JP2001098324A - Ear cracking preventive hot rolling method for stainless steel to prevent - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perfectly prevent the edge cracking of the both edges of a steel sheet or a steel strip at the time of rolling without reheating a slab in hot rolling for stainless steel and to produce a stainless steel sheet or steel strip free from defects without deteriorating the productive efficiency and fuel consumption unit. SOLUTION: A slab of stainless steel is heated at 1,100 to 1,250 deg.C, thereafter, at the time of rough rolling (before the rough rolling or in the process of the rough rolling), the edge faces of the slab made parallel to the rolling direction by finish rolling are applied with rolling reduction in the draft of >=20 mm at >=980 deg.C which is a recrystallization temperature region by using an edger or the like, and the crystal grains are refined to increase its strength, by which the ear cracking of both edge parts (edge face cracking) in the steel sheet or steel strip at the time of the rolling is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hot rolling method for preventing a steel plate or a steel strip from cracking during hot rolling of stainless steel.

[0002]

2. Description of the Related Art In hot rolling of stainless steel, there is a problem that defects such as edge cracks occur on both end faces parallel to the rolling direction of a steel plate or a steel strip during rolling.
The following hot rolling method for stainless steel has been proposed.

(1) JP-A-7-118742 (method for hot rolling stainless steel) When hot rolling austenitic stainless steel having corrosion resistance in a highly oxidizing environment, the stainless steel slab is 1200 After soaking in a temperature range of less than or equal to ° C, tentative rolling is performed, and then the length of the steel slab is partially rolled while being cooled with water, and then reheated at a temperature of 1200 ° C or less. By performing the lengthening rolling at a temperature of at least ° C, the heating temperature is defined in the two-heating hot rolling, and a part of the width rolling and the lengthening rolling is continuously performed in the first heat, Eliminating side cracks and warpage such as surface cracks and edge cracks during rolling is performed so that a steel sheet having good flatness can be obtained.

(2) Japanese Patent Application Laid-Open No. 5-263133 (Method of producing B-containing austenitic stainless steel without occurrence of ear cracks) After casting B-containing austenitic stainless steel used for a neutron shielding material, 1100 to 1220 ° C , And then subjected to intermediate hot rolling at a temperature of 950 ° C. or more at a rolling reduction of 30 to 70%.
Heating in a temperature range of １２1220 ° C. for 30 minutes or more, final hot rolling to a predetermined thickness, and refining the boride, so that a B-containing austenitic stainless steel without edge cracks can be obtained. .

[0005]

However, the conventional hot rolling method for stainless steel as described above is a method in which heating is performed once to perform a certain degree of rolling, and then heating is performed again to finish rolling. The production efficiency and the fuel consumption rate are greatly deteriorated as compared with ordinary rolling. In addition, during mass production, reheating is a significant shackle and is disadvantageous.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a hot rolling of stainless steel without reheating a steel slab and a steel plate or a strip at the time of rolling. Hot-rolling method of stainless steel that can completely prevent edge cracks at both ends of stainless steel and can produce stainless steel plates or strips without defects without deteriorating production efficiency and fuel consumption rate Is to provide.

[0007]

According to the present invention, in hot rolling of stainless steel, a slab is heated to a predetermined temperature and then subjected to finish rolling during rough rolling (before or during rough rolling). The edge of the steel slab that is parallel to the direction is reduced by an edger or the like in the recrystallization temperature range, and the edge cracks of stainless steel to prevent edge cracks (end face cracks) at both ends of the steel plate or strip during rolling. This is a hot rolling prevention method (claim 1).

In a conventional hot rolling method shown in FIG. 1 (a), it was found from a laboratory test that a coarse crystal structure of an end face of a steel slab remained after finish rolling, and ear cracks were generated based on the coarse grains. In the present invention, as shown in FIG. 1 (b), before the rough rolling (bending rolling) of the steel slab is started or during the rough rolling (bending rolling), it is rolled at the time of finish rolling using an edger or the like. By rolling down the end face of the steel slab parallel to the direction in the recrystallization temperature range, the crystal grains are refined and the strength is increased, and edge cracks at both ends of the steel sheet or the steel strip during rolling are completely prevented.

