JPH09279315A - Austenitic stainless steel for metal gasket and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce an austenitic stainless steel excellent in strength, high temp. strength or the like by subjecting a stainless steel stock having a prescribed componental compsn. to final cold rolling and aging treatment in succession under specified conditions. SOLUTION: A stock having a compsn. contg., by weight, <=0.10% C, <=1.0% Si, 1.0 to 10.0% Mn, <=0.01% S, <=3.0% Cu, 7.0 to 15.0% Ni, 15.0 to 25.0% Cr, <=5.0% Mo, 0.35 to 0.8% N, <=0.02% Al, and the balance substantial Fe is prepd. This stock is subjected to final cold rolling at a draft of <=30% and is thereafter subjected to aging treatment in the temp. range of 300 to 650 deg.C for >=1min. In this way, the austenitic stainless steel excellent in settling resistance and high temp. oxidation properties can be obtd.

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, fatigue resistance and high temperature oxidation resistance, and a method for producing the same.

[0002]

2. Description of the Related Art For example, a gasket for an internal combustion engine typified by a gasoline engine or a diesel engine includes a head gasket and an exhaust system gasket, and conventionally, asbestos-based materials have been used. However,
In recent years, the harmfulness of asbestos to the environment has become a problem, and metal gaskets made of stainless steel have been used as a substitute for gaskets containing asbestos as a main material.

[0003]

The stainless steel of this metal gasket has mainly been made of SUS301 series, but the load on the gasket increases as the performance of the engine becomes higher. In addition, high temperature strength, fatigue resistance, and high temperature oxidation resistance may be insufficient, which may cause deterioration of sealing property, high temperature fatigue, damage due to oxidation, and the like.

In the case of a metal gasket, a bead portion is formed on a stainless steel strip and a sealing action is performed at the same portion. However, as the environmental temperature around the gasket increases and the tightening load increases, the sealing performance deteriorates. Problems such as fatigue and damage due to oxidation occur. Therefore, it is required to develop a material that can withstand the environment in which the gasket is used.
The present invention has been made to solve such problems, and an object thereof is to provide an austenitic stainless steel for metal gaskets, which is excellent in strength, high temperature strength, fatigue resistance, and high temperature oxidation resistance, and a manufacturing method thereof. .

[0005]

The stainless steel according to the present invention for achieving the above object has a C content of C: 0.10.
% Or less, 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: 0.35 to 0.8%, A
L: 0.02% or less The balance is characterized by having a composition substantially consisting of Fe.

The present invention is characterized in that the content of N, which is effective for high temperature characteristics, 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. .

The present invention further has Nb + Ta: 0.03 to 0.5% and Ti: 0.
03-0.5%, V: 0.03-0.5%, W: 0.0
Any one of 3 to 0.5% or two or more thereof may be contained.

The present invention further aims at improving the hot workability, B: 0.001 to 0.01%, Ca: 0.001 to 0.
01%, Mg: 0.001 to 0.01%, and any one kind or two or more kinds may be contained.

[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 the improvement of strength. However, addition of a large amount lowers the solid solution amount of N, and
The upper limit is required to be 0.10% in order to combine with r to form a carbide and reduce the amount of solid solution Cr in the mother phase to deteriorate the oxidation resistance.

Si: 1.0% or less Si is an element mainly acting as a deoxidizing agent at the time of melting and refining. However, if contained in a large amount, the manufacturability is deteriorated, so the upper limit was made 1.0%.

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

S: 0.01% or less S becomes MnS and becomes a starting point of cracks during cold working, so that 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 and contributes to the stabilization of the austenite phase and improves the cold workability of austenitic stainless steel, but addition of a large amount reduces the strength. Therefore, the upper limit is set to 3.0%.

Ni: 7.0-15.0% Ni is an austenite forming element and contributes to the austenite phase stability. Therefore, 7.0% or more is necessary. However, addition of a large amount causes a decrease in strength and an increase in cost, so the range is set to 7.0-1.
5.0%.

Cr: 15.0 to 25.0% Cr is effective as an element for increasing the solid solution amount of nitrogen in stainless steel, improving the oxidation resistance and the corrosion resistance, and is a ferrite forming element. If it is 15.0% or less, the oxidation resistance is not sufficient, but as it increases, the solid solution amount of nitrogen, the oxidation resistance and the corrosion resistance increase. However, when it is 25.0% or more, precipitation of ferrite-austenite two-phase structure and σ phase is caused, so the range was made 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 the corrosion resistance. However, since it is a ferrite-forming element, if it exceeds 5.0%, it causes precipitation of a ferrite-austenite two-phase structure and σ phase, and deteriorates hot workability, so its range is 5.0%.
And

N: 0.35 to 0.80% N is an interstitial element and contributes to improvement of strength, stability of austenite phase and corrosion resistance, and strength improvement by aging treatment after working. If it is less than 0.35%, the effect is low, and if it exceeds 0.80%, the nitride does not completely form a solid solution and the solution temperature becomes high, and cold workability and toughness and ductility are deteriorated. It becomes impossible to process into.
Therefore, the range is set to 0.35% to 0.80%.

Al: 0.02% or less Al is used as a deoxidizer, but a large amount of AlN is added.
To reduce the effective N and reduce the high temperature strength, the upper limit was made 0.02%.

