US2595567A - Process for producing malleable iron castings - Google Patents

Description

May 6, 1952 L. c. CROME PROCESS FOR PRODUCING MALLEABLE IRON CASTINGS Original Filed March 5, 1945 5 Sheets-Sheet 1 Q Q Q Q Q Q q Q Q Q Q Q Q Q Q Q Q Q 52 g Q '3 g :3 3 g Q Q Q Q s Q l s Q Q no Q Q W 3mm BE M' w May 6,' 1952 1.. c. CROME PROCESS FOR PRODUCING MALLEABLE IRON CASTINGS Original Filed March 5, 1945 5 Sheets-Sheet 2 May 6, 1952 Original Filed March 5, 1945 L. C. CROME PROCESS FOR PRODUCING MALLEABLE IRON CASTINGS 5 Sheets-Sheet 5 u. /700 1' :1 "A M I m0 I I 900 y 6, 1952 L. c. CROME. 2,595,567

PROCESS FOR PRODUCING MALLEABLE IRON CASTINGS Original Filed March 5, 1945 5 Sheets-Sheet 4 y 1952 L. c. CROME 2,595,567

PROCESS FOR PRODUCING MALLEABLE' IRON CASTINGS Original Filed March 5, 1945 5 Sheets-Sheet 5 fiatented May 6, 1952 PROCESS FOR PRODUCING MALLEABLE IRON CASTINGS Lester C. Crome, West Alexandria, Ohio, assignor to The Dayton Malleable Iron Company, Dayton, Ohio, a corporation of Ohio Continuation of application Serial No. 581,034, March 5, 1945. This application August 2i,v 1949, Serial No. 112,144 a 8 Claims.

This invention relates to metal castings and a method of producing the same and more particularly to so-called malleable iron castings and a method for use in the production thereof.

One of the principal objects of the invention is to provide a method for producing malleable castings which have characteristics fully comparable with those of malleable castings as heretofore produced, but in which the annealing time is much less than that long period heretofore used in the heat treatment or annealing of malleable castings as' heretofore produced in the industry for many' years.

Still another'object of the invention is to provide a process of producing white iron castings which are ofsuch character that the annealing period used to change such white iron castings to malleable iron castings is reduced by as much as several days while malleable products are produced which have characteristics equal to those which are and have been secured in the white iron castings as formerly made and subjected to the much longer annealing periods heretofore in use.

Another object of the invention is to provide a process of producing malleable castings in which a small fraction of one-per cent of aluminum-is added to the molten white. iron just before pouring into the mold and a limited period of preconditioning or preheating is given to the resulting white iron castings at temperatures far below the minimum effective annealing temperature used in malleableized white iron castings, followed by subsequent annealing in theregular malleable process annealing temperature'range, whereby a greatly shortened time of annealing within such regular annealing-temperature range produced malleable castings at least asgood as malleable castings made as heretofore with the longer annealing time.

Another object of the invention isto provide a process of producing malleable castings in which a very small percentage of aluminum is addedto the molten white iron just before pouring it'into the mold, and a limited period of preconditioning or preheating is given to the resulting white iron casting'within a temperature range farbelow the minimum effective annealing temperature regularly used in annealing white iron castings to malleable iron characteristics, such preheating or. preconditioning step being separate and apart from annealing within such regular malleable process annealing temperature; range and effective to greatly reduce the length-of timeto which whiteiron castings have heretofore been subjected to the annealing temperature range, while producing malleable castings having characteristics at least as good as those long produced according to previous practices in the industry.

Another object of the invention is to provide a process of producing malleable iron castings which involves the addition of a small fraction of one percent of aluminum to a usual molten white iron after it is withdrawn from the melting furnace or cupola into a pouring ladle or the like and just before it is poured into the molds, the very small fraction of aluminum being added preferably, to the molten iron within the shortest practicable interval before the iron is'poured into the mold, a period of several minutes being generally satisfactory, and preheating or preconditioning the resulting casting by heating it for several hours at a temperature for below the minimum regular malleableizing annealing temperature, said temperature being within a range of approximately 400 to 800 F. and preferably at about 600 F., and such preheating or preconditioning taking place before the white iron casting'is subjected to annealing within the regu lar malleable process annealing temperature range.

Another object of the invention is to produce malleable castings by said process, which are at least equally as good as castings as-heretofore made and with considerable saving in annealing time and costs.

Qther objects and advantagesof the invention will be apparent from the description and the illustrative annealing charts: and the appended claims.

Thisapplication is a continuation of co-pend ingapplication Serial No. 581,034 filed-March 5', 1945, now abandoned.

Broadly speaking so-called iron castings, as-

produced in the foundry industry fall into the two general classes of grey iron castings and white ironca'stings. Thegre'y iron-castings, as

is well known, have the materials which go to make the molten metal which'is poured into the molds so selected that after it has been heated in the cupola orotheritype of furnace, themolten or malleableized iron castings, as heretofore made have been produced by using a suitable cupola or other type of furnace in which the various ingredients to make up the casting have been selected, according to practices which are well 'known and understood, to provide a molten metal mix which when withdrawn from the cupola or furnace into ladles or other pouring containers is of such character that when poured into the mold and cooled down to the solid casting it will be so-called white iron, all or most of the carbon being combined into compounds so that the casting is white in appearance and is also extremely hard, is brittle in the sense that it is very rigid and has substantially no ductility or capacity for bending and under suflicient force fractures or breaks apart rather than bending, and is practically impossible for use in ordinary machining operations. The practice has been to make these White iron castings from materials selected and so melted that the constituents which are present in the molten mix as it is poured into the mold will be such that by proper heat treatment or annealing the composition of the metal may be changed and the combined carbon affected so that its very hard compounds will be broken up and the casting will ultimately have somewhat the general appearance of a gray iron casting but in addition will have its internal characteristics such that it is no longer brittle but is ductile and subject to bending and elongation, thus making it usable for a great many different articles which could not be made from grey iron castings, and also adapting it to ready machining and to bending or deformation while still retaining adequate strength.

