JP2001226718A - Method for producing stainless steel sheet excellent in flatness after etching - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a high strength austenitic stainless steel sheet excellent in flatness after etching by a simple method without requiring equipment used exclusively for tension annealing. SOLUTION: An annealed austenitic stainless steel strip is subjected to cold rolling at a rate of decrease in thickness of 5% or more, is thereafter modified at an elongation percentage of 0.08% or more by a tension leverller, is successively subjected to threading treatment for imparting tension equivalent to 0.7 to 1.0 times the 0.2% proof stress of the cold rolling stock applied and is moreover subjected to annealing treatment at a material temperature of 700 to 800 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a stainless steel strip used for forming a shape of a target part by etching, and more particularly to a method for producing a high-strength austenitic stainless steel sheet having excellent flatness after etching.

[0002]

2. Description of the Related Art In recent years, members used for electronic equipment and precision equipment are required to have light weight or dimensional accuracy, and high strength characteristics and good flatness are strongly demanded for these materials. I have. In addition, in order to improve the adhesion with solder, an adhesive or a paint, or to impart design, a part of the surface is partially or entirely roughened by etching. May be applied. As these materials, in particular, high strength materials, cold-rolled austenitic stainless steel sheets are often used.

[0003] Cold-rolled austenitic stainless steel sheets are produced by changing the working ratio in finish cold rolling.
The strength level can be adjusted (temper rolling) using the work hardening phenomenon of the material. However, a stainless steel strip manufactured using ordinary cold rolling equipment cannot obtain sufficient flatness, and cannot be used as a material for parts with particularly strict dimensional accuracy. Therefore, tension leveler straightening or tension annealing is performed after cold rolling to improve flatness.

[0004] Generally, a stainless steel strip which has been subjected to a straightening treatment by a tension leveler facility after cold rolling is subjected to repeated bending and unbending in a state where a high tension is applied thereto. A large residual stress is generated in the vicinity. When the surface of a steel sheet cut from such a steel strip is etched to reduce its thickness, the balance of residual stress is lost, and the steel sheet is warped.

As a method of manufacturing a decorative sheet by etching the surface of a steel sheet, for example, Japanese Patent Publication No. 4-6922
No. 9, the tension imparting annealing at a temperature equal to or lower than the softening temperature of the material while applying a tension below the yield point to the steel sheet after cold rolling,
A method of performing so-called tension annealing is disclosed. This tension annealing method is used as a means for correcting the flatness of a high-strength stainless steel sheet and reducing the residual stress therein. However, the implementation of the tension annealing method requires the preparation of a complex dedicated heating facility.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a high-strength austenitic stainless steel having excellent flatness after etching by a simple method without requiring the above-mentioned dedicated equipment (tension annealing furnace). It is to provide a method for manufacturing a steel sheet.

[0007]

Means for Solving the Problems The present inventors have presumed that the "warp" generated after etching a stainless steel plate deteriorates the flatness, which is thought to be caused by the residual stress of the steel plate. Residual stress was investigated for stainless steel sheets with different manufacturing conditions. As a result, after adjusting the cold rolling condition and the straightening condition by the tension leveler, it was found that the residual stress can be reduced by applying a tension equivalent to 0.2% proof stress or less of the cold rolled material and further performing low temperature annealing. Completed the invention.

The gist of the present invention resides in the following method for producing a stainless steel sheet.

[0009] After cold-rolling the annealed austenitic stainless steel cold-rolled steel strip at a reduction rate of 5% or more in thickness reduction rate, the elongation rate is set to 0.08% or more and straightened by a tension leveler. A tension equivalent to 0.7 to 1.0 times the 0.2% proof stress of the rolled material is applied, and the material temperature is further increased to 700 to 800 ° C.
A method for producing a stainless steel sheet having excellent flatness after etching, characterized by performing an annealing treatment.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The cold-rolled austenitic stainless steel strip used in the production method of the present invention can be produced by a general method. That is, after a steel slab produced by the ingot-making method or the continuous casting method is formed into a steel strip by hot rolling, soft annealing, pickling and cold rolling are repeated to obtain a predetermined thickness.

