WO2022131504A1 - Austenitic stainless steel with improved high temperature softening resistance - Google Patents

Abstract

Disclosed is an austenitic stainless steel with improved high temperature softening resistance. According to the present invention, the stainless steel comprises, in weight%, C: 0.02-0.15%, N: 0.1-0.3%, Si: 0.2-0.7, Mn: 2.0-5.0%, Cr: 17.0-19.0%, Ni: 2.5-5.0%, Cu: 1.0-3.0%, and the balance being Fe and inevitable impurities and satisfies formula (1). Formula (1): -30≤ 551-462*(C+N)-9.2*Si-8.1*Mn-13.7*Cr-29*(Ni+Cu) ≤30, wherein C, N, Si, Mn, Cr, Ni, and Cu denote weight% of the respective elements.

Description

Austenitic stainless steel with improved resistance to softening at high temperatures

The present invention relates to austenitic stainless steel having improved resistance to softening at high temperatures, and more particularly, to austenitic stainless steel capable of preventing softening even at a high temperature of 500 to 600° C., which is mainly used for gaskets.

A cylinder head gasket or an exhaust manifold gasket of an automobile or motorcycle engine is a part exposed to repeated pressure fluctuations under high temperature, high pressure, and high vibration characteristic of an engine. In particular, since a high pressure is applied during compression to the automobile engine cylinder gasket, it must be in contact with both contacting counterparts with a high surface pressure in order to maintain the sealability of the combustion gas.

In a metal gasket used for an engine or exhaust gas path, it is common to secure surface pressure by forming continuous ridges of a certain height by bead forming by a press. In order to secure the sealing properties of the metal gasket, it is necessary to contact the contact material with a high surface pressure, and for this purpose, the strength and fatigue characteristics of the metal gasket are required.

As a gasket material, work-hardening metastable austenitic stainless steel (STS301 stainless steel, etc.) is applied.

In general, austenitic stainless steel is deformed by transformation from an unstable austenite phase to a martensite phase at room temperature during cold working, that is, transformation induced plasticity. At this time, since the generated processed induced martensite phase has high strength, the strength of the material also increases. Therefore, in order to secure the strength of the material, it is necessary to increase the cold rolling reduction ratio.

However, as the cold reduction ratio increases, the yield stress (0.2% yield strength) continuously increases, resulting in a rough surface during gasket molding, local stress concentration in the material, and necking in the bent portion. do. The above-mentioned surface and processing shape defects are factors that significantly deteriorate the gas sealing properties. That is, an increase in the cold rolling reduction rate acts as a factor that deteriorates toughness, fatigue resistance, and workability.

On the other hand, in a high temperature region of 500° C. or higher in which the gasket is used, the material is softened (strength decreased) as the above-described processed martensite phase is decomposed, and the stability is poor.

In order to solve the problem of reducing softening resistance in the high temperature range of 500~600℃, it is possible to consider the case of introducing high alloy Fe-Cr-Mn-Ni austenitic stainless steel and Inconel 718 as heat-resistant gasket materials. , there is a problem in terms of price competitiveness because it contains a large amount of expensive elements.

Therefore, it is possible to minimize the decrease in softening resistance in a high temperature range of 500 to 600° C. while securing strength and workability, so that it is required to develop an austenitic stainless steel applicable as a gasket material.

Embodiments of the present invention are intended to provide an austenitic stainless steel capable of securing softening resistance at a temperature of 500° C. or higher by refining crystal grains.

The austenitic stainless steel having improved resistance to high temperature softening according to an embodiment of the present invention is, by weight, C: 0.02 to 0.15%, N: 0.1 to 0.3%, Si: 0.2 to 0.7, Mn: 2.0 to 5.0% , Cr: 17.0 to 19.0%, Ni: 2.5 to 5.0%, Cu: 1.0 to 3.0%, the remaining Fe and unavoidable impurities, and satisfies the following formula (1).

Formula (1): -30≤ 551-462*(C+N)-9.2*Si-8.1*Mn-13.7*Cr-29*(Ni+Cu) ≤30

Here, C, N, Si, Mn, Cr, Ni, and Cu mean weight % of each element.

In addition, according to an embodiment of the present invention, the average grain diameter may be 10㎛ or less.

In addition, according to an embodiment of the present invention, Ca: 0.001 to 0.003%, B: 0.001 to 0.005%, P: 0.1% or less (excluding 0) and S: 0.01% or less (excluding 0) at least one of may further include.

