US1574374A - Process for treating iron - Google Patents

Description

Patented Feb. 23, 1926 UNITED STATES WILLIAM J. 'IDIEDEBICHS AND Anson HAYES, or AMES, IOWA;

rnocuss son TREATING men.

m Drawing. Application filed August 21, 1922, Serial No. 553,370. Renewed August 28, 1925.

To all whom it may concern:

Be it known that we, WILLIAM J D11.- DERICHS and Armor: HAYEs,each a citizen of the United States of America, and resident of Ames, invented a new and useful Process for Treating Iron, of which the following is a pecification.

The object of this invention is to p rovide a new and improved process for treating white cast iron, whereby an. iron is produced practically duplicating the properties of commercial malleable iron, and in a much shorter time than now required in the ordinary malleableizing process. V

A further object of this invention is to shorten the time required for producing malleable iron. I

These and other objects of the invention will be more clearly described in the specification and pointed out in the appended claims. a y

Any suitable type or form of furnace or so-called annealing oven may be employed in carrying out our improved process, and may be heated by any-of the well known fuels such as gas, oil, or powdered coal burned in connection with air; or theheat may be secured. electrically or by a combination of combustion and electricity. or in any other manner that maybe desired so long as the desired temperaturesand atmospheres are secured, y

The iron used in this process is known as white cast iron such as is used in making malleable castings. This white cast iron difi'ers principally from ordinary gray iron in that while both contain carbon the white cast ironcontains the carbonwholly or principally in the form of carbid of iron represented by the formula Fe G, while gray ca st iron contains the carbon to a greater degree in the form of graphite or graphitic carbon.

It is well known that ordinarily in making malleable castings the white iron is packed with some oxidizing or packing ma- 7 terial in sealed boxes or pots which are loaded into the furnace while the furnace is cold and the furnaceis then gradually raised to a temperature of between 800 and 850 degrees centigrade and maintained at that temperature for approximately sixty hours, after which the furnace is gradually cooled, the whole process requiring sex en to nine days of continuous operation. .In the making of malleable castings the iron car- Story County, Iowa, have.

bid is changed mainly to'iron and temper carbon or graphite, the resulting iron usu-' ally having a lower tensile strength than the whitecast iron from which it-was made,

malleable iron produced by thenow common and well known methods, but in a much shorter time.

In carrying out our improved process we do not necessarily pack the white iron castings as in the ordinary malleableizing process, although that may be done at times if desired. By omitting it considerable time is saved. When the packing is omitted the white iron castings may be supported in any suitable manner in the furnace to prevent sagging and warping under intense heat. The'pjrocess consists in heating for any length of time, raising the temperature of the white iron castings with convenient rapidity, either rapidly or slowly, 'to any point between the critical temperature of the material (about 7&0 degrees centigrade) and the point of incipient fusion and holding at the chosen higher temperature for a period of fifteen minutes to five hours, or more. The actual time required will depend upon the temperature chosen,-lower temperatures requiring longer times, and upon the chemical composition of the white iron being treated. In any case it is only desired to maintain the higher temperature until the massive cementite is practically all absorbed in the solid solution. We are satisfied that in most instances it would avail little to hold at the higher temperature for ya longer period than about five hours,

since practically all of the desirable change would have occurred in that time, especially if the high temperature employed is above l650'degrees F.; and that holding for longer periods would result only in a waste of time without corres onding benefit. If a high temperature 0 less than 1650 degrees F. is used the time required to practically comrapidly or slowly to a temperature either in the neighborhood of the critical temperature, either within or outside of the heating furnace. These operations may be repeated for any desired number of repetitions, that is to say, the material may be alternately heated to a point above the critical temperature and cooled to a temperature in the neighborhood of or slightly below the critical. The iron may be cooled 'in the furnace or in any suitable manner. It has been dem onstrated by experiment that the resultant product is aniron'possessing considerably greater strength than the white iron castings and also having a considerable de ree of ductility. The number of repetitions or alternate heatings and coolings, as well as the rates'of heating and cooling, may be varied in accordance with the properties desired in the product. I,

An additional or final step is added which characterizes the resultant product as malleable lron. The operations are carried out as above described, that is either a single heating to a point above the critical tem erature for a period of fifteen minutes to five hours or more followed by a cooling to a point in the neighborhood of the critical, or repetitions of such alternate heating and cooling; and the final step consists in making the final cooling extremely slowly. This results in a product duplicating approximately the properties of commercial malleable iron, that is having a tensile strength of from 44000 to 53000 pounds per square inch and an elongation or ability to stretch of fifteen per cent or more, in two inches. The process is much shorter than that now carried out to obtain commercial malleable iron.

Our experiments show that the treatment of the iron as described results in castings possessing a tensile strength, of from about 44000 to 53000 pounds per square inch or more and an elongation or ability to stretch of ten per cent, or more, in two inches, a material closely approximating the properties of commercial malleable iron, as above I set forth.

W'c have also found that by a'combination of the high temperature followed by a repetition of alternate heating and cooling; or vice verse, that is alternate heating and cooling, with a heating to higher temperature following or interposed, we obtain a resulting material of the same properties as that obtained by either one of the methods individually.

