US2087765A - Conversion of iron-carbon alloys into products of sheeted and other shapes - Google Patents

Description

Patented July 20, 1937 UNITED STATES 2,087,765 f 1'1' 1. CONVERSION F IRON-CARBON ALLOYS INTO PRODUCTS- OFc SHEETED AND OTHER SHAPES Nathan H.""Schermer," Youngstown, as-

signor to Stellum, Inc., Cleveland, jQhio, a f

corporation of Ohio ,No Drawing. Application February-1 7:

Serial No. 657,258 v 7 v 20 Claims. (01.148142).

This invention relates in general to the treatment of cast iron-carbon alloys, particularly white cast iron, for the obtaining of products in sheeted or other shapes with tensile strength and machinability, 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-,iwhite iron castings, which contain carbon in the 1 combined form, 1. e. cementite and pearlite, and whichv makes the metal hard 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 cast iron. 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 an-. nealing treatment changes the character of the castingfrom one having a white silvery crystalline fracture, in which no-graphite flakes are visible to the naked eye, to one having a dark gray, soft, velvety appearing fracture, in which the carbon has been precipitated or segregated into rounded masses, leaving little or no carbon combined with the iron. This change takes place at a temperature as low as 1250 F., but'occurs more efiectively at a temperature of 1350F. The ordinary commercial temperature range "for the treatment is from about 1250 F. to about 16'0oe F. This change in character of the metal is accompanied by a considerableincrease in strength manufacture of similar articles by stamping and other fabricating methods, and is moreover. at-

tended with dimcultieswhich are not encountered in ordinary stamping practice. In the manufacture of malleable iron castings for automobile brake drums, for example, only the most highly skilled foundries can be relied upon to .produce 5 sound castings, with a minimum of rejections.-

Due to shifting of the patterns in the'mold, the" sections of the castings are usually heavier than desired in the finished brake drum, and the ex-- cess metal is then required to be removed by slow 5 and expensive machining operations. Moreover,

certain defects, inthe castings, which become visible only after, machining, such- .as porosity; shrinks ,and cold shuts, result in rejections in addition to those resulting from theinitialcastlng' operations. I 4 g It is among the objects of this invention accordingly, to provide advantageous processes fordirectly working iron-carbon alloys, such as white iron castings, preferably by rolling, and. subsequently annealing on the order of malleabilizing,v 10 or bymalleabilizing and subsequently rolling, and. in either. case obtaining products of marked ductility, tensilestrength, resistance to corrosion, etc., as contrasted with the initial cast iron.:'-.A further object is the-production of such modified, 15 metalin the form of sheets, strip, bars, tubes, and v other shapes, suitable for use assuch,wor for. stamping or fabrication into other products. Other objects'and, advantages, will appear-as the. I a description proceeds. i 2

To the accomplishment of the foregoing and -f related ends, said invention, then, comprises the" features hereinafter fully described, and pa-rticularly pointed out inthe claims, the following description setting forth in; detail certain illus-. 25 trative embodiments of. the invention, these be-; ing indicative, however, of but a few', of thevarlous ways in whichthe principle of theinvention, may. be-applied. a In accordance with my invention, a melt is ;30 prepared and is cast into ingots, slabs, or forms as desired; For the composition of the melt some latitude is permissible; :however, in general, it is desirable that-the carbon be in the amount of from about, 1.50 to about 4.00. per cent, silicon 35 from about 0.45 to about 1.75 per cent, manganesebelow l per cent, phosphorus not exceeding 0.225 per centand desirably under 0.05 percent and suiphur'desirably notyexceeding 0.05- perucent.

Optionally also, I may add alloying metals, as40,

for instance molybdenum in amounts up to 1 per cent, 0.5 per. cent giving in general excellent: rea sults copper inv amounts up to 0.6 per cent, etc.