In addition, according to an embodiment of the present invention, the yield strength may be 450 MPa or more.

In addition, according to an embodiment of the present invention, at a temperature of 500 ℃ or more, the hardness may be 450 Hv or more.

In addition, according to an embodiment of the present invention, the elongation may be 35% or more.

A method of manufacturing austenitic stainless steel having improved resistance to high temperature softening according to another embodiment of the present invention, in weight %, C: 0.02 to 0.15%, N: 0.1 to 0.3%, Si: 0.2 to 0.7, Mn: 2.0 to 5.0%, Cr: 17.0 to 19.0%, Ni: 2.5 to 5.0%, Cu: 1.0 to 3.0%, including the remaining Fe and unavoidable impurities, hot rolling and hot annealing of a slab satisfying the following formula (1) step; cold-rolling the hot-rolled annealing material to a total reduction ratio of 50% or more; and heat-treating the cold-rolled material at 900°C to 1000°C.

Formula (1): -30≤ 551-462*(C+N)-9.2*Si-8.1*Mn-13.7*Cr-29*(Ni+Cu) ≤30

Here, C, N, Si, Mn, Cr, Ni, and Cu mean weight % of each element.

In addition, according to an embodiment of the present invention, during cold rolling, the total reduction ratio may be 70% or more.

In addition, according to an embodiment of the present invention, the hot rolling may be performed at 1,050 to 1,300 °C.

In addition, according to an embodiment of the present invention, after hot rolling, the step of solution heat treatment at 1050 to 1200 ℃ may be further included.

According to an embodiment of the present invention, it is possible to provide an austenitic stainless steel applicable as a gasket material because it is possible to secure softening resistance at a temperature of 500° C. or higher while ensuring strength and workability.

According to an embodiment of the present invention, it is possible to provide an austenitic stainless steel having a reduced nickel content while ensuring elongation and corrosion resistance comparable to the existing 301 stainless steel.

1 is a microstructure photograph taken with an optical microscope (Optical Microscope, 　OM) of Comparative Example 1 and Example 1 steel.

The austenitic stainless steel having improved resistance to high temperature softening according to an embodiment of the present invention is, by weight, C: 0.02 to 0.15%, N: 0.1 to 0.3%, Si: 0.2 to 0.7, Mn: 2.0 to 5.0% , Cr: 17.0 to 19.0%, Ni: 2.5 to 5.0%, Cu: 1.0 to 3.0%, the remaining Fe and unavoidable impurities, and satisfies the following formula (1).

Formula (1): -30≤ 551-462*(C+N)-9.2*Si-8.1*Mn-13.7*Cr-29*(Ni+Cu) ≤30

Here, C, N, Si, Mn, Cr, Ni, and Cu mean weight % of each element.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. The following examples are presented in order to sufficiently convey the spirit of the present invention to those of ordinary skill in the art to which the present invention pertains. The present invention is not limited to the embodiments presented herein, and may be embodied in other forms. The drawings may omit illustration of parts irrelevant to the description in order to clarify the present invention, and slightly exaggerate the size of the components to help understanding.

Also, when a part "includes" a certain component, it means that other components may be further included, rather than excluding other components, unless otherwise stated.

The singular expression includes the plural expression unless the context clearly dictates otherwise.

Hereinafter, an embodiment according to the present invention will be described in detail with reference to the accompanying drawings.

Methods for improving the strength of a material include solid solution strengthening, precipitation strengthening, dispersion strengthening, generation of martensite phase, crystal grain refinement, and the like. The method of refining the crystal grains of the material can not only expect an improvement in superior strength compared to the strength obtained through a conventional level of heat treatment, but also improve the strength and toughness, thereby improving the mechanical properties of the material. It is used as a useful tool to improve.

In addition, the method of refining the crystal grains of the material is attracting attention in various alloy fields because it can reduce defects inside the material, obtain a uniform material, and does not require the addition of additional alloying elements.

Specifically, as a method of refining the crystal grains of a material, as an example of a thermomechanical control process, a process induced transformation process (SIMRT, Strain-Induced Martensite and its Reverse Transformation) is widely used.

The processing induced transformation process is a method using the characteristic of reverse transformation of the martensite phase introduced during cold working to an austenite phase by cold working a material having a metastable austenite structure at room temperature and heating it to a temperature of 600° C. or higher.

Compared to untransformed austenite, the reverse transformation austenite phase has a higher dislocation density and fine grains, so the strength of the material can be improved, and the elongation rate is greater than that of the austenite phase before reverse transformation.

