JPH02175820A - Manufacture of steel sheet for shadow mask - Google Patents

Abstract

PURPOSE:To attain the reduction of residual stress simultaneously with the straightening of the shape of a strip after cold rolling by carrying out softening by the use of a cold rolled steel sheet for shadow mask which is previously cold-rolled as a material sheet, forming the above sheet to the final sheet thickness by means of cold rolling at the prescribed draft, and then applying temper annealing to the above sheet at specific temp. CONSTITUTION:A strip prepared by applying softening to a material sheet cold-rolled for use in steel sheet for shadow mask is cold-rolled at 70-85% draft and finished to the final sheet thickness, to which temper annealing is applied at 450-500 deg.C. By this method, sufficient tensile strength can be provided and also the height of center buckle and the reduction of residual stress can be simultaneously attained, by which the goods qualified for steel sheet for shadow mask can be obtained.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a method of manufacturing a steel plate for shadow masks used in cathode ray tubes for color televisions, and particularly relates to a method of manufacturing a steel plate for shadow masks used in cathode ray tubes for color televisions, and particularly relates to a method of manufacturing a steel plate for a shadow mask used in a cathode ray tube for a color television, and in particular, a method for manufacturing a steel plate for a shadow mask used in a cathode ray tube for color television. The present invention relates to a method for manufacturing a steel plate for shadow masks, which aims to improve the process and reduce residual stress.

(Prior art) Japanese Patent Laid-Open No. 61-49009 discloses that a shape correction tool using pressurized fluid is used to produce a steel plate for shadow masks with good flatness at a high yield. .

That is, a first step of bending a cold-rolled strip to a predetermined thickness at least once with a shape straightening tool using pressurized fluid with a bending radius of 8+ mm or less under tension, and the shape straightening tool a second step of applying at least one bend to the strip after the first step with an angle correction tool that uses pressurized fluid and has a bending radius that is twice or less than the bending radius of the shape correction tool; a third step of applying at least one bend to the strip after the second step using a parallel straightening tool using a pressurized fluid having a bending radius of 2 times or more and 6 times or less of the bending radius of the strip. This is a method of manufacturing a steel plate for a shadow mask.

(Problems to be Solved by the Invention) Shadow masks used in cathode ray tubes for color televisions are usually made of a cold-rolled low-strength carbon steel plate with a thickness of about 0.1 to 0.3 mm, and are made by photo-etching a large number of uniform etchings. However, if there is residual stress in the steel plate, uneven strain will occur during the etching process, causing phenomena such as non-uniformity in the shape and size of the micropores. This causes undesirable effects such as distortion on color television images.

In general, cold-rolled steel sheets have large residual stress in their surface layers. According to flatness correction by repeated cold bending, such as the method disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 61-49009, the flatness can be corrected considerably, but the distribution of residual stress in the thickness direction of the steel plate is Even if it is possible to change the maximum value, its maximum value is hardly reduced.

(Means for Solving the Problems) In order to solve the above-mentioned difficulties in manufacturing steel sheets for shadow masks, the inventor conducted various studies and developed a method of cold rolling using hot-rolled sheets as raw materials. A strip that has been subjected to softening annealing for the original steel plate for shadow masks is cold rolled at a reduction rate of 70 to 85% to achieve the final thickness, and then tempered and annealed at a temperature of 450 to 500°C to prevent the material from softening. It has been found that by doing this, it is possible to simultaneously improve the shape of the strip after rolling and reduce residual stress.

In this invention, a strip obtained by softening and annealing a steel sheet for shadow masks is subjected to cold rolling at a rolling reduction ratio of 70 to 85%, and then temper annealing is performed at a temperature of 450 to 500°C. This is a method for manufacturing a steel plate for a shadow mask, which is characterized in that it simultaneously improves the strip shape and reduces residual stress.

Now, the characteristic values generally required for steel sheets for shadow masks are tensile strength of 60 kg/nun" or more, flatness of 2.0 marks or less at medium elongation height, and residual stress (between the surface layer and center of the sheet thickness). Difference) C: 0.01wt or less is less than 10kg/fflm2, but the raw material for this type of steel plate is generally C: 0.01wt.
% or less, especially 0.002 to 0.006 L%, Sj
: 0. LwL% or less, especially 0.040wt% or less,
Mn: 0.1-0.5wt%, especially 0, 45
Ultra-low carbon steel with a composition range of wt% or less, Al: o, ot to 0.1wt%, especially 0.02 to 0.06wt%, with the remainder substantially consisting of Fe and unavoidable impurities. Cold-rolled plates are suitable. As such an original plate C:
0, 002sv t%, St: 0.021w
t%, Mn: 0.14wt%, P: 0.01
6wt%, S: o, oo'rwt%, Affi
: 0.042wt% The remainder is substantially composed of Fe.When a strip obtained by annealing a cold-rolled plate is cold-rolled at a reduction rate of 70% and finished to the final thickness, its characteristic value (marked with *) , Furthermore, the relationship between tensile strength, medium elongation height, and residual stress with respect to annealing temperature when temper annealing is performed at various annealing temperatures is shown with an O mark in Figures 1 to 3. That's right.