In the making of malleable castings, as heretofore practiced, the white iron casting has been subjected to a heat treating or annealing extending over a period generally of six to eleven days depending on type and size of the annealing oven and the shape and section of the casting. In other words, in addition to the time required for producing the molten mix which is withdrawn from the cupola or other furnace, pouring that white iron mix into the mold and allowing for .such time as may be required for the casting to cool throughout in the mold down to temperatures where it can be properly handled, it has for many years been the necessary and proper procedure to subject these castings to an annealing treatment in which the actual annealing temperatures are generally understood to range from about 1400" F. to about 1700 F. The malleableizing changes occurring during the anneal, as generally understood, probably start at about 1400 F., but the change in the casting characteristics is very slow at such temperature and increases very rapidly with increasing temperature. It is probably that a good anneal can be secured with a maximum temperature of 1500 F. but using a much prolonged anneal period. For practical commercial operations, therefore, it has been a general practice to raise the temperature up to about 1700 F. which is about the maximum temperature which can be used without causing objectionable warping, etc., resulting in weakness or loss of utility of the casting. The temperature of the white iron casting is kept within this active anneal range for sufiicient time to change the combined carbon and produce the ductility, elongation, machinability, etc., characteristics of a good malleableized casting.

The length of time during which the casting must be kept within the standard anneal range will vary somewhat according to the castingsection-the thicker the section the longer the time required. Generally speaking white iron castings to be malleableized throughout will not substantially exceed one inch in any section or thickness; and most malleable castings have an average thickness, or section, of less than one inch, although some portions may have a section of more than one incheven up to about 1 /2 inches. After the casting has been brought up into the annealing range it is maintained at such elevated temperature for many hours, or even several days, depending on the average and maximum section, the form of the casting, the maximum temperature maintained, and the composition of the molten mix from which the casting is made, as well understood in the industry.

In hand-fired mufiie-type annealing ovens, for example, it has been found in large scale commercial operations that castings such as truck axle housings having an average section of approximately inch to inch, with some portions having sections up to 1 /2 inches and the minimum section being about inch, the total cycle of heating may be as much as eleven daysincluding the time for bringing the temperature up to 1700 F., the time of anneal at that temperature, and the slow cooling from that temperature through the critical temperature down to about 1050 to 1200 F. at which temperatures the casting can be handled in the foundry without damage to the casting and without too much danger of injury or discomfort to the operator, and below which no further change seems to take place in the characteristics of the annealing casting. Practical considerations make such temperature range that generally used in the producing of malleable iron castings.

With some other type of annealing oven or furnace the over-all anneal cycle may be somewhat greater or lessdepending on the time required to bring the casting up into the most desirable annealing temperature range; but the actual time of anneal is substantially constant for a given casting and variation in the extent of the over-all anneal cycle will be attributable to the time of heating up the oven and the time allowable for cooling down through the critical temperature. The hand-fired muffle-type oven is referred to as one long used and generally understoodin the malleable iron industry.

This problem of prolonged annealing treatment in the securing of malleableized castings has been given constant and widespread thought throughout the foundry industry for many years with a view to substantially reducing the total time between the starting of the operation of melting and treating the various ingredients to make the white iron mix, the pouring of the casting and its cooling in the mold to the usable white iron casting and the prolonged annealing period without adversely affecting the character of the resultant malleableized casting. Such annealing periods have required equipment in whichthe output is limited so that enlarged output can be secured only as a result of very expensive installation of additional annealing furnaces,

etc.; and this fact has a very substantial eifecthereinafter specified, to the molten white iron mix after it is withdrawn and before it is poured into the mold to produce the White iron casting, by quick pouring of the mix, and by a preliminary heat treatment of the casting .at temperatures Well below those used for annealing, the six :to eleven day over-all annealing period or cycle pfa muifie-type annealing furnace referred to may be reduced as much as several days,.and corresponding reductions in annealing time secured in annealing furnaces of other types.

It is thought entirely unnecessary to illustrate, by drawing, any particular form of apparatus for preparing the molten mix, of a ladle or other device for receiving and pouring the molten mix, of the molds themselves, or of the annealing furnace, as these are well known in the art and may be of substantially the same constructions as heretofore used. The process of the present invention is usable in connection with white iron castings made by-these formerly existing furnaces or cupolas, annealing oven, etc. The drawing, therefore, illustrates the practicing of the invention by means of graphs, which relate to the annealing cycle after the casting to be malleableized has been produced.

Fig. 1 shows a graph which is typical of the annealing cycle in a hand-fired mufile annealing oven, when annealing a casting having average sectionthickness of about to 4,," with a minimum thickness of about and some sections of as much as about 1% to 1 a casting such as an axle housing for use in an automobile truck; this graph showing an actual anneal cycle in commercial operations in which .the oven was charged with eight tons of such castings;

Fig. 2 is a comparable graph showing the annealing cycle when using the present invention, in the same hand-fired muffle annealing oven, charged with the same quantity of the truck axle housings, and with the castings made from the same white iron mix but including a very small percentage of aluminum and after a four hour preheat at 600 F., that is not included in the p Fig. 3 is a graph showing the time and temperature lag in a pot oven which is powdered coal fired and charged with about fourteen tons of castings, packed in pots, and using this inventi0n--the dotted lines indicating the oven temperatures around the pots and the solid line the temperatures ofthe castings packed inside the pots, the lag being usual in such a furnace.

