JPH1085823A - Method for cooling high-temperature rail - Google Patents

Abstract

PROBLEM TO BE SOLVED: To cool a rail so that the generation of bend on the rail is prevented and hardness with which the stipulated value is satisfied is obtained at the time of forcedly cooling the high-temp. rail just after hot rolling for making the head part of the rail into fine pearlitic structure. SOLUTION: The sole part of the rail is forcedly cooled, before its finish rolling, with water which is jetted from nozzles 6 to the high-temp. rail 1 not lower than the temp. of the austenitic region during hot rolling and, next, the head part and sole part of this rail are forcedly cooled till the transformation in the head part is completed with a heat treating device. In this way, the head part of the rail is made into fine pearlitic structure without generating bend on the rail.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a hot rail immediately after hot rolling or a hot rail heated to an austenite temperature or higher for heat treatment after hot rolling. For cooling a high-temperature rail by forcibly cooling with a cooling medium such as air or water in order to obtain a fine pearlite structure.

[0002]

2. Description of the Related Art In order to improve the wear resistance and toughness of a rail head having a fine pearlite structure, a hot rail immediately after hot rolling, or austenitic steel for heat treatment after hot rolling. For a high-temperature rail heated to a temperature equal to or higher than the zone temperature, a heat treatment (SQ) device
In a state of being restrained by a clamp, a heat treatment (SQ) for forcibly cooling the head with a cooling medium such as air or water is performed.

[0003] From the viewpoint of the material that the rail head has a fine pearlite structure, it is sufficient to forcibly cool only the rail head, but if only the rail head is forcibly cooled, the rail top and bottom are asymmetric. As a result, when the rail is unclamped after cooling, a problem occurs that the rail is largely bent due to the stress existing inside the rail.

In order to prevent such a problem, for example, Japanese Patent Application Laid-Open No. 61-60827 and Japanese Patent Application Laid-Open
Japanese Patent No. 4923 discloses a head of a rail 1 as shown in FIG.
A method of simultaneously forcibly cooling the head 1a and the sole 1b of the rail 1 by a cooling medium injected from the upper header 2 provided on the side 1a and the lower header 3 provided on the sole 1b of the rail 1 (Hereinafter referred to as prior art) is disclosed.

[0005]

According to the prior art, the residual bending after cooling can be reduced as compared with the case where only the rail head is cooled. However, if the cooling of the rail foot 1b by the lower header 3 is too strong, the cooling speed of the rail foot will increase, and the hardness of the rail foot will become higher than the specified value (Hv: 410).

For this reason, there is a limit in cooling the rail sole 1b. Forcibly cooling the rail sole 1b together with the head 1a of the rail 1 does not provide a sufficient bending measure. On the other hand, there is a strong tendency that the entire rail bends downward as shown in FIG. FIG. 5B shows an upward bending state. As a result, a pressing step for correcting the shape is required, which hinders production efficiency and raises the cost.

In the method of cooling the head 1a and the sole 1b of the rail 1 at the same time as in the prior art, the hardness of the rail foot is suppressed to a specified value (Hv: 410) or less, and the rail is cooled. It is difficult to prevent bending.

[0008] Accordingly, an object of the present invention is to solve the above-mentioned problems by cooling the hot-rolled high-temperature rail in order to improve the wear resistance and toughness of the rail head with a fine pearlite structure. When forcibly cooling with a medium,
It is an object of the present invention to provide a method for cooling a high-temperature rail which does not cause bending of the rail and has a hardness satisfying a specified value.

[0009]

As described above, in order to prevent a problem that a large bending occurs in the rail due to the stress existing inside the rail after cooling, the rail 1 is used.
The head 1a and the sole 1b of the rails are simultaneously forcibly cooled, but the cooling of the rail sole 1b is limited,
Simply cooling the rail foot 1b together with the head 1a of the rail 1 does not provide a sufficient bending measure. That is, it is considered that cooling of the sole of the rail is limited due to material restrictions, and insufficient cooling of the sole of the rail occurs.

Therefore, the present inventors have repeated research on means for compensating for insufficient cooling of the soles of the rails other than the cooling step in the heat treatment (SQ) apparatus. As a result, during hot rolling, the sole of the high-temperature rail above the austenite temperature is cooled by a cooling medium such as water, and the temperature of the sole of the rail is lower than that of the head of the rail. It has been found that the head of the rail can be formed into a fine pearlite structure without bending of the rail by cooling in a heat treatment (SQ) apparatus.

[0011] The present invention has been made based on the above-mentioned knowledge, and it has been proposed that a hot-rolled rail having a temperature equal to or higher than the austenite zone temperature be subjected to a cooling medium before finishing rolling. Then, the head and soles of the heads and soles in the heat treatment (SQ) device are applied to the high-temperature rail at a temperature equal to or higher than the austenite zone temperature where the soles are forcibly cooled during the hot rolling. It is characterized in that the rail head is forcibly cooled with a cooling medium until the transformation of the rail head is completed, and thus the rail head has a fine pearlite structure without bending of the rail.

[0012]

DETAILED DESCRIPTION OF THE INVENTION In the present invention, for a rail having a high temperature equal to or higher than the austenite zone temperature during hot rolling, the sole of the rail is forcibly cooled by a cooling medium such as water before finish rolling. .