After the cold-rolled austenitic stainless steel strip obtained by the above method is annealed, cold rolling is further performed in the present invention. This cold rolling is performed in order to impart a desired material strength, and the cold working ratio is changed according to the desired strength. Here, in order to obtain a high-strength material equivalent to a stainless steel strip for a spring specified in JIS G4313 using cold working, a working rate of at least 5% or more is required. Although the upper limit of the working ratio is not particularly defined, it is desirable to set the upper limit to about 50% in order to secure the ductility when forming work is required later.

The austenitic stainless steel strip after cold rolling contains factors that impair flatness, such as edge waves and medium elongation. In order to remove this, correction is performed by a tension leveler facility. Here, the tension leveler equipment is an equipment that performs bending and bending back twice or more in a state where a steel strip is passed through a roller equipment to apply a constant tension to the steel strip.

In the present invention, the straightening condition by the tension leveler equipment is set such that the elongation rate is 0.08% or more (that is, the length of the steel sheet in a certain section becomes longer by 0.08% or more). If the elongation is less than 0.08%, the effect of correcting flatness cannot be sufficiently obtained. The upper limit of the elongation is not particularly specified, but if the elongation is excessive, the material may be broken.
A level that can correct flatness such as medium elongation (about 1.
Up to 0%).

In order to evaluate flatness such as edge wave and middle elongation, steepness is used. The steepness is a value calculated from a wavy form that occurs in the longitudinal direction of the steel sheet. As shown in FIG. 4, when the wave height is h and the wavelength is L, (h / L) × 1
This is the maximum value of the value represented by 00 (%). In the present invention, the steepness is desirably 1.0% or less, desirably 0.5% or less. This value corresponds to flatness such as edge wave and middle elongation required for a material for a member having strict dimensional accuracy.

Next, in the present invention, a tension of 0.2% or less of the cold-rolled material is applied to the steel strip after passing the tension leveler at room temperature (hereinafter, this is referred to as “tension application”). Do. This is for reducing the residual stress inherent in the material generated by the tension leveler passing plate and improving the flatness after etching. The equipment used at this time may be any apparatus having a pair of bridle rolls that can grip the steel strip and apply tension between the steel sheet rewind reel and the take-up reel. When a tension leveler is used, all the bending rolls existing between the pair of bridle rolls may be released from the steel strip.

If the tension applied to the steel strip during threading is less than 70% of the 0.2% proof stress of the cold-rolled material, the effect of reducing the residual stress cannot be obtained. Further, when the tension applied to the steel strip exceeds the tension corresponding to 0.2% proof stress, there is a possibility that the steel strip may break during threading. Therefore, the tension applied to the steel strip is
A tension corresponding to from 70% or more of the 0.2% proof stress of the cold-rolled material to 0.2% proof stress, that is, 0.7 to 1.0 times the 0.2% proof stress is appropriate.

FIG. 1 is a diagram showing the relationship between the tension applied to the steel strip at the time of applying tension and the curvature after etching. This figure shows the annealed 0.294 mm SUS 304 stainless steel cold-rolled steel strip subjected to cold rolling (working rate: 32%) and straightening by a tension leveler (elongation rate: 0.5%).
Using a steel strip of 0.2 mm (0.2% proof stress is 1180 MPa), the tension applied to the steel strip is converted to stress from 0 to 1215 MPa and tension is applied, and the steel sheet cut from the obtained steel strip is half-etched After that, it is the result of investigating the flatness.

Evaluation of half etching and flatness
This was performed by the method shown in FIG.

FIG. 2 is a schematic diagram for explaining a half-etching method and a flatness evaluation method. First,
As shown in FIG. 2 (a), a steel sheet 1 having a length L, a width B and a thickness t
A resist mask 2 for preventing etching is applied to one surface (the lower side in the figure) of the substrate. Next, the steel sheet 1 coated with the resist mask 2 is immersed in a solution of ferric chloride, and etching (half etching) is performed until the sheet thickness t becomes 1/2. The half-etched steel sheet 1-1 bends as shown in FIG. 2B if a residual stress is present. Further, when the resist mask 2 is removed, a curvature (warpage) occurs due to the residual stress of the steel plate 1-1. Assuming that the shape of this warpage is an arc, FIG.
strings as shown in (c) the length L ₁ and warpage h ₁ was measured to calculate the radius of curvature r by the following formula. _{r = 0.5h 1 {1 + L} 1 2 / (4 · h 1 2)} Half warp curvature after etching (ρ = 1 / r) corresponds to the magnitude of the residual stress existing in the steel sheet prior to etching.