[0009] In order to refine the crystal grains, it is necessary to perform the reduction in the recrystallization temperature range.
The recrystallization temperature range is 980 ° C or higher, and the reduction is performed at 980 ° C or higher (claim 3). The crystal grains can be refined by applying a reduction at any temperature in the temperature range of 980 ° C. or higher. In a temperature region lower than 980 ° C., the region becomes an unrecrystallized region. Therefore, even if a reduction is applied, the crystal grains cannot be refined.

It is desirable that the amount of reduction of the end face of the steel slab is 20 mm or more at both end faces. That is, as shown in FIG. 3, the total reduction amount is 10 mm (the reduction amount per pass is 5 m).
In the case of m × 2 passes), the amount of edge cracks can be reduced as compared with the conventional hot rolling method, but the effect of preventing ear cracks varies, and the total reduction amount is 20 mm (the reduction amount per pass is 10 mm × 2 passes).
In this case, ear cracks can be completely prevented, so that the total reduction amount is 20 mm or more, and ear cracks are completely prevented.

[0011] The heating temperature of the billet is 1100-1250 °.
The range of C is desirable (claim 2). Generally, as shown in FIG. 4, when the heating temperature of the slab is lower than 1100 ° C., the occurrence rate of rolling defects increases, and when the heating temperature is higher than 1250 ° C., the occurrence rate of rough surface increases.
The range is 50 ° C. In this temperature range,
The slab temperature at the time of slab end face pressure reduction can be 980 ° C. or higher.

The crystal structures of a test piece heated at 1230 ° C. for 2 hours were allowed to cool as they were, and those of the test pieces which were allowed to cool by applying only an edger pressure to the end face of the test piece were compared.
FIG. 5 (a) shows the crystal structure of the material which was left to cool only by heating, and FIG. As a result, it was found that the crystal structure was clearly different between the cooling after heating and the cooling after the edger, and the crystal grain was finer in the case where the edger was applied.

Further, in order to confirm that the difference between the crystal grains is inherited to this point, the crystal grains when both the test pieces were rolled until the tentering was completed were also observed (FIG. 6).
(a) and FIG. 6 (b)). Thus, it was confirmed that there was a difference in crystal grains after the tentering as well as immediately after the reduction by the edger. From the above results, it was proved that by rolling down the end face of the steel slab in the recrystallization temperature range, the crystal grains were refined and the strength was increased, so that ear cracks could be prevented.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on one embodiment shown in the drawings. FIG. 2 is an example in which the edge crack preventing hot rolling method of the present invention is applied to a thick plate production line. As shown in a schematic side view of the rolling line in FIG.
An edger 2 for pressing down both ends of the slab with a pair of left and right vertical rolls is provided in front of the rough mill 1, and the rough mill initial edging method of the present invention is performed in the following procedure (FIG. 2).
(b) is a schematic plan view showing the flow of the slab).

(1) The slab S heated to 1100 to 1250 ° C. in a heating furnace is turned 90 ° by a turntable or the like so that the slab width direction becomes the rolling direction. Tent rolling is performed.

(2) The slab S ₁ which has been subjected to the tentering rolling is rotated by 90 °.
By turning as the slab width direction perpendicular to the rolling direction, subjected to edging 2 paths edger 2 from this state, the rolling direction and parallel to both end surfaces of the slab S _1, parallel to the rolling direction in other words the finish rolling Both ends E are reduced. At this time, the slab temperature is 980 ° C. or more, and the rolling reduction is 10 mm or more per pass.

(3) After the edging is completed, the slab S ₁ is moved to 90
° Turn so that the slab width direction is the rolling direction,
From this state, two-pass tentering rolling is performed by the rough mill 1.
(4) the tentering rolled slab S ₂ by 90 ° turn as the slab width direction perpendicular to the rolling direction, performs out length rolled one pass in the rough mill 1 from this state.