Fig. 4 is a graph showing the annealing cycle in an electric heated laboratory furnace charged with one pound test bars which could be at atmospheric temperature or any temperature below about 400 F., and which are annealed so that in the temperature range between 400 and 800 F. the casting is given a preconditioning or preheating period during which its temperature is maintained substantially constant or within a comparatively narrow range, this preheating period being preferably 600 F. for a period of three hours as shown in the graph, after which the temperature is quickly raised to 1700 F. and maintainedat that temperature for approximately ten hours, and the casting is then allowed to cool somewhat slowly down through the critical anneal range after which it may be quickly cooled because the heating and cooling of such a furnace may be readily controlled as well as the maintaining of a substantially constant temperature within the heating capacity of the furnace; tand the ladle from the furnace.

Fig.5 is a graph of the same laboratory test furnace, charged with 20 one pound test bars of the same size and made from the same mix as those used in Fig. 4, in which the test bars had previously been preheated to 600 F. for three hours and then air cooled down to atmospheric temperatures and then subjected in the annealing cycle to a very rapid increase in temperature to 1700 F. and held at that temperatureforthe .same number of hours (10) and then allowed to cool as in Fig. 4.

In practicing the invention the constituents for producing a malleableizable white iron mix,

such as heretofore used in the industry are charged into the furnace or cupola and melted under such conditions that a molten iron mix having the constituents and characteristics heretofore present and used in the making of white iron castings to be malleableized by an- :nealing within the critical temperature range for the long periods required heretofore, as illustrated generally, e. g., in accordance with the conventional annealing cycle for a large mufile furnace handling large malleable cast- .ings as shown in Fig. l, is prepared and while the molten metal is in the ladle or other pouring device and just before the pouring, a very small percentage of aluminium is added to the molten metal mix so that it will melt and become incorporated into and through the molten metal in the ladle. Preferably the aluminum is put into the ladle before it is filled with the molten iron, thus giving thorough mixing of the aluminum and the iron as the iron pours into Also this should be just before the iron is poured into the mold. The time element is quite important and should be as short as practicable in the operation. The astonishingly beneficial effects of the aluminum rapidly decrease so that the molten iron with the added aluminum should perferably be poured immediately after the mixture is formed in the ladle. The effectiveness of the minute quantities of aluminum added seem to be not a straight line function but rather there is an almost immediate decrease of as much as about 10%; but thereafter the effectiveness decreases much more slowly. In practice it has been found that if poured into the mold within several minutes after the aluminum is added the effectiveness remains as much as about and for a period of as much as five to ten minutes the decrease in effectiveness is very slow and castings poured within such periods of time give such extraordina-ry results as described and as illustrated by comparison of the graph'of Fig. 2 with that of Fig. 1. In fact considerably shortened anneal periods have been secured when the molten iron is poured from large ladles holding enough iron for a large number of molds, requiring up to about twenty minutes for pouring. Some trial by the usual break test after annealing may be required for determining the time during which the aluminum remains sufliciently effective for various iron mixes, but in general it has been found that marked beneficial results can be secured if the iron for some forms of castingsis poured within a period of as much as about fifteen minutes. And for the truck housings, made from the iron mix herein referred to, the iron is usually poured within about three minutes and the described results secured.

For preferred results in making best quality malleable castings, heretofore, in general the carbon in the casting should be not in excess of 3%,

and with the average run of malleable castings much better results are attained if the carbon is not substantially above approximately 25-25%. And to avoid the danger of precipitating primary graphite in the castings-any substantial amount of which renders a white iron casting useless for annealing to malleable conditionand for achieving generally good quality malleable castings, the carbon range has been found best held down to approximately 23-25%.

The silicon range likewise is carefully controlled in the making of malleable castings and in general practice not more than about 1% of silicon is present in the casting, the range being preferably kept to about .75 to .90% in the casting, although a slight increase is permitted when the casting section is decreased. For air furnace melting the above indicated range of.

silicon of up to about 1% is usually found satisfactory while for duplexing it is desirable to have a somewhat higher silicon content such for example as up to about 1.5% silicon in the poured casting. For example, axle housings such as referred to have been satisfactorily made, using a powdered coal fired air furnace, from 60% sprue and so-called foreign scrap (i. e. such scrap as may be bought by the foundry from outside sources in the regular course of business) and 40% pig iron, with the constituents of the charge determined and controlled by regular technical service analyses so as to contain approximately 1.2% of silicon and 3% of carbon. Such charge when used in such an air furnace, melting about three tons of charge per hour, and having a maximum capacity of about thirty tons, and charged with from twenty to twenty-seven tons of the materials, and using a powdered coal flame properly regulated to be on the reducing side in combustion gives a satisfactory molten mix for such castings. Approximately .3% or somewhat more of silicon will be lost during the melting, and the carbon content will likewise be reduced within the range of 23-25%, and satisfactorily about 2.4%. In such a charge pig iron having a silicon content of about 1.5-1.7 and such carbon content that, when added to the carbon as contained in the sprue and foreign scrap used will bring the total percent of the carbon charge to about 3%, has been found to give satisfactory results. Such is a generally available commercial pig iron.

