JPS59185727A - Manufacture of cold rolled ferritic stainless steel plate having superior surface luster - Google Patents

Abstract

PURPOSE:To prevent the formation of white streaks and to maintain the superior surface luster of a hot rolled ferritic stainless steel plate by softening the surfaces of the steel plate by annealing so that the distribution of the surface hardness is made uniform before cold rolling the steel plate. CONSTITUTION:The surfaces of a hot rolled ferritic stainless steel plate are ground with a grinder to carry out deseaming, and before cold rolling the steel plate, the surfaces of the steel plate are softened by annealing so that the surface hardness is adjusted to <=+ or -15% of the average hardness of the central part. The steel plate is then cold rolled. The formation of white streaks due to the effect of the grinding is prevented, and the black luster peculiar to a ferritic stainless steel plate can be maintained.

Description

[Detailed Description of the Invention] (Technical Field) Ferritic stainless cold-rolled steel sheets, represented by JIS SUS 430, have an excellent surface gloss with a unique black luster. It is widely used as a decorative material for automobiles, etc., but a unique defect called a white streak pattern often occurs during the cold rolling process, and this is the biggest cause of significantly inhibiting the characteristic surface gloss mentioned above. .

Surface gloss, 30L due to effective avoidance of such white streaks
Therefore, it is desirable to establish a manufacturing method for cold-rolled sheets such as X.

(Problem) The above white streak pattern is in the normal rolling direction (hereinafter referred to as the downward direction).
A white streak-like pattern appears over the entire surface of the plate, and under a microscope, ciI fine defects in a direction perpendicular to the L direction (hereinafter referred to as the C direction) are observed to be lined up in the L direction, and the density of the fine defects is The difference corresponds to the white streak pattern observed visually.

1) The degree of inhibition of surface gloss by this white streak pattern is particularly noticeable depending on whether or not grinder 6JT was applied to the material, that is, the hot-rolled annealed ferritic stainless steel plate prior to cold rolling. There is a difference, and if it is not carried out, the occurrence of white streaks is quite small.

Therefore, it is thought that some kind of color tube caused by grinding with a grinder is the main cause of the white streak pattern, but the detailed mechanism has not yet been fully clarified, and of course, there are no reports on effective countermeasures. do not have.

Even if we are forced to search for related technologies, we can only cite attempts to improve the surface RFIT properties after cold rolling by improving the ridging properties of the mother plate. However, according to the experience of the inventors, such twisting property is only a secondary factor in inhibiting gloss in grinder materials.

As mentioned above, white streaks tend not to occur when hot-rolled annealed sheets are cold-rolled and are not ground using a grinder, but on the other hand, white streaks tend to occur less frequently due to problems such as material flaws and gold dust. However, it is impossible to completely eliminate grinding for all hot-rolled annealed sheets due to the process. Therefore grinder material? Developing a manufacturing technology for ferritic stainless steel cold-rolled mill plates that do not produce white streaks is an important issue.

(Motivation for the Invention) The inventors discovered the following new fact as a result of pursuing the cause of the occurrence of noticeable white streaks in grinder material.

°The cause of noticeable white streaks on the grinder material is
Due to the work hardening caused by grinding, the surface hardness distribution of the ground surface is high and uneven, and cracks occur in the hardened surface layer portion during rolling, and these cracks form R fine C in the final product. Due to remaining as a direction defect.

On the other hand, even if annealing is performed to soften the work-hardened surface layer of the surface ground by a grinder,
For example, if the hardness distribution of the surface layer is uneven, such as when the surface is particularly softened due to improper annealing, bit-like surface defects will occur during subsequent cold rolling, and these will remain in the final product. A rough white streak pattern on the skin.

Therefore, in the softening treatment by annealing, it is necessary to appropriately control the hardness distribution of the surface layer so that it does not become uneven, in order to prevent the occurrence of white streaks in the subsequent cold rolling.

(Purpose of the invention) When a hot-rolled annealed plate made of ferrite thread stainless steel is subjected to surface grinding using a grinder prior to cold rolling in order to remove material flaws and prevent so-called gold dust (hereinafter referred to as grinder material) Of course, in addition to the above, in cases where the surface layer has excessive hardness or a non-uniform or discontinuous hardness distribution, pre-treatment for cold rolling can significantly improve the surface gloss of this corridor board. It is the purpose of this invention to accomplish this.

(Structure of the Invention) In manufacturing a ferritic stainless steel cold steel plate with good surface gloss, the hardness distribution in the surface layer of the material before cold rolling, especially in the surface layer within 80 μm from the surface, is made appropriate. To do this, annealing is performed, and the surface hardness is adjusted to within ±15% of the average hardness of the central part of the leaf excluding the surface, and then cold rolling is performed. This is the gist of this invention, and with this, it is possible to reduce white streaks and produce ferritic stainless steel with excellent surface gloss.
Examples of heating methods include force heating, high frequency heating, and laser heating.

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

Regular SU S 480 hot rolled annealed plate (3.43mm thickness)
5 times with the 80Ti belt, then 2 times with the 100 belt,
・Next, the surface was ground once with No. 150 belt and once with No. 820 belt. The mineral oil removed was used, and the total grinding amount was 40 μm for each grinding (m).

