JPH04168227A - Production of austenitic stainless steel sheet or strip - Google Patents

Abstract

PURPOSE:To prevent the generation of pocket wave defects at the time of forming an austenitic stainless steel sheet or strip by heat-treating the final cold-rolled, finish-annealed and skin pass-rolled sheet under specified temp. conditions. CONSTITUTION:An austenitic stainless steel slab contg., by weight, <0.08% C, <2.0% Si, <5.0% Mn, 11-32% Cr, 5-25% Ni, <0.2% N or further at least one kind among 0.1-6.0% among 0.1-6.0% Mo, 0.1-3.0% Cu, 0.1-0.9% Nb, <1.0% Ti, V and Zr and <0.005% B is hot-rolled, annealed and cold-rolled into a sheet. The sheet is finish-annealed, then skin pass-rolled and finally aged at 300-700 deg.C for 5sec to 50hr. When the austenitic stainless steel sheet or strip is press-formed or roll-formed into a product, pocket wave defects, which means the ruggednesses of the bottom and side plate of the product, are never generated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for manufacturing an austenitic stainless steel plate or steel strip that can prevent pocket waves generated during press forming or roll forming.

[Prior Art] Normally, austenitic stainless steel sheets or steel strips are hot-rolled, hot-rolled, annealed, pickled, cold-tempered once or twice or more with an intermediate annealing in between, and then subjected to final annealing. The product is manufactured through skin pass rolling.

[Problem to be Solved by the Invention 1] By the way, when press forming or roll forming is performed on products made of these austenitic stainless steel plates or steel strips, pocket waves, which make the bottom plate and side plate parts of the processed product uneven, occur. (Also called oil can) occurs, which damages the appearance of processed products, which has become a problem. In addition, as an improvement to the conventional deep drawing process, as described in Japanese Patent Application Laid-Open No. 57-79122, aging for 10 seconds or more at a temperature of 100 to 450°C between cold rolling passes is performed during cold rolling. A method of improving deep drawability by applying it at least once is known. Regarding ferritic stainless steel, as described in JP-A-02-185916, weather resistance and
Methods have been proposed to ensure corrosion resistance and reduce pocket waves.

However, with regard to the prevention of pocket waves in austenitic stainless steel sheets or steel strips, a manufacturing technology that can fundamentally solve this problem has not yet been established.

An object of the present invention is to produce an austenitic stainless steel plate or steel strip that can prevent blurring and waves that occur during press forming or roll forming.

[Means to solve the problem The present invention is.

C: 0.08% by weight or less, Si: 2.0% by weight or less, Mn: 5.0% by weight or less, Cr: 11-32% by weight, N1: 5-25% by weight, N: 0.2% by weight % or less, with the remainder consisting of Fe and unavoidable impurities. After cold rolling, finish annealing and skin pass rolling, an austenitic stainless steel plate or steel strip is subjected to S at a temperature of 300 to 700°C.
This is a method for producing an austenitic stainless steel plate or steel strip, which is characterized by subjecting the method to heat treatment for 50 hours or less.

Further components of the austenitic stainless steel plate or steel strip include Mo: O, 1 to 6.0% by weight, Cu: 0.1 to 3.0% by weight, and Nb: O, L to 0.9% by weight.

T i, V, Zr: 1.0% or less, B: 0.0
It is even more preferable that it contains 0.05% by weight or less.

[Effect 1] When the present inventors press-form or roll-form an austenitic stainless steel plate or steel strip,
As a method to prevent pocket waves from occurring, conventional manufacturing processes, ie, after hot rolling, hot rolling annealing, pickling,
It was discovered that pocket waves can be prevented during press forming or roll forming by performing annealing under appropriate conditions following the manufacturing process of two or more cold rollings with intermediate or intermediate annealing, final annealing, and skin pass rolling. .

Hereinafter, the characteristic structure of the present invention and its operation will be explained.