Such a mix or charge when melted in the air furnace by means of powdered coal flames with the air controlled to give a proper melting flame and having a temperature of approximately 3000 F'., the iron being brought up to a temperature of around 2700 to 2800 F. and being poured normally at approximately 2750 F., will produce a molten iron which when poured into the ladle produces castings containing about .75-.9% of silicon, part of the silicon of the charge being lost in the furnace during the melting operation. The amount of carbon is also controlled by the composition of the ingredients charged so that it will not be in excess of 3%, usually considered the dividing percentage between grey iron and white iron castings. Preferably there is not in excess of 2.6% carbon in the molten mix withdrawn from the furnace, and with castings having the sections referred to, generally a carbon content in the range 2.32 .5 as stated above, as such percentages give no appreciable or adverse precipitation of primary graphite in white iron castings.

Such a charge, with usual small percentages of other constituents, when melted in such an air furnace with'a proper flame and under such controlled conditions, as well understood in the industry, will satisfactorily produce a molten iron which when poured will give castings having, in addition to the iron Per ent Silicon, about .85

Sulphur, about -f .10 Phosphorus, about .10 Manganese, about .35 Carbon, about 2.40

Castings of such composition give very satisfactory results in the making of malleable truck axle housing castings referred to. In actual practice such an air furnace with such a charge has been satisfactorily used for making castings of this invention, or regular malleable castings with the former longer anneal cycle, with melting operations continued for about two hours longer than the period theoretically necessary as stated above. Such additional heating gets the iron hot enough to handle properly and tends to prevent precipitation of primary graphite in the casting. With such conditions the molten mix is withdrawn into ladles holding about two hundred pounds each, the minute fraction of aluminum being preferably placed in the ladle as metallic aluminum so that as the molten iron mix is poured into the ladle the aluminum will melt and thoroughly admix with it. For truck housing castings such as referred to astonishing results in decreasing the time of annealing can be secured with the amount of metallic aluminum approximating about .02% based on the five or six hundred pounds of iron mix which is poured into the mold to produce a housing weighing about three hundred pounds. The most effective range in the amount of metallic aluminum used for castings, to give the greatly decreased annealing time, is about .003-.02%. It should be pointed out, however, that since the truck housing referred to is an unusually large malleable casting, and has some sections which are unusually thick, and it requires about three two-hundred pound ladles to pour one casting, the time element may be somewhat longer than would be the case if the casting were poured from a single ladle. Accordingly somewhat larger amount of aluminum is used, taking into account the decrease in effectiveness which occurs immediately after the mix, so that with this decrease there will still be an amount of aluminum, figured as metallic aluminum, within the range referred to.

Another charge which has been found satisfactory for making castings such as the truck axle housings referred to, and melted in a cupola type coke fired furnace, is one which contains 40% sprue which can have approximately the same silicon content as earlier finished castings, or satisfactorily about .9 to 1% silicon, 30% steel which contains no silicon or a mere trace, and 30% pig some of which is regular pig containing about 1.40-1.50% of silicon but with enough high silicon pig (such pig containing about 11% silicon) added to bring the charge to about 1.3%.

silicon and 3% of carbon, with the other minor constituents to give about the same percentages in the poured iron as above referred to. The percentage of carbon may be varied somewhat depending upon the operation of the cupola or the amount of carbon which is taken up or removed during the melting operationthe carbon content in the molten iron as stated being preferably below 3%, the usually recognized dividing line as between grey iron and white iron mixes and for truck housings of the kind referred to preferably about 2.4%-2.5 in the molten iron to be poured, as stated. Substantially exceeding .02% or perhaps .03%-as for the charge referred to above, poured from a large ladle so that a longer pouring period of possibly up to fifteen minutes may elapse with the referred to decrease in effectiveness of thealuminum-has been found to have objectionable and adverse results in the casting, forming bubbles and other extraneous materials as a result of reactions at the high temperatures of pouring, and generally speaking the thinner the section the more quickly it can be poured, and a tiny fraction of one percent of aluminum may be used.

By way of illustrating the most astonishing difference in the amount of time required for annealing the casting, the graphs illustrated in Figs. 1 and 2 are completely comparative as they represent the annealing cycle of the muffle furnace for the same truck housing casting and made from the same molten mix, except that in the graph illustrated in Fig. 1 no aluminum was added whereas in the graph of Fig. 2 the very small fraction of one percent of aluminum, within the range above referred to, was added, the casting in each case being cooled at the same rate in the mold.

It will be noted that in the graph ofFig. 1 the castings were brought up to the normally understood minimum annealing temperature of approximately 1400 F. and carried up to about 1700 F. and brought down to nearly 1400 F. and then cooled much more slowly at the end of the annealing through the recognized critical range of approximately 1300 F.-1400 F., and as a safety factor,- down to about 1200 F. The casting, as shown by the graph of Fig. 1 is thus within such annealing temperature range for approximately 155 hours; whereas in the samefurnace, with the small amount of aluminum added in the ladle just before pouring the casting, the casting was within this same annealin temperature range for approximately 70 hours, Thus by the addition of this very tiny fraction of one percent of aluminum to the molten iron the time within the annealing range was decreased by approximately 85 hours or roughly three days and thirteen hours. When it is realized that these are very large furnaces, which take a considerable time to bring up to the proper annealing temperature of 1400" and to the preferably maximum annealing temperature of about 1700 F., this represents a very large over-' all saving in time. And as white iron castings are always annealed to break down the combined carbon and impart th desired characteristics of duetility, elongation, etc., this means that a furnace can handle in roughly 125 hours when, the aluminum is used, castings which would take 210 hours where thealuminum is not used and under high grade malleable foundry practice as heretofore used.

Also, where-the heating of the annealing furnace is properly controlled so that the preheating or preconditioning in a temperature range between 400. and 800 F., and preferably at 600 can be attained as part of the heatin up of the furnace by controlling or retarding the rate of firing, the four hours of preconditioning which is found desirable for a large casting such as the truck housing referred to, may be included in the over-all annealing cycle and the total saving in time thus increased.

