JPH0499818A - Production of high-purity ferritic stainless steel sheet having excellent brightness - Google Patents

Abstract

PURPOSE:To obtain the high-purity ferritic stainless steel sheet having a smooth sheet surface and high brightness by applying work strains by rolling of the 1st pass to this steel sheet, then annealing the steel sheet at a high temp., thereby improving the structure not only in the surface of the sheet thickness but in the central part as well and obviating the generation or ridging in spite of rolling. CONSTITUTION:The desirable compsn. of the high-purity ferritic stainless steel to be used contains <=0.03% C, <=1.5% Si, <=1.0% Mn, <=0.04% P, <=0.01% S, <=0.70% Ni, 17.0 to 25.0% Cr, and <=0.03% N, contains >=1 kinds of either <=1.5% Cu or <=5% Mo, contains >=1 kinds of either of <=0.60% Nb or <=0.2% Ti, and consists of the balance Fe and unavoidable impurities. The hot rolled steel strip of this high-purity ferritic stainless steel is first rolled down at 5 to 30% by the cold rolling of the 1st pass and is then heat treated in a 950 to 1100 deg.C range at the time of cold rolling this steel strip. The steel strip is then cold rolled down to a prescribed thickness and is subjected to bright annealing.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a method for manufacturing a high-gloss, high-purity ferritic stainless steel plate.

<Conventional technology> High-purity ferritic stainless steel sheets have excellent corrosion resistance, workability,
Due to its excellent weldability, it is widely used in kitchen utensils, automotive decorative materials, etc.

However, although decorative factors are important in these applications, sufficient gloss is not always achieved.

On the other hand, Japanese Patent Publication No. 2-22128 discloses that, as a measure to prevent the deterioration of surface gloss due to white streaks in ferritic stainless steel, a hot rolled annealed plate that has been surface ground with a grinder prior to cold rolling is subjected to annealing treatment. It has been proposed that the hardened surface layer be softened by grinding.

However, when this method is applied to a high-purity ferritic stainless steel sheet, the improvement in gloss cannot be said to be sufficient.

<Problems to be Solved by the Invention> An object of the present invention is to propose a method for further sufficiently improving the glossiness of a high-purity ferritic stainless steel sheet.

<Means for solving the problem> The desirable composition of the high purity ferritic stainless steel that is the object of the present invention is C: 0.03% or less, Si: 1.5
% or less, Mn: 1.0% or less, p: o, o 4% or less, S: 0.01% or less, Ni: 0.70% or less, Cr: 17. O ~ 25.0%, N: 0.03% or less, Cu: 1.5% or less or Mo: 5% or less, and Nb: 0.60%
or Ti: 0.2% or less, and the remainder consists of re and other unavoidable impurities. When doing this, first, the first pass of cold rolling is performed to reduce the rolling by 5 to 30%, then heat treatment is performed in a temperature range of 950 to 1100°C, and then cold rolled to a predetermined thickness.
This is a method for producing a high-purity ferritic stainless steel sheet with excellent gloss, which is characterized by bright annealing.

<Function> The present inventors investigated various reasons why high-purity ferritic stainless steel lacks luster, and found that conventional softening annealing, which reduces the hardness of only the surface layer, causes ridges and ridges that occur during rolling to occur in the valleys. It has been found that it is not possible to prevent fine cracking in the C direction from occurring and deterioration of gloss.

Therefore, according to the present invention, by applying processing strain in the first pass of rolling and then annealing at high temperature, not only the surface of the plate thickness but also the structure of the central part is improved. The plate surface became smooth and a high-gloss, high-purity ferritic stainless steel plate was obtained.

In the present invention, the rolling reduction ratio of the first pass of cold rolling is 5 to 30%.
limited to the range of This is because if it is less than 5%, the structure improvement in the central part of the board will be insufficient, and even if the rolling reduction exceeds 30%, the living room improvement effect will be saturated.

In addition, in the present invention, the heat treatment temperature after one pass cold rolling is set to 95
Limited to the range of 0 to 1100°C. If the temperature is lower than 950°C, the structure of the central part of the plate will not be improved and ridges will occur during rolling. On the other hand, if the temperature exceeds 1100°C, the above effect is saturated.

The present invention is directed to a high-purity ferritic stainless steel plate, and its desirable composition will be mentioned below.

A very small amount of CTC is dissolved in steel, but most of the C is combined with Cr and precipitates mainly at the grain boundaries, degrading the corrosion resistance, so the less the better. Therefore, a large amount of C improves the corrosion resistance. The amount of Cr, which has the effect of reducing corrosion, is locally reduced, impairing corrosion resistance. In order to prevent this phenomenon, it is desirable to keep C content as low as possible, and from the viewpoint of industrial and economic melting technology, it is usually desirable to keep it at 0.03% or less.

