US2067293A - Process of rolling rails - Google Patents

Description

Patented Jan. 12, 1937 UNITED STATES PTET DFFIQE PROCESS OF ROLLING RAILS Pennsylvania No Drawing. Application July 16, 1934, Serial No. 735,429

10 Claims.

My invention relates to the rolling of rails and particularly to the rolling of heavy section rails used in main line steam railway service.

The object of the invention is to provide a rolling process which will eliminate or avoid the formation of discontinuities in rails variously referred to as flakes, checks or shatter cracks.

In the heads of rails, particularly in those of large cross section weighing 100 pounds per yard or more in which a relatively high carbon or high manganese steel is used, it is common to find numerous cracks or checks beneath the surface. These cracks rarely if ever extend to the surface of the rail and in order to detect them it is nec essary to section the rail head and generally to etch the surface of the section. However, they may appear occasionally on the fractured surfaces of rails broken in the drop test as spots differing in color from the major portion of the fracture and sometimes referred to as grey spots.

The greater number of. these shatter cracks are roughly circular and vary from pin head size to a half inch or more in diameter. Their width is so slight that for all practical purposes the faces of the crack may be considered to be in contact. The bright appearance of the crack faces which occasionally may be found on a rail fracture indicates that the cracks do not contain chemically active gases.

That shatter cracks are not of themselves as serious defects as they might seem is attested by the fact that an appreciable percentage of the rails which are in regular service contain them. They are recognized, however, as starting points for the dangerous type of fatigue failures known as transverse fissures and much effort has been devoted to eliminating them. It is generally accepted that shatter cracks form as the rail cools from the rolling temperature and are due to stresses resulting from non-uniform expansion and contraction of the metal in different portions thereof. The steps heretofore taken to eliminate them have therefore centered around controlled cooling of the rails and the development of steel for same, which has the maximum ductility consistent with the hardness required in the rail. To my knowledge, however, no rail manufacturer has succeeded in completely eliminating shatter cracks by control of steel making practice, and the controlled cooling processes that have been proposed and used are somewhat cumbersome and expensive. Furthermore, a slow cooling process, if. effective in eliminating cracks, has a tendency to reduce the hardness and strength of the rail below optimum values.

My invention comprises rolling standard rail ingots to blooms and, contrary to usual practice, in allowing the blooms to cool to below the transformation range before rolling them to rails. Preferably they are allowed to cool to substantially atmospheric temperature.

Rail ingots are usually broken down to blooms of convenient size on one mill and the blooms subsequently rolled to finished rails on a second mill. Heretofore, the blooms have either been transferred directly from the first mill to the second mill for final rolling, or if a higher temperature is required in the finishing mill, they are charged into a reheating furnace as they come from the blooming mill and brought up to the desired temperature. It has been found that a considerable percentage of rails rolled in this manner contain the shatter cracks above referred an ingot having a cross section of 23 by 28 inches,

and after stripping the ingot from the mold, charge it into a soaking pit in which its temperature is equalized to a suitable rolling temperature, say 2200 F. I then roll the ingot to a bloom having a cross section about 10 inches square,

and shear this into lengths from each of which a convenient multiple ofv the length of a finished rail may be rolled. The blooms or billets thus produced are allowed to cool before charging them into the reheating furnace. The rate of cooling and the minimum temperature reached may be varied to suit the character of steel being used, and the convenience of mill operations. My preferred practice is to pile the blooms in lifts of convenient size and thus to secure a considerably delayed cooling or pile anneal. When thus cooled in piles the blooms are allowed to reach a temperature of 400 F. or below. Ordinarily they are allowed to cool to atmospheric temperature, and they may, in fact, be kept in storage until it is convenient to use them.

In a modification of the process the blooms may be held upon a hot bed as they come from the first mill until they have passed through the transformation range, as indicated by their becoming magnetic and may then be charged into the reheating furnace.

The subsequent operation in either case consists in reheating the blooms to normal rolling temperature and rolling them to finished. rail section.

Various heat treatments have been proposed and used on finished rails to harden and toughen them, and these treatments may be used to advantage on rails rolled by my improved process. In fact, heat treatments involving drastic cooling of the rails are more practicable when applied to the improved rails produced by my process than to rails made by standard methods, and my invention contemplates the use of such treatments in combination with the improved rolling process.

The cooling of the blooms prior to final rolling undoubtedly tends to stabilize and refine the structure of the steel and to halt the growth of coarse crystals which takes place during the usual reheating operation. I have found that cracks may form in the blooms while cooling, and it is possible that a certain amount of internal stress is thereby relieved. When such cracks occur, I have found that they are satisfactorily welded shut in the subsequent rolling, if such rolling involves a reduction of about one and one half times the cross sectional area of the final product. However, I do not limit myself to any theory which would account for the improved condition of the rails rolled by my process.

From an operating standpoint it is sufficient to note that my process practically eliminates the formation of shatter cracks and that the added cost of heating cold blooms to rolling temperature is, in many cases, offset by the resulting independence of open hearth and rail mill operations. Thus by working the rail mill from a stock of cold blooms, it is no longer necessary to hamper open hearth-operations by the limitations of the rail mill or vice versa. Furthermore, sound rails can be produced without providing equipment for the controlled cooling of the finished rails, and the output of the mill can therefore be made independent of the capacity of any such equipment.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent is:

l. The process of manufacturing rails substantially free from shatter cracks which comprises rolling blooms, allowing said blooms to cool to below 400 degrees F., reheating said blooms and rolling rails therefrom.

2. The process of manufacturing rails substantially free from shatter cracks which comprises rolling blooms, allowing said blooms to: cool to substantially atmospheric temperature, reheating said blooms and rolling rails therefrom.

3. In the manufacture of rails substantially free from shatter cracks the steps of rolling an ingot to a billet having a cross sectional area at least two and one half times that of the finished rail, allowing said billet to cool to below 400 degrees F., reheating said billet and rolling it to the finished rail.

4. In the manufacture of rails substantially free from shatter cracks the steps of rolling an ingot to a billet having a cross sectional area at least two and one half times thatof the finished rail, allowing said billet to cool to substantially atmospheric temperature, reheating said billet and rolling it to the finished rail.

5. The process of manufacturing rails substantially free from shatter cracks which comprises rolling blooms, allowing said blooms to cool to below 400 degrees F., reheating said blooms, rolling rails from said blooms and allowing said rails to cool normally in the air.

6. The process of manufacturing rails substanr tially free from shatter cracks which comprises rolling blooms, allowing said blooms to cool to substantially atmospheric temperature, reheating said blooms, rolling rails from said blooms and allowing said rails to cool normally in the air.

7. The process of manufacturing rails substantially free from shatter cracks which comprises rolling blooms, allowing said blooms to cool to a temperature below the gamma-alpha transformation range, reheating said blooms and rolling rails therefrom.

8. The process of manufacturing rails substantially free from shatter cracks which comprises rolling blooms, forming piles of said blooms while above their transformation range, allowing said blooms in said piles to cool to below 400 degrees F., reheating said blooms and rolling rails therefrom.

9. The process of manufacturing rails substantially free from shatter cracks which comprises rolling blooms, subjecting said blooms to retarded cooling to below 400 degrees F., reheating said blooms and rolling rails therefrom.

10. The process of manufacturing hardened rails substantially free from shatter cracks which comprises rolling blooms, cooling said blooms to below 400 degrees F., reheating said blooms, rolling said blooms to rails, and hardening said rails by accelerated cooling.

ALBERT P. SPOONER.