US1724031A - Method of heat-treating bars - Google Patents

Description

- to resist wear.

Patented Aug. 13, 1929. i

U N l T E D S T A GEORGE LANGIEORD,

0F JOLIET, ILLINOIS, ASSIGNOR 'IO MCKENNA PROCESS OOIIPANY OF ILLINOIS, 0F J'OLIE'I, ILLINOIS, A CORPORATION OF ILLINOIS.

METHOD OF HEAT-TREATING BARS No Drawing.

This invention relates to the treatment of angle bars such as are Commonly used in railway joints, and more particularly to a method of oil tempering such bars as d1st1n guished from the present method of heat treating or oil quenching.

The bars used on rail joints are subjected to constant pounding as well as severe strains and bending stresses. For this reason these bars should possess great tensile strength and appreciable ductility while also having maximum hardness consistent with the required tensile strength and ductility, Prior to the present practice of heat treating angle bars, specifications for such bars usually called for a tensile strength of 60,000 to 75,000 pounds per square inch and a bend test. Since the present heat treating methods have gone into effect it has been possible to greatly increase the tensile strength of the bar, and the specifications for such bars now usually call for a tensile strength of 100,000 pounds per square inch and bend test. I have found that by my method it is possible to greatly increase the efliciency of the bar over bars treated by present methods. The ideal bar should have a tensile strength of approximately 125,000 pounds per square inch and should bend cold 90 degrees without cracking. 1 It is possible to roduce these results consistently by my method, whereas such results cannot be obtained by the present method of heat treating bars in general use.

By the present method of treating bars,-

the bar is first heated to the proper temperature formaximum hardness. This temperature will vary somewhat with the carbon content of the steel, the temperature decreasing with the increase in the carbon content.

- This temperature is what is commonly known as the hardenin temperature, being that temperature at w ich the greatest hardness and tensile strength of the steel is obtained upon cooling thereof. For a medium carbon steel thistem erature is approximately 750 degrees C. 2 practice the ening temperature and-is then relatlvely light oil of low viscosity and low flash point which is oil is that which is in common use in accord- I ance with the present practice and need not be described in detail, though particular at-' ccording to the presentbar is heated to the properhard- I quenched in present practice,

pre-heated to a tempera-L ture of approximately 150 degrees F. This Application filed April 2:7, 1927. Serial No. 187,123.

tention is called to the fact that this oil is of relatively low viscosity and low flash point and cannot be safely heated to a temperature above 150 degrees F. Since the temperature of the bar-is'approximately 750 degrees C., and the temperature of the oil bath is approximately 150 degrees cooling of the bar when it is plunged into the bath is very sudden. In fact, the bar may be considered as suddenly chilled, This is particularly true during the lowering of the temperature of the bar to 715 degrees 0., which takes place very rapidly. As 715 degrees C. is the critical changing point or temperature for steel of medium carbon content, the sudden chilling of the bar from approximately 750 degrees (lto and below 715 degrees C. is very objectionable as subjecting the bar to severe stresses and rendering it very hard. The bar resulting from this plunging into the oil bath and quick cooling or chilling is so hard as to be brittle. In a bar produced in this way the hardness, ten-' sile strength, and ductility are not properly related towithstand the constant pounding,

F., the

bending strains and" wear to which the bar is necessarily subjected in use. This bar is not entirely safe, due to its liability to fracture, but it has to be used as it is the best that can be produced by present practice.

In tempering steel for tool work and many other purposes, after being quenched and hardened as above described, it is subjected to further. treatment to draw or let it down. This further treatment includes the step of again heating the steel to a temperature somewhat below its temperature of recalescence, which is considerably below the temperature for maximum hardness, previously referred to. The reheated steel is then cooled in a second oil bath by being quenched therein, which serves to draw it back orlet down the steel so as to render it less hard and brittle while imparting to it greater strength and ductility. This step is, strictly speaking, the tempering of the. steel, but under the in order to efiect this result it is necessary to first harden the steel as above noted, and then temper it or let :it down.' This second step wh1ch. may be con,- sidered as the actual tempering of thesteel, is not practiced in the production of splice bars for rail joints as to do so would very materiall increase the cost of such bars rendering t e cost of production practically prohibitive. By my method the preliminary hardening and subsequent tempering can be eflected in but a single operation.

