US2219780A - Alloy steel - Google Patents

Description

Oct. 29,1940. I w. E. Jon Y I 2,219,780

ALLOY STEEL Filed Jan. 6, 1938 'I III) I rr mrmm WW :mnentor' 25 moderate section sizes by quenching in oil.

Patented Oct. 29, 1940 UNITED STATES 2,219,789 ALLOY s'rnnr.

Walter E. J ominy, Detroit, Mich., assignor to General Motors Corporation, Detroit, Mich, a corporation of Delaware Application January 6, 1938, Serial No. 183,573

3 Claims.

This invention relates to ferrous metal alloys and more particularly to alloy steels.

In many uses of articles. formed of steel the property of depth hardness is a highly desirable 5 characteristic. By depth hardness is meant the property of steel to become hardened in the heat treating operation to a distance below the surface. Since the rate of cooling of an article is slower below the surface than at the surface and becomes less as the center of the article is approached, it follows that a steel which hardens to the center of the article will harden with a slower rate of cooling than one which hardens only at the surface or slightly below. The depth hardening characteristics of steel .then become really a matter of required speed of cooling to produce full hardening. One of the principal reasons for using alloy structural steels is to obtain deep hardening characteristics and if it were not for this property of alloy steels the plain carbon steels'which are much lower in price could often be substituted for them. The deep hardening steels,- since they can be hardened with a lower cooling speed, may be-hardened in at least the An article which can be hardened by quenching in oil will, in general, be less distorted and have lower internal stresses than one quenched in water or other more drastic quenching media. In fact, for some automotive partslike ring gears, transmission gears and drive pinions, so much distortion occurs with water quenching that it is commercially impractical to harden by water quenching. In order to obtain steels with proper hardening properties, certain alloy steels have been heretofore proposed. Due to the cost of the alloying ingredients used, the alloy steels arecommonly quite expensive. I have found that with a steel of a the composition of my invention, the cost is materially reduced as compared with the 'alloy steels of the prior art. Accordingly, it is one object of my invention to provide an alloy steel having good depth hardening properties that is much more economical to manufacture than previously known alloy steels of similar characteristics. Other objects of my invention are to provide an alloy steel adapted for a wide variety of uses that is cheaper and more economical than expensive alloy steels heretofore employed; to provide a steel having excellent properties of fatigue resistance; to provide an alloy steel especially adapted for use in parts to be case carburized and to provide a case carburized article of alloy steel in which there is substantially noliypereuctectoid carbon in the caseportion thereof."v I

Other objects and advantages of my invention will become more apparent'from the following detailed description. I

My invention comprises an alloy steel consisting of carbon, manganese, silicon, molybdenum and iron as essential alloying ingredients. In addition, small amounts of impurities such 'as phosphorus, sulphur, etc., may be present. Gen- 10 erally, the impurities will be present in amounts comparable with known steels and should not be present in such quantities as to impart objectionable characteristics or unduly retard the beneficial effects of the other alloying constituents. 15 My improved alloy consists in the use of molybdenum in smaller amounts than heretofore considered commercially feasible in steels to be .hardened so far as I am aware. The use of molyb- I denum in the range later outlined in combination :0

with controlled amounts of silicon, manganese,

carbon and iron results in a steel having improved properties in accordance with the invention. In order to compare the depth hardening characteristics of the steel of my invention with vari- 26 ous commercial steels, I have developed a test specimen and test procedure. Referring to the drawing there is shown a test specimen l0, one inch in diameter and three inches long. It has a cup-shaped portion I! at oneend and a screw- 30 threaded opening I4 at the other. An adapter l6 connected to the screw-threaded end of the test bar secures the latter to a bracket'20. The

bracket holds the test specimen'in such a way that the cupped end is directly over a nozzle 22. 3'5 The test specimen is hardened by heating to the desired temperature and then cooling by spraying water into the cupped end and directly cooling this face only as shown in the drawing. A receptacle 24 collects the water 0 used in the cooling operation. After the specimen is cooled it isv removed from the fixture, a strip of ,metal isremoved by grinding to a depth, of .015, and the hardness measured at various points along this ground surface from the water 5 cooled end to the adapter end. From these readings the hardening characteristics of the steel are ascertained. For carburizing steels, the distance from the water cooled end, over which the hardness is 600 Vickers Brinell or above after car- 50 burizing and cooling on the fixture, is taken as a measure'of the hardening characteristics of the steel. A number of the more common carburizing steels have been tested in this way to show their relative hardness characteristics and some of these are included in Table 1. There are also included in Table lsome of the steels of my invention and it will be seen that the hardenability characteristics of these steels compare favorably with those of the alloy steels listed.