The form and dimensions of the molds may, of course, vary in accordance with the particular further purpose in view. For instance, for strip mill and universal mill work, it isldesirable \to' cast in slabs of about 3 inches thickness, "the width being dependent upon the width of ultimatesheet product desired, for instance 12 to 36 inches. For sheet mill rolling slabs. of -approximately inch' thickness are desirable. v

If the ingots or slabs are to be rolled without being previously *malleabilized, I: prefer where possible, tojiroll-them before theyghave cooledfl,

.down to an appreciable extent. For this purpose, they may be placed in a soakingpit or furnace wherein they are maintained at a temperature suitable for rolling, i. e., from about 1600 F. to about 2100 F. By rolling the ingots or slabs before they have cooled below about 1800 F., primary graphitization or malleabilization is avoided, and reheating between passes is avoided. Where it is not feasible to thus soak the ingots or slabs for rolling, they should be cooled or chilled as quickly as possible to prevent mecipitation of graphitic carbon, 'arid'this may be accomplished by positive chilling with exposure to circulating air, 'as distinguished from mere passive cooling .down as heretofore practiced. When these ingots or slabs are to be worked or rolled, they are first heated to a suitable temperature 1200" F.2100 F. and most desirably about 1600 F.2000 F. It is advisable to roll above 1200 F., on account of greater plasticity and economy in rolling at the higher temperatures. Where reheating between passes is necessary on account of the size of the piece, etc., reheating temperatures to about 1500 F.2000 F.

are usually preferable, although slightly" lower temperatures give good results. With a 3 inchwhite cast iron slab' as the 1starting material, and heating to about 1500 F., I have satisfactorily rolled down to a thickness for instance of 0. 16 inch in six passes. It is advisable in heating,'not to heat too long and cause precipitemperature furnace, in which rapid heating up to about l500 F.-2000 F. which then requires a relatively short time, may be effected, and the I slab fed to the rolls.

After the iron is worked or rolled down as desired, it is subjected to a heating-or anneal-' ing, somewhat on the order of malleabilizing.

Desirably, this heating is carried on with the temperature around 1500" to 1550" F. for a period of time depending upon the thickness of the material, and then the temperature may be slowly lowered to about 1200 F., whereupon it is desirable to then cool rapidly by removing from the fire and air-chilling. This gives a' better control of the grain-size of the ferrite and also makes possible obtaining of a more rounded character in the temper-carbon grains.

.By adding molybdenum to the melt initially, I have found that the annealing or malleabiliz-' ing treatment proceeds muchimore rapidly, and the time may be cut down accordingly. For instance,-with stock otherwise requiring about hours heating, with theincorporation of 0.25

percent of molybdenum in the melt, a heating The slabs may be ing. This gives a better control of the grain size of the ferrite and makes possible obtaining of a more rounded character in the temper-carbon.

The ingots, slabs or other forms thus malleabilized, are. then reheated for working or rolling, being first heated to a suitable temperature, 1000 F.-2000 F., and most desirably about 1000 F.-1600 F. Upon examining a section of the metal under the microscope after rolling, it .will be observed that the metal resembles wrought iron in appearance, that is to say, the black rounded masses of temper-carbon have .been elongated in the direction of rolling and flattened in the same manner that the slag inclusions in wrought iron appear elongated and flattened. The ferrite grains also appear distorted, as in wrought iron.

Sheets andother'stock produced by either of the methods which have been outlined can be employed for fabricating if desired, or can be further finished by cold-rolling. A final annealing at a temperature above 1200 F. is advantageous' after cold working."

Following such annealing treatment, the products are in a condition in which they can be readily stamped-or otherwise fabricated into various articles, including a great" number which have heretofore beenmade chiefly in theform of malleable iron castings.

Sheet stock rolled and annealed in accordance with my process has-a' superior resistance to corrosion as compared with sheet steel, and lends itself particularly to usage in exposed 1ocations. If desired, galvanizing or tinning, etc., may also be applied. 'On account of the properties of my materiahnitriding 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.

It will be understood that various products, in addition-to those stated, may be 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-roller sheets may be slit into strips (skelp), which are shaped into cylindrical form, welded and annealed; or the slabs or ingots may be rolled directly into skelp; which may be shaped into cylindrical form while hot, welded by well known electric welding processes and annealed, the annealing in either'case being optional. v

While certain temperature ranges for working or rolling have been specifically set forth, it will be understood that the rolling may be conducted at temperatures other than those set forth. In

general, the working or rolling may be carried but below that at whichthe metal loses its malle'-' ability, due to overheating.

While the term malleable iron" has been ap-" plied to products such as pure ,or puddled iron, and softor mild steels, which are admittedly malleable in various degrees and in a greater degree than malleable cast iron, such designation is entirely improper in the metallurgy of ferrous products, and it is therefore desired to particularly point out that the term malleable iron as used and contemplatedin the specification and claims is intended to mean malleable cast iron, which is a product only slightly malleable at ordinary temperatures, but is tougher than the cast iron from "which it is made. The term. malleable, as employed in this connection is intended to designate a relative condition between cast iron, which is practically devoid of malleability and malleable cast iron.

