set forth in Table I.

a of about 34% to about 67%.

Table I y Element Range Percent silicon 21 to 60 Percent calcium e 0.1 to 1 Percent iron. 6 to 20 Percent nickel Balance The nickelcontent will fall within the ranges It is essential that the nickel and silicon contents be maintained within the foregoing proportions in order that the desired combination of properties of the alloy be obtained. If the silicon content is not sufllciently high the melting, point of the alloy is high and solution in the molten iron is impeded. If the silicon is low the alloys do not have as effective chill reducing tendencies as with the optimum silicon content. When the silicon content is above the stated range, the melting point is raised again, with attendant difliculties, and maximum strength values in the resulting cast iron are not obtained. With the alloys pro-. vided by the present invention there is obtained an optimum or improved balance between proper graphitizing effect and pearlite strenthening effect. When the nickel and silicon contents are unbalanced, i. e., are outside the balanced ranges set forth hereinbefore, the alloy has decreased mobility, fluidity and activity. The calcium content in combination with balanced nickel and silicon contents are essential in order to impart consistent and effective inoculating power to the alloy. The effect of the small amount of calcium is not completely understood but it is thought that it mayact as a catalytic agent or act in some other manner since calcium itself apparently is not a powerful graphitizer in the small quantity involved in the present alloy. Whatever may be the eifect of calcium, .it has been found that calcium is an essential element in the present invention. The minimum amount,

.of calcium which will produce the desired results is about 0.07% but in order to obtain consistent results and to allow for losses in preparing the sidered to be the safe minimum. Thus when 1%,0! an alloy containing about 34% silicon with nickel in the proper balanced proportion but containing only about 0.002% calcium was added to a cast iron containing 2.2% carbon, 2.3% silicon and 0.7% manganese, the properties obtained in the cast ironwere much inferior to those obtained when a similar alloy containing about 0.29% calcium was added to the same cast iron. The cast iron treated with the alloy containing only 0.002% calcium had a iron was 37,800 pounds per square inch whereas the tensile strength of the latter cast iron was 60,800 pounds per square inch. The Izod impact strength of the former was 14 foot pounds whereas the latter had an impact strength of 31 foot pounds. Again,.the former sustained a transver'se load of 3080 pounds with a transverse deflection of 0.089 inch whereas the latter cast iron sustained a transverse load of 5175 pounds and had a transverse deflection of 0.160 inch.

The addition alloy for cast iron provided by the invention possesses a low melting point, high mobility, the property of being rapidly assimilated, the power to exert a positive and profound efl'ectin forcing the precipitation of graphite to occur at a higher temperature, the power to eliminate the presence of fine ferrite residues and the property of reducing chill. These properties must' be achieved by the simultaneous addition of the essential ingredients in a single alloy rather than through the separate addition of the individual constituents or parts of them. Thus, the addition of term-silicone. g., ferro-silicon containing about 85% silicon, did not give as consistent resuits. and did not produce as high transverse and impact properties as obtained by adding the improved alloy. Furthermore, the cast iron is not as sensitive to excessive additions of the improved alloy as it is to excess ferro-silicon. Excesses oilv the improved alloy stabilize the pearlite whereas excesses of ferro-silicon cause the formation of ferrite. Likewise the addition of nickel and of ferro-silicon, e. g., about 0.7% nickel and 0.4% of the 85% grade of ferro-silicon, did not give the consistent results obtained by adding an alloy having the balanced composition set forth herein, e. g., about 1% of an alloy containing about 35% silicon, 0.3% calcium, and the balance mainiy nickel and a small amount of iron. Also addition of the improved alloy gives superior reduction in chill and high strength and impact properties. Again, the addition of calcium silicide in amounts suflicient to introduce in the cast iron the same amount of calcium as introduced with the improved alloy did not produce a cast iron having as high strength or as greatlyreduced chill as was possessed by the cast iron treated with the improved alloy. Thus, in one instance, the introduction of 0.003% calcium as a calcium-silicon V alloy about 0.1% or 0.2% is more preferably conalloy, i. e., calcium-siiicide, containing about 32% calcium and about 68% silicon to a cast iron having a base composition of 2.25% total carbon and 2.25% silicon produced a cast iron having a total chill depth of 1.7 inches, a' clear white chill depth of 0.31 inch, and 'a tensile strength of 46,800 pounds per square inch. The addition of the same amount of calcium in the form of the improved addition alloys to the same base cast iron produced cast irons having total chill depths of 0.03 to 0.09 inch,,'clear white chill'depths of 0.02

