JP3496459B2 - Rolling method of ferritic stainless steel sheet - Google Patents

Description

Description: BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention prevents surface defects and roll surface roughness caused by scale during hot rolling of ferritic stainless steel, and improves the basic unit of roll. And a method for rolling a hot-rolled ferritic stainless steel sheet having a good surface. [0002] Ferritic stainless steel suffers from surface flaws, an important characteristic, when scale flaws are generated during hot rolling, so that re-pickling and surface polishing are required in the next step, so that product cost is reduced. And the productivity is reduced. Scale flaws during hot rolling of stainless steel are caused by peeling of the surface oxide film (scale), and it is known that increasing the heating temperature and increasing the thickness of the secondary scale is effective in preventing skin roughness. I have. Conventionally, Japanese Unexamined Patent Publication No. 7-284804 discloses a countermeasure for preventing roughening of stainless steel. This is because the surface roughness of the slab is determined by at least one method of grinding with a grinder or shot blasting or cutting with a tool or mill before charging the ferritic stainless steel to the slab heating furnace for hot rolling. Is set to 20 μm or more by Rmax to easily form a uniform and thick scale during slab heating, followed by hot rolling, which is a method for producing a ferritic stainless steel with few surface defects. [0004] In such a method, however, the amount of scale generated is larger than that of a smooth slab immediately after the slab is extracted from the heating furnace. Many of them are removed by the scale breaker on the slab exit side that removes the generated primary scale, and to prevent the roll surface roughening and the accompanying steel plate surface roughening that occurs in the later stage of rough rolling and the former stage of finish rolling. Had the problem that it was impossible. [0005] An object of the present invention is to produce a steel sheet having a good surface stably without roughening not only through rough rolling but also from slab heating to finish rolling. SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems, and heats a continuously cast ferritic stainless steel slab in a heating furnace, and performs rough rolling and finish rolling. In a series of hot rolling for producing a stainless steel sheet, the exit temperature of the heating furnace is set to 1200 to 1300 ° C., the rolling reduction of each pass during the rough rolling is set to 35% or less, and the first half of the finish rolling (F _{1 to} F ₃ stand) ) The rolling reduction of each stand is 30
% And the rolling speed of the final finishing stand is 700 m
The present invention proposes a method for hot rolling a ferritic stainless steel sheet, wherein the rate is not less than / min. Hereinafter, the hot rolling method of the present invention for preventing roughening of ferritic stainless steel will be described in detail. Burning (hereinafter referred to as rough skin) is, for example, CAM
PISIJ Vol. 6 (1996) -1346, this does not occur when the scale can be made thick and uniform, but when the heating temperature is low and the scale is thin, the steel sheet and the roll stick together when rolled. (Rough skin). If the temperature at the exit side of the heating furnace is less than 1200 ° C., the scale thickness on the surface of the steel sheet is so small that seizure occurs between the steel sheet and the roll, which is not preferable. If the temperature exceeds 1300 ° C., linear flaws due to grain boundary cracks of the steel sheet occur, which is not possible. Therefore, in the present invention, the heating furnace outlet side temperature is set to 1200 to 1300 ° C. The reasons for the regulation of rough rolling and finish rolling are as follows. [0009] The roughening of ferritic stainless steel occurs when the rolling reduction of the rough rolling exceeds 35% or the rolling reduction of the finish rolling exceeds 30% and the rolling speed of the final stand of the finish rolling is less than 700 m / min. Easy to occur.
If the rolling reduction exceeds 35% in the rough rolling, it is considered that the scale on the steel sheet surface is sheared, or the scale is cracked to increase the ratio of a new surface of the material, and the ground iron is likely to be in contact with the roll, causing seizure. Therefore, the rolling reduction in each pass of the rough rolling is 35% or less. When the rolling reduction exceeds 30% in finish rolling, seizure occurs for the same reason as in rough rolling.
On the exit side of the final stand, the rolling speed is 700 m / mi.
If it is slower than n, the contact time of the rolled material with the roll becomes longer, and the diffusion time of the metal becomes longer, so that seizure easily occurs. Therefore, the rolling reduction of the finish rolling is 30% or less, and the rolling speed of the final stand of the finish rolling is 700 m / min.
Above. [0011] The content of the ferritic stainless steel is as follows: C: 0.05% or less;
Stainless steel containing 0.3% and Cr: 16 to 20%. Further, Mo: 2.0% or less, Nb: 0.5% or less,
The effect can be obtained even with stainless steel in which rough surface is likely to be generated by adding at least one kind selected from Ti: 0.3% or less. DETAILED DESCRIPTION OF THE INVENTION A thickness 20 having the components shown in Table 1
An example in which hot rolling is performed using a ferrite stainless steel slab having a length of 0 mm, a length of 6 m, and a width of 1300 mm will be described. The rolling mill row of the rolling mill used is shown in FIG. In FIG. 1, a slab heated in a heating furnace 1 is roughly rolled by a rough rolling mill 3 having R _{1 to} R ₃ stands after the scale is peeled off by a scale breaker 2, and then denoted by F ₁ to F ₇ . It is finish-rolled by a finishing mill 4 having each stand, and is taken up by a down coiler 6 via a run-out table 5. The work roll diameter of the rough rolling mill 3 is 1500 m