The term white cast iron, as used in this application, is intended to designate an iron-carbon alloy which is within the melt analysis set forthin 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 .j. means and the steps herein disclosed, provided those stated by any 01 the following claims or their equivalent be employed. v t

I thereforeparticularly point out and distinctly claim as my invention:

1. The method which comprises hot rollin graphitizable white cast iron containing a graphitizing agent.

2. The method which comprises 3. As a new article of manufacture, a product formed'by hot rolling graphitizable white cast iron.

4. The method which comprises plastically 'dforming into products of sheeted and other shapes, j at a temperature above about 1200 F., iron-carbon alloys containing more than 2.00% and up to about 4.00% carbon and a graphitizing agent in an amount sufficient to permit the alloys tobe 40 -grapl'n'tized after deformation, and then graphitizing said alloys.

5. The method which comprises hot rolling a ferrous alloy containing more than 2.0% of carbon, and a graphitizing element in an amount sufiicient to permit graphitization of the alloy, and thereafter heat treating the alloy within the graphitizing range to precipitate substantially all of the combined carbon as graphite.

6. The method which comprises hot rolling,

white cast iron containing a graphitizing agent, and thereafter heat treating the same within the graphitizing range to precipitate substantially all of the combined carbon as graphite.

7. The method which comprises hot rolling white cast iron containing a graphitizing agent and then malleabilizing ,the same.

' 8. The method which comprises making graphitizable white iron castings, subsequently heating the same to above about 2000 F. and rolling. 9. As a new article of manufacture, a rolled wholly graphitizable iron-carbon alloy containit ing in excess of 2.00% carbon.

10. The method which comprises hot rolling white cast iron containing more than 2% and up to about 4% carbon and a. graphitizing agent in rollingwhite cast iron containing a graphitizing agent at a temperature above about 1200 F. and then malg leabilizing the same.

an amount sufficient to permit graphitization of... the product after rolling.

11. The method which compri'seshot rollingv white cast lron'containing morethan 2% and up to about 4% carbon anda graphitizing agent in an amount suflicient to" permit graphitization of the product after rolling, and then graphitiz ing the rolled product. I

12.'The method which comprises hot rolling graphitizable white ,cast 3 iron containing more than 2% and up toabout 4% carbon and from about .45% to about.1 .75%- silicon.

13. The method .whichcoi'nprises' hot-rolling white cast iron c'ontainingmore than 2% and up to about 4% carbon, from about .45%'to about then graphitizing the'productof said rolling.

14.v Asa new article-of manufacture;' a jprod 1.75% silicon, and'le'ss than 1% manganese, and

uct formed byhotrolling white cast iron containing more than 2% and-up to about4% fcarbon rolling.

15. Asa new article of manufactura aiijprod- 4 uct formedby hot rolling gr'aphitizablef'white cast iron containing morethan 2% and up to' about 4% carbonandfromabout .45 to about 1.75% silicon.

16. As a new article of manufacture, a prod uct formed by hotrolling graphitizable white cast ironcontaining' morel-than 2% and up .to about 4% carbon, from about .45%- to about' l.7 5%

silicon, and less than 1% manganese.

17. Themethod which comprises {plastically deforming into products of sheeted and other 'white cast iron containing more than 2% and .up

shapes,at a temperature above about 1200F to about 4% carbon and a graphitizing. agent in an amount sufiicient to permit the product to .be

graphitized after deformation, and then graphitizing said product." t a 18. The'method which comprises hot rolling.

white cast iron containing more than 2.0% of carbon, and a graphitizing element in an amount suificient to permit graphitizationofthe product, and thereafter heat treating the product within the graphitizing range to precipitate substantially all of the combined carbonas graphite.

19. The method of making ferrous'articles comprising forming an articleby hotworkingan ingot of an iron-carbon alloy containing :not less than about 1.5% of -carbon andals'o containing silicon and molybdenum, as graphitizing elements, and the remainder of the alloy being effectively iron, and heating the article at a temperature above its critical temperature to con vert a substantial proportion oi its carbon content to the graphitic state.

20.. The method which comprises hot 'rolling a ferrous alloy containing between about 2.1 and} 2.5% carbon and about .9% silicon, andthereafter heat treating the alloy within the graphitizing bined carbon as'graphite. H I

NATHAN H. SCHERMER.

range to precipitatesubstantiallyall the com-f and a graphitizing agentin an amountsufficient [to permit graphitization of the product after