(5) The slab is sent to a finishing mill (not shown) to finish it into a steel plate having a predetermined thickness and length. In this finish rolling, the edging portion of the slab is parallel to the rolling direction, and the edging refines the crystal grains at both ends of the steel plate and improves the strength. Is prevented.

[Numerical Example] An actual machine test was performed using test materials. The test material was SUS304 whose material is shown in Table 1,
The conventional hot rolling method and the hot rolling method of the present invention were implemented with a slab thickness of 200 mm, L / L rolling in the rolling direction, and a rolling thickness of 8 to 25 mm. In both the conventional method and the method of the present invention, the heating temperature is set to 1230 ° C. Also, in the conventional method, rough rolling is performed without rolling down the edge of the slab parallel to the rolling direction by the edger, and in the method of the present invention, the rolling down of the slab end face by the edger is reduced by 5 mm / pass (both ends) before starting the rough rolling. 2) for 10 mm / pass (at both ends)
A pass was performed and then rough rolling was performed.

[0020]

[Table 1] The graph shown in FIG. 3 is a test result in which the amount of edge cracks with respect to the rolling thickness is compared between the conventional method and the present invention. Was observed. In the case where the reduction amount was 5 mm / pass (total reduction amount 10 mm), the edge cracking amount was reduced as compared with the conventional material, but there was variation in the prevention of the ear cracking. 20mm)
In the case of the above, the ear cracks could be completely prevented. From this, the total reduction of the end face of the steel slab is 2
It is desirable to set it to 0 mm or more.

Although the above description has been given of hot rolling of a thick plate, the present invention is not limited to this, and it goes without saying that the present invention can be applied to hot rolling of a steel strip.

[0022]

According to the present invention, in the hot rolling of stainless steel, after the steel slab is heated to a predetermined temperature, the rolling is applied to the end face of the steel slab in the recrystallization temperature range at the time of rough rolling.
By using a simple method, it is possible to completely prevent edge cracks at both ends of a steel plate or a steel strip during rolling without reheating the steel slab as in the conventional method, thereby deteriorating production efficiency and fuel consumption rate. A stainless steel plate or a steel strip without defects can be manufactured.

[Brief description of the drawings]

FIG. 1 is a flow chart showing a conventional rolling method and a hot rolling method for preventing cracking of stainless steel according to the present invention.

2 (a) is a schematic side view of a thick plate rolling line, showing an example of a hot rolling method for preventing cracking of stainless steel according to the present invention. FIG.
(b) is a schematic plan view showing the movement of the slab.

FIG. 3 is a graph comparing the results of measures to prevent ear cracks by an actual machine test between the conventional method and the method of the present invention.

FIG. 4 is a graph showing a relationship between a slab heating temperature, a rolling failure rate, and a rough surface occurrence rate.

FIG. 5 is a photograph of a crystal structure of a metal. FIG. 5 (a) shows a case where the slab is heated and then left to cool, and FIG. 5 (b) shows a case where the slab is cooled by applying an edger.

FIG. 6 is a photograph of a crystal structure of a metal, where (a) is a photograph of FIG.
(B) shows the case where the slab of FIG. 4 (b) was tentatively rolled.

[Explanation of symbols]

 S: Slab (slab) E: Slab end face (edging point) 1: Coarse mill 2: Edger

Claims (4)

[Claims] In the hot rolling of stainless steel, after the slab is heated to a predetermined temperature, rolling is performed in the recrystallization temperature range on the end surface of the slab that is parallel to the rolling direction by finish rolling during rough rolling. A hot rolling method for preventing cracking of stainless steel. 2. The heating temperature of the billet is 1100 to 1250 °.
2. The hot-rolling method as claimed in claim 1, wherein the temperature is in the range of C. 3. The hot-rolling method according to claim 1, wherein the recrystallization temperature range is 980 ° C. or higher. 4. The method according to claim 1, wherein the amount of reduction of the end face of the billet is 20 mm or more.
3. The hot-rolling method for preventing cracking of stainless steel according to 2.