US2301932A - Heat treatment of ferrous metals - Google Patents

Description

Patented Nov. 17, 1942 UNITED [STATES PATENT OFFICE HEAT TREATMENfitifERROUS METALS Leslie Delancey, Ellenville, N. Y.

No Drawing. Application October 24, 1941, Serial No. 416,351

15 Claims. (Cl. 148-18) This invention relates generally to. improvements in the heat treatment of steel and more particularly to an improved quenching medium for use in connection therewith.

The principal object of this invention is to provide a quenching medium which, when used in the manner hereinafter indicated, will impart to steel desirable physical characteristics of hardness and toughness without quench cracking and which, in some instances and under certain conditions, may eliminate the necessity of drawing the temper of the hardened steel.

Thi application is a continuation in part of my earlier application Serial No. 344,671, filed July 10, 1940, which is now pending. Therein I disclosed a quenching medium of novel composition, and the manner and advantages of using it particularly in the heat treatment of, certain steel blanks for knives and other cutting tools. I now realize that my invention may be far more generally applied and that the advantages of.

my invention are not dependent upon a quenching medium of the exact composition disclosed in my earlier application but may be realized by the use of a quenching medium wherein the relative proportions of the ingredients are varied and supplemented in the manner and within the limits hereinafter set forth. Accordingly I shall set forth in this specification part of the subject matter of my previous application together with ad-- ditional information concerning my invention. A preferred embodiment of my invention as now understood, and typical applications thereof, will be described herein for purposes of illustration.

It is well known that the physical properties of non-austenitic steels may be advantageously affected by suitable heating and quenching. If it is desired to increase the hardness of steel it may be heated to a suitable temperature and then quenched and hardened by plunging it into a quenching medium. Without going into the theory of the attendant phenomena, it is recognized generally that the physical changes which take place in the steel are closely related to the rapidity with which the steel is cooled and that the latter depends upon the type of quench used, provided that the material has first been heated to its critical temperature. Although many different quenches have been proposed, the one most commonly used are water or oil. A water quench produces a more rapid cooling ofthe steel than an oil quench, and generally results in imparting a reater hardness to the steel. But this hardwing is accompanied by more embrittlement of is used. Therefore in many instances an oil quench is used even though the steel is not thereby hardened as much as it would be by the use of a water quench. The hardening of steel, particularly by quenching in water, sets up quench stress which often results in quench cracking, thus rendering the quenched article useless.

In the case of commonly used water or oil quenches, the rate of cooling is not uniform. Generally the cooling is at first relatively slow,

then more rapid, and finally slower when approaching room temperature. It is believed to be more desirable to cool steels at a substantially uniform rate than at a rate which varies greatly from start to finish of the quenching operation.

In the case of many steel articles hardened by quenching either in oil or water, it is common practice to render them more ductile by drawing the temper, that is, by reheating to a temperature well below that at which the quenching took I place.

The present-invention provide quenching media which may be used to harden all non-sustenitic steels, also irons which contain but small amounts of carbon. In many instances it is not necessary to subject the material to the operation of drawing the temper as the desired hardness and ductility may be obtained as a result of the original heating and quenching operation. Moreover, the ingredients of a quenching medium embodying the present invention may be so adiusted as to produce a substantially uniform rate of cooling.

For purposes of illustration, I will describe the heat treatment of a medium carbon steel known as SAE 1055 and a molybdenum steel also containing a medium amount of carbon and known as SAE 4140. The former contains from 0.50 to 0.60 per cent carbon, manganese within the range of 0.60 to 0.90 per cent, phosphorus less than 0.040 per cent, and sulphur less than 0.055 per cent. The latter, SAE 4140, contains from 0.35 to 0.45 per cent carbon, manganese within the range of 0.60 to 0.90 per cent, phosphorus not over 0.040 per cent, and sulphur not over 0.050

per cent, together with chromium within the 1 0.15 to 0.30 per cent.

the steel than is the case when an oil quench In order to harden the SAE 1055 steel it is first heated completely and uniformly to a temperature of about 1'510 F. This heating may be accomplished in any suitable manner as, for instance, in an electric mume furnace. when thoroushly heated the steel is plunged into a quenching medium or coolant which has the property of conducting heat away from the steel at such a rate that the desired hardness is produced without engendering sufiicient quench stress to bring about quench cracking.