' to 0.07 inch and tensile strengths of 57,500 to 60,800 pounds per squareinch. A cast iron produced by adding 0.1% of: calcium as calcium silicide gave a product having a tensile strength of 44,000 pounds per square inch whereas the addition of 0.003% calcium in the form of the improved alloy resulted in a product having a tensile strength of 60,000 pounds persquare inch. The addition of an alloy containing about 72% silicon and balance mainly nickel or of a similar alloy containing about silicon yielded a cast iron having infen'or strength compared with a cast iron produced by adding the improved balanced alloy of the invention. I

Incarrying the invention into practice it is 1 preferred to maintain the silicon, iron and nickel contents of the addition 'alloy within the ranges of about'27% -to 41% silicon, about 7% to 15% iron and about 50% to 65% nickel. An addition alloy falling within this range comprises about 38% silicon, 0.5% calcium, iron and 52% dental elements and minor constituents may be present in small amounts suchas occur in commercial practice or'in amounts not adversely affeoting the-desired properties. Usually the sum of the incidental elements will not exceed about 1% and the amount of any one element usually will not exceed about 0.25%. Thus, some of the alloys produced in accordance with the invention have contained 0.07% aluminum and/or 0.07% zirconium and/or 0.02% titanium and/or 0.01% to 0.2% carbon, etc. It is to be understood that when it is stated herein that the balance of the alloy is nickel or is substantially all nickel it is not intended to exclude amounts of incidental elements and minor constituents such as indicated herein or as occur in commercial practice or which will not adversely affect the desired properties. The examples set forth in Table II are illustrative of compositions within the scope of the present invention.

Table II Percent Percent Percent Percent Si Fe Ca Ni Some of the improvements in mechanical properties resulting from use of the addition alloys provided by the invention are illustrated in the following examples.

Example I Both portions of the melt were cast into arbitration bars having a diameter of 1.2 inches and-into blocks having dimensions of 1 inch by 5 inches by 4 inches. The blocks were chilled on the 1 inch by 5 inch face. The untreated iron had a hard mottled structure and was unmachinable. This untreated cast iron had'a total chill depth of 4 inches and a white chilled depth of 4 inches. The iron treated in accordance with the present invention had a relatively soft gray machinable structure and had a tensile strength of about 57,500 pounds per square inch. The treated cast iron had a total chill depth of 0.09 inch and a white chill depth of 0.07 inch.

Example 11 A melt of cast iron containing about 2.25%

carbon, 2.25% silicon and 0.9% manganese was established and then superheated to about 2930 F. Part of the melt was cast in an untreated condition and part was treated with about 1% of alloy similar in composition to those set forth in Table II and then was cast. Both portions were cast into arbitration bars and into blocks 1 inch by 5 inches by 4 inches, the 1 inch by 5 inch face being chilled. The comparative properties of the untreated and treated cast irons are I 12-inch span.

The more sensitive properties indicative of the improvements obtained by treatment in accordance with the invention are the decreased chilling capacity and the increased transverse strength and deflection.

The invention provides an addition alloy, and a method involving a late addition of said alloy, which when used in producing cast iron enables one to consistently control the microstructure of cast iron to obtain a structure substantially devoid of areas containing fine dentritic graphite usually associated with fine free ferrite. This feature of the present alloys is particularly advantageous where it is desired to increase the wear resistance and to decrease any tendency of the cast iron to gall and to scuff.