FIG. 1 shows an example of the results of measuring the thickness direction distribution of the surface hardness of the ground surface using a Hannemann microhardness meter. The surface of the plate that has been subjected to grinding in this manner is rapidly and significantly hardened on the surface side from a depth of approximately 10 μm, and exhibits a non-uniform (i!j+ thickness distribution).

The work-hardened layer with such an unbalanced hardness distribution cracks during cold rolling, and the cracks remain even after skin pass rolling, resulting in a white streak pattern on the product.

In addition, tests were conducted by varying the grinding conditions within a range that was compatible with removing scratches on the surface of the material, but there was no significant difference in the degree of white streaks, and it was not a fundamental solution. .

Furthermore, an example of the results of measuring the surface hardness distribution using a Hannemann microhardness meter when annealing was performed at 850° Cs8 osec to soften the surface hardened layer by grinding is shown in FIG. If the above-mentioned softening annealing is applied, only the surface layer will be excessively softened and the hardness will be unevenly distributed.If such a material is cold rolled, pit-like defects will occur during the rolling process. This caused a rough white streak pattern on the skin.

Therefore, in order to obtain a rolled material with an appropriate surface hardness distribution, in addition to the above-mentioned 5US4110, 5US484.5US was used.
444 and 5US430LX+7) Mother plates were prepared by subjecting each grinder material to softening annealing under various conditions shown in Table 1, and were compared with non-annealed materials.

In this case, a dregs heating method was used for the softening annealing treatment.

81 Annealing system 1 piece The material that has undergone each of the above softening annealing treatments is used as the base plate, and the plate thickness is 1 piece.
The gloss and whiteness of the final product were measured by cold rolling using a Sendzimir rolling mill, followed by conventional bright annealing and skin bath rolling.

The evaluation criteria for glossiness and whiteness are as follows.

Glossiness Glossiness measures the reflectance of the plate surface, and the measurement method is to irradiate the sample surface with a light beam of constant intensity at an incident angle of 20°, and measure the intensity of the reflected light at a position at a reflection angle of 20°. Measure with. The measured value is expressed as a relative value when the reflectance of the standard sample is 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 8 stimulus values of the reflected light. Tristimulus values are eight 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, the color 3D (the vertical axis takes the brightness of black and white, and the horizontal l1
Determine the position of the color of the sample in the solid n (indicated by mt) by taking the hue and saturation in ql+, and subtract the distance between that position and pure white from 100. represents the whiteness. Therefore, a whiteness of 100 is pure white, a whiteness of O is pure black, and the smaller the value, the more glossy the black color is.

Now, as shown in Fig. 8, when cold rolling is performed after annealing so that the surface hardness of the SUS4+3O mother plate is within ±15% of the average hardness of the central part of the material,
It was confirmed that both gloss and whiteness were significantly improved. Further, as shown in FIG. 4, approximately the same effect was obtained using 1 for the 5US434.444.480LX motherboard in the same manner.

When observing a product to which the manufacturing method of the present invention is applied using a microscope, it is found that the number of minute defects in the G direction and bit-like defects is extremely small.

'JJ,〒(7) I<-';C(D';@”
ML: , J: h4f j" 5 I>1'#
Similarly, by applying appropriate softening annealing to a rolled material that has a strong tendency to generate white streaks, it is possible to advantageously produce a cold-rolled ferritic stainless steel sheet with excellent surface gloss.

[Brief explanation of drawings]

Figure 1 is a hardness distribution diagram of the surface of the 5US13G mother plate after grinding with a grinder. Figure 2 is the hardness distribution of the surface of the 5US13G mother plate after grinding with a grinder.
e. Figure 8 is a graph showing the influence of the surface hardness distribution of the 5US430 motherboard on the gloss and whiteness after cold rolling. Figure 4 shows 5US484, SUS44, 4.5US48
6.0 20 is a graph showing the influence of the surface hardness distribution of the 0LX mother plate on the glossiness and whiteness after cold rolling.
40 60 80 100 Surface force (llfn) Figure 2 Surface or 9 imposition llfn) Procedural amendment July 5, 1981 1, Indication of the case 1988 Patent Application No. 60064. No. 3 Manufacturing method for cold-rolled steel sheets, relationship with the case of the person making the amendment' Patent applicant (125) Kawasaki Steel Corporation 5゜6, subject of amendment Detailed explanation column of the invention in the specification and drawing l specification "Laser heating" in line 5 of page 6 of the book is corrected to "laser heating," and "non-uniform," in line 18 of the same page is corrected to "non-uniform." Of the two drawings, Figures 3 and 4 are corrected as shown in the attached corrected drawings.

Claims (1)

[Claims] 1. An annealing treatment in which the surface hardness of the rolled material falls within ±15% of the average hardness of the central portion of the material excluding the surface layer when cold rolling ferritic stainless steel. 1. A method for producing a cold-rolled ferritic stainless steel sheet with excellent surface gloss, the method comprising subjecting it to cold rolling after subjecting it to cold rolling. 2. The method according to 1, wherein the rolled material is subjected to surface grinding using a grinder prior to cold rolling of the ferritic stainless steel WJ hot rolled annealed plate.