JPS59107027A - Production of ferritic stainless steel sheet having excellent surface gloss - Google Patents

Abstract

PURPOSE:To obtain a ferritic stainless steel which is decreased in white streak pattern and has excellent surface gloss by removing the surface layer under unstressed condition from the surface of a hot rolled and annealed steel sheet which is ground then subjecting the steel to cold rolling. CONSTITUTION:The surface hardened layer of a hot rolled steel sheet (4mm. thickness) of, for example, SUS430, which is ground is removed under unstressed condition without applying any working strain thereto. The removal of the surface layer is performed at least to 1mum depth. The removal is accomplished by a method of pickling the surface with a sulfuric acid, hydrofluoric acid, nitric acid, etc. or polishing electrically the surface. The hot rolled ferritic stainless steel sheet removed of the above-described surface layer is subjected to cold rolling. The ferritic stainless steel sheet with which the formation of a white streak pattern is extremely less and which has excellent surface gloss is thus obtd. even if the surface is ground.

Description

DETAILED DESCRIPTION OF THE INVENTION 10. Technical field to which the invention relates The present invention relates to a method for manufacturing a ferritic stainless steel sheet with excellent surface gloss, and in particular, with the development results related to the pre-treatment for cold rolling described in 7. The surface gloss of the i6VI board has been significantly improved.

Problems with the conventional technology Generally speaking, the so-called white streak pattern is seen as a problem as a defect that impedes the gloss of cold-rolled ferritic stainless steel plates, but the white streak pattern is scratched with a grinder prior to cold rolling. There is a marked difference depending on whether or not the
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 5US430, 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 entire surface of the board in the rolling direction (hereinafter referred to as the "downward direction"), and when observed under a microscope, fine defects are observed in the direction perpendicular to the rolling direction (hereinafter referred to as the "C direction").
Visually check the difference in density of minute defects lined up in the direction of v! ;l Corresponds to the white striped pattern to be adjusted.

As mentioned above, the degree of occurrence of this white streak pattern is much more noticeable when cold rolling is performed after applying a grinder to the grinder before cold rolling, compared to when rolling is performed without applying the grinder. , the latter has 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 against such development issues, but by simply improving the ridging properties of the base plate,
Although I can only cite examples of attempts to improve the surface quality of cold-rolled steel sheets, the knowledge on which this invention is based suggests that such threading properties are a factor that inhibits gloss when applied with a grinder. However, it is secondary and not the true cause of white streak formation.

As described below, only this invention can dramatically improve the surface gloss.

(Motivation for the invention) The inventors discovered that when grinding is performed before cold rolling (
As a result of investigating the cause of the noticeable uniformity of white streaks in grinder material (hereinafter referred to as grinder material), the following new facts were discovered.

The reason why white streaks occur noticeably on grinder materials is that the hardened surface layer created by the grinder cracks during rolling, and these cracks remain as fine defects in the C direction on the final product, resulting in white streaks. It becomes a 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. Surface layer removal treatment under stress 'FJA? By performing cold rolling after rolling, the white streak pattern is completely reduced, making it possible to manufacture a ferritic stainless steel plate with excellent surface gloss.

The surface layer removal treatment described above must be carried out to a depth of at least 1 μm on the ground surface of the grinder, and it is preferable in practical terms that the treatment be carried out by pickling or electrolytic polishing.

Example The present invention will be described in detail below based on Examples.

The surface hardness distribution when surface-grinding a normal 5US430 hot-rolled annealed plate (4-Ichihara) using a grinder]
As shown in the figure. The surface of the plate that has been subjected to grinding in this way 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 persist even after the skin bath. Because it remained, it had a white streak pattern. Although tests were attempted with various grinding conditions, there was no significant difference in the degree of white streaks, and no fundamental solution was 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 1 Pickling Conditions In this example, a pickling method was used, but any method such as electrolytic polishing may be used as long as the hardened surface layer can be completely removed without producing processing distortion noise.

After removing the surface hardening layer using a grinder and rolling the base plate to the full thickness (one thickness), bright annealing is performed and skin bath rolling is performed to determine the level of gloss and whiteness of the final product. is shown in Figure 2.

In the figure, the glossiness depends on the reflectance of the plate surface, and the thicker the value, the better the glossiness.

In addition, whiteness indicates the color tone of the board surface, and the smaller the value, the blacker the gloss.

The evaluation criteria for glossiness and whiteness are as follows.

9°C Glossiness is a measure of the reflectance of the board surface.The specific method is to irradiate a sample with a certain strong beam of light at an incident angle of 20°, and calculate the intensity of the reflected light by total internal reflection. Measure at an angle of 20°. The measured value is the reflectance of the standard sample "f:
It is shown as a relative value when it is set to 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 value of the reflected AC. 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. This a
Determine the position of the color of the sample in the color 3D (by taking the black and white brightness on the vertical axis and the hue and saturation on the horizontal axis, it is indicated by the position in the three-dimensional coordinates) from the stimulus value, The whiteness is calculated by subtracting the distance between that position and pure white from 100. Therefore, whiteness]00 is pure white,
The whiteness O is pure black, and the smaller the value, the more black the board can be said to be.

As shown in Figure 2, the surface layer after grinding is 1 μm thick.
It has been confirmed that when more than 100 m of molten metal is dissolved and removed and then cold rolled, both gloss and whiteness are greatly improved.

It can be seen that when the surface hardening layer formed by a grinder is dissolved and removed according to the present invention, cracks in the 0 direction are significantly reduced, which is extremely effective for the purpose of the present invention. In this example, SUS 430 was used as the test material, but the present invention has similar effects on ferritic stainless steels such as 8US4a4, 5US444, and stabilized steel.

As described above, according to the present invention, even in the grinder material, the occurrence of white streaks is extremely small and the surface gloss is excellent. It is possible to manufacture all ferritic stainless steel sheets.

[Brief explanation of the drawing]

Figure 1 is a graph of the surface hardness of a 5US430fJ plate that has been completely ground with a grinder, and the vjz diagram is a graph showing the level of glossiness and whiteness of the test material after removing stone chips from the hardened surface layer. Figure 1 (k import

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 coated with a thickness of at least 1 μm.
After applying stress-free surface layer removal treatment to a depth of
A method for producing ferritic stainless steel sheets with a glossy surface that is completely cold rolled. λ The method according to l, wherein the stress-free surface layer removal is pickling. 8. The method according to l, wherein the stress-free surface layer removal is electrolytic polishing.