JPH0542301A - Manufacture of rail - Google Patents

Abstract

PURPOSE:To improve the acceptance rate of product inspection by rolling so that the direction of segregation of a cast bloom which is continuously castled and which is cut in a prescribed length is made in the perpendicular direction to the web of rail. CONSTITUTION:The cart bloom 40 is rolled so that both long sides of the bloom correspond to the parietal face and bottom face of rail. Consequently, the center segregation S which is planarly present in the intermediate part in the direction of the short sides of the cast bloom 40 remains in a good state in the web part between the parietal face and the bottom face of rail, so excellent macroscopic structure can be obtained. By cutting the corner parts in the end parts in the longitudinal direction of the flat cast bloom which is cut in a prescribed length in the direction perpendicular to the long sides, generation of fish tail in the end part in the longitudinal direction in rough rolling can be prevented, difference between rolling reduction ratio in the directions of the long side and the short side is mitigated and generation of longitudinal crack in the end part can be prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rail manufacturing method using a flat bloom slab continuously cast and cut into a predetermined length.

[0002]

2. Description of the Related Art A flat bloom slab continuously cast and cut into a predetermined length is manufactured into a rail through rough rolling, intermediate rolling and finish rolling. In the rough rolling, the flat bloom slab is rotated around the longitudinal axis with an appropriate number of passes during rolling, stretched by changing the rolling direction by 90 degrees, and the cast structure is tempered.

In such rolling process, flat bloom slabs are apparent in Iron and Steel Handbook III (2), p. 767, FIG. 9.78 (edited by Japan Iron and Steel Institute, published January 20, 1982). Then, the cross section is reduced to a rectangular cross section while maintaining a similar shape. Then, after that, rolling is performed so that the short side of the flat cross section becomes the rail top surface and bottom surface.

That is, rolling is performed so that the direction of the center segregation line generated in continuous casting coincides with the direction of the rail web. This is because the rolling ratio of the long-side direction and the short-side direction of the bloom slab having a rectangular cross section is almost the same in the rough rolling, so that the occurrence of fish tail at the end as shown in FIG. It is intended to prevent the occurrence of cracks in intermediate rolling. After intermediate rolling, finish rolling is carried out and the final product is rolled into a cross-sectional shape.

[0005]

However, in recent years,
Since the inspection standards of customers were reviewed, among rails manufactured through the above rolling process, those manufactured from bloom slabs with large center segregation may not pass the macro inspection of the product cross section. There is a possibility that it will occur. An example of such a macro inspection is the 1989 version, AREA.
(American Railway Engineering Associatin).

In order to reduce the center segregation of the slab by continuous casting as described above, it is naturally conceivable to improve the operation at the stage of smelting and casting of steel, but the production cost rises. Therefore, cheap and easy-to-implement improvement measures have been sought.

The present invention has been made in view of the above circumstances, and is a method for manufacturing a rail that improves the passing rate of product inspection, reduces the occurrence of cracks at the end during rolling, and improves work efficiency. Is to provide.

[0008]

In the rail manufacturing method according to the present invention, a flat bloom slab continuously cast and cut to a predetermined length is rolled from a flat section to a square or a section close to a square. In the rail manufacturing method that goes through the process, the top surface and the bottom portion of the rail correspond to the long side of the flat bloom slab. Further, the corner portion of the end portion in the longitudinal direction of the flat bloom cast piece cut into a predetermined length is cut in a direction perpendicular to the long side.

A flat bloom cast slab is rolled from a flat cross section to a square or square cross section by increasing the reduction ratio in the long side direction and decreasing the short side direction, and then rolling the flat slab into a square or square section. The segregated portion, which was present in a planar shape in the portion, remains in a rod shape in the central portion of the rectangular cross section, and a good macrostructure can be obtained.

Further, by cutting the corner portion of the end portion in the longitudinal direction of the flat bloom slab cut into a predetermined length in a direction perpendicular to the long side, the fish is formed at the end portion in the longitudinal direction in rough rolling. It is possible to prevent the tail from being generated, and the difference in the reduction ratio between the long side direction and the short side direction is alleviated,
It is possible to prevent vertical cracks from occurring at the ends.

[0011]

Embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a process diagram showing a manufacturing process of a 50N rail. The bloom slab 40 continuously cast and cut into a predetermined length has dimensions of 250 mm × 350 mm square. In the rough rolling step, first, bloom slab 40
The caliber B1 and B2 follow the path of the arrow to increase the reduction ratio in the width direction (direction of arrow 42) to the reduction ratio in the thickness direction (direction of arrow 41) so that the cross section becomes a square or a square. To roll. The caliber B1 and B2 whose cross-sectional shape is a square or a shape close to a square is rolled after caliber K11 so that the direction of the center segregation line indicated by S is the width direction of the rail (arrow direction in FIG. 2). To do.