0.60-1.50%, balance iron plus minor amounts of impurities has good properties of depth hardening and good properties as regards fatigue resistance and is one that is economical in cost as compared with higher priced alloy steels. For

Tune 1 most purposes a narrower range of the several Distance from water cooled Per- Per- Per- Per- Per- Per- Per- Per- Mcciuaidend where S. A. E. steel cent cent cent cent cent cent cent cent E n hardness is Mn Cr Ni Mo Si P 8 grain size 600 Vickers Brinell or above Inches 19 031 6-7 .340 20 189 3-4 M's 18 019 3-4 2% 14 029 6 84a 19 012 6-8 2% 19 017 6-8 is 14 025 6 Bio 23 l. 07 $6, 18 1. 03 26 1. 10 2 25 l. 27 2% 22 1.08 21-; .35 1.06 1 22 1. 08 2% 27 1. 10 2 Z) 53 21 .96 1

In the steel of my invention the three alloying constituents, manganese, silicon and molybdenum within the ranges disclosed, are essential to produce good depth hardness. I have made steels in which only two of the three are present and when this is done substantially lower depth hardness is obtained. This may be observed from the following steels which were all tested for hardenability by carburizing eight hours at 1700 F. and cooling on the quenching fixture as already explained.

Di t .nce from water co led Per- Per- Per- Per- Grim] end he'e Steel cent cent cent cent hudness is 0 Mn Si Mn e 000 Vickers Brinell or abmc l Inches .23 .90 1.13 2; .07 .98 .69 -6 )1; i5 .34 97 4-5 .11 .24 .93 4-5 5'3 09 86 Trace 5-6 14 07 99 Trace 10 4 6 fie It will be noticed that steels C-78 and C-10 in which the molybdenum was omitted have a low hardenability rating for alloy steels as compared with steels in accordance with my invention.

.and silicon are within the desired range and as little as .05% molybdenum is added, a very definite increase in the hardenability characteristic of the steel is obtained, as indicated in the steels of my invention in Table 1. Further increase in molybdenum content gives additional Increase in increase in hardness penetration. the manganese content with the same molybdenum likewise gives an increase in hardenability characteristic.

I have found that an alloy in accordance with my invention consisting of molybdenum .05-.15%,

carbon AIS-1.20%, manganese 0.90-1.60%, silicon Iron plus minor amounts of impurities Balance My new alloy is especially adapted for parts requiring case carburizing, for example, ring gears and the like. For this purpose the carbon content of the articles to be carburized will be preferably within the range .05-.30%. The com-.

bination of the several alloying elements in the amounts specified is such that an article formed from the alloy after carburizing has substantially no hypereutectold carbon in the case. This permits quenching the article directly from the carburizing box, at say a temperature of 1700 F., for example, and obtaining a very hard martensitic surface of approximately eutectoid carbon concentration, whereas most alloy steels when similarly treated provide a softer austenitic surface of hypereutectold carbon. I

A steel made in accordance with my invention has a wide variety of uses in the construction of parts for automobiles where alloy steels are required due to severe conditions of operation.

The. steel of my invention is a steel of great strength and is resistant to fatigue. The manufacture thereof entails no special difllculties.

I claim:

1. A case carburized article having a core composed of the following elements as essential ingredients in substantially the following proportions:

Percent Carbon- .05- .30 Manganese .90-1.60 Silicon .60-1.50 Molybdenum.- .05- .15 Ir Balance said article having a case of approximately eutectoid carbon content.

2. A case-carburized article having a core composed of the followingelements as essential ingredients in substantially the following proportions:

Per cent Carb n .05- .30

-5 Manganes .95-1.30 Silk-m1 .901.25 Molybdenum .05- .12- km Balance said article having a case of approximately eutectoid carbon content.

3. A case carburized alloy steel article having a case of approximately eutectoid carbon concenwhen quenched direct from the carburizing me-.

dium at substantially the carburizing temperature having a hard, martensitic surface of ap- 10 proximately eutectoid carbon concentration.

WALTER E. J OMINY.

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