As is apparent from FIG. 1, when the tension at the time of applying tension exceeds 0.7 times (825 MPa) the 0.2% proof stress of the cold-rolled material in terms of stress, the warpage curvature (ρ) increases. It decreases as you do. The tension is 0.2% proof stress of the material (118
0MPa), the warp curvature becomes almost 0 (zero).

In the present invention, low-temperature annealing is performed in order to further greatly reduce the residual stress of the steel strip which has been reduced by applying the tension-applying plate and to reduce the warpage after etching. Residual stress is significantly reduced due to the combined effect of the tension applying threading and low-temperature annealing. As equipment for this purpose, ordinary continuous bright annealing equipment can be used. In this process, the material temperature is set to 700 to 800 ° C. If the treatment temperature is lower than 700 ° C., the effect of reducing the residual stress cannot be sufficiently obtained. On the other hand, when the temperature exceeds 800 ° C., the material is softened, and the strength characteristics deteriorate. The annealing time is desirably about 30 seconds to 10 minutes. If the holding time of the low-temperature annealing is less than 30 seconds, the effect of reducing the in-plane uniform residual stress of the steel sheet cannot be sufficiently obtained. However, if the holding time exceeds 10 minutes, the material may be softened and the strength properties may be reduced. The low-temperature annealing treatment has an effect of improving the spring limit value and suppressing a dimensional change due to reheating in addition to reducing the residual stress.

In order to guarantee the flatness after etching, the austenitic stainless steel sheet used particularly for a member having strict dimensional accuracy needs to have a warp curvature after half etching of 0.0030 mm ^-1 or less.

FIG. 3 is a diagram showing the relationship between the low-temperature annealing temperature and the curvature after etching.

FIG. 3 shows a SUS 30 having undergone the following processing.
4 shows the results of examining flatness and material hardness after half-etching a steel sheet. That is, the annealed sheet thickness 0.29
Cold rolling on 4mm SUS 304 stainless cold rolled steel strip (work rate 32
%) And a tension leveler (elongation: 0.5%) and a steel strip with a thickness of 0.200mm (0.2% proof stress is 1180MPa), and the tension given to the steel strip is converted into stress, equivalent to 1110MPa. Was given. Then raise the temperature of the material to 550 ° C
To 825 ° C. for 1 minute. The flatness after the half etching was evaluated by the above-mentioned curvature.

As is apparent from FIG. 3, the reason why the hardness of the material is higher than the hardness before the processing when the processing temperature of the material is 550 to 650 ° C. is in this temperature range where the hardening due to aging occurs. This is because the hardness has increased. The curvature after etching decreases as the processing temperature increases. When the annealing temperature is 700 ° C. or more, the warpage curvature becomes 0.0030 mm ⁻¹ or less, and the flatness is improved. However, when the temperature exceeds 800 ° C., the hardness of the material rapidly decreases. For this reason, in the present invention, the low temperature annealing temperature is set to 700 to 800 ° C. This temperature range is a range in which the so-called recovery phenomenon in which the processing strain inherent as dislocations in the material disappears works effectively, and it is separately tested that the temperature is lower than the temperature at which the material begins to soften due to the recrystallization phenomenon. Confirmed by

[0026]

[Example] SUS 304 and SU specified in JIS G4313
Annealed stainless steel strip of S301 (sheet thickness 0.220mm,
217 mm, 0.183 mm and 0.179 mm) were rolled at the cold rolling reduction shown in Table 1 to obtain a steel strip having a thickness of 0.15 mm. The strength characteristics of these steel strips were measured by Vickers hardness measurement specified in JIS Z2244, and the 0.2% proof stress of the material was measured by a tensile test specified in JIS Z2241. The measurement results are shown in Table 1.

