JPH0751729A - Descaling and pickling method for hot rolled stainless steel sheet and its line - Google Patents

Abstract

PURPOSE:To prevent the intergranular corrosion due to mixed acids by subjecting a hot rolled stainless steel sheet to a grinding treatment by a mechanical scale breaker, then to a shot blasting treatment, followed by a sulfuric acid pickling treatment and a grinding treatment by grinding brush rolls and finally a nitric acid electrolytic treatment. CONSTITUTION:The mechanical scale breaker, shot blasting device, sulfuric acid tank, grinding brush roll device and nitric acid electrolytic tank are arranged in this order in the line for descaling the hot rolled stainless steel sheet subjected to hot rolling and annealing. The heavy grinding brush roll device is used as the grinding brush roll device of this line. The heavy grinding brush roll referred to here is a grinding brush roll formed by spirally arranging bar- shaped bodies and grinding element members consisting of spring members bonding these bar-shaped bodies, specifying the angle between the surface in the longitudinal direction of the roll shaft and the spiral surface of the grinding element members to >=3 deg. and providing the respective grinding element members with bulging parts for regulating the movement of the grinding element members in adjoining directions.

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 hot rolled stainless steel sheet, and more particularly to a descaling / pickling method and its line.

[0002]

2. Description of the Related Art In descaling and pickling of hot rolled stainless steel strips, mechanical scale breakers (referred to as MSB), shot blasts, sulfuric acid tanks, mixed acid tanks, and (nitric acid + hydrofluoric acid) are generally used. Descaling / pickling equipment is used. A nitric acid tank may be installed after the mixed acid tank, if necessary.

In Japanese Patent Laid-Open No. 53-108830, the MSB
According to the method, a scale is divided by, a pre-pickling is performed, shot blasting is used, grinding is performed with a rotating brush, and then pickling is performed.

[0004]

It should be noted here that in any of the conventional methods, a mixed acid of nitric acid and hydrofluoric acid (hereinafter referred to as mixed acid) is used for pickling steel strip. It is that. The mixed acid removes scale, which is an oxide, by the reducing action of hydrofluoric acid, and passivates the surface of the stainless steel strip with nitric acid to generate corrosion resistance peculiar to stainless steel. In addition, mixed acid can change the strength of its action by changing the mixing ratio and temperature of each, and it is relatively easy to deal with differences in the amount of dissolution due to the components of the steel strip, etc. is there.

However, mixed acid has a drawback that it selectively erodes grain boundaries when the steel strip is not in a state of complete solution heat treatment or when stress is extremely concentrated on the surface of the steel strip. This intergranular erosion remained as microscopic flaws even after cold rolling, and became a factor that impedes gloss and polishability.

Therefore, in the case of producing a bright annealed material which is particularly required to have a luster or a product which is required to be abraded, cold rolling is carried out after polishing the surface of the steel strip with a grinder to remove the grain boundary erosion grooves. Is going. Further, in order to remove the grain boundary erosion groove, the concentration and temperature of the mixed acid are raised and dissolved in the acid. If such a method is adopted, if the metal content dissolved in the mixed acid exceeds the allowable dissolution amount, it will be precipitated as sludge in the pickling tank or tank, so it is necessary to clean this sludge regularly.

An object of the present invention is to provide a descaling / pickling method for a stainless hot-rolled steel strip and a line therefor, which solves the above-mentioned problems associated with grain boundary erosion.

[0008]

[MEANS FOR SOLVING THE PROBLEMS] In the present invention, when descaling a hot rolled and annealed stainless hot rolled steel sheet, it is first treated by a mechanical scale breaker, then shot blasting treatment, and then sulfuric acid pickling treatment. Then, a descaling and pickling method of the hot rolled stainless steel sheet is characterized by performing a grinding treatment with a grinding brush roll, and finally performing a nitric acid electrolytic treatment. Further, the present invention is a hot rolled and annealed stainless steel. A descaling / pickling line for stainless hot-rolled steel sheets, characterized in that a mechanical scale breaker, a shot blasting device, a sulfuric acid bath, a grinding brush roll device, and a nitric acid electrolysis bath were placed in that order in the line for descaling hot-rolled steel sheets. is there. In the above line, it is desirable to use a heavy grinding brush roll device as a grinding brush roll device.

The term "heavy grinding brush roll" as used herein refers to Japanese Patent Laid-Open No.
As disclosed in JP-A-315582, a rod-shaped body containing abrasive grains having a diameter of 3 mm or more is radially mounted on a roll shaft, and has a polishing performance almost equal to that of a grinding wheel or a polishing disk. Is to have. More specifically, in a brush roll mounted with a rod-shaped body containing abrasive grains having a diameter of 3 mm or more on a roll shaft, radially with respect to the shaft circumference through a spring material, and assembled in the axial direction. The rod-shaped body and the grinding element body made of a spring material that is coupled to the bar-shaped body are arranged in a spiral shape, and the angle between the surface in the roll axis length direction and the spirally arranged surface of the grinding element body is 3 degrees or more. It is a grinding brush roll in which each grinding element body is provided with an enormous part that restricts the movement of the body in the adjacent direction.

