JPH0447012B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method for manufacturing austenitic cold-rolled stainless steel strip with few surface defects, and in particular to a manufacturing method that can prevent minute defects caused by grinding with a grinder. Used in the manufacturing field. [Prior art] Austenitic stainless steel cold-rolled steel strip is generally produced by annealing, pickling, and grinding the hot-rolled steel strip.
It is manufactured through processes such as cold rolling-annealing and pickling-temper rolling. This grinder grinding process is carried out to remove surface flaws that occur during annealing and pickling of the hot-rolled steel strip. If this process is omitted, noticeable surface defects on the hot-rolled steel strip will remain even after cold rolling. Often reduces product value. The problem here is that although conspicuous surface defects in hot-rolled steel strips can be removed by grinding, minute defects still remain. As a countermeasure against this problem, Japanese Patent Application Laid-Open No. 52-36397 has been disclosed. As shown in Fig. 3, an endless grinding belt 6 is pressed against a steel strip 4 passing between breaker rolls 2 with a contact roll 8 and a biri roll 10, and grinding oil is sprayed onto the grinding part with a spray nozzle 12 for grinding. In the device, a new spray nozzle 14 is installed at the exit part of the grinding position of the endless grinding belt 6, and grinding oil is sprayed to flow out the grinding debris.
This removes the grinding swarf that conventionally adhered to the grinding belt 6 and caused clogging, improving grinding efficiency and preventing scratches caused by the grinding swarf. However, even with this method, there is a problem that micro defects on the surface cannot be prevented. [Problems to be Solved by the Invention] An object of the present invention is to solve the above-mentioned problems of the prior art and to provide a method for producing an austenitic stainless steel cold-rolled steel strip with fewer microscopic surface defects. [Means and effects for solving the problems] The gist of the present invention is as follows.
That is, in a method for producing an austenitic stainless cold rolled steel strip in which a hot rolled steel strip is subjected to processes such as annealing, pickling-grinder grinding-cold rolling-annealing, pickling-temper rolling, etc., the grinder grinding step A cold-rolled austenitic stainless steel with few surface defects, characterized by comprising: an atmospheric annealing step to reduce the surface hardness to 200 or less on a Bitkers scale between the cold rolling steps, and a pickling step following the atmospheric annealing step. This is a method of manufacturing steel strip. The present inventors conducted various studies regarding minute surface defects when grinding a hot rolled steel strip with a grinder, and as a result, the following facts were found. (A) When grinding is performed, the part to be ground is work-hardened and the hardness of the grinding marks increases, and these grinding marks do not disappear even during cold rolling and remain and become micro defects. (B) Grinding debris generated during grinding with a grinder is
By increasing the pressure of the grinding oil injected into the grinding section in a conventional conventional grinder, the phenomenon of adhesion to the grinding belt and clogging can be almost eliminated. (C) Due to the pressure increase of the grinding oil mentioned above, the amount of grinding swarf adhering to the steel strip surface decreases, but it does not disappear completely, and a small amount of adhering grinding swarf is removed from the steel strip surface by work rolls during cold rolling in the subsequent process. This causes micro defects. (D) Non-metallic inclusions such as slag that were involved during smelting are exposed to the surface by grinding the steel strip with a grinder.
This is pushed into the surface by work rolls during cold rolling, causing micro defects. The problems that occur in coils that have been subjected to grinding as described above can be roughly divided into four types, as described above, but the second item (B) is the one published in Japanese Patent Application Laid-Open No. 52-36397.
This problem can be solved by increasing the spray pressure of the grinding oil in the conventional spray method. Regarding the remaining items (A), (C), and (D), we found the following countermeasures. (A) The problem that the grinding marks remain due to work hardening of the part to be ground during grinding without being eliminated by cold rolling can be solved by performing annealing for softening. (C) Among the grinding chips adhering to the surface of the steel strip, those that are firmly embedded and cannot be removed by brushing with water are removed by pickling. (D) Non-metallic inclusions such as slag that are drawn in during smelting are exposed to the surface layer by grinding the steel strip, and micro defects that are pushed in by work rolls during cold rolling are annealed in the air. This can be prevented by scaling the surface layer and then pickling to remove inclusions exposed on the surface along with the scale. The present invention newly incorporates these measures into the process, and consists of an air annealing process and a pickling process. First, the atmospheric annealing process of the present invention will be explained. Work hardening of austenitic stainless steel is a well-known phenomenon, and Figure 2 shows the work hardening of the surface layer due to grinder grinding when the base material of SUS304 steel, which is a representative steel type, has a Bitkers hardness of 170. , the outermost layer has increased to about 250 Hv. Next, the stainless steel, which has been hardened to a surface hardness of 245 on the Bitkers hardness by grinding, is annealed in the air at various temperatures, then pickled, cold rolled, and
The surface condition was investigated by performing annealing, pickling and temper rolling, and the results are shown in Table 1. From the results in Table 1, the surface hardness needs to be 200 or less in Hv in order to prevent micro defects. Therefore, in the present invention, the Hv was limited to 200 or less by atmospheric annealing.

【table】

[Table] Figure 1 shows the relationship between temperature, time, and softening during annealing of SUS304 stainless steel. In Hv
To soften to below 200, heat at 1100℃ x 0.5 minutes.
It can be seen that annealing is required at or above the line connecting 1000°C x 0.8 minutes. Next, pickling to remove scale generated during the annealing and inclusions exposed on the surface layer is preferably carried out under the conditions shown in Table 2 below. These may be used alone, but it is more effective if a plurality of them are combined.

〔Example〕

A SUS304 stainless steel hot-rolled steel strip was subjected to grinding to remove hot-rolling defects, and the surface hardness at that time was Hv=241. This steel strip was annealed in the air at 1050° C. for 1 minute, and then immersed one after another under the conditions shown in Table 3 below to completely descale it.

〔Effect of the invention〕

As is clear from the above examples, the present invention involves grinding a hot-rolled steel strip with a grinder, then performing atmospheric annealing and pickling to reduce the surface hardness to 200 or less on a Vickers scale.
By subsequently performing cold rolling, the incidence of microdefects in the austenitic stainless cold rolled steel strip was significantly reduced from 40% to 2%, and the surface quality was significantly improved.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the relationship between time, temperature and softening during annealing of SUS304 stainless steel, and Figure 2 is a diagram showing the relationship between softening and time during annealing of SUS304 stainless steel.
A diagram showing the work hardening of the surface layer of SUS304 stainless steel by grinding with a grinder, and FIG. 3 is a schematic front view of a grinding device showing a conventional stainless steel grinding method. 4... Steel strip, 6... Endless grinding belt, 12,
14...Spray nozzle.

Claims (1)

[Claims] 1. In a method for producing an austenitic stainless steel cold rolled steel strip in which a hot rolled steel strip is subjected to processes such as annealing, pickling-grinder grinding-cold rolling-annealing, pickling-temper rolling, etc., the grinder grinding step and During the cold rolling process the surface hardness increases to Bitkars 200
A method for producing an austenitic stainless steel cold rolled steel strip with few surface defects, the method comprising the following atmospheric annealing step and a pickling step following the atmospheric annealing step.