US2087767A - Conversion of iron-carbon alloys into products of sheeted and other shapes - Google Patents

Description

Patented July 20, 1937 2,087,767 CONVERSION or IRON-CARBON, ALLOYS,

INTO PRODUCTS OTHER SHAPES Nathan H. .Schermer, Detroit, Mich. assignor tol- Stellum, Inc., Cleveland, Ohio, a corporation 01' Ohio No Drawing. Application April 17, 1936,

I Serial No. 75,014

'12 Claims. (01. 148-12) This invention relates in general to the treatment of cast iron-carbon alloys, particularly white cast iron.

. precipitated or segregated into rounded masses,

cast iron, for the obtaining of products in sheeted or other shapes with tensile strength andmachinability, corrosion resistance, etc. as good or better than customary in malleable iron.

For the manufacture of malleable iron castings, it has been customary to subject the white iron castings, which contain carbon in the combined form, i. e., cementite and pearlite, and which makes the metalhard and brittle, to a suitable heating or' annealing treatment, thereby changing the combined carbon to an amorphous free carbon in the form of temper-carbon, the metal becoming ductile',and known as malleable The annealing treatment usually consists in slowly heating the castings to a temperature of about 1500 F., maintaining them at this temperature'for about fifty hours, and then cooling them very slowly. This annealing treatment changes the character of the casting from one having a. white silvery crystalline fracture, in

which no'graphite flakes are visible to the nakedeye, to one having a. dark gray, soft, velvety appearing fracture, in which the carbon has been leaving little or no carbon combined with the iron. This change takes place at a temperature as low as 1250 F., but occurs more effectively at a temperature of 1350' F. The ordinary "conunercial temperature range for the treatment is from about 1250 F. to about 1800 F. This'change in character of the metal is accompanied by a considerable increase in strength and ductility of the castings, as a result of which they are better able to withstand shock than gray iron castings. Malleable" iron castings are accordingly extensively used for agricultural implements, automobiles, railroads, pipe fittings. and hardware.

The manufacture of malleable iron castings is, however, very costly, as compared with the manu-v facture of similar articles by stamping and other fabricating methods, and is moreover attended with dimculties which are not encountered in ordinary stamping practice.

' ture of malleable iron castings for automobile desired in the finished brake drum, and the 'ex-' cess metal is then required to be removed by slow and expensive machining operations. More over, certain defects in the castings, which be- In' the manufac-- come visible only after machining, suchas porosity, shrinks and cold'shuts, result in rejections in addition to those resulting from the initial casting'operations. I

It is among the objects of this invention ac- 5 cordingly, to provide advantageous processes for working iron carbon alloys, suchas white iron} castings, by malleabilizing'and subsequently rolling, and obtaining products'of 'markedductilityj tensile strength, resistance to corrosionyetc 'as 10 contrasted with the initial cast. iron. A further objectis the production of such modifiedmetal in the form of sheets, strips, bars, tubes, andfother shapes, suitable for useas such, or for stamping or fabrication into other products; Other ob- 5 I jects and advantages will tion proceeds. Tojthe accomplishment of the "foregoing and related ends, said invention, lthen,;comprises the appear 88 de scripa' features hereinafter fully described, and particuo I larly pointed out in the claims, vthelfollo'wing description settingforth inde'tail certain illu'stra tive embodiments of the invention, these' being indicative,-however, of buta few, of the various ways in which the principle of the invention'may 25 beapplied. U

In accordance withmy invention, a. melt i s prepared andiscast into ingots, slabs, or 'forms as de-, sired. For the composition of the melt some latitude is permissible; however, in general, it is de- 30 sirable that the carbon be in the amount of r from about 1.50 to about 4.00 per cent, silicon from about 0.45 to about 1.75 percent, manganese lie-' low 1 percent, phosphorus notexceeding 0.225 per ,cent'and desirably under 0.05 per' cefnt'and 35 sulphur desirably not exceeding 0.05 per cent. Optionally also, I may add alloying metals, as for instance, molybdenum in amountsup to 1 per cent, 0.5 per cent giving in general excellentresult; copper inamounts up to 0.6 per cent, etc. 40

The form and" dimensions of the molds may of course, vary in accordance with the particularfurther purpose in view. For instance,for"strip mill and universal mill work, it is desirable to cast in slabs of about 3 inches thickness, thewidth 45 being dependent upon the vwidth of ultimate, sheet productdesired'for instance 12 to 35 inches; For sheet mill rolling slabs of approximately V; H inch thickness are desirable.

The ingots, slab s or other forms are first mal 50 leabilized by heating or annealing them at a temperature or temperatures within themalleabilizing range, 1. e., about 125 0'F. to about 1800 F., and slowly cooling the same,the"purpose ofl such treatment'being to decompose all or amaior' part of the combined carbon, causing the carbon to be precipitated in the form of free or temper carbon. The free, massive cementite can best be broken up above about 1400 F., but the'excess carbide which exists; when cooled, as pearlite, must be decomposed below this temperature. The length of time necessary to produce the desired malleabilization depends, of course, on the particular analysis of the form and upon the.

thickness or dimensions of same. In actual prace tice, the metal is heated to the maximum desired temperature within the graphitizing range and maintained at such temperature for the desired period, after which it is slowly'cooled to and below about 1400 F., the cooling period being approximately the same as the heating period. Be-

low about 1250 F., the cooling may be rapid, if desired. A typical annealing cycle is, as follows:--

