JP3279384B2 - Manufacturing method of fatigue resistant rail - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a fatigue-resistant rail, in which the head and the bottom of the rail are work-hardened and a compressive residual stress is applied at the same time.

[0002]

2. Description of the Related Art In Japan and overseas, speeding up trains has become a paramount task with the aim of further improving the efficiency of railways.
Active studies are underway to achieve km / h. Under these circumstances, the safety of rails supporting trains is becoming more and more important in order to carry passengers safely to their destinations, and there is a strong demand for extending the service life of rails and improving their resistance to destruction. I have. Above all, in overseas railways, brittle cracks developed in the rail abdomen of the roller-corrected rail, leading to derailment and fatal injury, so the abdominal brittle crack growth characteristics were emphasized, and the abdominal brittle crack growth A rail with excellent characteristics is desired.

In order to increase the fatigue damage resistance of the rail, it has been found that the use of the residual stress is most effective in combination with the reinforcement of the rail material. It has been studied whether to impart effective compressive residual stress to fatigue damage resistance. For example, Japanese Patent Application Laid-Open No. 4-1
No. 7921 discloses that by reducing the roller diameter of a normal roller straightening machine in which the rollers are arranged in a staggered manner to 50 mm to 300 mm, the vicinity of the rail surface of the roller contact portion is plastically deformed more than the inside of the rail surface, and the rail surface is deformed. Techniques for inducing compressive residual stress in the layer are introduced. However, this technique is required when large compressive residual stress is required.
Since the straightening load of the roller straightening machine reaches approximately 150t, a small diameter roll of 50mm to 300mm cannot withstand the straightening load, so a backup roller is required, which complicates the structure of the straightening machine, increases equipment costs, and further maintenance. Due to problems such as cost and wastefulness of roller replacement due to roller wear, it is desired to develop a lower cost and more efficient residual stress control technique.

Further, it has been determined that the tensile residual stress in the longitudinal direction generated on the head surface and the bottom surface of the roller straightening rail has an adverse effect on the abdominal brittle crack growth characteristics, and as a result, the tensile residual stress is converted into a compressive residual stress. It was found that brittle crack growth was stopped by this, or the crack was propagated to the bottom side with a short crack length. However, there has not been found any means for efficiently reducing the residual stress on the rail head surface and the bottom surface by roller straightening to the compression side at low cost.

[0005]

In order to drastically solve the above-mentioned problems, it is necessary that the roller diameter of the roller straightening machine be as small as 50 mm to 300 mm, otherwise the rail surface will be reduced. No compressive residual stress. In other words, it is concluded that when the roller diameter is large, the plastic deformation of the rail surface layer is restricted due to the large contact frictional force between the rail and the roller. Furthermore, the present inventors have conducted a detailed study and found that, in roller straightening, the rail surface at the roller contact portion receives a compressive stress due to the straightening load and a compressive bending stress as a beam. It turned out that it was difficult to deform. This phenomenon is significantly affected by the roller diameter. Therefore, if there is no compressive bending stress as a beam, even a roller having a relatively large diameter can easily give a compressive plastic deformation in the longitudinal direction of the rail surface layer at the roller contact portion. It was also found that the rolling load at that time was significantly smaller than the load for normal roller correction.

[0006] Based on these findings, a roller straightening method was developed in which the head and bottom of the rail can be simultaneously changed to compressive residual stress using relatively small-diameter rolls facing each other after normal roller straightening. That is, both the head and the bottom of the rail subjected to the normal roller straightening exhibit tensile residual stress, but thereafter, only the rail head and the bottom surface layer are straightened and rolled simultaneously with a small-diameter roller, so that the longitudinal length of the surface layer is reduced. It was found that plastic deformation of compression can be easily applied in the direction, the tensile residual stress generated by the roller straightening can be changed to the compressive residual stress, and further, the reduction surface layer can be hardened by work hardening.

[0007]

SUMMARY OF THE INVENTION The present invention has been made based on the above findings, and the gist of the present invention is to provide a rail that travels through a straightening machine in which rolls are arranged vertically in a staggered manner. An upper roll having a concave cross-sectional shape having a roll diameter of 100 to 600 mm and a rail tread having a curvature equal to or equal to the curvature of the rail head by contacting the rail head, and a curvature in contact with the bottom of the rail; Is a pair or two or more pairs of reduction rolls composed of a lower roll having a convex cross-sectional shape of 200 to 1000 mm, and a Hertz stress of 900 to 3000 MPa.
This is a method for producing a fatigue-resistant rail that is reduced in the range of (1).

Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 illustrates the method of the present invention. In FIG. 1, 1 is a rail, 2 is a guide roll, 3 is a straightening roll, 4 is a pair of upper and lower rolls, or a pair of two or more reduction straightening machines. That is, while being guided by the guide rolls 2, the rails 1 that have passed through the bending straighteners in which the straightening rolls 3 are arranged vertically in a staggered manner are pressed down and straightened by one or two or more pairs of upper and lower rolls.

In the present invention, the upper and lower rollers of the draft reduction machine 4 have a diameter (D) of 100 to 600 as shown in FIG.
mm. As still another feature, the rail tread surface of the upper roll (a) in contact with the rail head side has a concave cross-sectional shape having a curvature equal to or less than 1.2 times the curvature of the rail head. On the other hand, the lower roll (b) in contact with the rail bottom has a curvature in the roll axis direction of 200 to 1000 mm.
Has a convex cross-sectional shape. Such a roll arrangement in the present invention is achieved by first straightening the rail with a conventional roller bending straightener having good productivity, and then using a reduction straightener to prevent fatigue damage and abdominal brittle crack propagation characteristics. It is intended to efficiently apply the residual stress at low cost.

That is, in the present invention, first, the straightening roll 3
Are arranged in a staggered manner in the running direction of the rail 1 to repeatedly straighten the running rail 1. In this state, although the rail is almost straight, the rail head and bottom have a tensile residual stress of about 200 MPa in the longitudinal direction of the rail. However, the rail head and bottom surface layer are subjected to compressive plastic deformation in the longitudinal direction of the rail by rolling down the straightening machine 4 of the opposing rolls thereafter to compress the rail head and bottom surface layer from tensile residual stress. It can be changed to residual stress.

Particularly, in the present invention, the diameters of the upper and lower rolls and the curvature in the axial direction of the roller of the straightening machine 4 are limited by applying a compressive residual stress to the rail head and the bottom surface layer, which increases fatigue resistance, and simultaneously work hardening. Range. That is, the reason why the diameter of the upper and lower rolls is limited to 100 to 600 mm is to efficiently give a stronger plastic deformation in the longitudinal direction of the rail surface layer in contact with the rolls than in the rail. Giving a plastic deformation stronger than the inside of the rail in the longitudinal direction of the rail surface layer is for work hardening the rail surface layer and imparting compressive residual stress.
When the roll diameter is smaller than 100 mm, work hardening and compression residual stress can be generated by plastic deformation of the rail surface layer, but the roller diameter is small, so the roller can withstand the load that gives strong plastic deformation to the rail surface. However, even if a backup roll is placed on the back of a small-diameter roll and can withstand a load that gives strong plastic deformation to the rail surface, work hardening and compressive residual stress due to plastic deformation of the rail surface layer are more than 100 mm in roller diameter. There is a problem that it is not much different from the one and that the equipment is expensive.
On the other hand, in the case of a roll having a diameter exceeding 600 mm, stronger plastic deformation begins to occur inside the rail than the rail surface layer,
Conversely, tensile residual stress is generated on the rail surface, and there is a problem that the fatigue damage resistance of the rail and the abdominal brittle crack propagation characteristics are impaired.

The upper roll contacting the roller head with the curvature in the roller axial direction has a concave cross-sectional shape having a curvature equal to the curvature of the head of the rail to be corrected or 1.2 times or less than the curvature of each part of the rail head. The reason for limiting to is to apply strong plastic deformation to the surface layer of the part where fatigue damage is likely to occur on the rail,
This is for generating a larger compressive residual stress. That is, if the radius of curvature is smaller than the radius of curvature of the head of the rail, the roll does not contact the surface of the rail head, and no plastic deformation can be applied to each part of the surface of the rail head. If the radius of curvature exceeds 1.2 times the curvature of each part of the rail head, the part where the roll contacts is only the center part of the rail head, and the residual tensile stress remains in the non-contact part, and the fatigue damage resistance of the rail Because it cannot be improved.

On the other hand, the reason for limiting the axial curvature of the lower roll in contact with the rail bottom to 200 to 1000 mm is as follows.
This is because the tensile residual stress in the vicinity of the center of the rail bottom generated by the roller straightening is changed into the compressive residual stress and, at the same time, the part is strengthened by work hardening. That is, if the roller axial curvature is 200 mm or less, the entire area near the center of the rail bottom where the residual tensile stress remains cannot be rolled down, and
If the curvature exceeds mm, the contact area at the bottom of the rail becomes large and sufficient work hardening and compressive residual stress cannot be induced at the roller contact portion.