It should be noted that in connectionwith these known to me.

10 particular castings, which have been produced commercially in the old way (i. e. without the addition of the very small amounts of aluminum followed by the controlled preheat or preconditioning) the annealing time cycle as shown in Fig. 1 is an actual one typical of large scale commercial production, And the castings of this invention, with the greatly reduced annealing time were produced from the same furnace charge, melted under the same conditions, using the same molds and poured and cooled in the molds under the same conditions and time factors. It has been found thatv to secure the benefits of the present invention the aluminum should be added as metallic aluminum, or if combined with other usable metals, e. g., as alloys, correction should be made so as to add on the basis of metallic aluminum. The aluminum is added asv small pieces of aluminum or aluminum scrap, and in very small quantities varying somewhat with the form of casting, the maximum section, the formof mold, the rate of cooling in the mold and the time required for pouring the molten iron, Satisfactory operations have been secured within a range of about .003 to about .02 or .03 of aluminum on the total mix, or with some special forms of castings, molten mixes, extra long periods before pouring into the molds, perhaps slightly above or below such percentage range. It has long been known that aluminum will act as a graphitizing agent in cast iron and as a deoxidizing agent in the steel industry. But. if used in sufiicient amount tomaterially help graphitizing during annealing it would be in such large amount as to produce primary graphite and occluded aluminum oxide rendering the casting useless for the malleable iron industry. Even such small amounts as .l% produce very objectionable quantities of primary graphite. But its use in the present invention is entirely different and produces entirely different results from any use of aluminum in metallurgy, as This seems to b due to the use of such small quantities, small fractions of one percentamounts so small asto be of no consequence if it were relied on as a graphitizing agent. Secondly, even when used in such very small quantities the resultant mix must be poured quickly to secure the most beneficial results. Third, the casting must be given a preheat of about two through four hours with n a temperature range of approximately =l00-800 F. I have found that best results are secured if the reheat is carried out at a substantially uniform temperature of 600 F., as shown in Fig. 4, but this is not essential because the preheat may be secured by so firing the oven that the temperature is controlled within the 400800 F. zone to give the pro-heat period before the casting is brought up to the critical anneal range starting at about 1400" F. as stated above. By controlling the firing of the muffle the temperature may be slowed down within this 400-800 F. ran e to give this preheat. Likewise with respect to the present invention it is. app rently unimportant whether the preheat or preconditioning treatment is carried on inside the annealing even as part of the total annealing cycle or is carried on se arately as a preheating after which the preheated castings can be air cooled to normal tem eratures. and then subjected to the annealing cycle or placed in the annealing oven while hot after the preheat cycle. Experience, based on treatment of a variety of castings, made from the aluminum-containing molten white. iron mix. in practical foundry operations. has shown that it does not matter whether the white iron is cooled after the preheat treatment and then put through the annealing oven or is given one continuous heating cycle which includes the preheat period as shown in the several views of the drawing. After the preheat treatment within this 400 to 800 F. rang :with 600 as giving satisfactory results with all types of castings, in the heat treatment in the annealing oven it does not matter how soon the metal reaches high temperature of approximately 1700 F. This is not true with a conventional slow graphitization process whereby white iron has the combined graphite changed or graphitized to give the recognized malleableized characteristics, as it has been found from years of experience of the slow or prolonged process of annealing that the iron can be heated rapidly up to approximately 1500 F. but that if it is heated too rapidly between 1500 and 1700 F. this too rapid increase in temperature will tend to slow the graphitization process and will require prolongation of the period during which the casting is maintained at approximately the 1700 level. This is not true, however, with castings made according to this process, and it will be noted, referring particularly to Figs. 4 and 5 which show annealing cycles on smaller castings carried out in an electric furnace specially equipped with controls to give desired rates of heat input and temperature changes and to measure the temperature changes accurately, that in Fig. 5 the temperature rise after the three hour preheat at 600 F. is very rapid,

\ the temperature being increased from 600 F. to

1700 F. in two hours. In Fig. 4, in which the casting has been given the preheat treatment prior to its introduction into the electric furnace, it will be noted that the temperature is increased to 1700 F. in approximately two and one-half hours. It will be understood of course that the time required for the annealing cycle depends not only on the section but also on the melting practice which controls the constituents in the molten mix and the amount of aluminum used, which varies according to the form and section of the casting, for a given mix and given cooling in the mold and also for any given set of such conditions varies with the time elapsing before pouring so that somewhat higher or lower amounts of aluminum may be required accordingly. Therefore test bars or castings will have to be made, as is standard foundry practice, and subjected to preheat and a subsequent annealing cycle in order to determine the most desirable preheat period for a given annealing cycle and the most desirable annealing cycle for a given preheat, using the same molten white iron mix. The standard malleable iron test bar has a 4;" diameter gage length with diameter gri ends and is usually fed through risers at both ends.

As shown in the graphs of Figs. 4 and 5, twenty test bars each weighing one pound and heated three hours at 600 F., were heated quite rapidly to 1700 and maintained at that temperature for ten hours, after which they are illustrated as being brought down rather rapidly in an interval of somewhat less than two hours to a temperature of approximately 1400" and then allowed to cool at a slower rate down to the final temperature at which they are removed from the oven.

