JPH08165519A - Production of austenitic stainless steel foil for spring - Google Patents

Abstract

PURPOSE: To produce a stainless steel foil for spring excellent in the shape after half-etching treatment to the one side surface by executing a skinpass rolling after bright-annealing the austenitic stainless steel cold-rolled thin sheet under non-oxidizing gas having a specific nitrogen concn. CONSTITUTION: After bright-annealing the austenitic stainless steel thin sheet worked to 0.04-0.30mm thickness by the cold-rolling at about 1100 deg.C four about 20sec under the non-oxidizing gas atmosphere composed of mixed gas of 10vol.% nitrogen concn. and the balance hydrogen gas, the skin pass rolling is executed at >=35% draft to make the foil material having about 76μm thickness. The quantity of nitrogen infiltrating onto the surface of the stainless steel foil is restrained by limiting the nitrogen content in the bright-annealing atmosphere, and the austenitic stainless steel foil for spring having small warp after half- etching treatment to the one side surface, is produced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an austenitic stainless steel foil for springs, which has a small warpage after one-side etching treatment and is used for precision springs of electronic equipments and precision machines requiring excellent spring characteristics. Is.

[0002]

2. Description of the Related Art Conventionally, precision springs made of austenitic stainless steel foil have been used in precision equipment such as gimbal springs and suspensions that support magnetic heads of hard disks. Along with the advancement of the precision of equipment, there is a strong demand for a precision spring that is excellent in the shape of the spring (in particular, the warp after half-etching on one side) and has high spring characteristics.

As a method of manufacturing the above-mentioned spring, a cold-rolled austenitic stainless steel thin plate is bright annealed (for example, in a non-oxidizing gas atmosphere of 75 vol% hydrogen gas and 25 vol% nitrogen gas), and then prepared. Usually adopted is a method of performing quality rolling to produce an austenitic stainless steel foil for springs having the target strength characteristics, and then processing the foil into a predetermined shape by single-sided etching with a reagent etc. to make a precision spring. Has been done.

However, when the austenitic stainless steel foil for springs manufactured by the conventional method is subjected to the one-sided etching treatment, a warp as shown in FIGS. 1 and 2 occurs. It is considered that this warp is caused by the balance of the residual stress in the sheet thickness direction being destroyed by single-sided etching of the foil having different sectional residual stresses in the sheet thickness direction at the central portion and the surface layer portion.

It is considered that the factor of the warp is due to the difference in the component composition, hardness distribution (residual stress), etc. between the surface layer portion and the central portion of the foil. Regarding the component composition, nitrogen in the gas used for bright annealing infiltrates from the surface of the foil and the nitrogen in the surface layer increases (nitriding). It is considered that the difference in residual stress between the surface layer portion and the central portion becomes large because the work hardening characteristics are different.

Conventional hydrogen gas 75% by volume and nitrogen gas 2
When bright annealing is performed in a 5 vol% non-oxidizing gas atmosphere, nitrogen gas in the non-oxidizing atmosphere gas enters the surface of the stainless steel foil to increase the amount of nitrogen in the surface layer of the foil. When this foil is temper-rolled and half-etched on one side, the foil warps and cannot be used as a precision spring.

[0007]

In order to solve the above-mentioned problems, the present invention suppresses the amount of nitrogen penetrating into the foil surface layer by limiting the upper limit of the nitrogen gas concentration in the non-oxidizing gas atmosphere of bright annealing. Thus, it is an object of the present invention to provide a method for producing an austenitic stainless steel foil for springs, which has a small warpage after the one-side half etching treatment.

[0008]

That is, the gist of the present invention is to cold-roll 0.04 to 0.30 mm.
Austenitic stainless steel for spring, which is characterized by performing bright annealing of an austenitic stainless steel sheet having a plate thickness in a non-oxidizing gas atmosphere having a nitrogen gas concentration of 10 Vol% or less, and then performing temper rolling with a rolling reduction of 35% or more. It is in the method of manufacturing steel foil.

[0009]

The stainless steel foil for springs of the present invention is limited to austenitic stainless steel from the viewpoint of high strength and corrosion resistance by cold working. Further, since the above-mentioned problem of warpage occurs when the plate thickness is about 0.15 mm or less, the target is an austenitic stainless steel spring having this plate thickness.

The material sheet thickness before bright annealing is 0 in consideration of the sheet thickness of the foil product (0.15 mm or less) and the rolling reduction (35% or more) of the temper rolling for ensuring the target spring strength. ．
It was set to 04 to 0.30 mm. Next, the conditions of the bright annealing of the present invention will be described. The present inventors found that when the surface layer nitrogen increase amount ΔN (wt%) of the foil (nitrogen amount wt% of the surface layer 2 μm−average nitrogen amount wt% before bright annealing) increases, the warp after the single-sided half etching treatment becomes remarkable. I found it to grow.