. Hours Time heating to 1500" F 45 Time holding at 1500 FL. J 50 Time cooling 60 stance, with stock otherwiserequiring about 100 hours heating, with the incorporation of 0.25,

desired properties. Y r v .The aforesaid treatment, as previously stated,

By adding molybdenum tothe melt initially, I have found that the annealing or malleabilizing treatment proceeds much more rapidly, andthe time maybe cut down accordingly. For inper cent of molybdenum in the melt, a heating time of about 36 hours is' sufiicient to obtain the results in a malleabilization or, precipitation. of all or a major part of the combined carbon, the precipitated carbon segregating into rounded masses of temper-carbon distributed throughout 7, a more or less homogeneous matrix of ferrite,

or relatively pure 'iron crystals,and insuch a way that the, resulting malleable iron is extreme ly ductile and canbe readily rolled or otherwise worked. l

,The ingots, slabs or other forms thus'malle- 4 vabilized, are then reheated for working or rolling,

being first heated to a suitable temperature. The temperature for working or rolling is that, below which rolling is difficult in ordinary rolling mill operations, while the maximum temperature, which I term the critical temperature, and which is dependent on the analysis and other, factors, is that which separates the ferritic and austenitic phases of the metal, and above which a resolution of the temper carbon takes place. The rolling, in other words, is conducted while the metal is in the ferritic state. The minimum rolling temperature, in practice, is about 1000 F., while the maximum temperature may be as high asrabout 1500 F., depending upon the analysis of the metal; Upon examining a section of the metal under the microscope after rolling, it will be observed that the metal comprises a matrix wherein are substantially uniformly distributed and substantially uniformly distorted deposits of free graphite in the form of elongated flakes arranged in approximately parallel relation.

Sheets and other stock produced by the methods which has been outlined can'be employedfor fabricating if desired, or can be further finished by cold-rolling. A final annealing at a temperature above about 1000" F. isv advantageous after cold working, for the purpose of removing rolling strains and to effect recrystallization or equiaxing of the distorted ferrite crystals, such annealing treatment being similar to that employed for annealing plain low-carbon steel sheets. The temperature range for this final anneal is approximately the same as that for rolling, as hereinbefore described.

Following such annealing treatment, the products are in a condition in which they can be readily stamped or otherwise fabricated into va ,rious articles, including a great number which have heretofore been made chiefly in the form of malleable iron castings.

Sheet stock rolled and annealed in accordance with our process has a superior resistance to corrosion as comparedwith sheet steel, and lends itself particularly to usage in exposed locations. If desired, galvanizing or tinning, etc. may also be applied. On account of the properties of my material, nitriding is especially feasible, and as shaped into desired articles, it may be thus hardened or nitrided by heating with ammonia, along known or practical lines. J

It willbe understood that various products, in addition to those stated, maybe made from the iron-carbon alloy slabs or ingots and that various articles, in addition to those described, may be made from such products. In making tubes, for example, the rolled sheets may be slit into strips (skelp), which are shaped into cylindrical form,-

welded andannealed; or theslabs or ingotsmay tion and claims is intended to mean fimalleable cast iron, which is a product only slightly malleable at ordinary temperatures, but which is tougher than the, white cast iron from which it is made. The term fmalleable, as employed' in this connection is intended to designate a relative condition between white cast iron, which is practically devoid of malleability in its cold state, and malleable cast iron". 7

The term (white cast iron, asused in this application, is intended to designate an iron-carbon alloy which is within the range of the melt analysissetforth in the specification. While it usually contains from about 2.00% to about 3.00% carbon and from about .45% to about 1.75% silicon, it may be more generally defined as aniron-carbon alloy containing more than about 2% carbon which solidifies and cools to ordinary temperatures without the formation of I graphite.

This application is a continuation-in-part of:

my applications Serial No. 619,814, filed June 28,1932, and Serial No. 25,310, filed June 6, 1935.

Other modes of applying the principle of my invention may be employedinstead of the one explained, change beingmade as regards the means and the steps herein disclosed, providedthose stated by any of the following claims or their equivalent be employed.

, I therefore particularly point out and distinct-- ly claim as my invention:

1. The process which comprises malleabilizing a white cast iron casting, and thereafter rolling said casting into sheets and other commercially useful products at a temperature not in excess of the lowest temperature at which the temper carbon recombines with the iron.

2. The process which comprises malleabilizing a white cast iron casting, and thereafter rolling said casting at a temperature above about 1000" F., but below the lowest temperature at which the temper carbon recombines with the iron.

3. The method which comprises rolling into sheets and other commercially useful products malleabilized iron-carbon alloys containing from about 1.50% to about 4.00% carbon.

4. The method which comprises rollingmalleable cast iron at a temperature of from about 1000 F. to about 1500 F.

5. As a new article of manufacture, a sheetlike product formed by rolling va malleabilized iron-carbon alloy containing from about 1.50% to about 4.00% carbon.

6. As a new article of manufacture, a sheetlike product formed by rolling malleable cast 8. The method which comprises heat treating.

white cast iron within the malleabilizing range to precipitate substantially all of the combined carbon as temper carbon and thereafter rolling the same into sheets and other commercially use- 1 said cast iron to a rolling temperature, and roll--' ing saidcast iron into sheets and other products.

10. A metal product comprising rolled graphitic iron having a ferrous matrix wherein aresub I stantially uniformly distributed and substantialv ly uniformly distorted deposits of'free graphite in the form of elongated flakes arranged in approximately parallel relation.

11. A metal product comprising rolled graphit 10 iron having a matrix of ferrite with elongated v substantially uniformlydistorted deposits of free graphite uniformly distributed therein in parallel relation. I

12. The method for making rolled shapes of malleable iron wherein iron as ingots of white