[0010]

According to the present invention, by using the grinding brush rolls in the above order without using the mixed acid generally used in the descaling of the hot strip of stainless steel,
Since grain boundary erosion can be prevented, there are no factors that hinder gloss, and the gloss after cold rolling improves. As a result, the surface grinder process can be omitted even when producing a bright baked pure material, and labor saving and process saving can be realized. Further, for those which require polishing depending on the purpose of use, the surface roughness has already been lowered, so that the polishing property is improved and the number of polishing steps can be reduced.

The sludge generated by grinding using the heavy grinding brush roll has relatively large particles and is a metal powder, so that it can be easily settled and separated. Alternatively, electromagnetic separation is possible. However, when pickling (mixed acid treatment) is performed as in the past, metal ions (F
Separation of e ^{n +} , Cr ^{n +} , Ni ^{n +} ) is very difficult and costly.

On the other hand, when the amount of this metal ion exceeds the allowable amount of dissolution, it becomes sludge (main component FeF ₃ .3H ₂ O), which is precipitated in the pickling tank or circulation tank, and it is necessary to perform periodical removal work. This sludge has very small particles (5-200μ
Therefore, it is difficult to separate, and at the same time, it is a dangerous work since it is handled at the same time as the mixed acid. However, the present invention can solve all the above problems.

[0013]

EXAMPLE FIG. 1 shows a descaling / pickling line 1 according to the present invention.
The cross-sectional schematic diagram of an Example is shown. Figure 2 shows conventional descaling.
It is a cross-sectional schematic diagram of the typical example of a pickling line. A metallographic photograph of the surface of an austenitic stainless hot-rolled steel strip descaled by the line of the present invention shown in FIG. 1 and the conventional line shown in FIG. 2, and further the steel strip surface after cold rolling and annealing pickling 3 shows a photograph of the metal structure in comparison with FIG.

In the method of the present invention, since descaling by mixed acid is omitted, the grain boundary erosion which is conventionally seen is not seen, but only the grinds by the heavy grinding brush roll are seen.
Furthermore, it can be seen that when this is cold rolled, the concave flaws found in the conventional method are not seen. FIG. 4 is a comparison of the glossiness of the plate surface after cold rolling according to the method of the present invention and the conventional method, and FIG. 5 is a comparison of the roughness.

As the results of the surface metallographic photograph of FIG. 3 are supported, when the steel strip obtained by the method of the present invention is cold-rolled, its glossiness is (here, the glossiness is JIS Z874).
70 by the average value (according to the specular gloss measurement method specified in 1)
It has improved from 0 to 800, and the average roughness (Rz) is 1.
Since it is from 9 μm to 0.6 μm, the average number of polishing is
Halved from 4.1 to 2.0.

[0016]

EFFECTS OF THE INVENTION According to the present invention, in descaling of a hot rolled stainless steel strip, instead of using a conventional mixed acid, grinding is performed with a grinding brush roll, and passivation is then performed with nitric acid. This has made it possible to improve the glossiness after cold rolling and to omit the grinder step before cold rolling. In addition, since sludge treatment by human power in the mixed acid tank is eliminated and grinding dust removal processing by a grinding brush roll can be easily automated, dangerous work can be eliminated and labor costs can be reduced.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing an example of a facility layout of the present invention.

FIG. 2 is a schematic sectional view showing an example of a conventional equipment layout diagram.

FIG. 3 is a photograph of surface metallographic structures of a hot-rolled steel strip and a cold-rolled steel strip treated by the conventional method and the method of the present invention.

FIG. 4 is a graph showing the glossiness after cold rolling according to the method of the present invention and the conventional method.

FIG. 5 is a graph showing plate surface roughness after cold rolling according to the method of the present invention and the conventional method.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Junichi Yamamoto 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Kawasaki Steel Co., Ltd. Chiba Steel Works (72) Inventor Nio Yokozawa 1 Kawasaki-cho, Chuo-ku, Chiba-shi Kawasaki Steel Co., Ltd. Chiba Steel Works (72) Inventor Masahiko Ito 1 Kawasaki-cho, Chuo-ku, Chiba City, Chiba Prefecture Kawasaki Steel Co., Ltd. Chiba Steel Works (72) Satoshi Tsuzuki, 1 Kawasaki-cho, Chuo-ku, Chiba City, Chiba Prefecture Kawasaki Steel Co., Ltd. Chiba Works (72) Inventor Setsuo Hotani 1452 Foki, Nogami Town, Seagrass County, Wakayama Prefecture Hotani Co., Ltd.

Claims (3)

[Claims] 1. When descaling a hot-rolled and annealed hot-rolled stainless steel sheet, it is first treated with a mechanical scale breaker, followed by shot blasting, then sulfuric acid pickling, and then with a grinding brush roll. A descaling / pickling method for hot-rolled stainless steel plates, characterized by grinding and finally electrolytic treatment with nitric acid. 2. A mechanical scale breaker, a shot blasting device, a sulfuric acid bath, a grinding brush roll device, and a nitric acid electrolysis bath are arranged in this order in a line for descaling a hot-rolled and annealed stainless hot-rolled steel sheet. A descaling and pickling line for stainless hot rolled steel sheets. 3. The descaling / pickling line for hot-rolled stainless steel sheet according to claim 2, wherein the grinding brush roll device is a heavy grinding brush roll device.