I have found that it is possible to produce a bar tempered to give the proper degree of hardness combined with the proper tensile strength and ductility to resist wear and breakage under continual pounding in a single operation. A bar produced in accordance with my method possesses much greater tensile strength than the bars produced in accordance with the present practice, while also possessing the same and, in some instances, even a greater degree of hardness and ductility, these three factors being properly related to give maximum efiiciency. I attribute this largely to the fact that, in practicing my method, the bar instead of being suddenly chilled has its tem perature reduced comparatively slowly from approximately 7 50 degrees C. to 715 degrees 0., which latter temperature is, as previously noted, the critical temperature of change of steel of medium carbon content under consideration. As will be readily understood by those skilled in the art, this temperature will vary with the carbon content of the steel being treated. In practicing my method, instead of employing a relatively light oil heated to approximately 150 degrees F. I employ a very thick mineral oil with a high Viscosity and high flash point which is pre-heated to a temperature of 200 degrees F. to 250 degrees F., the latter temperature being preferred. In practice the average temperature of this oil is approximately 230 degrees F. This oil is a steam refined oil without tar or asphaltum, and

has a flash point over 550 degrees F. and a viscosity of 145 sec. at 210 degrees F., being an extremely thick mineral oil. Ordinary quenching 011, such as that used in treating bars according to the present practice above outlined, has a flash point of from 285 degrees F. to .300 degrees F., and a viscosity of 145 sec. at 90 to 100 degrees F.

In practicing my process or method, after the bar has been heated to the proper temperature, which in my process, as in the present practice, is its hardening temperature, it is immersed in the oil bath which is maintained at a temperature of approximately 230 degrees F. The temperature of the bar, as it enters the oil bath is approximately 750 degrees 0. As the temperature of the bath is approximately 230 degrees F. the lowering of the temperature of the bar to 715 degrees C. will take place much more slowly than in the case where a light oil is used as in the present practice. This slow cooling of the bar to and below the critical temperature of steel is of the utmost importance in my method as it effectually prevents the sudden chilling and consequent hardening to an undesirable extent of the such as that bar, while hardening the bar sufiieiently to enable it to withstand the wear to which it is subjected in use. After the bar has been immersed in the oil and cooled to the proper temperature, it is removed from the oil bath and the bars are stacked in a pile, the bars being placed as closely together as practical and permitted to cool slowly. In an atmosphere of approximately 60 degrees F. the bars will cool in from 18 to 24 hours. This gradual cooling of the bars is desirable as avoiding any undesirable stresses due to sudden cooling, and increases the strength and ductility of the bars.

While my process is well adapted for tempering newly formed bars, it is also well adapted for tempering reformed bars, in which latter case I find that even better results can be obtained by introducing a further step into the method. In practicing my method in connection with the reformed bars, I prefer to employ a press, such as that disclosed in my co-pending application for means for reforming worn angle bars, Serial No. 122,864 filed July 16, 1926, which has matured into iPatent N 0. 1,712,506, dated May 14, 1929. The bar to be reformed is first heated to its proper hardening temperature, and the bar is then placed in the 6 effect thereon, such as would be caused by spraying water alone onto the bar. The bar is then immediately immersed in the oil bath in the manner described, the re maining steps of treatment of the bar being the same as first described. The initial momentary cooling of the bar by the vapor or air and water spray I find to be of assistance in tempering the bar, and the operation of the die members on the bar serve-s to compact the metal resulting in a bar of maximum efiiciency. My method is particularly adapted for use in connection with reformed bars, though it is not by any means limited to this one use. This method is well adapted for retreating bars which may be reformed or not, as conditions may require, which bars do not possess the requisite characteristics in all respects to render them fit for use in rail joints. It will also be obvious that my method can be used for many other purposes than that of treating bars for rail joints as, obviously, there are many cases where steel bars used for other purposes should possess great tensile strength combined with ductility and relatively great hardness.