[0027]

[Table 1]

The steel strip after cold rolling was subjected to straightening by a tension leveler, application of tension and low-temperature annealing under the respective conditions shown in Table 2. Here, as the equipment for passing the tension, the normal leveling equipment was used to open all the leveler rolls so that the steel strip did not come into contact with the leveler rolls. As the equipment for low-temperature annealing, a continuous bright annealing equipment with a heating furnace length of 9 m was used. The passing speed of the low-temperature annealing was 8 m / min.

[0029]

[Table 2]

The obtained steel strip has a width of 650 mm and a length of 1200 m
m was cut out of the steel sheet, and the flatness of the steel sheet, such as edge wave and middle elongation, was evaluated by the aforementioned steepness. In addition, the evaluation of the flatness after etching was as follows.
A 100 mm steel plate was cut out, and the curvature of the steel plate after half etching was measured. Further, the Vickers hardness of the steel sheet was measured. Table 2 shows the results.

As is clear from Table 2, in the steel sheets manufactured by the method of the present invention (test numbers 1 to 6), the steepness is in the range of 0.4 to 0.8%, and the flatness such as edge wave and middle elongation is obtained. Is good. Also, the curvature after half etching is
It is in the range of 0.0016 to 0.0021 (mm ^-1 ), and the flatness after etching is both good. Furthermore, the hardness after low-temperature annealing is Vickers hardness of 309 to 430, and no decrease in strength characteristics due to annealing is observed.

On the other hand, the steel sheets of Test Nos. 7 to 9 of the comparative example are examples in which the low-temperature annealing treatment is not performed. In any case, the warp curvature after half etching is in the range of 0.0094 to 0.037 (mm ^-1 ), and the flatness after etching is poor.

The steel sheet of Test No. 10 is a steel sheet which has not been subjected to a tension-applying sheet, has a large curvature curvature after half-etching of 0.0094 (mm ^-1 ), and is inferior in flatness after etching.

In the steel sheets of Test Nos. 11 and 12, the tension of the tension-applied strip is 0.54 times and 0.50 times the 0.2% proof stress of the steel sheet, and the warp curvature after half-etching is as large as 0.0076 and 0.0072 (mm ^-1 ). And poor flatness after etching.

The steel sheet of test number 13 has an annealing treatment temperature of 68
Since the temperature is as low as 0 ° C, the curvature after half-etching is 0.005
It is as large as 2 (mm ^-1 ) and is poor in flatness after etching.

The steel sheet of Test No. 14 had an annealing treatment temperature of 82
Since the temperature was as high as 0 ° C., the hardness of the steel sheet was as low as 266 in Vickers hardness.

The steel sheets of Test Nos. 15 and 16 are examples in which the tension leveler was not corrected, and the steepness was 1.7
% And 1.3%, which are inferior in flatness.

[0038]

The method of the present invention produces a high-strength austenitic stainless steel sheet having excellent flatness after etching by specifying cold rolling conditions, tension leveler conditions, tension passing conditions and low-temperature annealing conditions. can do. This method does not require a special tension annealing equipment, and can be carried out if there is a usual tension leveler equipment for producing stainless steel and a continuous bright annealing furnace.

[Brief description of the drawings]

FIG. 1 is a diagram showing a relationship between a tensile stress applied to a steel sheet during tension application and a warp curvature of the steel sheet after half-etching.

FIG. 2 is a schematic diagram for explaining a half-etching method and a flatness evaluation method.

FIG. 3 is a diagram showing the relationship between the material temperature during low-temperature annealing and the curvature of the steel sheet after half-etching.

FIG. 4 is a diagram for explaining a method of calculating a steepness for evaluating flatness generated in a steel plate.

[Explanation of symbols]

1. Low temperature annealed steel sheet 1-1. 1. etched steel plate Resist film

Claims (1)

[Claims] Claims: 1. After cold rolling an annealed austenitic stainless steel strip at a working ratio of 5% or more with a reduction rate of thickness, straightening by a tension leveler with an elongation rate of 0.08% or more, 0.7% of 0.2% proof stress of the cold rolled material
A tension equivalent to ~ 1.0 times is applied, and the material temperature is increased by 700
A method for producing a stainless steel sheet having excellent flatness after etching, characterized by performing an annealing treatment at a temperature of up to 800 ° C.