It has long been considered desirable by metallurgists and others concerned with the art of heat treating, that quenching media be evolved which will impart physical property characteristics to non-austenitic ferrous metals, when properly heated and quenched, which differ materially from those imparted by water or the various oil quenching media now in general use. One of the longstanding problems of the steel industry is that where water is employed as the quenching medium, due largely to the rapidity of rate of cooling caused by the water, the resultant physisary hardness is not imparted to the material, and the other physical properties are also improperly developed.

The hardness imparted by a water quench has in many instances been found necessary in order to avoid the undesirable features of the oil quench, and the quench cracking brought about by the employment of so radical a coolant as water has been found the lesser evil in comparison with the undesirable results following the employment of an oil quench.

One of the basic needs of the industry, therefore, and one of the important attributes of my invention, is the obtaining of a desired hardness and at the same time obtaining it without quench stress suilicient to produce cracking, and also obtaining said hardness without sacrificing as much ductility as is sacrificed in bringing about that hardness by the use of the water quench.

I have brought about-thisresult by enablin the desired hardness to be. obtained at a slower cooling rate than that secured with water. I

' have discovered that "I can'secure the desired condition by the selection of ingredients which bring about reaction between an alkali and an acidulous substance in the presence of an oil. The resulting oil-water emulsion will give a hardness which is out of proportion to the slowness of the cooling rate evolved, and at the same time will result in a mitigation of quench stress and conservationof ductility out of proportion to the amount of hardness obtained as quenched. I have found that one of the ways in which this desirable condition can be brought about is by the employment of the ingredients hereinafter set forth. It is desirable, in all applications of my quenching discovery, that there be a slight preponderance on the acid side.

It has been found desirable to seek a uniform emulsion condition, stable against heat and salts, and in that connection emulsifiers such as "Naconor and oleic acid have been found efllcacious.

The quenching medium which I prefer to use may be prepared from readily available materials. I find that a satisfactory quench may be produced by mixing the following ingredients in the following proportions, namely, 2 gallons of cider vinegar containing at least 4% acetic acid,

high, for example, in the neighborhood of 8%.

then a very small amount, approximately 5 grams, of sodium hydroxide may be added to reduce the acidity of the mixture.-

For purposes of analysis I have selected a quenching medium in which the above mentioned ingredients were mixed substantially in the proportions indicated above. The weight of each ingredient and the percentage thereof in relation to the whole were as follows:

Pounds Per cent An analysis of the foregoing gave the following results:

Vinegar Acetic acid per cent 5.57 Non-acid (H2O) --do 60.83 Oil 25.42 Naconol (wetting agent) do 0.31 Sodium hydroxide do 0.04 Wood ashes- Moisture do 0.03 Acid insoluble 1.60 40 Silica per cent 1.48

Acid soluble 6.13

Iron oxide per cent-- 0.08 Aluminum oxide do 0.17 Manganese oxide do 0.15 Calcium oxide do 2.97 Magnesium oxide -do 0.14 Potassium oxide do 0.48 Sodium oxide do 0.04 Chloride do 0.01 Sulfate do 0.07-

tioned ranging from 2% to 2% quarts. With less or more oil the cooling rate exhibits a cer-- tain lack of uniformity. By way of specific illustration, several inch round, 4 inch long bars of SAE 1055 steel were heated to a temperature of 1510" F. and then quenched one after another in different quenching media. The quenching medium used in each instance was difierent in that slightly different amounts of oil were used. The first of these quenching media contained the following ingredients mixed in the following proportions, namely, 2 gallons of vin- 7 egar, 2 quarts of SAE 30 oil, 2 pounds of wood "piclrlingl? 2,801,982 ashes, ounce of Naconol, and grams of sodium hydroxide. The other quenching media were the same except that the oil was successively increased by ,4; quart until the last medium of the series containing a total of 3 quarts of oil, instead of 2 quarts, was obtained. In each instance the temperature of the test bar was recorded by means of a thermocouple mounted therein and the drop in temperature plotted to produce a cooling curve.