In order to secure the strength and workability of the austenitic stainless steel, the present inventors derived the stability range of the austenite phase considering both the amount of martensite produced during cold working and the reverse transformation temperature related to the grain size of the austenitic stainless steel.

The austenitic stainless steel having improved resistance to high temperature softening according to an aspect of the present invention is, by weight, C: 0.02 to 0.15%, N: 0.1 to 0.3%, Si: 0.2 to 0.7%, Mn: 2.0 to 5.0% , Cr: 17.0 to 19.0%, Ni: 2.5 to 5.0%, Cu: 1.0 to 3.0%, remaining Fe and unavoidable impurities.

Hereinafter, the reason for numerical limitation of the alloying element content in the embodiment of the present invention will be described. Hereinafter, unless otherwise specified, the unit is % by weight.

The content of C is 0.02 to 0.15%.

Carbon (C) is an effective element for stabilizing the austenite phase, and in the present invention, 0.02% or more may be added to secure the strength of the material. However, when the content is excessive, it not only reduces cold workability due to solid solution strengthening, but also induces grain boundary precipitation of Cr carbides by combining with Cr, thereby reducing ductility, toughness and corrosion resistance, and martensite transformation start temperature (Martensite Start temperature). , Ms) is lowered, so there is a problem that strength cannot be secured because the generation of stress-induced martensite is not smooth during cold working, and the upper limit can be limited to 0.15%.

The content of N is 0.1 to 0.3%.

Nitrogen (N), like carbon, is an effective element for stabilizing the austenite phase, and may be added in an amount of 0.01% or more to secure corrosion resistance. However, if the content is excessive, it not only reduces the cold workability due to solid solution strengthening, but also reduces the surface quality by forming pores during casting, and the martensite transformation initiation temperature (Ms) is lowered to reduce the stress martensite during cold working. Since there is a problem that strength cannot be secured due to poor production, the upper limit can be limited to 0.3%.

The content of Si is 0.2 to 0.7%.

Silicon (Si) is an element that acts as a deoxidizer during the steelmaking process, and may be added in an amount of 0.2% or more to secure corrosion resistance. However, when the content of silicon, which is a ferrite phase stabilizing element, is excessive, delta (δ)-ferrite is formed in the cast slab to reduce hot workability, and there is a problem in that the ductility and toughness of the steel are lowered in the solid solution strengthening effect. , in the present invention, the upper limit may be limited to 0.7%.

The content of Mn is 2.0 to 5.0%.

Manganese (Mn) is an austenite phase stabilizing element added instead of nickel (Ni) in the present invention. It is effective in improving cold rolling properties by suppressing processing-induced martensite formation, and increasing the solubility of nitrogen (N) during the steelmaking process. 2.0% or more can be added as an element to However, if the content is excessive, the martensite transformation initiation temperature (Ms) is lowered, so that the generation of stress-induced martensite during cold working is not smooth, and the surface quality is reduced due to surface oxidation during hot rolling and reverse transformation heat treatment. , since the increase in S-based inclusions (MnS) may reduce the ductility, toughness and corrosion resistance of the steel, the upper limit thereof may be limited to 5.0%.

The content of Cr is 17.0 to 19.0%.

Chromium (Cr) is a basic element that stabilizes ferrite and contains the most among elements for improving corrosion resistance of stainless steel. In the present invention, 17.0% or more may be added to suppress the formation of martensite phase. However, when the content of chromium, which is a ferrite phase stabilizing element, is excessive, delta (δ)-ferrite is formed in the cast slab to reduce hot workability, and stress-induced martensite is not smoothly generated during cold working, and martensite is formed. During reverse transformation annealing by increasing the reverse transformation temperature from the site phase to the austenite phase, there is a problem in that crystal grains of austenite rapidly grow, and the upper limit thereof may be limited to 19.0% in the present invention.

The content of Ni is 2.5 to 5.0%.

Nickel (Ni) is the most powerful austenite phase stabilizing element, and as its content increases, the austenite phase is stabilized to soften the material. In the present invention, in order to secure hot workability and cold workability of the material even when Mn is added in a certain amount or more, and to suppress the growth of austenite grains by lowering the reverse transformation temperature from martensite to austenite, Ni is added by 2.5% or more. it is essential However, if the content is excessive, as Ni is an expensive element, it causes an increase in raw material cost, and the martensite transformation initiation temperature (Ms) is lowered, so that the generation of stress-induced martensite is not smooth during cold working, so strength is secured. Since there is a problem that it cannot be done, the upper limit can be limited to 5.0%.