The alloy provided by the invention hasa melting point under about 1900 F., e. g., about 1800 F., which is considerably lower than that of the commonly used addition alloys and inoculants. Furthermore the alloy possesses a high solution rate in molten iron which contributes to obtaining consistent results, The alloy is further characterized by the fact that it is substantially free from tendencies to form undesirable slag.

The invention provides a method of producing improved cast iron which comprises establishing a melt of cast iron, incorporating into the melt the addition alloy provided by the invention, and casting the treated melt. In general, it has been found desirable to cast the melt shortly after the addition of the alloy. For example, a body of metal weighing up to 1000 pounds will be poured within about 1 to 15 minutes after the alloy addition. However, a large ladle of metal, e. g., 5 tons or over, may stand 30 minutes to an hour and a half before being poured. In general, the time between the addition of the alloy and pouring may vary from one minute to one and a half hours, depending on the size of the body of metal being poured, its tapping temperature and the desired pouring temperature. Usually the melt should be poured at a temperature of at least 2550 F., preferably at least 2600 F. However,

the mold material may limit the maximum pouring temperature and when the temperature of the melt is high may require that the treated and overcomes the shortcomings of untreated or 2%. 'The alloy may be added in the furnace I or in the ladle in lump form or in crushed form but is preferably added to the melt in a ladle just prior to casting and is preferably added in a crushed form. I In carrying outthe present invention the amount of silicon introduced with the addition alloy should be taken into consideration in'determining the proper silicon content of the melt before addition of the alloy in order to arrive at the desired final silicon content. The

amount of silicon in the alloy introduced into' is characterized by randomly distributed graphite,

as distinguished from dendritic graphite, and by a freedom from pulverulent ferrite, and possesses unimpaired or increased tensile strength, transverse strength, deflection, toughness, density, wear resistance, growth resistance, etc.-, while avoiding excessive increases or decreases in hardness and avoiding other shortcomings resulting from the use of prior art addition alloys or inoculants, such as hard spots, internal defects, pin holes, white edges and corners, an open. iron, formation of klsh on the melt, etc. The balanced composition of the alloy promotes the inoculation reaction, prevents the formation of a dendritic graphite structure and, in addition, tends also to prevent the formation of primary or fine free ferrite associated with the dendritic graphite as distinguished from secondary or more massive well scattered free ferrite. The use of the alloy in producing cast iron provides castings which. possess greater density as observed by X-ray inspection. The tendency to produce hard spots is substantially eliminated thus providing castings with improved machinability. After adding the alloy provided by the invention the surface of the melt is clean and is not covered with undesirable oxide, as frequently is the case for some inoculants. By using the alloyof the invention, the desired effects can be produced without greatly increasing the silicon content of the molten iron thereby providing wider latitude of use in different cast iron mixtures. The alloy also permits a greater latitude of compositions to secure the desired properties than do some prior alloys.

In carrying the invention into practice it has been found that the advantages of the alloy provided by the present invention over addition alloys and inoculants used heretofore are particularly outstanding when used in the production of the lower carbon content irons. Thus, an addition of about 1% of the addition alloy contemplated by the invention not only produced randomly distributed graphite in a low carbon iron containing about 2.25% total carbon and 2.25% silicon, but also raised the tensile strength over 20,000 pounds per square inch to produce a strength of abo t 68,000 pounds per square inch. This is a desirable advantage as the lower carbon content cast irons sufier particularly from the tendency to form an undesirable dendritic structure, especially in the general vicinity of the surface.

, In treating the higher carbon content cast irons, the alloy of the present invention also possesses advantages. It avoids the shortcomings which accompanied the use of prior alloys in higher carbon cast irons.

