US2087766A - Method of making rolled products - Google Patents

Description

Patented July 20,1937

UNITED s ATEs METHOD OF MAKING ROLLED raonuo 'rsp I V v V Duncan P. Forbes, Erwin J. Mohr, and Fritz W.

Meyer, Rockford, Ill., assignors to Gunite Foundries Corporation, Rockford, 111., a cor-1 poration of Illinois No Drawing. Application March 11, 1933,

Serial No. 660,440

13 ClaimS.-- (Cl. 148-12) This invention relates to the manufacture of rolled products of graphitic iron and we have successfully made rolled sheets, plates and bars of such metalby the methods herein set forth.

By the term graphitic' iron we mean iron .containing any form or precipitated free carbon, and by the term graphite we mean such free carbon. v

The invention proved and novel method for .the manufacture of ,rolled shapes ofgraphitic iron wherein the cost of manufacture and the time required to carry out the method are materially reduced and wherein numerous difficulties incident to the manufacture of such products are overcome.

I The products are novel and commercially useful materials having amongother properties advantageous corrosion resistant qualities; These ment brings about favorable rolling conditions and permits greater reductions at each pass through the rolls, there are certain disadvantages to such a method. For example, when the composition of the metal is such that longheating periods are required to decompose the cementite, decarborization of the surface of the ingots may occur. .Furthermore, it will be obvious that certain expense is involved in such heat treatment for fuel in heating the furnace and labor in transferring the ingots. Furthermore, thisheat treatment consumes a certain amount of time which in some instances would also be disadvantageous. We have found'through the actual manufac ture of such products that certain advantages will accrue from rolling the white iron ingots as such without prior heat treatment. We have found that by rolling the white iron directly, the rate of decomposition of the cementite may be accelerated and that the cementite will be largely eliminated, and with metal of some analysis may be entirely eliminated, during the relatively short time required for rolling. In other words, the cementite decomposes at a much faster rate while the metal is being rolled than would otherwise be the-case at the same temperature. Consequently,

contemplates a generally im-- when-the metalis rolled as ingots of white iron, the cementito willbejentirely or largely elimi nated during the rolling operations, thusfeither entirely obviating the'necessity for heating the metalto decompose the cementite' or greatlyv reducing, the time required to bring lthis labout,

Therefore, inmost instancesa great economy is I effected by proceeding'directly to the heat treating of metal to produce any of a plurality of.

matricesor complete the elimination of combined, carbon from the metaFas hereinafter described, while the metal is still in the heat of rolling.

The first step in the method consists in the production of suitable" ingots'ofwhite cast iron. The ingots may have any convenient size or shape and may be formed by pouring'into metal molds; green or dry sand moldsgorcore sand, or {any other molds customary in foundry practice; The

analysis of this iron willdepend to some extent upon the heat treatment adopted and upon the ultimate product desired, as "will presently fbe described. The ingots will'contain a certainp'roportion of massive cementite (iron carbide) which under heattreatment can'be' decomposed with a resultant precipitation of graphite in the metal. Unles's otherwise expressly statedqthe' term cementite used throughout this specification and the appended'claimsis intended to mean iron carbide as a distinct crystalline constituent formed upon solidificationof the metal and; not cementite formed at temperatures below this point. We heatv these white'iron ingots to a rolling temperature and while at this elevated temperature roll the-ingots into the'desired shapes, such as sheets, bars, and the like.

Our experience teaches us'that in general" the rollingcan best be carried out at temperatures between about 1800 F., and the temperature at v which a liquid phase begins' to appear in the metal. Inmost cases this will be about'i2l00" F. It may begpossible, however, with metal of certainanalysis to roll at slightlyylower temperatures,-but, in general, it seems that the best rolling temperature is the highestternp'erature' ob-' v tainable without the presence 'of a liquid phase.

.Any conventional rolling mechanism'may be employed, but it will be found that as rolling pro ceeds, the operation becomes. increasingly diffi cult. wehave found to be 'due to the rapid I V v drop in temperature of the iron and the rapid decrease in ductility with change in temperature.

However, ifthe'metal is reheated one or more times during the rolling to maintain the temper- I ature above'about 1800 F.', the'desir'ed reduction in section may be satisfactorily accomplished.

