JPH07216450A - Production of austenitic stainless steel excellent in spring characteristic - Google Patents

Abstract

PURPOSE:To stably produce an austenitic stainless steel having high hardness and high strength, excellent in spring characteristic, and having superior surface quality by hardening an austenitic stainless steel stock by means of cold rolling and successively softening this stock by means of annealing at relatively low temp. CONSTITUTION:A slab of austenitic stainless steel is cold-rolled at >=20% draft to work this slab into a sheet of desired thickness while hardening the material. Then, annealing is done at a leatively low temp, between 650 and 900 deg.C to regulate the hardness of this sheet to a desired hardness while softening the material. By this method, a spring material, excellent in spring characteristic, having high strength and high hardness, and excellent in surface quality, can be produced at a low cost.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spring having improved spring properties and a method for producing austenitic stainless steel for general hard materials. In addition, in the present specification, the elasticity is, for example, a large spring limit value with respect to hardness,
It is the property that cracks are less likely to occur during bending.

[0002]

2. Description of the Related Art Conventionally, austenitic stainless steel has been used as a general hard material for a VTR cassette tape holding plate material, a floppy disk shutter material, a fluorescent lamp hanging metal fitting, and the like. For these austenitic stainless steels, as a hardness adjusting means, for example, 1100 ° C
As described above, after the final softening annealing at a relatively high temperature, hardening by temper rolling may be further performed at 350 to 550 ° C if desired.
The aging treatment is being done in.

However, in this conventional method,
It was difficult to adjust the hardness to the target because the stability of the austenite phase changes with the fluctuation of rolling temperature or the change of component values due to seasonal changes.

Further, in this method, since hardening is carried out by cold rolling (temper rolling) after the final softening annealing, the surface film (oxide film mainly composed of SiO ₂ ) of the steel sheet formed by the final softening annealing is destroyed. This is a problem because it often drops off locally, resulting in uneven gloss. Further, the temper-rolled material obtained by this method has a drawback that the spring property is poor.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a spring having a high hardness and a high strength, which can be used for springs and general hard materials which are required to have a good spring property, and which has an excellent surface quality. It is an object of the present invention to provide an inexpensive method for producing good austenitic stainless steel.

[0006]

Here, the present inventors
After various studies, the inventors have completed the present invention by discovering that the above object can be stably achieved by carrying out softening by annealing at a relatively low temperature after hardening by cold rolling.

Here, the gist of the present invention is that an austenitic stainless steel material is hardened by cold rolling with a rolling reduction of 20% or more to a desired plate thickness and then 65
A method for producing austenitic stainless steel with excellent spring properties, characterized by adjusting the hardness to a desired hardness while softening it by a heat treatment at a temperature of 0 ° C. or higher and 900 ° C. or lower.
From another aspect, the present invention is a method for manufacturing a spring material of austenitic stainless steel manufactured as described above.

[0008]

FIG. 1 shows the difference in the basic idea between the conventional hardness adjusting method and the hardness adjusting method of the present invention for the hard material of SUS304 which is a typical austenitic stainless steel. It is a conceptual diagram.

That is, the conventional method is cold rolling → softening annealing.
(1000 ° C or higher) → temper rolling (in some cases, strain aging treatment is performed at 350 to 550 ° C). This is a method in which temper rolling is performed after the final softening annealing, and the desired hardness is adjusted by changing the cold rolling rate at that time, and the hardness is adjusted by so-called work hardening. In other words, it is a method of increasing the hardness to the target value.

On the other hand, according to the method of the present invention, austenitic stainless steel is previously cold-rolled at a rolling reduction of 20% or more to a desired plate thickness and hardened, and then heat-treated at a temperature of 650 ° C. to 900 ° C. Then, the hardness is adjusted to a desired hardness, and is a method of adjusting by softening the hardness of the material subjected to processing strain. In other words, it is a method of reducing the hardness to a target value of hardness.

FIG. 2 is a graph illustrating how the Vickers hardness is lowered by the heat treatment used in the method of the present invention. Specifically, an austenitic stainless steel sheet (SUS304) is cold-rolled, It is the graph which connected the curve of the conditions of equal hardness when softening the material made into Vickers hardness 444 by heat processing. As a matter of course, the hardness decreases as the heat treatment temperature rises, and also changes depending on the time in the furnace. In the present invention, it is understood that the desired hardness can be easily obtained by appropriately adjusting the heat treatment temperature and the treatment time by utilizing these relationships. In addition, SUS304
Needless to say, the hardness can be adjusted by using the same relationship with other austenitic stainless steels.