Nb + Ta: 0.03 to 0.5%, Ti:
0.03-0.5%, V: 0.03-0.5%, W:
0.03 to 0.5% Nb + Ta, Ti, V, and W contribute to refining the crystal grains and improving the strength, and thus may be added alone or in combination of two or more if necessary. However, if it is less than 0.03%, the effect is small, and if added in a large amount, it binds to nitrogen and reduces the amount of solid solution N, so the upper limit was made 0.5% or less.

B: 0.001 to 0.01%, Ca: 0.
001-0.01%, Mg: 0.001-0.01% B, Ca, and Mg are elements which improve hot workability, and are 0.001%.
The effect is obtained at 001% or more, but if it exceeds 0.01%, the hot workability is deteriorated, so the range is made 0.001 to 0.01%.

The invention of claim 4 relates to a method for producing stainless steel for gaskets, and the gist thereof is to subject the material adjusted to the above components to final cold rolling at a reduction rate of 30 to 70%. . When this cold-rolled material is used in an atmosphere exposed to high temperatures such as an exhaust system gasket, the nitride is precipitated by aging, so that the hardness is improved and the high temperature strength and the settling resistance are improved. . If the rolling reduction range is less than 30%, the hardness cannot be increased by aging, and if it exceeds 70%, overaging occurs in the gasket use atmosphere, and the hardness decreases and the settling resistance decreases. It was set to 30 to 70%.

A fifth aspect of the present invention relates to a method for producing a stainless steel for a gasket, and the gist thereof is to subject the material adjusted to the above components to final cold rolling at a rolling reduction of 30% or more, and then 300 Aging treatment is performed in the temperature range of 650 ° C. for 1 minute or more. This is because when it is not used in an atmosphere exposed to high temperature like the above exhaust system gasket, hardness is improved by aging treatment in advance, high temperature strength,
It is characterized by improving the resistance to settling. Reduction rate 30
If it is less than%, an increase in hardness due to aging cannot be obtained. Further, if it is less than 300 ° C., age hardening does not occur, if it exceeds 650 ° C., it is conversely softened, and if the aging time is less than 1 minute, the hardness increase due to aging is small, so that the range is 30% or more, and the aging condition is 300 to 300. It was set to a temperature range of 650 ° C. for 1 minute or more.

[0024]

Embodiment 1 Next, in order to further clarify the characteristics 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, this was slab-rolled, further cold-rolled, subjected to solution heat treatment at 1050 ° C., and subsequently processed at a rolling reduction of 40%. This thin plate material was aged at 500 ° C. for 10 minutes, and in this process, a sample was taken in a solution heat treatment state, before and after the aging treatment,
A tensile test was performed. In addition, as the evaluation of the oxidation resistance, a width of 10 mm and a length of 25 m are obtained from the plate material in the solution heat treatment state.
A test piece of m, thickness 3 mm, and # 320 emery paper, the entire surface of which was polished, was prepared and repeatedly subjected to an oxidation test. The test conditions are heating at a temperature of 600 ° C and 800 ° C (8 minutes), 30
After holding for minutes, it was left to cool at 30 ° C. for 22 minutes. Taking 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 before the test measured in advance was obtained, and the value was divided by the surface area of the test piece. The amount was increased by oxidation. Comparative steel is JIS SUS301, S
US 304. The results are shown in Table 2.

Next, for the purpose of evaluating high temperature strength (hardness), settling resistance, and optimizing the reduction rate, during the above cold working,
Raw materials with different rolling reductions were manufactured, placed in a heating furnace at 600 ° C., and after a certain period of time, samples were taken out and 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 1 to 8 of the present invention are S
Compared to US301 and SUS304, 0.2% proof stress and tensile strength after cold rolling are excellent as they are in solution heat treatment. Further, it is expected that the strength will be further improved by the aging treatment.
It is also superior in oxidation resistance to the comparative steel. Next, as shown in FIG. 1, the invention steel is excellent in high temperature strength (hardness) and settling resistance. However, at a high temperature, with a reduction rate of 80%, the hardness rapidly decreases due to overaging, so it is necessary to avoid it.

[0029]

INDUSTRIAL APPLICABILITY As described above, the present invention relates to an austenitic stainless steel excellent in strength, high temperature strength, fatigue resistance, and high temperature oxidation resistance and a method for producing the same, and is most suitable as a material for gaskets.

[Brief description of drawings]

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

Claims (5)

[Claims] 1. By weight% C: 0.10% or less 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: 0.35 to 0.8% Al: 0.02% or less The balance has a composition consisting essentially of Fe. Austenitic stainless steel for metal gaskets characterized by 2. In addition to the components of claim 1, Nb + Ta, T
Any one or more of i, V, and W is Nb + Ta: 0.03 to 0.5% Ti: 0.03 to 0.5% V: 0.03 to 0.5% W: 0.03 An austenitic stainless steel for a metal gasket, characterized by being contained in an amount of up to 0.5%. 3. In addition to the components of claim 1 or 2, B, C
a, any one kind of Mg, or two or more kinds were contained in an amount of B: 0.001-0.01% Ca: 0.001-0.01% Mg: 0.001-0.01%. Austenitic stainless steel for metal gasket. 4. A method for producing an austenitic stainless steel for a metal gasket, which comprises subjecting the material adjusted to the composition of claim 1, 2 or 3 to final cold rolling at a reduction rate of 30 to 70%. 5. The material prepared according to claim 1, 2 or 3 is finally cold-rolled at a rolling reduction of 30% or more and then 3
A method for producing an austenitic stainless steel for a metal gasket, which comprises subjecting an aging treatment to a temperature range of 0 to 650 ° C for 1 minute or more.