It is; therefore, advisable to locate the heating furnace in such proximity to the rolling process as to prevent excessive loss in temperature of the metal between the heating furnace and the rolls. Care should be taken to select the proper amount of reduction at, each pass. The amount of reduction at each pass will depend upon the temperature ofthe metal as it enters the rolls, the type of billet,'the type of mill, the

contemplates various forms adapted to produce a product of commercially usa ble characteristics and involves the heat treatment'of the metal, the type of heat treatment depending upon the ultimate product desired andthe analysis of the metal. Thus, in order to produce a product of predetermined physical characteristioawe control both the analysis of the 'metal'and the heat treatment,

imparted to the metal. This heat treatment also results in the production of uniform products from rolled materials which might otherwise have uncertain and erratic'microstructure; The

heat treatment thus serves two purposes, that of bringing the parts, of each rolled form and also the various rolled forms touniformity and that.

of imparting desired, structural characteristics to the material.

, One purpose of thepresent invention is to produce a rolled graphitic iron wherein the graphite is distributed in a matrix of ferrite. To produce such a material, we may take 'a'rolled material,

formed in the manner above described, from white iron ingots capable of being graphitized and hav ing a carboncontent preferably not less than 1.5%, a percentage of carbon plus a percentage of silicon greater than about 2.9%, and a manganese content which is twice the percentage of sulphur plus about .10% to 30%. When this iron is such that the percentage of carbon is about 1.5% to 2.20% and the percentage of carbon plus the percentageof silicon content is greater than 3.10% preferably about 3.5%, the cementite of the metal will have been completely decomposed during the rolling operation, while with metal falling within substantially theremainder' of the, first above-mentioned range there is apt to be a' certainamount of residual cementite after the rolling operations are completed. After the rolling operations, the rolled metal is placed in a furnace and is .held within the graphitizing range (with most metals between 1350 F. and 1750 F.)

until the cementite has been completely broken down. Where the metal is ofan analysis such that the cementite is completely'broken ,down' posed to form graphite. The metal is then.

cooled to atmospheric temperature, preferably at a rapid rate. The resultant product willbe material having the graphite in elongated substantially parallelly arranged form dispersed in a matrix of ferrite. Examples 1' and 2 are given by way of illustration, Example 1 illustrating the manner in which a material may be made wherein the cementite is completely decomposed during the rolling operations, while Example 2 illustrates the method wherein the metal as it comes fromthe rolls'contains some residualcementite.

IExamplc 1.--'-An ingot of %"'thickness was prepared of white iron of the following analysis:

, Carbon 1.7%, silicon 1.65%, manganese 30%, sulphur .08% phosphorous .10%.

p This ingot was heated to 1950 F., and as soon as it had reached .a substantially uniform temperature was rolled into sheets of a thickness of inch using a reduction of approximately 15% for each pass through the rolls. (We have used a 30% reduction at each pass with satisfactory results.) When the tem- 1 perature of the'metal dropped below about 1800 F., it was reheated to 1950 F. and rolling continued until the desired size and thickness of sheet was obtained, reheating as frequently as necessary to keep the material in reliable condition. After rolling was completed, the material was placed in aheat treating furnacebefore excessive loss of temperature hadoccurred and was held at about 1350[F. fortwelvej hours. It was then removed from the furnace and allowed to cool'in air.

Example Zr-An ingot was prepared of white iron of the ffollo win g analysis: Carbon 2.40%, silicon .90%', manganese".30 sulphur .08%, and phosphorous .16 Thesewhite iron ingots were heated to 1950 F. and rolled as soon as they hadreached uniformtemperature using a reduction of ap roximately 15 for each pass through the rolls. 'As described in Example 1, the metal was reheated as frequently as necessary to maintain it in condition. After rolling was completed, the

material was placed in a heat treating furnace before excssive loss of temperature had occurred and held'at about 1700 F.'for eight hours. The metal was then cooled in the furnace to 1350" F.

and held for twenty-four hours. Thereafter the allowed to cool in air.

In both Examples 1 and'2, the final product consisted of a rolled graphitic iron wherein the graphite or tempercarbon was in the form of elongated susbtantially parallelly disposed deposits in a matrix of ferrite.

However, as previously pointed out, valuable described and immediately after the rolling 'oper-' ations the rolled metal was coiled to atmospheric,

temperature. The resultant product consisted of a matrix which was largely pearlitic but con tained a small amount of massive cementite and elongated parallel deposits of graphite.

