US2279716A - Rail treatment - Google Patents

Description

, Patented Apr. 14, 19 42 RAIL TREATMENT Henry W. Nieman, Bethlehem, Pa... assignor to Bethlehem Steel Company, a corporation of Pennsylvania No Drawing. Application September 8, 1938, Serial No. 223,961

Claims. (Cl. 148-215) My invention comprises the step of supplying heat energy to a rail, after it leaves the rolls, sufficient in amount and over a sufficient periodof time to efiect the removal of all consequential amounts of hydrogen before the rail ever cools to temperatures at which the hydrogen causes the formation of cracks. The nature of my invention will be more apparent following an exposition of the principles upon which it rests, and the presentation of illustrations of its application.

During the manufacture of rails, which manufacture includes the steps of making the steel from which the rails are rolled, more or less hydrogen may be dissolved in the hot steel, as steel, at high temperatures, both in the liquid and in the solid states, is capable of taking hydrogen into solution. I have discovered that rails, the steel of which has taken up hydrogen during manufacture, frequently contain small cracks in their heads. These cracks I designate "hydrogen cracks" to distinguish from cracks due to other causes, thermal cracks," for example. These cracks are dangerous in that they tend to develop during rail service into fissures which are large enough to cause rail failure- I have found that these cracks are formed, following the rolling operatlon, during the cooling to atmosphere temperatures from the rolling temperatures. The cracks are not formed, however, until the rails have reached a comparatively low temperature; when the rails are cooled in the normal way on the hot bed the cracks are formed at a temperature bel w 250 F., while with more rapid cooling they may occur at temperatures up to about 350 F. The temperature at which cracks form, due to the presence of hydrogen, I designate the hydrogen cracking temperature." It is to be understood that this temperature varies somewhat with d fferent conditions such as the rate of cooling, composition of the steel, and the amount of hydrogen present.

To prevent the formation of these cracks I treat the rails after their manufacture to remove the hydrogen before the rails have cooled from the mill heat to a temperature where the cracks could be formed. I do this by furnishing heat to the rails in amount and for a time sufiicient to cause the removal of substantially all the hydrogen before the rails have cooled to the hydrogen cracking temperature. Once the hydrogen has been removed the rails may then be cooled with impunity .so far as the formation of hydrogen cracks is concerned.

V As an example of removal of hydrogen, I may put the rails into a furnace and supply suflicient heat to keep the rails at a relatively elevated temperature until substantially all of the hydrogen has been removed. The time required for removing the hydrogen varies with the conditions, such as the temperature of the furnace, the amount of hydrogen present in the steel, and the composition of the steel. Probably the most important factor to consider is the temperature of the furnace. At a temperature just below the critical range the removal of hydrogen is most rapid. Holding the rails in a furnace having a temperature just below the critical range for an hour, or even somewhat less, is suflicient to remove substantially all of the hydrogen, even when the hydrogen is present in considerable amount. If the furnace is operated at lower temperatures, the time of holding must be increased.

At 1000 F. two hours is usually required where the hydrogen is present in considerable amount. At 700 F. four hours; and at 400 F. eight hours. At temperatures above the critical range the gas is removed more slowly than at temperatures just below the critical. Holding the rail in the furnace at a temperature of 1500 F., I found that it required about twice as long as if the rail were held in a furnace at 1200 F, to remove the same amount of hydrogen.

It should be noted that, in thus treating a rail, the time factor is important. Not only is heat energy furnished to the rail but it is furnished for a time long enough to get rid of all consequential amounts of hydrogen, the necessary length of time depending upon the temperature at which the rail is held in the furnace, the amount of hydrogen present, composition of steel, etc.