11 The present invention follows the conventional manufacturing process to produce 300 to 70
It is characterized by performing aging heat treatment at a temperature range of 0°C for 5 seconds or more and 50 hours or less. The reason why the aging temperature was limited to 300°C is that the effect of preventing pocket waves is low below 300°C, so the lower limit was set to 300'C. In addition, the reason why the upper limit was set at 700°C is that if the temperature exceeds 700°C, the effect will be saturated, corrosion resistance will deteriorate significantly, and the surface shape of the material will deteriorate. . Further, the reason why the heat treatment time was set to be 5 seconds or more is because the effect is small if the heat treatment time is less than 5 seconds, so the lower limit is set to 5 seconds. Further, the reason why the heating time was set to 50 hours or less is that if the effect exceeds 50 hours, the effect reaches almost a saturation value and the corrosion resistance of the surface deteriorates significantly, so the upper limit was set to 50 hours.

(2) In addition, in the present invention, the composition of the austenitic stainless steel plate or steel strip is ■ C: 0.08
% by weight or less, Si: 2.0% by weight or less, Mn: 5.0% by weight or less, Cr: 11 to 32% by weight, Ni: 5 to 25% by weight, N: O-2% by weight or less. The remainder is Fe and unavoidable impurities.

■ In addition to the above component (■), Mo: 0.1 to 6.0% by weight, Cu: 0.1 to 3.0% by weight, Nb: 0.1 to 0.9% by weight, Ti, V, Zr: 1.0% by weight or less, B: 0.00
It is even more preferable to use an austenitic stainless steel plate or steel strip containing 5% by weight or less.

The reasons for limiting each of the above components will be explained below.

Cr: Cr is an important component indispensable for improving corrosion resistance. The reason why the amount of Cr added was set at 11% by weight or more is that the corrosion resistance is not sufficient if the amount of Cr added is less than 11% by weight, so the lower limit was set at 11% by weight. Also, 32% by weight
The reason for the following is that when the amount exceeds 322 circles, the effect of improving corrosion resistance becomes saturated and the moldability decreases, making it uneconomical, so the upper limit was set at 32% by weight.

N and N are effective components for improving corrosion resistance and wear resistance. However, this effect becomes saturated when the content exceeds 0.2% by weight, and corrosion resistance and processability tend to decrease. Therefore, the upper limit was set at 0.2% by weight. Further, the lower limit is not limited because no matter how low the N amount is, it will not have any adverse effects.

C: A lower C value is preferable from the viewpoint of intergranular corrosion susceptibility. However, if the content exceeds 0.08% by weight, susceptibility to intergranular corrosion increases and corrosion resistance significantly decreases, so the upper limit was set at 0.09% by weight.

Ni: Ni is an element effective in forming austenite, and at least 5% by weight or more of Ni is required to stabilize the austenite structure. Therefore, the lower limit was set at 5% by weight. The reason why the upper limit is set to 25% by weight is that if it exceeds 25% by weight, grain boundary precipitation of carbides is promoted, hot workability is inhibited, and the material becomes extremely hard, resulting in deterioration of moldability.

Mn: Like Ni, Mn is also an austenite forming element, so by increasing the amount of Mn added, the austenite phase can be stabilized and the amount of Ni added can be reduced. Furthermore, although the addition of Mn is effective in improving hot workability, if the amount added exceeds 5% by weight, moldability and corrosion resistance deteriorate, so the upper limit was set at 5% by weight.

Si: Si is a useful component because it has a deoxidizing effect, but if the amount added exceeds 3.0% by weight, it will promote weld cracking and embrittlement, become hard, and reduce formability. The upper limit was set to 2.0%.

Mo: Mo is an element that improves corrosion resistance, but when the amount of Mo is 0.
The reason why it is set at 1% by weight or more is that the minimum required amount of Mo to be added is 1% by weight or more in order to suppress the progress of pitting corrosion.
The lower limit was set at 0.2% by weight.

Further, the reason for setting the content to be 6.0% by weight or more is that even if it exceeds 6.0% by weight, the effect is saturated and it becomes hard (and the moldability is significantly lowered), so the upper limit was set to 6.0% by weight.

Cu: Cu is also an element that improves corrosion resistance, but the reason why the amount of Cu added is set to 1% by weight or more is because the addition of 1% by weight of O without grooves has almost no effect in suppressing the progress of pitting corrosion.
The lower limit was set at 0.1% by weight. The reason for setting the upper limit to 3.0% by weight is that if it exceeds 3.0% by weight, the effect will be saturated and the moldability will decrease.
It was expressed as weight%.

Nb, Ti, V, Zr, B: Nb, Ti, V, Zr, H
Each element is a carbide- and nitride-forming element and improves corrosion resistance and moldability.