Example 4.-White iron ingots. having the analysis given in Example 2 were rolled as therein describedand the rolled metal was allowed to cool to atmospheric temperature immediately after rolling. The product contained no massive cementite, and the matrix was largely pearlitic having elongated substantially parallelly disposed deposits of graphite [The lnvention'also contemplates the production of rolled shapes wherein the matrix consists 7;

of pearlite or sorbite. For the production of such a product, we prefer to start with a white iron which has a'carbon' content'preferably notless than about 1.5%, a percentage of carbon plus a percentage of silicon content greater than about 2.9%, and a manganese content which'is twice pletely decomposed during the rolling operations.

These white iron ingots are rolled, as previously described, and then placed in a heat treating furnace. that there will be residual cementite in the metal after the completion of the rolling operations, the

metal is held at a temperature within the graphitizing range until the cementite has beencompletely decomposed. The metal 'iisthen brought to above the critical temperature, but preferably not more than about 200 F. thereabove and is then cooled through the critical temperature at a speed such as to'retain the combined carbon in the matrix in the form of pearlite or sorbite. The best results are usually obtained when cooling takes place rapidly in air. Examples 5 and6 are given by way of illustration, Example 5 illustrating a method wherein the cementiteis com pletely decomposed in the rolls, and Example 6 showing a method wherein the product of the rolling operations contains residual cementite.

Example 5.A white iron ingot having a carbon content of 1.70%, silicon 1.65% ,manganese sulphur .08%, and phosphorous '.10% was heated to about 1950 F. and rolled as soon 'asthe metal had become uniform in temperature, using a reduction of about 15% at each pass, the metal .tially uniform in temperature.

the rolling operation was then placed ln'a heat being reheated as frequently as necessary to maintain it in rolling condition. The metal was then placed in a heat treating furnace and brought to about 1600 F. only long enough to" secure uniform temperature. Thereafter the metal was cooled rapidly to atmospheric temperature as by cooling in air. i l

Example 6.A white iron ingot was made of the following analysis: Carbon 2.40%, silicon .90%, manganese .80%, sulphur .0'1%, and phosphorous .16%. The ingots were then heated to about 1950 F. and rolled as described "in the first example as soon as it had become substan- The product of treating furnace and brought to about 1700" F. for eight hours, and was then broughttoa'uniform temperature of about1600 F. and thereafter cooled rapidly through the critical temperature to room temperature, forexample, as by cooling in air.

The products of the methods described in Examples 5 and 6 showed a pearlitic matrix containing elongated clusters of graphite or temper carbon.

The invention also contemplates-the produc-' tion of products wherein the matrix consists-of spheroidized eutectoid cementite distributed through ferrite crystals. In making such a prod uct, we prefer to roll a white iron ingot wherein the carbonis preferably notless than about 1.5%,

the percentage of carbon plus the percentage of silicon is greater than about 2.9%; and the man- 7 Where the analysis of the iron is such percentageof sulphur plus 30% .to ..80%.' "The ingots are heated directly to the rolling tem perature and rolled, as previously, described. The' product of the.rollingfoperation-s' is placedfin a 3 'ganese content, isabout twice-the percentage of sulphur,plus';.10% to .80%, preferablytwice the.

furnace andheld ,within-fthe. graphitizing range until the'residu'a'l cementite has been-complete ly decomposed f-The metahis then cooled through the critical temperature at a {speed such as to retain the combined carbon in thematrix in the form'of pearlite or sorbite, as for'example by cooling in air, and is thenheld at or reheated to the spheroidizing range "(about.,1200 to 1300, 'F.) ,foras'ufficient timetofspheroidizethe p'earlite oi sorbite to thedesired degree. .Ex

ample "'Ij'is given by. way of'illustra'tion I of a satis-.,

factorymanner of producing this type of product.

exam le 7.-'-A whitefiron. ingot having" the analysis set forth 'infl Ex'ample 5was madeand rolled in the mannerjalready described, After the material had been rolled to'the desired shape it was held at about 17.00" F. for about eight hours and was then cooled at the rate of aboutf600'" per hour through the "critical temperature (in this case about-1375f F. ),.Jand thenheld at'a temperature ofv about1 275 F. for twenty-four hours. It' was thereafter cooledto roomtemperature. This metal had a matrix of finely spheroidized' cementite uniformly distributed through ferrite crystals and elongated. substantially parallelly disposed. deposits of. graphite were embedded in this matrix. I a f It iwillbe seen that in our process we use as a starting "point white iron and proceedto roll this metal at'an elevated temperature. In this way, we are enabled to materially accelerate the. v

rate at which the cenientite is decomposed, thereby materiallyfreducing' the time required for the production of certain desirable product's. By