The reason for limiting the Hertzian stress of each roll of the drafting straightener to 900 to 3000 MPa in the present invention is to generate plastic deformation necessary for minimizing irregularities on the rail surface on the rail surface layer. . That is, when the Hertzian stress on the rail surface in contact with the roll 4 is smaller than 900 MPa, the plastic deformation of the rail surface due to the rolling reduction becomes small, and the effect of improving the unevenness of the rail surface and the wavy deformation in the rail longitudinal direction is not sufficient. On the other hand, 3000MPa
When the Hertz stress exceeds, the effect of improving the unevenness of the rail surface and the wavy deformation in the longitudinal direction of the rail is almost the same as the case of 3000 MPa, and the rolling load becomes excessively large, which is not preferable because a problem arises due to facility restrictions. According to the method of the present invention as described above, it is possible to manufacture a rail having a long service life by applying a compressive residual stress.

[0015]

EXAMPLES Next, specific examples of the present invention will be described. In order to confirm the effectiveness of the rail residual stress control method according to the present invention, the residual stress control experiment by the rolling reduction according to the present invention and the roller correction with a conventional roller straightener were performed using a 12 m rail of JIS60k of ordinary carbon steel. The surface residual stress and the actual rail rolling fatigue damage life under water lubrication were compared. Correction conditions and respective results are compared between the method of the present invention and the conventional method, and are shown in Tables 1 and 2.

[0016]

[Table 1]

[0017]

[Table 2]

As is apparent from the test results, it is clear that the residual stress control method according to the present invention is very effective. That is, in the case of the conventional rail with the roller straightened, a tensile residual stress of 200 to 245 MPa is generated in the rail longitudinal direction at the top and bottom of the rail, and
In a rolling fatigue damage test of a real rail under water lubrication, a crack was generated from the top of the rail where tensile residual stress exists at a passing tonnage of 79.5 million tons. On the other hand, in the method of the present invention, in the case of the rolled rail, the residual stress in the rail longitudinal direction at the top and bottom of the rail is -167 as shown in Table 1.
Compression of -216 MPa, the rolling fatigue fatigue life under actual lubrication under water lubrication is 357.3 million tons, which is about four times longer than that of the conventional method, and shows extremely excellent rolling fatigue resistance.

Table 2 shows the residual stress and the like when the rails were straightened by five pairs of draft reduction machines. The reason that the rolling fatigue resistance is excellent is that the rail surface layer is work-hardened by light rolling, and that a large compressive residual stress is generated on the surface.
Because of the excellent rolling fatigue damage resistance, it is considered that there is a great effect on the rolling fatigue damage peculiar to a high-speed railway called "dark spot" which has been apparent in the Shinkansen and the like. On the other hand, the abdominal brittle crack growth characteristics were also separately tested, and the brittle crack growth length of the conventional rail reached about 400 mm, but when the residual stress was controlled by the present invention, the abdominal brittle crack was only 30 mm. It could be stopped just by making progress.

[0020]

As described above, the residual stress control method of the present invention can be efficiently carried out at a low cost without lowering the productivity, and further, the fatigue damage resistance of the rail and the abdominal brittle crack row growth characteristics are remarkably improved. It can be improved.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing one embodiment of the method of the present invention.

FIG. 2 is an explanatory view showing an example of a pressing roller used in the method of the present invention.

[Explanation of symbols]

 Reference Signs List 1 rail 2 guide roller 3 straightening roller 4 reduction roller

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kazunari Tanaka 1-1, Hibata-cho, Tobata-ku, Kitakyushu-shi, Fukuoka Nippon Steel Corporation Yawata Works (72) Inventor Takahito Akiga Tobata-ku, Kitakyushu-shi, Fukuoka No. 1-1 Tobata-cho Nippon Steel Corporation Yawata Works (72) Inventor Kazunori Seki 20-1 Shintomi, Futtsu-shi, Chiba Nippon Steel Corporation Technology Development Division (56) References JP 2-282426 (JP, A) JP-A-4-17921 (JP, A) JP-A-4-300026 (JP, A) JP-A-6-279846 (JP, A) JP-A-3-9222 (JP, A) U) (58) Fields surveyed (Int. Cl. ⁷ , DB name) B21D 3/05 B21D 3/02 C21D ⁷ /00-7/13

Claims (1)

(57) [Claims] A rail running through a straightening machine in which the rolls are arranged in a staggered manner in a vertical direction is provided with a roll having a diameter of 10 mm.
An upper roll having a concave cross-sectional shape having a radius of 0 to 600 mm and having a curvature equal to or less than 1.2 on the rail tread of the roll contacting the head of the rail, and a curvature in contact with the bottom of the rail; A pair of rolls having a convex cross section having a convex cross section of 200 to 1000 mm and a pair of two or more pairs of draft reduction machines, wherein the draft correction is performed in the range of 900 to 3000 MPa in Hertz stress. Manufacturing method.