m, the work roll diameter of the finishing mill 4 is 820 mm for the F _{1 to} F ₃ stands and 700 mm for the F _{4 to} F ₇ stands. [0013] The ferrite stainless steel slab is
It is heated to 200 ° C. for 2 hours,
A 0 mm slab was rolled to a 30.3 mm thick sheet bar. In the rough rolling stands R ₁ and R ₂ , three-pass reverse rolling was performed, and in R ₃ , one-pass rolling was performed. Thereafter, tandem rolling was performed using a finishing mill 4 having seven stands, and the plate was rolled to a thickness of 3.5 mm. In order to investigate the relationship between the rough rolling conditions and the surface properties of the sheet bar, the heating temperature and the rolling reduction of the rough rolling were changed as shown in Tables 2 and 3. Table 2, the heating temperature (heating furnace exit side temperature), the table showing the finishing mill entry side temperature, rolling reduction and F ₁ entry side of the steel sheet (sheet bar) surface texture, Table 3, this in performing the rolling It is a table | surface which shows reduction ratio distribution of rough rolling of invention and conventional conditions. FIG. 2 shows the results. When the heating temperature was higher than 1300 ° C., line flaws were generated, and when the temperature was lower than 1200 ° C., surface roughness was generated. The occurrence of these surface defects did not depend on the setting of the rolling reduction. Moreover, the heating temperature is 1200-1.
Under the condition of 300 ° C., the conditions of the rough rolling reduction, B-1, B-2
No surface roughening was observed when rolling was performed at the rolling reduction setting of, but it was found that roughening occurred at any setting of the rolling reduction under the conventional condition A. When the surface temperature of the sheet bar at a heating temperature of 1200 to 1300 ° C is good, the temperature of the steel sheet on the entrance side of the finishing mill is 1000 to 1100.
° C. Next, an experiment was conducted to examine the finish rolling conditions and the state of the steel sheet surface after the finish rolling. Tables 4 and 5 show the experimental conditions and results. Table 4 shows reduction rate setting, the relationship between the finishing mill final exit side rolling speed and the steel sheet surface texture after rolling completion of the stand F _7. Table 5 is a table showing the reduction ratio distribution of the finish rolling when rolling is performed in Table 4. At this time, the temperature of the steel sheet on the entrance side of the finishing rolling mill was 1050 ° C., and no roughening was observed in the state of the sheet bar. The results are shown in FIG. As a result of the experiment, the steel sheet surface was good under the rolling reduction conditions of P, R, S, and T among the conditions in Table 5 and the rolling speed was 700 m / min or more.
Even if the rolling speed is as low as 690 m / min under the rolling reduction conditions of, or even if the rolling speed is high, the finishing stands F ₁ , F ₂
It was found that under the condition where the reduction ratio of the sample was 32%, which was a large reduction ratio of Q, skin roughness occurred. [Table 1] [Table 2] [Table 3] [Table 4] [Table 5] As a countermeasure for preventing roughening of a ferritic stainless steel sheet, conventionally, there has been an increase in the heating temperature or care of a slab. However, heating at a high temperature has a problem that line flaws are easily generated. There was a problem that it could not be prevented only by controlling the temperature conditions of the steel sheet, and that even if the slab was cared for, the rough surface could not be completely prevented and the production cost increased. According to the present invention, rolling conditions for rolling ferritic stainless steel can be optimized, and a stable and good steel sheet surface can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view showing a hot rolling facility used in an experiment. FIG. 2 is a diagram showing a relationship between a maximum rolling reduction of a rough rolling pass and a slab heating temperature. FIG. 3 is a diagram showing the relationship between the maximum draft of a finishing stand and the speed of a steel sheet on the exit side of a final stand of a finishing mill. [Description of Signs] 1 Heating furnace 2 Scale breaker 3 Rough rolling mill 4 Finish rolling mill 5 Run-out table 6 Down coiler

──────────────────────────────────────────────────の Continuing from the front page (72) Inventor Toshio Ima 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Kawasaki Steel Engineering Co., Ltd. (72) Inventor Yasuo Yarida 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Kawasaki Steel (56) References JP-A-63-162818 (JP, A) JP-A-57-22802 (JP, A) JP-A-9-25516 (JP, A) JP-A-9-137230 (JP JP, A) JP-A-8-300006 (JP, A) JP-A-10-17938 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B21B 1/00-3/02

Claims (1)

(57) [Claims 1] In a series of hot rolling, a continuous cast ferritic stainless steel slab is heated in a heating furnace, rough-rolled and finish-rolled to produce a stainless steel sheet. After setting the exit temperature of the heating furnace to 1200 to 1300 ° C. and performing rough rolling at a rolling reduction of 35% or less during rough rolling, the rolling reduction of each stand in the first half (F _{1 to} F ₃ ) of finish rolling is performed. 30% or less, rolling speed of the final finishing stand is 700m
A method for rolling a ferritic stainless steel sheet, comprising finish-rolling at a rate of not less than / min.