As a stainless steel having a high hardness and a spring property, which is the object of the present invention, austenitic stainless steel is a general material, and other stainless steels are inferior in formability. Therefore, in the present invention, the object is austenitic stainless steel.

In the present invention, the cold rolling rate prior to the heat treatment is limited to a reduction rate of 20% or more. The reason is that when the rolling reduction is less than 20%, the initial hardness before the heat treatment is soft and the hardness cannot be adjusted by softening by the subsequent heat treatment. The rolling reduction is preferably 40% or more, more preferably the rolling reduction is 50% or more.

In the present invention, the heat treatment temperature range is from 650 to
Limit to 900 ℃. The reason is that as shown in FIG. 2, when the heat treatment temperature is lower than 650 ° C., there is almost no softening effect,
This is because while it is easily cracked during bending, the hardness drops sharply above 900 ° C, and the desired performance as a general hard material such as spring properties cannot be obtained. Therefore, the heat treatment temperature range after cold rolling is 650 ℃ or more and 900 ℃ or less, preferably 700
~ 850 ℃

According to the present invention, the conventional temper rolling step can be omitted, the heat treatment temperature is low, and at the same time, a treatment similar to the strain aging treatment is carried out. Manufacturing cost reduction is realized.

Further, the low-temperature annealing after cold rolling according to the present invention exhibits not only the function of adjusting the hardness but also the function of precipitating carbides, so that the etching property of the austenitic stainless steel obtained is improved.

Further, according to the present invention, after the heat treatment for adjusting the hardness is not performed, the cold rolling is not carried out, so that the surface film is not destroyed and thereby the uneven gloss can be prevented. .

The hardness adjusted by the method of the present invention (Vickers hardness) is 370-420 (SUS3
04H), 310 ~ 350 (SUS304 3 / 4H), 250 ~ 290 (SUS304 1 /
2H) In addition, Vickers hardness 490-550 for SUS 301
(SUS301EH), 430 ~ 489 (SUS301H), 370 ~ 429 (SUS301
3 / 4H), 310 to 369 (SUS301 1 / 2H). This fully covers the range of hardnesses obtained by conventional methods. Next, the operation and effects of the present invention will be described in detail by examples.

[0019]

EXAMPLES As shown in Table 1, the materials manufactured by the method of the present invention using SUS304, the materials manufactured by the comparative method in which only the heat treatment temperature is outside the scope of the invention, the materials manufactured by the conventional method of temper rolling, and SUS301 were used. The materials manufactured by the method of the present invention were examined for Vickers hardness (Hv), spring limit value, bendability, and gloss unevenness.

The bendability was determined by the presence or absence of cracks after 90 ° knife edge bending. The gloss unevenness was determined by visual observation, and the case where there was no band-shaped pattern was good, the case where there was no band-shaped pattern was bad, and the case where there was an extremely mild band-shaped pattern was judged to be slightly poor.

As shown in Table 1, the material produced by the method of the present invention has a high spring limit value and an excellent spring property even though the hardness is equivalent to that of the conventional method. Further, the material of the comparative method heat-treated at a low temperature showed cracks in the bending test, whereas the material of the method of the present invention did not crack at all.

Further, the steel sheet produced by the method of the present invention had no gloss unevenness, whereas the conventional method produced gloss unevenness. As described above, although the method of the present invention is a simple production method, the material produced by the method is
It had unprecedented quality.

[0023]

[Table 1]

[0024]

Industrial Applicability According to the present invention, a high strength, high hardness austenitic stainless steel hard material excellent in spring property and a spring material can be manufactured at a low cost with good surface quality, and thus has an extremely high industrial value.

[Brief description of drawings]

FIG. 1 is a basic conceptual diagram of the hardness adjustment of the method of the present invention and the conventional method.

FIG. 2 is a diagram illustrating how the Vickers hardness is reduced by the heat treatment used in the method of the present invention. Specifically, austenitic stainless steel (SUS304) is cold-rolled to have a Vickers hardness of 444. It is the graph which connected the curve of the conditions of equal hardness when softening the heat-treated material by heat treatment.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Sada Ikeda 4-53-3 Kitahama, Chuo-ku, Osaka City Sumitomo Metal Industries, Ltd.

Claims (1)

[Claims] 1. An austenitic stainless steel material,
A spring property characterized by adjusting the desired hardness while softening by heat treatment at a temperature of 650 ° C or more and 900 ° C or less after hardening by cold rolling with a rolling reduction of 20% or more to a desired thickness Of excellent austenitic stainless steel.