properly regulating the analysis of the metal, we are enabled to bring aboutcomplete decompositionof the cementite during the rolling operations, thereby completely 'eliminating the necessity for 'holding themetal at anelevated temperature. until the 'cementite has been decomposed. In those instances wherev the cementite is not completely decomposed during the rolling of the metal, the .heattreatnient required for the completion of this decomposition is greatly reduced in. time and may be combined withsome other subsequent heat treatment'and be carried out in the same furnace, as .a-preliminary' step of such heat treatment. Inthis manner, frequent transfers or" the "metal from 'fumace ,to'

furnace is eliminated and aconsiderable saving inheat and time isefiected since whatwould; otherwise be two separate heattreatments are combined intoa single continuous treatment at" required temperatures.

cementite' will depend to a certain degree upon .the extent of the working of the metal but in commercial operations the reduction of section is usually suflicient toresult in the decomposition of at least a large part of thecementite and ;60 The amount of the decomposition of the when the analysis is favorable, as, herein, de-.

. scribed, allof the cementite' will be decomposed;

Some allowances will have to be madefwhen the rolling operations depart from the customary reductions.

As one phase ofou'r invention, we regulate the analysis of the white iron, and, after rolling,

subject the'rolled'materialto certain heat treat ments to produce uniformproduots of definite,

yet variable physical properties. This heat treat ment normallyserves two purposes. It serves first to produce resultant products of certain-predetermined physical properties,thereby enabling us to produce productssuitable and valuable for certain definite requirements; However, in'addivtion to this function of the heat treatment, the

steps also serve to bring'the'rolled metal into uni formity regardless of the particular nature of its matrix; It will be understood that during and prior to'the rolling operations the'ingots are sub:

jected'to variable conditions so that in many instances there will be a'variation in the microstructure of the metal of the different ingots, and frequently a variation in the microstructure of various parts of the same sheet or bar rolled from an ingot. Forsome uses the'metal will, of course, be satisfactory regardless of these variables.

However, the heat treatment after the rolling operations serves to overcome this lack of funiformity so that the productjffof themethod may have uniformity throughout each piece and throughout the various piece 1 New and novel products result from the method above disclosed, such products being described and claimed in our above-mentioned copending application. These products have certain new and commercially valuable properties. Cast iron and metals containing graphite have long been well known for their corrosion resistance properties, particularly .corrosion due to atmospheric exposure and underground services. For this use the metals must in many cases be thin in section; In the past, metals for this purpose have been non-ferrous metals or steel alloys which contain substantial quantities of other metals, such as chromium, copper, nickel, etc. These alloys are relatively expensive. The difficulty has been that while iron containing graphite has in the past been available .in the form ofindividually'cast platesfthere is a limitationto the minimum section which can be cast of graphite bearing iron.

That is, in the past there has been no method of making graphite bearingiron' in sheets of sufficient size and thinness of section to permit the generaluse of such metals for corrosion resistance purposes or for other 'purposesto which such' metal in the sheet form might be adapted. ,Our method completely obviates this difficulty and permits the rolling of such metal in very thin section and in relatively large sheets. The method brings about the production of uniform sheets of graphite bearing metal of predetermined properties with almost the'same facility with which steel sheets are made, thus opening up a large variety of new materials for the. sheet metal industry. 'I'he'method also permits the production of graphite bearing metal in shapes and sizes which have heretofore not been obtainable.

A number of uses for the metals made in accordance with our method might be listed. The

metal made in accordance with Examplesl and 2 is valuable for use in fabrication where draw ing and forming operations are necessary.- The metal made in accordance with Examples 5 and 6 will be of particular value-where wear' resistance and corrosion resistance are important, such, for

example, as in the manufacture of elevator buckets. Metal made in accordance with the seventh example possesses corrosion resistance as well as high strength and ductility, and is of a particular valuein the manufacture of such materials as ship plates, coal hoppers, .tanks,and the like. Q '1 We'have dealt} throughout this specification with the compositionof the metal as this is concerned withcertain'well known' constituents. It

will vbe understood, however," that numerous other elementsmay be present in the metal or may be added thereto which will or mayv effect the method or the product-some beneficially and some otherwise.

' While we havethus described and illustrated specific embodiments of our invention, we are aware that numerous. alterations and changes may be made without departing from the spirit of the invention and .the scope of theappended claims; in which- We claimi V l L'Themethod for treating graphitizable white cast iron containing a graphitizingagent to ac,- ceierate'the decomposition of the cementite which includes heating said iron the. temperature above about 1800 F. and thereafter plastically deforming the same.