The reason why the amount of Nb added is set to 0.1% by weight or more is that if the amount of Nb added is less than 0.1% by weight, the effect of suppressing the grain boundary precipitation of carbides is not observed and no improvement in corrosion resistance can be expected. The content was 1% by weight. The reason for setting the content to 0.9% by weight or less is that if it is added in excess of 0.9%, the amount of carbonitrides precipitated increases, and conversely, the workability is impaired, so the upper limit was set to 0.9% by weight.

The amounts of Ti, V, and Zr added are 1.0% or less, and the amounts of B are each 0.0%. The reason for setting the OO content to 5% by weight or less is that molding processability deteriorates when added in excess of the above-mentioned values, so the upper limit was set at 1.0% by weight.

[Example J The present inventors heated an austenitic stainless steel slab having a chemical composition as shown in Table 1 to 1200° C., and then hot rolled it to a thickness of 4 mm.

0,3 after hot rolling treatment and annealing in the temperature range of 800℃1100℃
Cold rolled to a thickness of mm and then heated at 800°C to 1100°C
After final annealing, a steel plate was manufactured using a normal manufacturing process in which skin bath rolling (reduction ratio: equivalent to about 1%) was performed. These materials are then heat treated under various conditions as shown in Tables 2 to 4, and a stainless steel plate or steel strip l is rolled in the rolling direction 2 into the shape shown in Figure 1. Pocket wave 3 created by molding and roll forming
The relationship between the degree of heat treatment and heat treatment conditions was investigated.

FIGS. 2 and 3 show the relationship between the degree of pocket waves and heat treatment conditions, respectively. As a measure for quantitatively evaluating the degree of pocket waves, we decided to quantitatively evaluate the size of pocket waves by scanning an eddy current displacement meter at the center of the wave where pocket waves are most likely to occur. Experimental results are shown in Tables 2 to 4.

According to Tables 2 to 4, the generation of pocket waves can be prevented by applying heat treatment under appropriate conditions specified by the present invention in addition to the normal manufacturing process with skin pass rolling as the final process. is recognized.

In addition, in Tables 2 to 4, the degree of pocket waves (A-D) is as follows: A: Good pocket wave resistance, wave height h w <
0.5 mm.

B: Wave height 0.5 m m≦h w < 1.5 m
m, C: Wave height 1.5 mm m≦h w <2.
5 mm, D: Wave height hw≧2.5 mm.

respectively.

In addition, the corrosion resistance was evaluated according to JISD 02 shown in Table 5.
The appearance photograph after 3 cycles of the CASS test based on 01 was image-processed, and the rusted area was relatively evaluated.

The criteria for judgment is that less than 20% of the rusted area is considered good;
% or more was considered defective.

[Effects of the Invention] As described above, according to the present invention, it is possible to produce an austenitic stainless steel plate or steel strip that can prevent pocket waves generated during press forming or roll forming.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram showing a molded material for roofs, Figure 2 is a line showing the relationship between annealing temperature and pocket wave height, and Figure 3 is a line diagram showing the relationship between annealing time and pocket wave height. ,
FIGS. 4 and 5 are graphs showing the relationship between the rusting area ratio, heat treatment time, and heat treatment temperature, which were determined by image processing the external appearance photographs after three cycles of the CASS test. ■...Stainless steel plate 2...Rolling direction

Claims (1)

[Claims] 1 C: 0.08% by weight or less, Si: 2.0% by weight or less, Mn: 5.0% by weight or less, Cr: 11 to 32% by weight, Ni: 5 to 25% by weight, After cold rolling, finish annealing, and skin pass rolling an austenitic stainless steel plate or steel strip consisting of N: 0.2% by weight or less, with the remainder being Fe and unavoidable impurities, it is heated at a temperature of 300 to 700°C for 5 seconds or more. 1. A method for producing an austenitic stainless steel plate or steel strip, characterized by subjecting it to heat treatment for 50 hours or less. 2 The austenitic stainless steel plate or steel strip further contains Mo: 0.1 to 6.0% by weight, Cu: 0.1 to 3.0% by weight, Nb: 0.1 to 0.9% by weight, and Ti. , V, Zr: 1.0% by weight or less, B: 0.005% by weight or less. manufacturing method.