In Fig. 1, using the old annealing cycle and without aluminum the axle housings are heated up to 1700 within a period of three to five days, are maintained at that temperature for thirty-six to forty-eight hours, are then allowed to cool somewhat rapidly down to approximately 1400,

this cooling period occupyin a minimum of 24 hours, after which the castings are allowed to cool more slowly through the critical end of the annealing cycle down from 1400" to 1200 F. over a period of approximately forty-two hours and are then allowed to cool at substantially the same rate until they are at a sufficiently low temperature to be removed from the annealing oven. If the character of the white iron casting, as a result of the constituency of the molten mix from which it is poured were materially changed, or the thickness of the casting section varied, this preheat period would correspondingly vary and the periods of heating within the anneal range of 1400 to 1700 and of cooling would likewise vary. And as stated the most desirable period of preheat can be determined by the use of test bars or by the common break test in which some of the castings are broken to observe the effect of the anneal.

The aluminum, in the practicing of this invention, has been added to the molten white iron mix in the form of small pieces of metallic aluminum which melt and diffuse through the molten mix. When using scrap which may contain aluminum or any aluminum alloys, the proper correction should be made to insure the introduction of aluminum within the very minute ranges above specified with reference to metallic aluminum.

Why the aluminum has this effect is not fully understood. It is known that when hard iron graphitizes to form malleable iron, the smaller the carbon nodules produced, the more numerous they will be. The more numerous those carbon nodules are, generally speaking, the closer together they will be and the shorter the time required for graphitization. Nevertheless no means has been known before, whereby graphitization could be produced except by prolonged heating at high temperatures. While I am not fully advised as to why the astonishing results of this invention are secured, it is a fact that such effects do occur. And it is my understanding that the desirable results of my invention flow from producing more and smaller carbon nodules, and that nuclei must be set up on which the carbon could precipitate. After a long time of working upon this in the laboratory, and also using the invention in large scale commercial production, the successful and predictable results of this invention were secured. Not until the present invention. so far as I know, has there been any such shortening of the anneal cycle with standard malleable practices, mixes and equipment. The addition of the very small quantities of aluminum to the metal mix as described brought about the astonishing, controllable and commercially usable shortening of the annealing cycle while still producing high quality products, And so far as I know the present invention is the only way in which adequate graphitization can be secured, to match the best and most highgrade malleable castings made under the long annealing cycles as heretofore referred to. And it is my belief that by the use of the very small percentages of aluminum as described, very many more nuclei are set up upon which much smaller carbon nodules are produced, the nuclei in this case being believed to be submicroscopic particles of aluminum precipitated from solid solution in the iron at a temperature between 400-800 F. during the preheating or preconditioning treat ment preceding the malleableizing treatment of the annealing cycle.

It has been found, as may be clearly demoncasting.

13 strated by photomicrographs, that with white iron castings made from a given molten mix, and of a given form and section and poured and cooled in the mold under the same conditions, the introduction of the small fraction of a percent of aluminum has an astonishing result upon the size of the nodules of graphitized carbon which is present in the casting after annealin as well as upon the general distribution of those nodules. For example in a, truck housingsuch as herein referred to, it has been found in actual commercial operations that by using the charges specified above as exemplary of satisfactory charges for melting in an air furnace and a coke charged cupola respectively the molten iron produced, which has not more than .9-1% silicon and carbon content in the molten iron within the range of about 2.4% to not in excess of 3%, and with similar cooling after'addition of the small amount of aluminum before pouring will give castings in which th size and uniform distribution of the carbon nodules in the finally annealed casting will be shown by photomicrographs as markedly different when the preheat or preconditioning treatment is given within the temperature range of 400-800 F.( and preferably at about 600 F.), from thesizes and distribution of the carbon nodules in such castings made from the same charge and molten iron and with the same cycle of annealing but Without the small fractions of aluminum and the preheat. Such photon'iicrographs show that the nodules of carbon after the so-called graphitizing action which occurs during the anneal will average approximately the size of the average of carbon nodules present in castings made from the same mix and properly annealed but without the addition' of aluminum and the 'preheat treatment. Ofcourse there are some variations, even for a given form of casting having the same size and weight and variations in section; but generally speakingit has been found that the average size of the-carbon nodules in the annealed casting wili be not more than the average size of those in the same castings made according to regular malleable practice; And also thenodul'es will be more uniformlydistributed throughout the casting; It should be pointed out that there may be some "few relatively large nodules in castings made according to the present invention. particularly in the portion adjacent the surface of the casting but the sizes and numbers ofthese are relatively so small as to present no objectionable effects in subsequent machining and use or the And the number of larger nodules is astonishingly reduced below the number present in the same malleable castings, made with the same mix, without aluminum and annealed according to regular practice.

Also, with test bar castings which are in diameter, where the test bars are made from such molten mixes as described, using the small fractionofa percent of aluminum and having the preheat at the lower temperature ranges followed'by annealing within the regular annealing range, the average size of the nodulesappears in photo-micrographs to be on the average about the size of the nodules in identicaltest bars made from the same mix without the additions of small fractions of aluminum and preheat.

While the method and product herein described constitute preferred embodiments of the invention, it is to be understood that the invention is not limited to this precise method and product, and that changes may be made therein without departing'fr om the scope of theinvention which. is. defined inrthe. appended claims.