As previously stated, the hardening temsquare inch perature of the steel will vary in accordance with the carboncontent. It is also true that the temperature of the steel bar when it is removed from the bath should be varied in accordance with the carbon content, to obtain the best results. A bar of medium carbon steel, the average steel bar, should be heated to approximately 750 degrees C. and withdrawn fromvthe oil bath at approximately 300 degrees F. A low carbon (10%) Bessemer steel bar should be heated well above 750 degrees C. and withdrawn from the bath at about 215 degrees F., the bath having the same temperature. A high carbon (.60%)

steel should be heated to approximately 750 degrees (1. and quenched slightly below this temperature, being withdrawn from the bath at approximatelyv 400 degrees F. As illustrative of the results which it is possible to obtain by my method, 1. give the follow.-

1. A low carbon (10%) Bessemer bar, having a tensile strength of 70,100 pounds per had its tensile strength raised to 1042,000 pounds per square inch ing in accordance with my method, this bar bath at 300 degrees after treatment being 113,000

being quenched in the oil bath at a temperature above 750 degrees C. and withdrawn at the oil temperature, about 215 degrees F.

2. A medium carbon, open hearth bar, previously heat treated and having a tensile strength of 101,000 pounds per square inch, treated by my method by quenching at close to 7 50 degrees C. and withdrawing from the F, had 1ts tensile strength raised to 121,000 pounds per square inch.

3. A high carbon (.60%) open hearth bar having a tensile strength of 110,000 pounds per square inch had its tensile strength raised to 113,000 pounds per square inch ,by my method, this bar being quenched in the bath at a temperature somewhat under 750 degrees O. and withdrawn at 400 degrees F.

4. A high carbon, open hearth bar, previously heat treated and having a tensile strength of 130,000 pounds per square inch, entirely toohard and brittle to be safe, was treated in accordance with my method by quenchingat a dull red below 7 50. degrees C. and withdrawing from the bath at 400 degrees F, the tensile strength of the bar pounds per square inch.

5. A high carbon, open hearth bar, previously heat treated with a tensile strength of 142,000 pounds to the square inch, which is much too high forsafety, was treated by heating to a temperature below 7 50 degrees C. and then letting it cool to 550 degrees 0.,

by treat essarily vary considerably in accordance with the carbon content and the condition of the steel. These are, however, factors which can be readily appreciated by those skilled in art and proper allowance made. While it is well known in this art to quench the bars in a comparatively light oil, so far as 1 am aware, no one has ever before quenched bars in a heavy oil as a step in the process or method of tempering such bars. In fact, it has always been thought, and generally accepted in the art, that it was necessary to quench the bars in a light oil in order to obtain the desired hardening effect. I believe, therefore, that this particular step in the oil tempering of bars and other steel articles is broadly new.

What ll claim is 1. A method of treating steelbars consisting in heating the bar to approximately its hardening temperature, immersing it in an oil bath preheated to a temperature sufficiently high to lower the temperature of the bar comparatively slowly to the critical temperature for the steel, the bar being cooled by the bath to a temperature below said critical temperature, and then removing the bar from the bath and slowly cooling it.

2. A method of treating steel bars consisting in heating the bar to approximately its hardeningtemperature, immersing it in an .oil bath preheated to a temperature sufficiently high to lower the temperature of the bar comparatively slowly to the critical temperature for. the steel, and then removing the bar from the bath and slowly cooling it.

3. A method of treating steel bars consisting in heating the bar to approximately its hardening temperature, immersing it in a bath of oil of high viscosity and high flash point heated to a suificiently high temperature to avoid quick quenching or lowering of the temperature of the bar to the critical temperature for the steel, and then removing the bar from the bath and slowly cooling it.

4. A method of treating steel bars consisting in heating the bar to approximately its hardening temperature, immersing it in a bath of .oil of high viscosity and high flash point preheated to a temperature of: approximately 200 degrees 13. withdrawing the bar from the bath at a temperature at leastequal to the bath temperature, and then cooling the bar.

A method of treating steel bars consisting in heating the bar to approximately its hardening temperature, immersing it 1n a bath of oil of high viscosity and high 5 temperature, and then cooling the bar.

6. A method of treating steel bars consisting in heating the bar to approximately its hardening temperature slowly lowering the temperature of the bar to the critical 10 point for the steel, and then slowly cooling the bar.

7. In the treatment of steel bars, the step of immersing the bar at a temperature above 715 degrees C. in an oil bath preheated to :1 minimum temperature of approximately 200 degrees F. and lowering the temperature of the bar comparatively slowly to 715 de grees C.

8. A method of treating steel consisting in heating the steel to approximately its hardening temperature and then slowly quenching it in oil to the critical temperature of the steel.

In witness whereof, I hereunto subscribe my name this 14th day of April, 1927.

GEORGE LA NGFORD.