JP3347582B2 - Austenitic stainless steel for metal gasket and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an austenitic stainless steel for metal gaskets, which has excellent strength, high-temperature strength, resistance to settling and high-temperature oxidation, and a method for producing the same.

[0002]

2. Description of the Related Art For example, gaskets for an internal combustion engine represented by a gasoline engine and a diesel engine include a head gasket and an exhaust gasket. Conventionally, a gasket mainly using asbestos has been used. However,
In recent years, the harmfulness of asbestos to the environment has become a problem, and a metal gasket using stainless steel has been used as a substitute for a gasket mainly containing asbestos.

[0003]

The stainless steel of the metal gasket has been mainly of SUS301 type, but the load on the gasket increases with the improvement of the engine performance. Insufficient high-temperature strength, anti-shattering resistance, and high-temperature oxidation properties may cause deterioration in sealability, high-temperature fatigue, and damage due to oxidation.

[0004] In the case of a metal gasket, a bead portion is formed in a stainless steel strip and a sealing action is performed in the portion. However, as the environmental temperature around the gasket increases and the tightening load increases, the sealing performance decreases. Problems such as fatigue and damage due to oxidation occur. Therefore, development of a material that can withstand the environment in which the gasket is used is required.
The present invention has been made in order to solve such problems, and an object of the present invention is to provide an austenitic stainless steel for a metal gasket having excellent strength, high-temperature strength, anti-shattering property, and high-temperature oxidation property, and a method for producing the same. .

[0005]

According to the present invention, there is provided a stainless steel having a C content of 0.10% by weight.
%, Si: 1.0% or less, Mn: 1.0 to 10.0
%, S: 0.01% or less, Cu: 3.0% or less, N
i: 7.0 to 15.0%, Cr: 15.0 to 25.0
%, Mo: 5.0% or less, N: 0.41 to 0.8% or less, Al: 0.02% or less The balance is substantially Fe.

The present invention is characterized in that the content of N, which is effective for high-temperature properties, is increased as compared with the above-mentioned SUS301-based material, and the content of Al, which is an adverse effect of N addition, is specified. .

In the present invention, Nb + Ta: 0.03-0.5%, Ti: 0.
03-0.5%, V: 0.03-0.5%, W: 0.0
Any one or more of 3 to 0.5% may be contained.

In the present invention, B: 0.001 to 0.01%, Ca: 0.001 to 0.
One or two or more of 0.1% and Mg: 0.001 to 0.01% may be contained in an amount of 0.1% or more.

[0009]

The reasons for limiting the range of the components of the present invention will be described.

C: 0.10% or less C is an interstitial element and contributes to improvement in strength. However, the addition of a large amount decreases the amount of solid solution of N and increases the C content.
In order to combine with r to form a carbide, reduce the amount of solid solution Cr in the matrix and deteriorate the oxidation resistance, the upper limit must be 0.10%.

Si: 1.0% or less Si is an element mainly acting as a deoxidizing agent during refining and refining. However, if contained in a large amount, the productivity is deteriorated, so the upper limit was set to 1.0%.

Mn: 1.0 to 10.0% Mn is an austenite-forming element and significantly increases the amount of solid solution of nitrogen, thus contributing to improvement in strength. Therefore, it is necessary to add 1.0% or more. Also, 10.
If it exceeds 0%, the hot workability deteriorates. Therefore, the range is set to 1.0 to 10.0%.

S: 0.01% or less S becomes MnS and becomes a starting point of cracking during cold working, so that the cold workability is significantly deteriorated. Therefore, the upper limit is set to 0.01%.

Cu: 3.0% or less Cu is an austenite-forming element that contributes to the stabilization of the austenite phase and improves the cold workability of the austenitic stainless steel. Therefore, the upper limit is set to 3.0%.

Ni: 7.0 to 15.0% Ni is an austenite-forming element and contributes to austenite phase stability. Therefore, 7.0% or more is necessary. However, the addition of a large amount leads to a decrease in strength and an increase in cost.
5.0%.