What is :claimedtis:

I. The. process of; making malleable iron castings which consists in forming a molten malleableizable white iron mix, adding to said molten mix just: before pouring a predetermined small percentage of about: 0.02-0.03 of aluminum: in such amount as to effect a marked reduction'in the size andincrease in the number of the nodules of graphitized carbon produced in the casting after malleablizingbut. insufficient in amount to produce primary graphitization of the combined carbon. in the casting as poured, pouring the casting, cooling and removing the casting from the mold as a white. ironcastingsubstantially free of graphitization, subjecting the casting to a preliminary heating within the temperature range of about 400 to 800 F. for a limited period of time to develop said marked reduction in the size of the nodules of graphitized carbon produced in the malleable iron casting during subsequent annealing, and thereafter malleabli'zing the casting by subjecting said casting to a malleablizing heat treatment, the time during'which the casting is subjected to said malleablizing treatment together with the time of said preliminary heating being substantially less than the heating time required to produce a malleablized casting from the same mix in the absence of said aluminum addition under otherwise comparable conditions. 4

2. The process of making malleable iron castings' which consists in forming a molten malleableizable white iron mix, adding to saidmolten mix just before pouring a predetermined small percentage of about 0.003-0.03% of aluminum in such. amount as to effect a marked reduction in the size and increase in the number of the-nodules of graphitized carbon produced in the casting after malleablizing but. insufiicient in amount to produce primary graphitization of the combined carbon in the casting as poured, pouring the casting, cooling and removing the casting from. the mold as a white iron casting substantially free of graphitization, subjecting the casting to a preliminary heatingv within the temperature range of about400 to 800 F. for a limited period of time to develop said marked reduction in..the size of the nodules of graphitized carbon produced in the malleable iron casting, and thereafter malleablizing the casting by subjecting said casting to a malleablizing heat treatment, the time during which the casting is subjected to said malleablizing treatment together with the time of said preliminary heating being substantially less than the heating time required to produce a malleablized casting from the same mix in the absence of said aluminum addition under otherwisecomparable conditions. 3. The process of making malleable ironcastings which consists in forming a molten malleableizable white iron mix, withdrawing a portion of said molten mix for pouring into a mold, just before pouring said molten mix and. within a period prior to pouring in the mold not to exceed approximately ten minutes adding aluminum thereto in a small modifying quantity not exceeding about 0.02-0.03% of molten metal mix. and in suilicient amount to eifect a marked reduction in the size of the nodules of graphitized carbon in the malleable iron casting but insufiicient in amount to produce graphitization of the combined carbon in the white iron casting as formed,

15 pouring the casting as a white iron casting substantially free of primary graphitization, cooling and removing the casting from the mold, heating the casting for a period of time not to exceed six hours within the temperature range of about 400 to 800 F. to develop said eifect on the size of the nodules of graphitized carbon produced in the malleable iron casting, and thereafter malleablizing the casting by subjecting said casting to a malleablizing heat treatment, the time during which the casting is subjected to malleablizing heat treatment being substantially decreased with reference to the time required to malleablize a comparable white iron casting in the absence of said addition of aluminum.

4. In the manufacturing of malleable castings the method which comprises forming malleablizable white iron castings substantially free from primary graphite and poured from a quantity of molten white iron withdrawn from the melting furnace for pouring into the mold and containing a predetermined small percentage of about 0.02-0.03% of aluminum added to the molten withdrawn white iron such a short time before pouring that about ninety per cent of the aluminum remains effective and in sufiicient amount to effect a marked reduction in the size of the nodules of graphitized carbon produced in the malleable iron casting but insufiicient in amount to produce graphitization of the combined carbon during formation of the white iron casting, preheating said casting a limited period of about several hours within the temperature range of about 400 to 800 F. for sufiicient time to develop said effect on the size of the nodules of 'graphitized carbon produced in the malleable iron casting, thereafter malleablizing the casting by heating said casting up through the minimum initial annealing temperature of 1400 F. to approximately 1700 F., maintaining the casting at said temperature of approximately 1700 F. for a limited period of time and then cooling the casting at a controlled rate down through the critical cooling portion of the anneal cycle within the range of approximately 14001300 F. to L effect malleablizing changes, the time required for maintaining the casting within the annealing cycle from the initial minimum 1400 F. through 1700 F. and down through the critical cooling range of 1300 F. being considerably less than, by as much as one-half, the annealing time re quired for a similar castin made from the same mix but without said addition of aluminum and said preheating.

5. In the process of manufacturing malleable castings, melting the various constituents according to standard practice to produce a molten malleableizable white iron mix, withdrawing a portion of said white iron mix for pouring into the mold, adding thereto a predetermined small percentage of about 0.02-0.03% aluminum in such amount as to effect a marked reduction in the size of the nodules of graphitized carbon produced in the malleable iron casting but insufficient in amount to produce graphitization of the combined carbon during formation of a white iron casting, said aluminum being added tosaid white iron mix just before pouring and within a controlled period of time which maintains about ninety per cent of said aluminum available to produce said effect on the size of the nodules of graphitized carbon produced in the malleable iron casting, preheating said white iron casting for several hours within a limited temperature range of about 400 to 800 F. for

sufficient time to produce a greatly increased number of graphitization nuclei available during graphitization occurring within the annealing temperature range, malleablizing the casting by heating said preheated casting up through the minimum initial annealing temperature of ap proximately 1400 F. to approximately 1700. F., maintaining said casting for a limited period at 1700 F.,'and then cooling said casting down through the critical range of approximately 14.00-1300 F. to effect malleablizing graphitization with the nodules of graphitized carbon substantially uniformly distributed through the casting as nodules of reduced size within the range of th to th of the size of nodules of graphite obtained in comparable malleable castings made from the same molten white iron mix and annealed through the same temperature ranges but without the addition of said aluminum and without said preheating.

