US2029819A - Differentially heat-treated cast steel wheel - Google Patents

Description

Patented Feb. 4, 1936 PATENT oFFics .DIFFERENTIALLY HEAT-TREATED cssr STEEL WHEEL Alfred w. Gregg and Raymond 11.

Q bus, Ohio, assignors Company, Columbus,

1 Ohio -No Drawing. Application Serial No, 620,976

, I 3 Claims. (01. 295-49) This invention relates to the manufacture of I cast steel wheels, particularly car wheels, and

an object of the invention resides in the facile and economical production of an improved car wheel comprising an integral casting of a suitable alloy steel having a tread region of great hardness for maximum wear resistance and a hub or axle region of alower state of hardness for ready machinability.

Car wheels are usually formed from cast iron, rolled steel and cast steel. having a tread of substantially 350 to 400 hardness on the Brinell scale, has been used widely, irrespective of its inherent brittleness, due primarily to its relatively low cost and the decided resistance to wear afiorded by its hardened tread.-- The popularity of the cast iron wheel has been steadily diminishing for some time past forthe reason that higher car speeds and heavier loads render theuse of such wheels hazardous. In fact, severaldmportant railroads have discontinued the use of cast iron wheels in both freight and passenger equipment.

Many railroads now use the rolled st'eel car wheel because of its greater resistance tobreakage as compared to the cast iron wheel. However,

the usual rolled steel wheel has approximately "the same Brinell hardness in both tread and hub, and because the hub must be machinable the hardness of the" tread is in the neighborhood of 200 on the Brinell scale which is. not sufllcient to give the long wear possible with a tread of greater hardness.

The cast steel wheel has always given'excellent service. In the past it has been an expensive and difiicult process to produce a differentially hardened wheel which difliculty' has been overcome by the process andproduct described below. i v

Thus with ordinary methods of manufacture, if the tread region thereof through heat treat ment, by quenching, possesses a desirable high degree of hardness, the hub region is usually too hard to admit of conveniently executed machine tool operation, such as the machining of the axle bore and, conversely, if the hub region of such cast steel wheels is susceptible to machining, the tread region then usually possesses an undesirably low state of hardness, which is not conducive to maximum wear resistance. Y

Therefore, it is a leading object of the invention to provide a cast steel car wheel composed of uniform steel alloy throughout its mass which, through the selection of special ingredients entering into the composition of the alloy, may, dur- The cast iron wheel,

' especially alloy steels ingredients which are to Frank, Columto The Bouncy-Floyd Ohio, a corporation of ing course of' manufacture, be subjected to a process of diiferential hardening, afterthe disxclosure set forth in ourcopending application, Serial No. 463,777, now Patent No. 1,859,623, to

secure therein a hard wear-resisting tread 5 throughout and a machinable hub and, further,

to produce such a wheel at a cost comparable with that of the ordinary rolled steel wheel. The differential heat treating or hardening process is based upon the difference in hard- 10,

ness producedin several types of alloysteels,

I having rapid or active transformation points, by a different rate of cool- 'ing in different regions of the same casting. In this process, the cast steel wheel is heated uniformly to a point above the critical range and then quenched in a fluid medium. During such heating and quenching, there is positioned in and around the axle bore of such a wheel a relatively close fitting plug or plugs so that by 2 reason of the heat retaining properties of the plug or plugs, the cooling rate of the axle region during quenching is relatively retarded during the quenching steps as regards the unprotected tread region which is directly immersed in the quenching media. Therefore, the tread region is rapidly cooled to a temperature below the criticalrange to produce an extremely-hard state whereas the axle region byreason of its relatively delayed rate of cooling, due to the produced by the retained heat in the plug or plugs.

For instance, the tread may possess hardness of approximately 275 to 500 on the Brinell' scale while the hub or axle region under these conditions of manufacture, will possess, by the same method of measurement, a hardness not sub- 40 stantially in excess of 225 and usually below 210.. We have discovered, in adapting this process, which is termed differential heat treatment in the following claims, to a cast steel car wheel that it is necessary to employ carefully selected be used in the composition' of the alloy For instance, we have found that an alloy steel which possesses sluggish or retarded transformation points is of little or no value when difierentially heat treated by the above described process, since it tends to remain just as hard in the annealedor air cooled condition as if quenched and consequently defeats In accordance with the present invention,

contents of the steel to secure rapid or active transformation properties therein-and thereby render it adaptable to the differential heat treating process.

The steel which is now considered to be well adapted to said process in the manufacture .of cast steel wheels is characterized by its pronounced ability upon liquid quenching to pro-' duce a troosto-martensitic or martensitic structure and-where more slowly cooled, a sorbitic or sorbito-pearlitic structure. As examples of several very satisfactory combinations of alloys and carbon,'the following are cited:

Y Percent Carbon .25 to .40 Manganese .90 to 1.50 Molybdenum .20to -.40 Silicon .20to .50 The balance iron with exception of incidental impurities or Percent Carbon I .25 to .40 Manganese .90 to 1.50 Molybdenum .20 to- .40 Chromium .25 to 1.00 Y Silicon .20 to .50

and the balance iron, incidental impurities excepted or,

Percent Carbon .25 to .40 Manganese .60 to .75 Chromium .50 to 1.00 Nickel 1.50 to 2.25

and the balance iron.

As examples of unsuitable combinations of carbon and alloy metals, the following may be given as typical:

0 Mn 0: V or Me W Percent Percent Percent Percent Percent .15 to .30 so to 1 00 4.00 to 0.00 .25 to .05 .15 to .30 so to 1 00 4.00 to 0100 i. 00

' 1 sulphur.

sorbite-pearlite formation.

balance iron with exception of incidental impurities. e

, It is believed that, generally, any steel of austenitic structure at room temperature is, owing to its very low transformation points, unsatisfactory as a composition material in the formation of a car wheel in accordance with the invention. However, by the employment of the permissible formulae, above given, the steel body responds readily to produce a cast steel wheel 1 having the desirable physical characteristics set forth, together with simplicity and economy in manufacture.

What is claimed is:

l. A cast steel wheel possessing diiferentially hardened tread and axle regions and formed from the following ingredients in substantially the relative proportions given:-

Percent Carbon .25to .40 Manganese .90 to 1.50 Molybdenum .20 to .40 Chromium .10 to 1.00 Silicon .20 to .50

the balance being iron with the exception of incidental impurities such as phosphorus and 2. A cast steel wheelpossessing differentially hardened tread and axle regions and comprising:

Percent Carbon .25 to .40 Manganese .90 to 1.50 Molybdenum .20 to .40

the balance being substantially iron.

3. A cast alloy steel wheel having a rapid transformation point and' comprising carbon about .25% to .40%, manganese about .90% to 1.50%, molybdenum about .20% to .40%, silicon about .20% to and the balance principally iron, said wheel having a tread region of martensite-troostite formation and a hub region of I] N ALFRED W. GREGG.

- -RAYMOND H. FRANK.