Cr: 15.0 to 25.0% Cr is effective as an element for increasing the amount of solid solution of nitrogen in stainless steel, improving oxidation resistance and corrosion resistance, and is a ferrite-forming element. If it is less than 15.0%, the oxidation resistance is not sufficient, but as the amount increases, the nitrogen solid solution amount, the oxidation resistance, and the corrosion resistance increase. However, when the content exceeds 25.0%, a ferrite-austenite two-phase structure and a σ phase are precipitated, so the range is set to 15.0% to 25.0%.

Mo: 5.0% or less Mo is effective as an element for increasing the amount of nitrogen dissolved in stainless steel and improving corrosion resistance. However, since it is a ferrite-forming element, if the content exceeds 5.0%, precipitation of a ferrite-austenite two-phase structure and a σ phase is caused, and hot workability is deteriorated.
And

N: 0.41 to 0.80% or less N is an interstitial element and contributes to improvement of strength, stability of austenite phase, improvement of corrosion resistance, and improvement of strength by aging treatment after processing. If it is less than 0.35%, the effect is low, and it is necessary to be 0.41% or more to obtain a more reliable effect. On the other hand, when the N content exceeds 0.80%, the nitride does not completely form a solid solution, so that the solution temperature becomes high and the cold workability and the toughness and ductility are deteriorated. Becomes Therefore, the range is set to 0.41
To 0.80%.

Al: 0.02% or less Al is used as a deoxidizing agent.
The upper limit was set to 0.02% in order to reduce the effective N and lower the high-temperature strength.

Nb + Ta: 0.03-0.5%, Ti:
0.03 to 0.5%, V: 0.03 to 0.5%, W:
Since 0.03 to 0.5% Nb + Ta, Ti, V, and W contribute to refinement of crystal grains and improvement in strength, one or more of them may be added as necessary. However, if it is less than 0.03%, the effect is small, and if added in a large amount, it binds with nitrogen and lowers the amount of solute N, so the upper limit is made 0.5% or less.

B: 0.001-0.01%, Ca: 0.
001-0.01%, Mg: 0.001-0.01% B, Ca, Mg are elements that improve hot workability.
The effect can be obtained at 001% or more, but when it exceeds 0.01%, the hot workability deteriorates conversely, so the range was made 0.001 to 0.01%.

A fourth aspect of the present invention relates to a method of manufacturing stainless steel for a gasket. The gist of the present invention is to subject a material adjusted to the above components to final cold rolling at a rolling reduction of 30 to 70%. . When this cold-rolled material is used in an atmosphere exposed to high temperatures, such as an exhaust gasket, nitrides precipitate due to aging, so that hardness is improved, and high-temperature strength and anti-shattering properties are improved. . If the rolling reduction range is less than 30%, the increase in hardness due to aging cannot be obtained, and if it exceeds 70%, overaging occurs in the atmosphere in which the gasket is used, and the hardness decreases and the settling resistance decreases. 30% to 70%.

The invention of claim 5 relates to a method of manufacturing stainless steel for a gasket. The gist of the invention is that after subjecting a material adjusted to the above components to final cold rolling at a rolling reduction of 30% or more, 300% The aging treatment is performed in a temperature range of up to 650 ° C for 1 minute or more. This is because when not used in an atmosphere exposed to high temperatures like the exhaust gasket described above, the hardness is improved by aging treatment in advance,
It is characterized by improving the settling resistance. Reduction rate 30
%, The increase in hardness due to aging cannot be obtained. When the temperature is lower than 300 ° C., age hardening does not occur, and when the temperature is higher than 650 ° C., it softens. On the other hand, when the aging time is shorter than 1 minute, the increase in hardness due to aging is small. The temperature was 650 ° C. for 1 minute or more.