To remove the hydrogen it is not necessary that the rail be maintained at a constant temperature in the furnace. The important thing is to furnish heat to the rails for a sufliciently long period of time to maintain the rails above the temperature at which cracking occurs to eifect the removal of all consequential amounts of hydrogen. For instance, the rail may be cooled on the hot bed in the normal way to, say,

2 400 F., then placed in a furnace where the temperature rises slowly or rapidly to, say, 1200" F., and then removed and cooled to atmospheric temperature at any convenient rate. Again, the rail might be allowedto cool to 500 F., reheated to a temperature above the critical range, cooled rapidly through the critical range, and then cooled in the normal way on the hot bed. It

should be borne in mind, however, that the rail must-be maintained above the hydrogen cracking temperature suiliciently long to effect the removal of .all consequential amounts of hydrogen,'and that this time will vary depending upon the temperatures utilized for effecting the removal of hydrogen. For example, if the rail is cooled in the normal way to 400 F. and then reheated to 1000 F., a longer time would be required to permit of the escape or hydrogen than if the rail were to be reheated to a temperature just below the critical.

The essential thing to remember is that the rail must be maintained about 200 to 250" F. for a sufficient time to eliminate substantially all of the hydrogen, the time allowed for the removal of hydrogen varying with the temperatures to which the rails are subjected.

As will have been evident from the above description, the hydrogen by furnishing heat energy for a sufiicient time at temperatures above, as well as below, the critical range. In any case, however, it is important that the rapidity through the critical range in order to secure the necessary rail hardness.

My process is applicable to rails-whether cooled through the critical range on the hot bed in the usual way or subjected to a more accelerated cooling through the critical range by the application of water or other cooling medium.

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

1. A process for making a rail, comprising the steps of cooling the rail through the critical range at a rate at least as great as'that which normally occurs on the hot bed, placing the rail may be gotten rid of rail be cooled with suflicient- 400 degrees Fahrenheit to 1000 degrees Fahrenthe production of in a furnace and supplying heat thereto before it has cooled to 250 F. to maintain the rail at a temperature above 250? ,F. for a sufficient time to eliminate substantially all of the hydrogen before the rail has cooled to 250 F.

2. A process for making a rail, comprising the steps of cooling the rail through the critical range at a rate at least as great as that which normally occurs on the hot bed, placing the rail in a furnace and supplying heat thereto before it has cooled to 250 F. to maintam the rail at a temperature above 250 F. for a sufficient time to eliminate substantially all ofthe hydrogen before the rail has cooled to the hydrogen cracking temperature. z

3. A process of making a hot rolled steel .rail comprising holding said rail at a temperature of 400 to 1200 F. for a time of at least one hour to eliminate substantially all of the hydrogen and prevent cracking of said rail at lower temperatures, said treatment being applied subsequent to the production of the finished hot rolled product and prior to the cooling of the rail below 400 F. 4. A process of making a hot rolled steel rail comprising holding said rail at a temperature of heit for a time of substantially more than one hour, the time of such holding being increasingly greater as the temperature of holding is lowered, to eliminate substantially all of the hydrogen and prevent cracking of said rail at lower tempera tures, said treatment being applied subsequent to the finished hot rolled product and prior to the cooling of the rail below 400 degrees Fahrenheit.

5. A process of making a hot rolled steel rail, comprising holding said rail at a temperature of 250 F., to the critical range for a time of at least one hour to remove all consequential amounts of hydrogen and prevent cracking of said rail at lower temperatures, said treatment being applied subsequent to the production ofr the finished hot rolled product and prior to the cooling of the rail below 250 F.

HENRY W. NIEMAN.

cnn'rmicmz 0F comc'non. I Patent no. 2,279,716. April 1h, 191,2.

- mnmy u. n'mmw.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: P'ago 1, first column, 1111658, for "atmosphere" read --atmoepher1cpage 2, firat column, line 22 for "about" read --above--; and thatthe said Lettera Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office- Signedeni sea1edth1s'9th' day of June, A. n. 1912.

4 Hem-y \Tm Aradnle, v (Seal) I 4 Acting commissioner of iatents.