Thus, in producing cast iron piston rings a product is obtained having randomly dispersed graphite instead of a detrimental dendritic graphite, without the shortcomings of producing kish on the molten metal or of producing a. cast product having excessivelyreduced or increased hardness, or hard spots, pin

holes, slag inclusions, internal defects; chilled edges, etc. Freedom from dendritic graphite and from hard spots are particularly important in producing piston rings and other cast iron products where optimum or high properties and machinability are desired. For example, the presence of a dendritic graphite structure in piston rings produced according to prior practice is a frequent occurrence and causes scuiling to such an undesirable extent that during the breakingin period, before the engine can be placed into actual use for the intended purpose, the rings no longer perform properly. Again, by way of example, the presence of hard spots is also a common occurrence in plston'rings and causes machining diiliculties, not only by impairing the tools and markedly reducing their life, but by within the range of about 3.25% to 4.1% carbon and about 2.2% to 3.1% silicon. More preferred ranges comprise about 3.65% to 3.95% carbon and 2.3% to 3.0% silicon, e. g., about 3.75% carbon and 2.75% silicon. The silicon content includes the amount introduced iby'the addition alloy.

- As pointedout hereinbefore, chromium-plating amounts sumcient to obtain inoculating effects of piston rings has been used in order to overcome their shortcomings and incosistent properties. It is believed that it will not be necessary to chromium-plate piston rings produced in accordance with the present invention in,view of their consistently good properties and structure and their freedom from defects. The use of the present invention in the production of piston rings markedly reduces the loss due to rejections. For example, the loss of one producer of piston rings was reduced from the prior high figure of over about 30% rejections to a new low figure of under. about 3% rejections. Piston rings produced as set forth herein possess markedly reduced usceptibility to scumng, longer operating life, improved density and improved tensile strength compared to the properties of chine tool bed or frame results in the production of a product substantially free from hard spots, deleterious dendritic graphite and fine free ferrite which is iisuau associated with dendritic graphite. Such a machine tool bed or frame is machinable and exhibits, good wear resistance and ,less scuffing andgalling than beds or frames having a dendritic graphite structure in association with fine free ferrite.

The use of the present alloys in producing cast iron pistons, for example, Diesel engine pistons having chilled grooves, results inthe consistent production'of a product which is machinable and which does not suffer from impaired strength;

pin holes, and/or the other shortcomings encountered in cast iron produced with prior known alloys. Thus, in producing a cast iron containing about 3.15% carbon, 1.75% silicon, 1% nickel, 0.75% molybdenum and 0.15% chromium for chilled grooved-Diesel engine pistons, a late addition of about 1% of the improved alloys resulted in the production of a machinable cast iron havinga tensile strength of about 62,000 pounds per square inch with a chill depth of only about /32 inch on a test chilled block. When a late addition of about 1%0f an alloy containing approximately 25% to 50% chromium,.e. g.,

.40% chromium, %to 25% silicon, e. g.,

silicon, 5% to 15% manganese, e. g., 12% manganese, 0.2% to 2% calcium, often also containing 0.2%- to 2% titanium, and balance mainly iron was used instead of the present improved alloys a tensile strength of about 65,000 pounds per square inch was obtained but this was accompanied by a much greater chill depth on a similar test chilled block of about /a2 inch. When a 1% late addition of an alloy containing about 92% nickel and 6% silicon was used a tensile strength of about 63,000 pounds per square inch and a chill depth of about /32 inch was obtained.

When a late addition of ferro-silicon was used a tensile strength of 63,000 pounds per square inch and a chill depth of about "/ai inch was cast iron for use in the production of pistons and other'cast iron products.

bodies; bushings, grate bars, hardware, plumbing goods, and numerous other cast iron products where machinability, maximum strength, wear 1. An addition alloy for cast iron comprising about 28% to 33% silicon, about 0.3% to 1% calcium, 8% to 12% iron and 58% to 62% nickel, the sum of the silicon, iron and nickel contents being approximately 98% of the alloy.