The content of Cu is 1.0 to 3.0%%.

Copper (Cu) is an austenite phase stabilizing element, and in the present invention, it is added by 1.0% or more in order to soften the material by reducing Stacking Fault Energy (SFE). However, if the content is excessive, the martensite transformation initiation temperature (Ms) is lowered, so that the generation of stress-induced martensite during cold working is not smooth, and the raw material cost is increased, and hot brittleness is caused. can be limited to 3.0%.

In addition, according to an embodiment of the present invention, Ca: 0.001 to 0.003%, B: 0.001 to 0.005%, P: 0.1% or less (excluding 0) and S: 0.01% or less (excluding 0) at least one of may further include.

The content of Ca is 0.001 to 0.003%.

Calcium (Ca) is an element that suppresses the formation of MnS steel-making inclusions generated at grain boundaries when Mn is contained in a large amount. In the present invention, 0.001% or more may be added to improve the cleanliness of the material. However, when the content is excessive, there is a problem that Ca-based inclusions are generated to deteriorate the hot workability and surface quality of the material, so the upper limit can be limited to 0.003%.

The content of B is 0.001 to 0.005%.

Boron (B) is an effective element for suppressing crack generation during casting and securing good surface quality, and may be added in an amount of 0.001% or more. However, if the content is excessive, there is a problem that nitride (BN) is formed on the surface of the product during the annealing/pickling process to deteriorate the surface quality, so the upper limit may be limited to 0.005%.

The content of P is 0.1% or less (excluding 0).

Phosphorus (P) is an impurity that is unavoidably contained in steel and is an element that causes intergranular corrosion or inhibits hot workability. In the present invention, the upper limit of the P content is managed as 0.1%.

The content of S is 0.01% or less (excluding 0).

Sulfur (S) is an impurity that is unavoidably contained in steel, and is an element that segregates at grain boundaries and is a major cause of inhibiting hot workability, so it is desirable to control its content as low as possible. In the present invention, the upper limit of the S content is managed as 0.015%.

The remaining component of the present invention is iron (Fe). However, since unintended impurities from raw materials or the surrounding environment may inevitably be mixed in the normal manufacturing process, this cannot be excluded. Since these impurities are known to any person skilled in the art of manufacturing processes, all details thereof are not specifically mentioned in the present specification.

As described above, in metastable austenitic stainless steel, martensitic transformation occurs by plastic (cold) working at a temperature higher than or equal to the martensitic transformation initiation temperature (Ms).

As the applied strain continues, a continuous phase transformation occurs, and this phase transformation increases the strength until the austenitic stainless steel is damaged. Strength can be secured only by controlling the fraction of martensite phase generated during cold working.

On the other hand, the above-mentioned martensitic phase fraction depends on the austenite phase stability.

The upper limit temperature at which the phase transformation occurs by such plastic working is expressed by the Md value, and is a measure of the degree of phase transformation occurring by the processing.

In particular, when 30% strain is applied, the temperature (°C) at which 50% of the phase transformation to martensite occurs is defined as Md ₃₀ . When the Md ₃₀ value is high, it is easy to generate the processing-induced martensite phase, whereas when the Md ₃₀ value is low, it can be determined that the processing-induced martensite phase is relatively difficult to form. In general, the Md ₃₀ value is used as an index for determining the degree of austenite stabilization of conventional austenitic stainless steels, and can be expressed by the component relational expression of Equation (1) below.

Formula (1): 551-462*(C+N)-9.2*Si-8.1*Mn-13.7*Cr-29*(Ni+Cu)

The present inventors confirmed that the higher the value of Equation (1), the more active the transformation from the austenite phase to the martensite phase occurred due to external stress, but surface defects occurred and the workability decreased. It was tried to control the transformation amount of processing-induced martensite through the value.

In the austenitic stainless steel having improved resistance to high temperature softening according to an embodiment of the present invention, the Md ₃₀ value expressed by Equation (1) satisfies the range of -30°C to 30°C.

When the value of Equation (1) is less than -30°C, the processing-induced martensite phase acting as a nucleation site cannot be secured, and the average grain size cannot be derived to 10 μm or less. On the other hand, when the value of Equation (1) is too high, the austenitic stainless steel of the above-mentioned alloy composition is accompanied by a sharp work-induced martensitic transformation behavior due to external deformation. Accordingly, there is a problem that surface defects of the austenitic stainless steel occur and workability is reduced, so that the upper limit of Equation (1) is limited to 30°C.