Like C, NUN exerts harmful effects, so it is desirable to keep it as low as possible, but in this case as well, it is desirable to set the upper limit to 0.03%, taking into account industrial and economic melting technology.

Si: If Si exceeds 1.5%, it increases the strength of the steel and deteriorates its ductility, so it is desirable to set the upper limit to 1.5%.

Mn: If Mn exceeds 1.0%, corrosion resistance will be significantly deteriorated, so it is desirable that the upper limit is 1.0%.

p, S: P, S are elements that are unavoidably mixed in from raw materials during the melting process, and if the amount exceeds p: o, o4%, s: o, ot%, corrosion resistance and workability deteriorate, so the upper limit is P: 0.0
4%, S: 0.01% is desirable.

Ni: If Ni exceeds 0.7%, it increases the strength of the steel and deteriorates workability, so it is desirable to set the upper limit to 0.7%.

Cr: Cr is at least 17% to maintain corrosion resistance
is necessary. However, if it exceeds 25%, the toughness and ductility of the steel will decrease, and plate breakage or edge breakage will occur during the material manufacturing process, such as the cold rolling process, which will significantly impair manufacturability.
It is preferably 5% or less, preferably in the range of 17 to 25%.

Cu, Mo: These components alone or in combination are effective for corrosion resistance. Even if Cu exceeds 1.5% and MO exceeds 5%, the corrosion resistance improvement effect is saturated and workability decreases, so the upper limits can be set to Cu: 1.5% and Mo + 5.0%. desirable.

Nb, Ti: These components alone or in combination can
It is effective for intergranular corrosion by fixing 10N, but Nb: 0.6
If added in excess of 0%, Ti: 0.2%, saturation will occur and the toughness will decrease, so the upper limit is set to Nb: 0.60%, T:
i: Desirably 0.2%.

<Example> High-purity ferritic stainless steel having the composition indicated by Nα1 to 5 in Table 1 is melted, made into a slab by continuous casting, and then hot-rolled as usual to produce a hot-rolled steel strip with a plate thickness of 4M. And so. After rolling and annealing this hot-rolled steel strip at the rolling reduction ratio of the first bath shown in Table 1, both were cold-rolled to a thickness of 0.4+nm.
The final product was brightly annealed and skin-pass rolled, and its gloss and whiteness were measured and evaluated.

As is clear from Table 1, sample material No. of the present invention example.

1 to 3 all have glossiness (20') of 1000 or more,
It was found that a whiteness of 27.0 or less was evaluated as good, whereas Comparative Example No. 4.5 had a low gloss and a high whiteness and was evaluated as poor.

The evaluation criteria for glossiness and whiteness are as follows.

Glossiness Glossiness measures the reflectance of the board surface based on JIS Z 8741, and the measurement method is at an incident angle of 20
The sample surface is irradiated with a light beam of a constant intensity at an angle of 20°, and the intensity of the reflected light is measured at a reflection angle of 20°.

The measured value is shown as a relative value when the reflectance of the standard sample is 82.0. Therefore, the larger the value, the better the gloss.

Transparency whiteness indicates the color spacing of the plate surface based on Hunter whiteness: W (Lab), and the specific measurement method is to irradiate a sample with white light and measure the tristimulus value of the reflected light. Measure. Tristimulus values are three independent quantities that determine color, and are calculated from the ratio curve of sensory stimulation by a spectrum of unit energy. The color is expressed as a position in three-dimensional coordinates by taking the brightness and the hue and saturation on the horizontal axis.) The position of the color of the sample was determined, and the distance between that position and pure whiteness was subtracted from 100. The whiteness is expressed as a value. Therefore, a whiteness of 100 is pure white, and a whiteness of 0
is pure black, and the smaller the value, the blacker the luster.

<Effects of the Invention> In the present invention, after rolling a high-purity ferritic steel sheet in the first bath,
High-temperature annealing makes it possible to obtain high-gloss cold-rolled products, which has great industrial effects.

Claims (1)

[Claims] When cold rolling a high-purity ferritic stainless steel hot rolled annealed steel strip, the first pass of cold rolling requires 5 to 30%
A method for producing a high-purity ferritic stainless steel sheet with excellent gloss, which comprises rolling down, heat-treating at a temperature range of 950 to 1100°C, cold-rolling to a predetermined thickness, and bright annealing.