With the amount of oil in the proportion of 2% quarts the cooling time was approximately seconds and the rate substantially uniform. with increased amounts of oil up to 2% quarts, the cooling time increased to approximately 31 15 seconds but the rate remained substantially uniform.

Ordinarily the hardening of steel in the manner herein described is followed by tempering or drawing the temper in order to relieve internal stresses and render the steel less brittle. Following the usual practice, two inch diameter bars of SAE 1055 steel were heated to 1510 F. One bar was quenched in water and the other in the quenching medium of this invention and Q5 both were then drawn at 1000 F. in order to produce samples for subjection to various physical tests. The tests showed a substantially higher tensile strength in the case of the bar quenched with the quenching medium of this invention, the same hardness, and no quench cracking.

The foregoing has dealt mainly with the hardening of SAE 1055 steel, but the quench of this invention may also"be advantageously used in 5 connection with the hardenlngof SAE 4140 steel with comparable results, namely, an increase in tensile strength over that developed by quenching in oil without sacrificing the hardness obtained when a so-called oil quenching medium is employed. In this case the steel should be heated to about 1525 F. before quenching and usually reheated to about 1000 F. to draw the temper.

when it is not desirable todevelop the maximum hardness possible by theusepf the quench-- ing medium herein described, the drawing operation may be dispensed-withby a suitable ad- Justment of the oil content of the quenching medium herein described. I have heretofore de- (:0 scribed the use of oil in proportions ranging from 2 to 3 quarts combined with other ingredients in the amounts first above stated. By increasing the amount of. oiljup to asmuch as 5 or 6 quarts instead of 2 to 3 quarts and heating and .35 quenching SAE 1055 steel in the manner above described, I find that a satisfactory hardness is developed together with a toughness or ductility and lack of brittleness which makes the steel useful without a subsequent drawing operation.

It is a well known problem of the art of heat treating steel that when the oil quench is employed, a very thick outer scale is obtained on the material treated, which scale is difficult to remove in the operation commonly known as (:5

Where water is used, the result is substantially as above described, with the added diillculty presented by corrosion. Where pieces treated in any application of my quenching media are subjected to "pickling," the scales are re- 70 moved in the "pickling" operation far more quickly than where the quenching media has been oil or water, and the resulting surface of the material is infinitely more smooth and regular and generally desirable than that obtained-75 after the "pickling operation where the material has been quenched in water, oil, or any other known quenching media.

The invention may be variously embodied and applied within the scope of the subJoined claims.

I claim as my invention: I 1. A coolant for quenching ferrous metals resulting from the mixture of wood ashes, mineral oil and cider vinegar, which contains at least 4 per cent acetic acid, in the proportions of about 2 pounds of wood ashes, about 2 quarts of mineral oil, and about 2 gallons of cider vinegar.

2. A coolant for quenching ferrous metals resulting from the mixture of wood ashes, mineral oil and cider vinegar, in the proportions of about 2 pounds of wood ashes, from about 2 to about 3 quarts of mineral oil, and about 2 gallons of cider vinegar.

3. A coolant for quenching ferrous metals resulting from the mixture of wood ashes, mineral oil, cider vinegar and an emulsifier, in the proportions of about 2 pounds of wood ashes, from about 2 to about 3 quarts of mineral oil, about 2 gallons of cider vinegar, and about /2 ounce of emblsifier.