From Figure 1, in order to satisfy the tensile strength requirements, the annealing temperature should be 500"C or less, and from Figures 2 and 3, in terms of medium elongation height and residual stress, the annealing temperature should be 450"C. It turns out that the above is necessary.

Therefore, by performing temper annealing in the temperature range of 450 to 500°C, we can satisfy the tensile strength, medium elongation height,
At the same time, residual stress can be reduced.

(Function) The reason why the above-mentioned composition of the cold-rolled original sheet for a steel sheet for a shadow mask is desirable in the present invention is as follows.

C: 0.01 int% or less C is because if it exceeds 0.01 int%, the coefficient of thermal expansion becomes excessive.

Si: 0.1 wt% or less This is because if Si exceeds 0.1 wt%, it will not soften sufficiently even if annealed.

Mn: Q, 1 to 0.5 wt% Mn contributes to improving hot workability, so 0.1 wt%
This is because the coefficient of thermal expansion becomes excessive if it exceeds 0.5 wt%.

Af: 0.01 to 0.1 wt% Al is suitably in the range of 0.01 to 0.1% as an acid agent.

In addition to the above, P: 0.03wt% as an impurity in steel
Hereinafter, S: It is desirable that the content be 0.04 wt% or less.

A hot-rolled sheet of raw material is cold-rolled to form an original sheet, and then cold-rolled at a reduction rate of 70 to 85% to finish it to a specified thickness, but if the reduction rate is less than 70%, it is too soft and insufficient. Since sufficient mechanical strength cannot be obtained, and if it exceeds 85%, there are manufacturing restrictions, so it is limited to a range of 70 to 85%.

Finally, temper annealing is performed in an atmosphere mainly consisting of nitrogen gas in a temperature range of 450 to 500°C, and the reason for limiting this temperature range is as described in FIGS. 1 to 3.

(Example) An embodiment of the present invention will be described below.

A hot-rolled plate with a thickness of 2.0 mm is milled by a tandem mill to a thickness of 0.6 mm.
Cold rolled steel plate cold rolled into a plate (C: 0.002wt%,
Si: 0.021wt%, Mn: 0.14wt%
, P: 0.016ivt%, S: 0.007wt
%^1: 0.042wt%, balance Fe) was degreased as a base plate, then subjected to softening annealing, passed through a cold strip mill again, and cold rolled to 0.15mm (
When the final cold rolling (near 5%) was carried out, the tensile strength of this strip was 75 kg/mm'', the mid-elongation height was 3.5 marks on average, and the shape was rather poor, with the surface layer and center of thickness The residual stress calculated by taking the difference between the parts is also 40 kg/
The steel plate was as large as "nun" and was unsuitable as a steel plate for a shadow mask as it was.

On the other hand, the above strip was subjected to N2: 95 Vo
When thermal annealing was performed at 500'C in an atmosphere of 1% or more, the tensile strength was 65 kg/me'', the average elongation height was 0.8'', and the residual stress was 5 kg/mm'', making it a steel plate for shadow masks. I was able to obtain a qualified product.

In this way, it was possible to salvage strips that were conventionally unsuitable for use as steel plates for shadow masks, and a significant improvement in yield was achieved. Furthermore, since shape correction and residual stress reduction can be performed in one process, there is also a great economic effect.

(Effects of the Invention) According to the method of the present invention, it is possible to bring about a remarkable effect in improving the shape and reducing residual stress of a steel plate for a shadow mask after rolling, and it is also useful in terms of improving the yield of products.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the relationship between tensile strength and annealing temperature, Figure 2 is a diagram showing the relationship between medium elongation height, and Figure 3 is a diagram showing the relationship between residual stress.

Claims (1)

[Claims] 1. A strip obtained by softening and annealing a cold-rolled original sheet for shadow mask steel sheets is cold rolled at a reduction rate of 70 to 85% to achieve the final thickness, and then heated to 450 to 500°C.
A method for producing a steel sheet for a shadow mask, characterized in that the strip shape after cold rolling is improved and the residual stress is reduced at the same time by performing temper annealing at a temperature of .