FIG. 1 is a plan view showing an arrangement of water cooling nozzles of a cooling device arranged on a hot rolling line. FIG. 2 is a front view of the cooling apparatus, and a rail 1 has a head 1a and a sole 1b.
Is laid on its side. As shown in the drawing, seven nozzles 6 are directed toward the sole 1b of the rail 1 on the carriage 5 on the entry side of the finishing mill 4, for example, with a long diameter 520.
mm, so that an elliptical cooling area with a short diameter of 120 mm is obtained,
It is installed at a distance of 520mm in the line direction and 200mm away from the back of the rail foot. By the water jetted from the seven nozzles 6, the sole 1b of the rail 1 is uniformly and forcibly cooled.

The cooling of the sole 1b of the rail 1 must be performed before the finish rolling of the rail 1 which has been rough-rolled and intermediate-rolled by a hot rolling mill. The reason is that the subsequent stress becomes zero by finish rolling. If the sole 1b of the rail 1 is cooled after the finish rolling, thermal stress is generated in the rail due to rapid temperature change due to water cooling, and this thermal stress causes bending of the rail after cooling. As a result, a straight shape cannot be obtained.

The hot-rolled rail having a temperature equal to or higher than the austenite region temperature is carried into a heat treatment (SQ) device, and is fixed with a bending restraint clamp in the heat treatment (SQ) device. As shown, rail head 1a
By the upper header 2 provided on the side and the lower header 3 provided on the side of the rail foot 1b, both the head 1a and the foot 1b are forcibly cooled until the pearlite transformation of the head 1a is completed.

Thus, the structure of the head 1a of the rail 1 becomes a fine pearlite structure, and the rail after cooling does not bend even after the rail is naturally cooled by removing the bending restraint clamp.

The line speed during hot rolling in the hot rolling mill is changed to change the water cooling time (t) of the sole of the rail with respect to the high-temperature 25 m rail before finish rolling, and the water cooling time (t) is changed. The relationship with the bending (h) generated on the rail after the cooling was completed was examined, and the results are shown in FIG.

From FIG. 4, it can be seen that there is an optimum cooling time (t) at which the bend (h) can be made zero. That is, if the cooling time (t) for the high-temperature rail during hot rolling is controlled within a range of 3 to 3.8 seconds, the allowable range of the bending (h) is -62.5 mm / 25 m to 62.5 mm / 25 m. It can be.

[0019]

【Example】

Embodiment 1 Next, the present invention will be described with reference to an embodiment.
As shown in FIG. 1 and FIG.
In order to obtain an elliptical cooling area having a short diameter of 120 mm, seven water spray nozzles 6 are provided at a fixed distance a (520 mm) in the line direction and at a fixed distance b (200 mm) from the back of the rail foot.
Is placed on the entrance side of the finishing mill 4 and the sole device 1b of the 25m rail 1 is cooled by a cooling device having a length of 7m.
Water-cooling was performed for 3.5 seconds under the conditions of m ³ / h and a line speed of 3 m / min. Then, the rail whose foot sole 1b was water-cooled was finish-rolled by the finishing mill 4.

Next, the hot-rolled rail 1 is loaded into a heat treatment (SQ) apparatus, and is fixed by a clamp for restraining a bend.
From the state where the surface temperature was 790 ° C. to 500 ° C. below the end of the pearlite transformation of the rail head, both the rail head 1a and the rail sole 1b were forcibly cooled by a cooling medium such as air. Next, the rail 1 was detached from the clamp, and the rail was carried out of the heat treatment (SQ) device. After that, the rail 1 was naturally cooled on the cooling floor.

As a result of measuring the bending of the 25 m rail after cooling as described above, the bending was extremely small at 11 mm. [Comparative Example 1] In a hot rolling mill, without cooling the soles, heat treatment (SQ) was performed on a 25 m rail that had been subjected to normal hot rolling including rough rolling, intermediate rolling, and finish rolling. The apparatus was cooled under the same conditions as in Example 1. As a result of measuring the bend of the 25 m rail after cooling in this way, the bend was 398 mm, which was the specified value 6
It was much larger than 2.5 mm, and cold shape correction was required.

[0022]

As described above, according to the method of the present invention, before the finish rolling of a hot rail having a temperature equal to or higher than the austenite zone temperature during hot rolling, the sole of the rail is exposed to water or the like. By forcibly cooling with a cooling medium,
After cooling of the rail head and soles in the heat treatment (SQ) device, the bending generated on the rail after the release of clamp restraint is extremely small, and the bending in the subsequent cooling process hardly occurs. Satisfactory hardness is obtained, eliminating the need for a press step for shape correction,
Many industrially useful effects are obtained, such as the productivity does not decrease.

[Brief description of the drawings]

FIG. 1 is a plan view showing a water cooling nozzle arrangement of a cooling device arranged in a hot rolling line for carrying out a method of the present invention.

FIG. 2 is a front view of FIG.

FIG. 3 is a layout view of a rail cooling header used in the method of the present invention.

FIG. 4 is a diagram showing a relationship between water cooling time and bending in a hot rolling mill.

FIG. 5 is an explanatory diagram showing a downward bending state and an upward bending state of a rail.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Rail 1a Rail head 1b Rail foot 2 Upper header 3 Lower header 4 Finishing mill 5 Carrier 6 Nozzle

Claims (1)

[Claims] 1. A hot-rolled rail having a temperature equal to or higher than an austenite zone temperature is forcibly cooled by a cooling medium before finishing rolling of the rail, and then hot-rolled. In the heat treatment (SQ) device, the head and soles of the high-temperature rail whose temperature is equal to or higher than the austenite region where the soles of the rails are forcibly cooled are forcibly cooled by a cooling medium until the transformation of the rail heads is completed. Thus, a method of cooling a high-temperature rail, characterized in that the rail head has a fine pearlite structure without bending of the rail.