Next, a method for manufacturing an austenitic stainless steel having improved resistance to high temperature softening according to another aspect of the present invention will be described.

A method of manufacturing austenitic stainless steel having improved resistance to high temperature softening according to an embodiment of the present invention, in weight%, in weight%, C: 0.02 to 0.15%, N: 0.1 to 0.3%, Si: 0.2 to 0.7, Mn : 2.0 to 5.0%, Cr: 17.0 to 19.0%, Ni: 2.5 to 5.0%, Cu: 1.0 to 3.0%, including the remaining Fe and unavoidable impurities, hot rolling and hot rolling a slab satisfying the following formula (1) annealing; cold-rolling the hot-rolled annealing material to a total reduction ratio of 50% or more; and cold-rolling and annealing the cold-rolled material at 900°C to 1000°C.

Formula (1): -30≤ 551-462*(C+N)-9.2*Si-8.1*Mn-13.7*Cr-29*(Ni+Cu) ≤30

Here, C, N, Si, Mn, Cr, Ni, and Cu mean weight % of each element.

The explanation of the reason for limiting the numerical value of the alloy component content is the same as described above.

A slab having the above composition may be subjected to conventional casting, hot rolling, solution heat treatment and pickling to manufacture a hot-rolled annealed material.

For example, the slab can be hot rolled at a temperature of 1,050 to 1,300 ° C, which is a normal rolling temperature, and solution heat treatment is performed in a temperature range of 1,050 to 1,200 ° C to remove surface defects of the hot-rolled steel sheet and dissolve precipitates. can be performed. In this case, the solution heat treatment may be performed for 60 to 120 seconds.

Thereafter, the hot-rolled steel sheet may be pickled to remove surface scale, and then cold-rolled to manufacture a thin film.

During cold rolling, the austenite phase of the hot-rolled annealed steel sheet is transformed into a processing-induced martensitic phase by processing, and as the rolling reduction increases, the fraction of the martensite phase increases, thereby increasing the yield strength of the material.

In the present invention, during cold rolling, a relatively high reduction ratio of 50% or more is applied to promote the production of processed induced martensite to secure a yield strength of 500Mpa or more. Preferably, the total reduction ratio can be controlled to 70% or more.

Next, a heat treatment process of reverse transformation of the processed organic martensite produced by cold rolling into austenite is performed.

The heat treatment for forming the reverse transformation austenite phase may be performed in the range of the austenite reverse transformation completion temperature (Austenite finish temperature, hereinafter AF) to AF+50°C.

When the reverse austenite transformation proceeds, the lower the reverse transformation heat treatment temperature, the easier it is to nucleate the grains, and at the same time suppress the grain growth of the reverse transformation austenite phase, so that the grains of the final steel can be finely derived. Accordingly, the reverse transformation heat treatment temperature is preferably controlled to be low in the vicinity of the austenite reverse transformation completion temperature AF.

In the case of metastable austenitic stainless steel according to the disclosed embodiment, reverse transformation heat treatment may be performed at 900°C to 1000°C for 10 seconds to 10 minutes.

In this way, when the cold-rolled material is manufactured by controlling the cold-rolling ratio and the heat treatment temperature together with the alloy component, it is possible to secure fine grains advantageous for securing strength and workability.

The cold-rolled material thus manufactured has an average grain size of 10 μm or less.

In addition, the manufactured cold rolled material has a yield strength of 450 MPa or more.

In addition, the manufactured cold-rolled material can secure a hardness of 450 Hv or more even at a temperature of 500 ° C. or more.

Hereinafter, it will be described in more detail through preferred embodiments of the present invention.

Example

With respect to the component ranges in [Table 1] below, a slab was prepared through ingot melting, heated at 1,230 ° C. for 2 hours, and then hot rolled to a thickness of 3 mm was performed. After hot rolling, 1,050 Solution heat treatment was performed at ℃. Next, the hot-rolled coil was subjected to cold rolling at a reduction ratio of 50%, and heat treatment was performed at 900° C. for 1 minute.

In Table 1 below, the value of Formula (1) is a value derived by substituting the weight % of each alloy element into the following Formula (1).