2. The method of rolling sheets, bars, and'other shapes'from graphitizable white cast iron containingagraphitizing agent wherein the decom position of the cementite of the iron is accelerated by hot.rolling of the metal above about 1800 F. and the metal is, thereafter held at -atemperature within the graphitizing range to decompose the residualfcementite.

a. The method of making rolled shapes er graphitio iron, comprising bringing to the hot rolling temperature white iron wherein the-carbon is'about 1.5% to about 2.0% and the percentage of carbon plus the percentage of silicon manganese equal to twice the percentageof sulphur plus .10% to .80%, rolling said iron, heat I treating the same in the graphitizing range to decompose the cementite remaining after the roll-..

ing operations and cooling at a rate to produce a pearlitic matrix.- I '5. The method of making rolled shapes of graphitic iron, comprising bringing to the hot rolling temperature above about 1800 F.'white iron wherein the carbon content is between about 1.5 and 2.20% and the percentage of carbon plusthe percentage of silicon is not. less,than about 3.10%, rolling saidiron and cooling said iron from-a point slightly'above the critical temperature at a speed such as to retain the combined carbon in the matrix in the form of pearlite.

6. The method of making rolled shapes of graphitic iron comprising bringing to the hot rolling temperature above about 1800 F. white iron of an analysis within the following limitscarbon not less-than about 1.5%,percentage of carbon plus percentage of silicon'greater than about 2 .9%, manganese, equal to twice the per-x centage of sulphur plus 110% to .80%, rolling said iron to deform the same and decompose the major portion of the cementite thereof, thereafter hold-' ing, the same at a temperature within the graphitizingrange to decompose. the residual cementite,

cooling the iron from a point'slightly above thecritical temperature through the critical temperature at a speed such as to retain the combined carbon in the matrix in the form of pearlite, and then holding the metal at a spheroidizing temperature to spheroidize the pearlite.

7. The method of making rolled shapes of graphitic iron which consists in producing ingots of white cast iron containing a graphitizi'ngagent, causing said ingots to be brought as ingots of white cast iron to a temperature above about 1800 F. but below the temperature at which a liquid phase appears in the metal of said ingots, and reducing said ingots to rolled forms of a desired by rolling the ingots first while at substantially saidhigh temperature and then successively while the ingots are at atemperature above about 1800" F., reheating of the ingots between successive rolling operations being resorted to when necessary to maintain the ingots at a temperature above about 1800 F. until so reduced.

8. The methodior making rolled shapes of graphitic iron wherein white iron containing a graphitizing agent is rolled at temperatures above about 1800 F.

9. The method for making rolled shapes of V graphitic iron wherein iron containing a graphitizing agent is rolled as ingots of white iron at a temperature above about 1800 F., and therolled metal is then held at a temperature in the graphitizing range until the massive cementite is substantially completely decomposed.

10. The method of making rolled shapes of graphitic iron comprising bringing to a hot rolling temperature above about 1800 F. an iron carbon alloy of an analysis within the following limits-carbon not less than about 1.5%;, percentage .of carbon plus percentage ofsilicon greater than about 2.9%, manganeseequal 'to twice the percentage of sulphur plus about .10%

to 30%, hot rolling said metal at a temperature above aboutl800" F. and thereafter subjecting the rolled metal to a heat treatmentln the graphitizing range to precipitate at least .a

portion of the combined carbonjas graphite;

11. The method of'making rolled shapes of graphitic iron, comprising bringing .to the hot rolling temperature above about 1800 F. an'ironl carbon alloy wherein the carbon is about 1.5% to about 2.2% and thepercentage of 'carbon plus. the percentage of silicon is not less than about 3.10%, andhot rolling said metal to deform the 3 same anddecompose the cementite.

12. The method for making rolled shapes of graphitic iron wherein iron containing a graphitizing agent is rolled as ingots of white iron at completely decomposed and is then subjected to a heat treatment to develop a predetermine microstructure ofthe matrix. I a

13. The method'for making rolled shapes of graphitic iron wherein iron containing a graphitizing agent is rolled as ingots of white iron at i 0 temperatures above about 1800 F; to deform the same and decomposexthe cementite, and is thereafter subjected to a heat treatment to develop a a 2'0. temperatures above about 1800" F., the rolled metal is then held at a temperature in the graphi- 1 -tizing range until the cementite is substantially