6. The process of making malleable iron castings which consists in forming a molten malleableizable white iron mix, adding to said molten mix just before pouring a predetermined small percentage of about 0.02-0.03% of aluminum such that upon cooling of the white iron casting the aluminum will be insufficient in amount to cause any substantial graphitizing as the white iron casting is formed, said aluminum in said non-graphitized casting being in solid solution, pouring the casting, cooling and removing the casting from the mold as a white iron casting substantially free of graphitization, subjecting the casting to a preliminary heating within the limited temperature range of about 400 to 800 F. for a limited period of time of the order of about two to four hours to precipitate the aluminum to said solution providing a large number of aluminum nuclei, said nuclei being effective for the combined carbon to cause a marked reduction in the size and increase in the number of carbon nodules produced in the malleablized casting, malleablizing the casting by subjecting said casting to a malleablizing heat treatment whereby said combined carbon is rapidly affected and precipitated on said large number of aluminum nuclei, the time during which the casting is subjected to said malleablizing treatment together with the time of said preliminary heating being substantially less than, by as much as onehalf, the heating time required to produce a malleablized casting from the same mix in the absence of said aluminun addition under otherwise comparable conditions.

7. The process of preparing malleable iron castings which comprises adding about 003% to about 03% aluminum to a malleableizable white iron mix just before casting, casting the aluminum-containing mix, preheating the casting at a comparatively low temperature of about 600 F. for about four hours then heat treating the casting through standard annealing temperatures of 1400 to 1700 F. for a period of time of about three to four hours, and controlling the cooling of the casting to retain the same at a temperature of the order of about 1400" to 1300 F. for a predetermined time interval of approximately one-half hour.

8. In a process for making malleableized white iron castings with improved microstructure and substantially reduced annealing time, the steps of adding to a molten malleableizable white iron mix just before pouring a limited amount less than enough to cause primary graphitization during cooling and solidification of said casting of from 0.003% to 0.03% aluminum, thereafter pouring said mix into a mold substantially immediately to form said casting with a white iron microstructure characterized by having substantially all the carbon present in combined form and being substantially free of graphite, removing said White iron casting from the mold and subjecting said casting to a preliminary heat treatment at approximately 400 F. to 800 F. for about two to four hours, and thereafter malleableizing said casting by subjecting it to an annealing cycle for conversion of said combined carbon to nodules of graphite in the form of temper carbon substantially uniformly distributed through said casting, the composition of said casting ithout said addition of aluminum being such as would produce before annealing an all-white iron and the time for said annealing cycle being substantially less by as much as onehalf than the time necessary to malleableize a casting of the same composition but Without said aluminum addition and said preliminary heat treatment.

LESTER C. CROME.

REFERENCES CITED The following references are of record in the file of this patent:

18 UNITED STATES PATENTS Number Name Date 2,227,217 Crafts Dec. 31, 1940 2,260,998 Lorig Oct. 28, 1941 2,370,225 Boegehold Feb. 2'7, 1945 OTHER REFERENCES Alloy Cast Irons Handbook, published by Amer. Foundrymens Assoc, Chicago, 111., 2nd Ed, 1944, pages 153, 159, 160, 161 and 223.

Elsea et al: The Effect of Copper Content and Low Temperature Pretreatment of Some White Irons on Malleabilization. Pub. in Transactions Amer. Foundrymens Assoc, Chicago, 111., 1942, vol. 50, pages 1032-1058, especially pages 1032 and 1057.

Chromium, A1 and Ti in Malleable Cast Iron, A. Landa et a1., Liteinoe Delo, 1935, No. 5, pages 21-30. Abstracted, in Chem. Abstracts, col. 4797, vol. 30.

Hruska: Aluminum Improves Malleable Cast Iron Properties, pub. in The Foundry, vol, 59, January 1, 1931, pages and '71.

Claims (1)

1. 2. THE PROCESS OF MAKING MALLEABLE IRON CASTINGS WHICH CONSISTS IN FORMING A MOLTEN MALLEABLEIZABLE WHITE IRON MIX, ADDING TO SAID MOLTEN MIX JUST BEFORE POURING A PREDETERMINED SMALL PERCENTAGE OF ABOUT 0.003-0.03% OF ALUMINUM IN SUCH AMOUNT AS TO EFFECT A MARKED REDUCTION IN THE SIZE AND INCREASE IN THE NUMBER OF THE NODULES OF GRAPHITIZED CARBON PRODUCED IN THE CASTING AFTER MALLEABLIZING BUT INSUFFICIENT IN AMOUNT TO PRODUCE PRIMARY GRAPHITIZATION OF THE COMBINED CARBON IN THE CASTING AS POURED, POURING THE CASTING, COOLING AND REMOVING THE CASTING FROM THE MOLD AS A WHITE IRON CASTING SUBSTANTIALLY FREE OF GRAPHITIZATION, SUBJECTING THE CASTING TO A PRELIMINARY HEATING WITHIN THE TEMPERATURE RANGE OF ABOUT 400* TO 800* F. FOR A LIMITED PERIOD OF TIME TO DEVELOP SAID MARKED REDUCTION IN THE SIZE OF THE NODULES OF GRAPHITIZED CARBON PRODUCED IN THE MALLEABLE IRON CASTING, AND THEREAFTER MALLEABLIZING THE CASTING BY SUBJECTING SAID CASTING TO A MALLEABLIZING HEAT TREATMENT, THE TIME DURING WHICH THE CASTING IS SUBJECTED TO SAID MALLEABLIZING TREATMENT TOGETHER WITH THE TIME OF SAID PRELIMINARY HEATING BEING SUBSTANTIALLY LESS THAN THE HEATING TIME REQUIRED TO PRODUCE A MALLEABLIZED CASTING FROM THE SAME MIX IN THE ABSENCE OF SAID ALUMINUM ADDITION UNDER OTHERWISE COMPARABLE CONDITIONS.

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