As a concrete example of what we have obtained in our-experiments, we recite one instance by way of illustration only. A bar of white iron was heated to 1000 degrees centigrade, with the furnace, held at that ture (for ashort period of time) and the extremely slow cooling, whereby we obtain in a much shorter time than now required, a product possessing the characteristics of commercial malleable iron.

Likewise by way of illustration, we heated white cast iron bars beyond the critical temperature, in fact to about 850 degrees centigrade, and cooled them successively to a point in the neighborhood of or below the critical temperature, for eight successive repetitions, then heated again and cooled extremely slowly, at the rate of about or somewhat less than five degrees centigrade per hour, and obtained a product having 46000 pounds strength per square inch and an elongation of 17.5 per cent.

The overall time required for the experiments of which the above are two concrete examples was in the'neighborhood of fortyfive hours, but in these experiments, as a precautionary measure, 'the slow cooling was continued over a much greater range than necessary, so that it is certain this overall time can be materially reduced.

Referring to the final cooling of the castings at an extremely slow rate, we have found that a cooling at the rate of about or somewhat less than live degrees centigrade per hour gives the best result, but a somewhat more' rapid cooling may be employed without departing from our invention, but with ratherless of the characteristic malleable properties in the resultant product.

When speaking of the critical temperature of the material, the fact should-be borne in mind, which is well known in metallurgy, that the critical temperature can be, and is, undercooled by a rapid cooling, and therefore will be reduced by heating to a temperature above the critical and cooling fairly rapidly; so that in thereafter heating to the critical temperature, it is obvious that a lower actual temperature will'be involved. The language of this specification and the appended claiins is used with this fact in mind and should be so construed.

lVe claim as our invention- 1. The process for the heat treatment of castings from white cast iron which consists in (1) subjecting'of the casting to a temperature above the critical temperature of the material for a period of from fifteen minutes to five hours or more but only until the iron carbid present is practically all ab sorbed in the solid solution, which means that in irons of commercial composition the combined carbon is reduced to approximately nine-tenths of one percent; (2) the cooling of the casting to a lower temperature in the neighborhood of the critical temperature; and (3) the cooling of the casting to room temperature.

2. The process for the heat treatment of castings from White cast iron which consists in (1) subjecting of the casting to a temperature above the critical temperature of the material for such time only that the iron carbid present is practically all absorbed iu the-solid solution, or in other words that in irons of commercial composition the combined carbon is reduced to substantially nine-tenths of one percent, this requiring from fifteen minutes to five hours or more; (2) the cooling of the casting to a temperature inthe neighborhood of the critical temperature; and (3) the cooling of the casting at an'extremely slow rate.

'3. The 'rocess for the heat treatment of castings rom white cast iron which consists in (1) vsubjectin of the casting to a temperatureconsiderably above the critical temperature of the material for a period of from fifteen minutes to five hours, or more, until the iron carbid present is practically all absorbed in the solid solution or in other words v until in irons of commercial composition the combined carbon is reduced to substantially nine-tenths of'one percent; (2) the cooling of the casting to a tempera ture in to a still lower point. i 4 v '4. The process for the heat treatment of castings from white cast iron which consists in (1) the subjecting of the casting to a temperature above the critical temperature of the material, (2) the cooling of the of the material, (2) the cooling of the casting to a temperature in the neighborhood of (3) the the tem the neighborhood of the critical temperature; and (3) the cooling of the casting igrees the critical temperature, (3) alternate repetition of the above named steps and (4) a final heating to a point above the critical temperature followed by an extremelyslow cooling, at the rate of about five degrees centigrade per hour.

6. The process for the heat treatment of castings from White cast iron which consists in (1) the subjectingof the eastin to a heating considerably above the critical temperature of the material, (2) the cooling of the casting to a temperature in the neighborhood of the critical temperature,

(3) the heating of the casing to a tem er'ature above the critical temperature, (4 the 00011110, of the-castin to a temperature in the neighborhood of t e critical temperature (5) the repeati'n of steps (3) and (4) alternately and permitting the casting to cool to a still lower temperature.

7. The process for the heat treatment of castings from white cast iron which consists in (1) the subjecting of thev'casting to a heating inthe neighborhood of 1000 degrees Centigrade more orless for a period rangingfrom about fifteen minutes to five hours or more, (2) the cooling of the easting toatemperature of between about 850 degrees'and about 740 degrees centigrade, maintaining of the-casting at about erature recited in step (2) for a time .su cient to allow a suitable approach to chemical equilibrium of the constituents,

and (4) the cooling of the casting at a slow hour. a

8. The process. for the heat treatment of castings-from white cast iron. which consists in r (1.) the subjecting of the casting to a heating in the neighborhood of 1000 degrees centigrademor'e or less for-a period ranging fromabout fifteen minutes to five hours or more, (2) the cooling of the cast ing to a temperature between about 850 deand about 740 degrees centigrade, ,(3) the maintaining of such temperature fora time sufficient to allow a suitable a p'roaeh to chemical equilibrium of the constituents, and (4) the cooling of the casting. Signed at Des Moines, in the bounty of Polk and State of Iowa, this 18th day of August, 1922. i a

WILLIAM J. DIEDERICHS. ANSON HAYES.