US2087346A - Method of producing steel rails - Google Patents

Description

July 20, 1937. .1. JOHNSTON 2,087,346

METHOD OF PRODUCING STEEL RAILS Filed Aug. 21, 1950 wwv ATTORNEYS Patented July 20, 1937 2,087,346 METHOD or PRODUCING STEEL RAILS John Johnston, United States Short Hills, N. J., assignor to Steel Corporation, N. 31., a corporation of New Jersey New York,

Application August '21, 1930, Serial No. 476,868 9 Claims. (Cl. 14821.5)

My invention relates to methods of making rails of steel or ferrous metal and more particularly to methods of controlling the cooling of been rolled.

An object of the invention is to provide a method of controlling the cooling of rails such that the residual lengthwise tensile stresses which may occur in the head of finished rails are effectively reduced.

10 In making rails heretofore the rails, after having been rolled from a hot ingot, are permitted to cool by exposure to the atmosphere or to currents of air. 'This cooling isfof sufiicient rapidity to obviate undue softening pf the Imetal and to 5 keep the area or space required by the rails also falls more rapidly than all while coo 'ng within a commercially practicable and economic limit. The heat is given up by the atmosphere, or to the cooling air currents, from the exposed surface of the rail, and immediately heat from the interior of the rail begins to pass towards the somewhat cooler surface. This passage the interior towards the surface of the rail, and this gradient is greater the greater the rate of cooling and the consequent more rapid transfer of heat outwards through the cross section of the rail.

The temperature difference between the interior and the surface is also greater, the greater the cross-sectional dimension of the rail and the the rail, such as the web and flanges, in which the ratio of extent of surface to volume is greater, in the thicker parts, such as the head, in which the ratio of surface to volume is less. These differences are also greater the larger the rail. Under the relatively rapid cooling now usual in practice, the temperature diiference between the inner portion of the .head and the appreciable, particularly in the larger and heavier rails.

Within a temperature range, notably from about 750 C. (1400 F.) to about 550 C. (1000 F.) steel undergoes transformations which are accompanied by a sharp The exact temperature of initiation of these transformations and the rate at which they proceed towards completion, depend primarily upon the composition of the steel, but also to some extent upon other factors such as the mode and rate of cooling. Because of' the temperature dltl'erence; through the rail section. alluded to of heat necessarily in-- volves a drop, or gradient, in temperature from web or flange may 'be quite' increase in its volume.-

- necessarily longer path of shortest travel of the heat. The temperature of the thinner parts of" above, the completion of these transformations times in different portions of occurs at different the rail, being in general latest in those portions furthest away from the surface. The change in volume accompanying these transformations, therefore, also occurs at different times in different portions of the rail; and consequently a series of stresses is set up in the rafl' in this period of its cooling.

These stresses may, with inappropriately rapid cooling, be so considerable as to be potentially dangerous as internal sources of weakness, particularly in the temperature range before the fullest strength of the s eel has developed; in any case they set up, in the finished cold rail, a series of residual stresses which can, by appropriate'means, be observed directly.

Systematic, direct, extended measurement of these residual stresses has shown that there may be, in the head of the rail, residual longitudinal. I

coupled with similar observations which show how' these residual stresses rail change when the rail is put in actual service, have led me to the belief that the head of a new rail should preferably be as free as practicable from longitudinal tensile stresses, and that the stress gradient should preferably be uniform and invention comprises the methods described in the following specification.

The various features of the apparatus are illusin the head of theture of transformation for the particular steel comprising the rail. The particular temperature of transformation will vary with any given steel with respect to the rate of cooling from temperatures above the upper critical temperature. The rate of heat loss is then restricted, thus more nearly equalizing the temperature throughout the rail. .The proper rate of loss of heat varies with the dimensions of the rails to be cooled, andmust be adjusted accordingly. In all cases it should be sufllciently slow to enable all parts of the cross section of the rail to be within the temperature range .of this transformation at approximately the same parts of the rail, particularly in the head of the rail, to undergo the volume and structure change with a minimum of strain and distortion.

The cooling of the rail is continued at this retarded rate for a time after it has fallen below the transformation temperature, for example, it may be cooled at this rate to 550 C. (1000 F.) or even lower, thus ensuring the substantial completion of the structure and volume changes, and the maximum practicable equalization of such stresses as may have arisen, before the more rapid cooling to atmospheric temperature is resumed. Thereupon the normal, rapid or even an enhanced rate of cooling may be resumed.