4. A coolant for quenching ferrous metals resulting from the mixture of wood ashes, mineral oil, cider vinegar, and sodium hydroxide, in the proportions of about 2 pounds of wood ashes, from about 2 to about 3 quarts of mineral oil, about 2 gallons of cider vinegar, and about 5 grams of sodium hydroxide.

5. A coolant for quenching ferrous metals resulting from a mixture of wood ashes, mineral oil, cider vinegar, sodium hydroxide and an emulsifier, in the proportions of about 2 pounds of wood ashes, from about 2, to about 3 quarts of mineral oil, about 2 gallons of cider vinegar, about 5 grams of sodium hydroxide, and'about 0.5 ounce of an emulsifier.

6. A coolant for quenching ferrous metals consisting of the following ingredients substantially in the following proportions by weight, namely, water about per cent, mineral oil about 25 per cent, acetic acid about 5 per cent, an emulsifier less than of 1 per cent, sodium hydroxide less than 1 of l per cent, the remainder consisting of the chemical constituents of wood ashes substantially in the proportions normally present therein.

7. A coolant for 'quenchingferrous metals resulting from t'he'fmixture of the following ingredients substantially in the following proportions by weight, namely, water about 60 per cent,

acetic acid about 5 per cent, wood ashes about '7 per cent, an emulsifier and sodium hydroxide together less than 1 per cent, and the balance mineral oil.

8. A coolant for quenching ferrous metals re- 0 sulting from the mixture of the following ingredients substantially in the following proportions, by weight, namely, cider vinegar from about to about per cent, wood ashes from about 7 to about 9 per cent, an emulsifier about fly of 1 per cent, and mineral oil from about 15 .to about 25 per cent.

9. A coolant in the form of an emulsion for quenching ferrous metals consisting principally of water and mineral oil in the proportions, by weight, of approximately 60 parts of water to 25 parts of oil, together with approximately 5 parts of acetic acid and 8 parts of wood ashes.

10. A coolant in the form of an emulsion for quenching ferrous metals consisting principally of oil and a solution of less than ten per cent concentration of a weak acid, the amount of acid solution substantially exceeding the amount of oil, and the said emulsion also containing the chemical constituents of wood ashes in an amount substantially less by weight than the amount of oil.

11. The improvement in the art of hardening and toughening steel which consists in heating a steel blank to a temperature in the neighborhood of 1510" F. and quenching the blank in a coolant resulting from the mixture of wood ashes. mineral oil and dilute acetic acid substantially in the proportions of 2 quarts of mineral oil, 2 pounds of wood ashes, and 2 gallons ot a 4 per cent solution of acetic acid.

12. The improvement in the art of hardening and toughening steel which consists in heating a steel blank to a temperature in the neighborhood of 1510 F. and quenching the blank in a or hardening and quenching the blank in an emulsion consisting of water, mineral oil, wood ashes and a weak acid in approximately the following proportions, by weight, namely, 60 parts of water. 15 to 25 parts of oil, 8 parts of wood ashes, and 5 parts of acid.

14. The improvement in the art of hardening and toughenim steel which consists in heating a steel blank to a temperature about 1510 F. and quenching the blank in an emulsion consisting principally of oil, and a solution of less than 10 per cent concentration of a weak acid, the amount of acid solution substantially exceeding the amount of oil and the said emulsion also containing wood ashes in an amount substantially less by weight than the amount of oil.

15. The improvement in the art of hardening and toughening steel for use without subjecting the same to the usual drawing operation which consists in heating aesteel blank to a temperature of about 1510 F. and quenching the blank in an emulsion consisting of a solution of less than 10 per cent concentration of acetic-acid, wood ashes and mineral oil in approximately the following proportions, namely, 2 gallons of acetic acid solution, 2 pounds of wood ashes, and from 3 to 6 quarts of mineral oil.

' LESLIE DELANCEY.