Therefore, the appropriate bright annealing conditions for suppressing the invasion of nitrogen into the surface layer of the foil and the increase of nitrogen in the surface layer were examined. Plate thickness shown in Table 1 0.109 to 0.1
Bright annealing (non-oxidizing gas atmosphere) and temper rolling (reduction rate) using 90 mm austenitic stainless steel sheet 3 grades (A, B, C) under the conditions shown in Table 2 and Table 3 (continued from Table 2). : 30 to 60%) to produce an austenitic stainless steel foil for springs having a plate thickness of 0.076 mm.

The plate thickness produced by the above method is 0.076 mm.
An analytical sample and a warp measuring test piece were cut out from the austenitic stainless steel foil for spring. Nitrogen analysis is JIS
It was measured by G1228 (a method for determining nitrogen in iron and steel). In addition, the amount of warpage was evaluated by subjecting the test piece for warpage measurement to one-side etching with a ferric chloride aqueous solution to half the plate thickness, and evaluating the amount of warpage in mm by the method shown in FIG.
In the present invention, the warp amount is 3 per 50 mm in length.
The target was less than mm.

Next, as a quality characteristic of a spring,
A tensile strength σ _{B of} 130 kgf / mm ² or more is required. Using Material A having a large work hardening rate (Table 1), an appropriate reduction rate of temper rolling for securing the tensile strength σ _B was examined. FIGS. 3 and 4 show the relationship between the amount of warpage of an austenitic stainless steel foil for springs having a plate thickness of 0.076 mm, the increase amount of nitrogen in the surface layer of the foil ΔN, and the nitrogen concentration in the non-oxidizing gas atmosphere of bright annealing.

As is clear from FIGS. 3 and 4, when the nitrogen content in the non-oxidizing gas atmosphere exceeds 10%, the surface layer nitrogen increase amount ΔN remarkably increases, and the warpage amount exceeds the target of 3 mm. Therefore, the nitrogen gas concentration in the non-oxidizing gas atmosphere of the bright annealing is set to 10 Vol% or less. It is preferably 5% or less. In temper rolling, the appropriate rolling reduction is determined by the target tensile strength and elongation. For example, tensile strength σ _B (kgf
/ Mm ² ) and the temper rolling reduction ratio are shown in Fig. 5. In order to secure the target tensile strength σ _B 130 kgf / mm ² or more, the reduction ratio should be 35% or more. I understand.

[0015]

EXAMPLES Table 1 shows chemical components, and Tables 2 and 3 show bright annealing conditions, temper rolling conditions and evaluation results of the present invention and comparative examples. In each of Examples 1 to 5 of the present invention, the nitrogen gas concentration in the non-oxidizing gas atmosphere of bright annealing is 10 Vol% or less, and the warp amount after the one-side half etching treatment is 50 m in length.
3 mm or less per m is good. On the other hand, Comparative Examples 6-9
And 11, 12 have the nitrogen gas concentration of 10 Vol%.
And the warp amount is 6 mm or more, which is far from the target value. In Comparative Example 10, the reduction ratio of the temper rolling is too small and the target tensile strength σ _{B of} 130 kgf / mm ² or more is not satisfied.

[0016]

[Table 1]

[0017]

[Table 2]

[0018]

[Table 3]

[0019]

According to the present invention, it is possible to produce an austenitic stainless steel foil for springs which has an excellent shape after the one-side half etching treatment.

[Brief description of drawings]

FIG. 1 is a view showing a test piece for measuring a warp amount after a one-sided etching treatment and an etching treatment method.

FIG. 2 is a diagram showing a method of measuring a warp amount after a one-sided etching process.

FIG. 3 Nitrogen concentration in non-oxidizing gas atmosphere (Vol%)
FIG. 5 is a diagram showing a relationship between the surface layer (2 μm) and the amount of warpage after the one-sided etching treatment.

FIG. 4 Nitrogen concentration (Vol%) in a non-oxidizing gas atmosphere
It is a figure which shows the relationship between the surface layer (2 micrometer) nitrogen increase amount (DELTA) N.

FIG. 5 is a diagram showing the relationship between the reduction ratio of temper rolling and the tensile strength.

Claims (1)

[Claims] 1. A cold-rolled austenitic stainless steel sheet having a thickness of 0.04 to 0.30 mm is brightly annealed in a non-oxidizing gas atmosphere having a nitrogen gas concentration of 10 Vol% or less, and then a rolling reduction of 35% or more. 2. A method for producing an austenitic stainless steel foil for springs, characterized in that the temper rolling is performed.