[0024]

Embodiment 1 Next, in order to further clarify the features of the present invention, the embodiment will be described in detail below. The chemical components shown in Table 1 were melted in an arc furnace, and the components were refined and adjusted by AOD to produce a 1300 kg steel ingot. Subsequently, it was subjected to slab rolling, cold rolling, solution treatment at 1050 ° C., and further processing at a reduction of 40%. This sheet material was aged at 500 ° C. for 10 minutes. In this step, a sample was taken before and after the aging treatment in the solution heat treatment state,
A tensile test was performed. In addition, as an evaluation of the oxidation resistance, a width of 10 mm and a length of 25 m were obtained from the plate in the solution heat treatment state.
A test piece was prepared by polishing the entire surface with # 320 emery paper having a thickness of 3 mm and a thickness of 3 mm, and repeatedly subjected to an oxidation test. The test conditions were heating to a temperature of 600 ° C. and 800 ° C. (8 minutes), 30 minutes.
After holding for 30 minutes, it was allowed to cool at 30 ° C. for 22 minutes. With this as one cycle, the weight of the test piece after a total of 96 cycles (96 hours) was measured, the difference from the weight measured before the test was determined, and the value obtained by dividing the difference by the surface area of the test piece was calculated. The amount was increased by oxidation. Comparative steel is JIS SUS301, S
US 304. Table 2 shows the results.

Next, for the purpose of evaluating the high-temperature strength (hardness) and the settling resistance and optimizing the rolling reduction, at the time of the above-mentioned cold working,
A material having a reduced draft was manufactured, and the material was put into a heating furnace at 600 ° C., and after a certain period of time, a sample was taken out and its hardness was measured. The result is shown in FIG. The comparative steel is JIS SUS301.

[0026]

[Table 1]

[0027]

[Table 2]

As shown in Table 2, the steels of the present invention 1 to 7
Compared to US301 and SUS304, 0.2% proof stress and tensile strength after cold rolling are excellent as solution heat treatment. Further, the aging treatment can further improve the strength.
The oxidation resistance is also superior to the comparative steel. Next, as shown in FIG. 1, the inventive steel is excellent in high-temperature strength (hardness) and anti-settling resistance. However, at a high temperature, at a rolling reduction of 80%, the hardness rapidly decreases due to overaging, so that it is necessary to avoid the hardness.

[0029]

As described above, the present invention relates to an austenitic stainless steel excellent in strength, high-temperature strength, anti-shattering property and high-temperature oxidation property and a method for producing the same, and is most suitable as a material for a gasket.

[Brief description of the drawings]

FIG. 1 is a view showing a relationship between hardness after heating at 600 ° C. and heating time in the steel 1 of the present invention.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-7-3407 (JP, A) JP-A-7-3406 (JP, A) JP-A-64-56858 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) C22C 38/00-38/60 F16J 15/08

Claims (5)

(57) [Claims] C: 0.10% or less by weight% Si: 1.0% or less Mn: 1.0 to 10.0% S: 0.01% or less Cu: 3.0% or less Ni: 7. 0 to 15.0% Cr: 15.0 to 25.0% Mo: 5.0% or less N: 0.41 to 0.8% or less Al: 0.02% or less The balance substantially consists of Fe. Austenitic stainless steel for metal gaskets, characterized by having 2. The composition according to claim 1, further comprising Nb + Ta, T
Nb + Ta: 0.03 to 0.5% Ti: 0.03 to 0.5% V: 0.03 to 0.5% W: 0.03 Austenitic stainless steel for metal gaskets, characterized in that it is contained in an amount of 0.5%. 3. The composition according to claim 1, further comprising B, C
a, one or more of Mg are contained in an amount of B: 0.001 to 0.01% Ca: 0.001 to 0.01% Mg: 0.001 to 0.01% Austenitic stainless steel for metal gaskets, characterized by: 4. A method for producing an austenitic stainless steel for a metal gasket, comprising subjecting a raw material adjusted to the composition of claim 1 or 2 or 3 to final cold rolling at a rolling reduction of 30 to 70%. 5. After subjecting the raw material adjusted to the component of claim 1, 2 or 3 to final cold rolling at a rolling reduction of 30% or more, 3%
A method for producing an austenitic stainless steel for a metal gasket, wherein the aging treatment is performed in a temperature range of 00 to 650 ° C for 1 minute or more.