The cooling of the rails may be accomplished in any suitable apparatus. In the apparatus illustrated in the accompanying l are placed onand transand are moved progressively over the hotbed from one end to the other as indicated by the arrow in Fig. 1. While the rails are on the hotbed they are cooled by currents of air, set up by convection or otherwise, which rise upwardly between and about the rails; The rate or cooling is deter mined primarily or very largely bythe rate of movement of these air currents. When the tem perature of the surface of the rails drops to about 700 C. (1300 F.) or somewhat lower, they enter a closed chamber I2 having louvres l3 and M in its lower and upper walls to control and limit'the upward passage of air about the rails in the chamber. Flaps l5 and I6 may be provided at the rail entrance and exit openings of-the chamber.

The position or angle of the louvres l3 and I4 may be individually regulated to cool the rails to any rate, within limits, in the critical temperature range and immediately subsequent to it. The rails then pass under the flap l8 to the outer atmosphere, whereupon the usual more rapid cooling takes place. The rate of cooling of the rails after the retarded cooling in the chamber l2 has been completed may even be increased to compensate for the relatively longer time and greater space required for the period of retarded cooling.

'It will be understood, however, that other apparatus may be used in the carrying on of the method of cooling in my invention and that various modifications of the form of the apparatus may be made. One such modification is to car y out the retarded and controlled cooling in a vertical, enclosed part of the hotbed, so arranged time and to enable the various rail, equalizing the in the above method the steel comprising comprises hot iormation, equ

' approximatin that the rails in a horizontal position move up one side and down on the other, being discharged for final cooling on a hotbed of the ordinarytype; in this case again, the flow of air past the cooling rails is controlled by suitable louvres or flaps.

What I claim is:

1. The method of treating rails which comprises heating the rail to temperatures above the critical temperature of the steel comprising the rail, cooling the rail to a temperature approximating the transformation temperature of the steel comprising the rail, equalizing the temperaturedifierentials in said rail at said temperature and thereafter slowly and uniformly cooling the rail during the period of transformation and at least to temperatures approximating 550 C.

'2. The method of treating rails which comprises heating the rail to temperatures above the critical temperature of the steel comprising the rail, cooling the rail to temperatures below the critical temperature but above about the transformation temperature of thesteel comprising the temperature differentials in from-said cooling and thereuniiormly cooling the rail said rail resulting after slowly and temperatures at least approximating 550 C.

3..I'he method of treating rails which comprises heating the rail to temperatures above the critical temperature of the steel comprising the rail, cooling the rail to temperatures appro mating 700 C. but not temperature of the said steel, equalizing the temperature diflerentials in said rail, slowly and uniformly cooling the railthrough the said transformation temperature and" at least to, temperaturesapproximatlng 550 C. and thereafter cooling in any convenient manner to normal temperatures.

. 4. The meth or manufacturing rails which compriseshot worhng the rail to the desired final size, cooling the rail to temperatures approxiniating the transformation temperature of the rail, equalizing the temperature diflerentials in said rail slowly and unirormly cooling the rail through said transformation temperature and to temperatures approximating 550 C. and thereafter cooling the rail in any convenient manner to normal temperatures.

5. The method or manufacturing rails which working the rail to the desired final size, cooling the rail to a temperature below the critical temperature or the steel comprisins the rail but above about the temperature or transthe temperature diflerentials in said rail, and slowly and uniformly cooling the rail through the said transformation temperature and to temperatures approximating 550 C. and thereafter cooling in any convenient manner to normal temperatures.

flnal size, the rail to temperatures approximating 700 C. but above the transformation temperature oi the steel comprising the rail, equalizing the temperature dlflerentials in the temperatures approximating 550 C. and thereafter cooling in any convenient manner to normal temperatures.

I 7. In the manufacture of steel rails, the method or cooling the hot rolled rails which comprises rapidly cooling the rail to temperatures the transformation temperature for the steel composition comprising the rail, re-

' through the transformation temperature and to below the transformation tarding the rate of cooling of the rail'during the period of transformation to obtain a substantially 'orm temperature throughout the heads of said rails and thereafter slowly and uniformly cooling said rails at least to temperatures approximating 550 C.

-8. In the manufacture of steel rails, the

' method of cooling the hot rolled rails which comprises rapidly cooling the rail to temperatures approximating the Y transformation temperature for the steel composition comprising the rail, retarding the rate of cooling of the rail during the period of transformation to obtain a substantially uniform temperature throughout; the heads of said -rails,'slowly and uniformly cooling said rails at least to temperatures approximating 550 C.

9. In the manufacture of steel rails, the' method of cooling the hot rolled railswhich comprises cooling the rail at any desired rate to a temperature below the critical temperature but above about the temperature of transformation of the steel comprising the said rail, equalizing the temperature difierentials in the rail, slowly and uniformly cooling the rail through said 7 transformation temperature at a rate substantially adapted to maintain all parts of the rail during transformation at substantially the same temperature, slowly and uniformly cooling the rail to temperatures approximating 550 C. and thereafter cooling the rail at a more rapid rate to atmospheric temperatures.

JOHN JOHNSTON.

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