2. An addition a'lloy for cast iron comprising about 28% to 33% silicon, 0.3% to 1% calcium, 8% to 12% iron and the balance substantially all nickel.

3. An addition alloy for cast iron comprising about 27% to 41% silicon, 0.1% to 1% calcium,

7% to 15% iron and the balance substantially all nickel.

4. An addition alloy for cast iron comprising about 27% to 41% silicon, 0.1% to 1% calcium, 7% to 15% iron and 50% to 65% nickel, the sum of the silicon, iron and nickel contents being approximately 98% of the alloy.

5. An addition alloy comprising about 27% to 50% silicon, 0.1% to 1% calcium, a small amount up to 20% iron and the balance substan- It is to. be observed that the present invention provides amethod' which is applicable to the production of gray cast irons in general, i. e., cast irons which when solidified contain graphite in any kind of matrix, to control the microstructure of the cast iron and to obtain a structure containing randomly distributed graphite and substantially devoid of areas containing fine dendritic graphite usually associated with .fine free ferrite,'or to obtain wear resistance by increasing the resistance to scuffing and galling or to decrease the chill without impairing the strength or to improve machinability by eliminating hard spots, chill, etc. In some cases it has been found that a dendritic structure may occur very near the surface of the casting, say within about 0.02 or 0.03 inch of the surface, but this portion is so shallow that it is removed by the conventional machining required to produce the finished surface, e.-,g., the surface which it is desired shall exhibit high resistance to scuffing, and high wear resistance, etc. The invention can be applied to cast iron produced in the cupola, electric furnace or any other furnace used in the production of cast iron.

Ihe present invention is applicable to the production of gray cast iron products requiring good structure control, such as machine tool beds and frames, cylinder blocks, cylinder liners, piston rings for airplane engines, pistons, high strength gears, crankshafts, camshafts, brake" 'drums, clutch plates, exhaust manifolds, connecting rods, valve stem guides, dies, pump and valve pressure tially all nickel.

. 6. As an article of manufacture, an addition alloy for molten cast iron made of a nickel alloy containing about 27% to 50% silicon, 67% to 34% nickel,- a small amount up to 20 ,5 iron and 0.07% to 1% calcium,said alloy being characterized by a melting point under about 19009 F., a high rate of solution in molten cast iron and by theproperty of being capable of inoculating cast iron to yield a gray cast iron product substantially devoid of dendritic graphite. l

7. A method of making cast iron products which comprises establishing a molten bath of cast iron, introducing therein about 0.25% to 5% of an alloy comprising about 27% to 41% silicon,

0.1% to 1% calcium, 7% to 15% iron and the balance substantially all nickel, and casting said molten cast iron shortly thereafter.

8. A method of producing cast iron which comprises establishing a molten bath of cast iron, incorporating in said bath about.0.25% to 5% of an addition/alloy comprising about 27% to 50% silicon, 0.1% to 1% calcium, a small amount up to 20% iron, and the balance substantially all nickel, and thereafter casting said molten cast iron.

9. A method of controlling the microstructure of cast iron to obtain a cast iron having a structure containing randomly distributed graphite which comprises establishing a molten bath of --cast iron, incorporating in said bath a small amount of an alloy containing about 27% to 50% silicon, a small amount up to 20% iron, 0.07% to 1% calcium and the balance substantially all nickel, and casting the thus-treated molten cast "iron whereby a cast iron product is obtained having amicrostructure containing randomly distributed graphite and substantially devoid of dendritic fine graphite.

10. An addition alloy containing about 27% to iron to yield a gray cast iron product substan- 41% silicon, 0.07% to.1% calcium, and 50% to v tially de'void of dendritic graphite. 65% nickel, said alloy being characterized by a I 11. An addition alloy comprising about 27 melting point under about 1900 F., by a high to 50% silicon, 0.1% to 1% calcium, 6% to 20% rate of solution in molten cast iron, and by th 5 iron and the balance substantially all nickel. property of being capable of inoculating cast JOHN T. EASH.