That is, the two long sides of the bloom slab correspond to the top surface 1 and the bottom surface 3 of the rail shown in FIG. 2 (the direction of the segregation line of the bloom slab is perpendicular to the web portion 2 of the rail). Rolling). As a result, the center segregation indicated by S, which was present in the plane in the middle portion of the bloom slab in the short side direction (arrow 41 direction), was good in the web portion 2 between the top surface 1 and the bottom surface 3 of the rail. It will remain in such a state. In order to reduce the generation of fish tails, it is desirable to increase the number of passes of calibers B1 to K3 in rough rolling.

Next, in the rough rolling, the difference in the rolling ratio of the bloom slab 40 in the thickness direction (arrow 41 direction) and the width direction (arrow 42 direction) is alleviated to prevent the generation of fish tails and the intermediate rolling. The cutting of the corners of the cast slab that reduces the occurrence of cracks at the ends will be described. Bloom slab 4
Cut off the corner at the end of 0 (hereinafter referred to as corner cut)
The formed shape is shown in FIG. The cross-sectional shape of the bloom slab 40 is 250 mm × 355 mm, and FIG. 3A shows a case where both corners of the end of the bloom slab 40 are corner cut. Length is a,
It is shown by b. Further, FIG. 3B shows a case where one corner of the end portion is obliquely cut toward the other corner.

Table 1 shows the numerical values of the corner cut dimensions a and b.

[0015]

[Table 1]

Test No. 1 has no conventional corner cut and is rolled so that the top and bottom surfaces of the rail correspond to the short side 43 of the bloom slab. Also, test number 2
All of Nos. 5 to 5 are rolled so that the top and bottom surfaces of the rail correspond to the long side 44 of the bloom slab (so that the segregation direction of the bloom slab is perpendicular to the web of the rail). Of test numbers 2 to 5, test number 2 is a corner cut as shown in FIG. 3 (A), but the cutting length a in the long side direction of the bloom slab is not so large.

Test number 3 is obtained by increasing the cutting length a of the bloom slab in the long side direction from that of test number 2, and the uncut portion of the long side of the bloom slab is
It is 1/3 of the length of the long side. Test number 4 is test number 3
The cutting length a of the bloom slab in the long side direction is made larger than that of No. 1, and the uncut portion of the long side of the bloom slab is zero. Test number 5 is shown in FIG.
It is cut as in (B).

As a result of this test, the test No. 1 had cracks at the ends during intermediate rolling as shown in FIG. On the other hand, in the case of test number 2, there was a tendency for improvement against cracking. Test Nos. 3 and 4 were satisfactory without causing any hindrance to the rolling process. In Test No. 5, there was a tendency that the temperature at the sharp corner side of the bloom end decreased during rolling, and it was bent and rolled toward the sharp corner side. Also, if the corner cut dimension to the long side is less than 1/5 of the length of the long side 44, the effect on cracking is reduced, so the corner cut dimension to the long side is 1/5 of the long side length. It is desirable to be set to ½.

The invention of the present application is not limited to the above-mentioned embodiment, and the design can be changed as appropriate such that corner cutting is performed at one or both ends of the bloom end.

[0020]

According to the present invention, the segregation direction of the bloom slab continuously cast and cut into a predetermined length is perpendicular to the web of the rail (the top and bottom surfaces of the rail are bloom-cast). Rolling (toward the long side of the strip) improves the product inspection pass rate. Further, corner cutting of the end of the bloom slab prevents the occurrence of edge cracking during rolling, thereby improving the efficiency of rolling work.

[Brief description of drawings]

FIG. 1 is a process drawing showing a procedure for manufacturing a rail from a bloom cast piece.

FIG. 2 is a perspective view showing a rail.

FIG. 3 is an explanatory view showing a corner cut of a bloom cast piece.

FIG. 4 is a schematic view showing edge cracks generated in an intermediate rolling process.

[Explanation of symbols]

 1 top surface 2 web 3 bottom surface 40 bloom slab 43 short side 44 long side S line indicating the direction of segregation line

Front Page Continuation (72) Inventor Hideyuki Yamanaka 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Steel Pipe Co., Ltd.

Claims (2)

[Claims] 1. A method for manufacturing a rail, which comprises a step of rolling a flat bloom slab continuously cast and cut into a predetermined length from a flat cross section to a square or a section close to a square, wherein a top surface and a bottom portion of the rail are A rail manufacturing method characterized in that it corresponds to the long side of a flat bloom slab. 2. A flat bloom cast slab cut into a predetermined length is cut off at a corner portion at an end portion in a longitudinal direction in a direction perpendicular to a long side, and then manufactured. Rail manufacturing method.