JPH0336891B2 - - Google Patents

Description

[Detailed description of the invention]

B. Technical field to which the invention pertains The present invention relates to a method for producing ferritic stainless steel sheets with excellent surface gloss, and in particular, the invention has been developed with respect to pre-treatment for cold rolling, and this type of steel sheet has significantly improved surface gloss. It has been achieved. (b) Problems with the prior art In general, so-called white streaks are considered a problem as a defect that impedes the gloss of cold-rolled ferritic stainless steel sheets, but these white streaks are created by grinding prior to cold rolling. It is thought that some kind of influence from the grinder is the cause of the white streak pattern, but the detailed mechanism has not yet been fully clarified. In other words, cold-rolled ferritic stainless steel sheets, such as SUS430, have a unique black luster and are widely used in kitchen appliances, automotive decorative materials, etc. due to this characteristic. A unique defect called a white streak pattern occurs in the process, and this is the biggest cause of inhibiting surface gloss. A white streak pattern is usually a white streak-like pattern that occurs on the front surface of the plate in the rolling direction (hereinafter referred to as the L direction), and when observed under a microscope, it is found that fine defects are observed in the direction perpendicular to the rolling direction (hereinafter referred to as the C direction). The difference in density of fine defects arranged in the same direction corresponds to the white streak pattern observed visually. As mentioned above, the degree of occurrence of this white streak pattern is much more noticeable when cold rolling is performed after grinding before cold rolling, compared to when rolling is performed without grinding. In the latter case, there are very few white streaks. However, due to material flaws and a problem called gold dust, it is impossible to completely eliminate grinding for all hot-rolled annealed sheets, so even when grinding is done, white streaks are not present. The development of manufacturing technology that would prevent this from occurring had become an important issue. (Relationship with prior art) There is no conventional technology to compare with for such development issues, and the only attempt is to improve the surface quality of cold-rolled steel sheets by improving the ridging properties of the base plate. Although I can only cite examples, the knowledge on which this invention is based shows that such ripping is a secondary factor in inhibiting gloss when applied with a grinder, and is not a true white product. It is not the cause of muscle development. As described below, it is possible to dramatically improve surface gloss only by this invention. (Motivation for the Invention) The inventors investigated the cause of the noticeable white streaks that occur when a material is subjected to grinding before cold rolling (hereinafter referred to as "grinder material"), and as a result, discovered the following new fact. The reason why noticeable white streaks appear on grinder materials is that the hardened surface layer created by the grinder cracks during rolling.
This remains as a fine defect in the C direction on the final product, resulting in a white streak pattern. On the other hand, it has been found that if the work-hardened layer on the surface caused by the grinder is removed by some method, white streaks will not occur even in the grinder material. (Solution Means) Based on the above knowledge, the present invention aims to produce a ferritic stainless steel plate with good surface gloss by grinding the surface of a hot-rolled annealed plate without applying processing strain. By performing surface layer removal treatment under stress and then cold rolling, it is possible to reduce white streaks and produce a ferritic stainless steel sheet with excellent surface gloss. Here, the above-mentioned surface layer removal treatment must be applied to a depth of at least 1 μm on the ground surface of the glider, and it is preferable to carry out the treatment by pickling or electrolytic polishing. EXAMPLES The contents of the present invention will be explained below based on examples. Figure 1 shows the surface hardness distribution of a regular SUS430 hot-rolled annealed plate (4 mm thick) when the surface was ground using a grinder. The surface of the plate subjected to such gliding is rapidly and significantly hardened from a depth of about 10 μm on the surface side, and this work-hardened layer causes cracks during cold rolling, and these cracks remain even after skin pass. Because of this, it had a white striped pattern. Although tests were attempted by varying the grinding conditions, there was no significant difference in the degree of white streaks, and a fundamental solution could not be achieved. Next, this grinder material was pickled under various conditions shown in Table 1 to create base plates with different amounts of surface layer dissolved and removed.

[Table] Although a pickling method was used in this example, any method such as electrolytic polishing may be used as long as the hardened surface layer can be removed without adding processing strain. After removing the surface hardened layer using a grinder, the mother plate is rolled to a product thickness (1 mm), bright annealed, and then skin pass rolled to determine the level of gloss and whiteness of the final product. 2
As shown in the figure. In the figure, the glossiness depends on the reflectance of the plate surface, and the larger the value, the better the glossiness. In addition, whiteness indicates the color tone of the board surface.
The smaller the value, the blacker the gloss. The evaluation criteria for glossiness and whiteness are as follows. Glossiness Glossiness measures the reflectance of the board surface, and the specific method is: at an incident angle of 20°,
A light beam of a certain intensity is irradiated onto the sample, and the intensity of the reflected light is measured at a reflection angle of 20°. Measured values are expressed as relative values when the reflectance of the standard sample is assumed to be 8.2. Therefore, the larger the value, the better the gloss. Whiteness Whiteness indicates the color tone of the plate surface, and the specific measurement method is to irradiate a sample with white light and measure the tristimulus values of the reflected light. Tristimulus values are three independent quantities that determine color and are calculated from a curve of the proportions of the senses stimulated by a spectrum of unit energy. From these tristimulus values, we can determine the position of the color of the sample in the color solid (the color is expressed as a position in three-dimensional coordinates by taking black and white brightness on the vertical axis and hue and saturation on the horizontal axis). decided,
The whiteness is calculated by subtracting the distance between that position and pure white from 100. Therefore, a whiteness of 100 is pure white, a whiteness of 0 is pure black, and the smaller the value, the more black the board can be said to be. As shown in Figure 2, when cold rolling is performed after the surface layer after grinding is dissolved and removed by 1 μm or more,
It was confirmed that both gloss and whiteness were significantly improved. It can be seen that when the surface hardened layer formed by a grinder is dissolved and removed according to the present invention, cracks in the C direction are significantly reduced, which is extremely effective for the purpose of the present invention. In this example, as the test material
Although SUS430 was used, the present invention has similar effects on general ferritic stainless steels such as SUS434, SUS444, and stabilized steel. As described above, according to the present invention, it is possible to produce a ferritic stainless steel sheet with extremely low occurrence of white streaks and excellent surface gloss even when used as a grinder material.

[Brief explanation of drawings]

Figure 1 is a graph of the surface hardness of the SUS430 mother plate that has been ground with a grinder, and Figure 2 is a graph showing the level of gloss and whiteness of the sample material after the hardened surface layer has been dissolved and removed.

Claims (1)

[Claims] 1 The surface of a hot-rolled annealed ferritic stainless steel plate is ground with a grinder, and then the ground surface is subjected to stress-free surface layer removal treatment to a depth of at least 1 μm, and then cold-rolled. A method for producing a ferritic stainless steel sheet with excellent surface gloss. 2. The method according to 1, wherein the stress-free surface layer removal is pickling. 3. The method according to 1, wherein the stress-free surface layer removal is electrolytic polishing.