Formula (1): 551-462*(C+N)-9.2*Si-8.1*Mn-13.7*Cr-29*(Ni+Cu)

	C	N	Si	Mn	Cr	Ni	Cu	P	S	Formula (1)
Example 1	0.11	0.210	0.45	3.9	18.0	3.5	1.5	0.04	0.004	-24.17
Example 2	0.05	0.180	0.3	3.6	17.7	3.7	2.0	0.04	0.004	5.03
Comparative Example 1	0.06	0.22	0.55	4.3	18.7	4.2	1.4	0.04	0.004	-36.84
Comparative Example 2	0.08	0.16	0.4	3.2	17.3	3.2	1.3	0.04	0.004	43.01

After heat treatment, the yield strength and grain size of each steel sheet were measured.

Specifically, a tensile test was performed at a speed of 20 mm/min using a test piece processed according to the JIS 13B standard, and yield strength (MPa) was measured.

The average grain size was measured by photographing with an optical microscope (Optical Microscope, OM) after performing nitric acid electrolytic pickling on the cold-rolled steel sheet. Through an image analyzer of the obtained microstructure photograph, arbitrary 3 points of the steel plate were measured, and then the average value was expressed.

Meanwhile, in order to improve the hardness of the austenitic stainless steel, temper rolling was performed with a work roll having an average roughness of #600 or more, and the hardness and formability of the temper rolling material were evaluated.

The hardness of the temper rolling material was shown in Table 2 below by measuring the hardness value of the surface portion under the condition of Vickers hardness (1 kg/f).

For the formability test of the temper rolling material, Ericsson evaluation was introduced. Specifically, plastic workability evaluation was performed at a speed of 1 ton of black load and 10 mm/min of blank speed.

On the other hand, by visually observing the surface of the temper rolling material, the presence/absence of surface irregularities and roughness was confirmed as an index for judging the surface quality.

Next, after the temper rolling material was subjected to annealing softening heat treatment at 500° C. and 600° C. for 1 hour, respectively, the hardness value of the surface part was measured under the condition of Vickers hardness (1 kg/f), and it is shown in Table 2 below.

	heat-treated material		temper rolling material			softening material
	yield strength	Average grain size (㎛)	Hardness (Hv)	formability elongation	surface quality	500℃	600℃
Example 1	552	≤ 10	496	Good	Good	517	463
Example 2	564	≤ 10	498	Good	Good	543	457
Comparative Example 1	486	≥ 10	493	Good	Good	472	403
Comparative Example 2	612	≤ 10	492	error	error	502	472

1 is a microstructure photograph taken with an optical microscope (Optical Microscope, 　OM) of Comparative Example 1 and Example 1 steel.

Referring to FIG. 1 , in Comparative Example 3 to which general heat treatment conditions were applied, the average grain size was 32 μm and exceeded 10 μm, whereas Example 3 was heat treated at a temperature near the austenite reverse transformation completion temperature (AF). In the case of , the average grain size was as fine as 8 μm.

Referring to Table 2, in the case of Examples 1 to 4 that satisfy the alloy composition, the range of values of Equation (1), and the average grain size conditions suggested by the present invention, it is possible to secure a yield strength of 450 MPa or more, as well as temper rolling It was confirmed that excellent elongation of 35% or more and surface quality could be secured. In addition, it was possible to secure a hardness of 450 Hv or more even at a high temperature of 500 to 600 ° C, and it was confirmed that softening can be prevented, so that it can be applied as a gasket material.

In the case of Comparative Example 1 in which the value of Equation (1) is less than -30, it can be seen that the physical properties of the temper rolling material are good, but the softening resistance at high temperature is relatively poor.

In the case of Comparative Example 2 in which the value of Equation (1) exceeds 30, it can be confirmed that a large amount of martensite is generated during temper rolling, and formability and surface quality are poorly derived.

As such, according to the disclosed embodiment, by controlling the alloy component and the relational expression to derive the grain size to 10 μm or less, excellent elongation and surface quality of 35% or more can be secured during temper rolling, and the gasket application temperature is 500 to It is possible to manufacture austenitic stainless steel that can prevent softening in the temperature range of 600 °C.

In the foregoing, exemplary embodiments of the present invention have been described, but the present invention is not limited thereto, and those of ordinary skill in the art are within the scope not departing from the concept and scope of the claims described below. It will be understood that various changes and modifications are possible.

According to an example of the present invention, while ensuring strength and workability, it is possible to secure softening resistance at a temperature of 500° C. or higher, so that it can be applied as a gasket material. In addition, it is possible to provide an austenitic stainless steel having a reduced nickel content while securing elongation and corrosion resistance comparable to the existing 301 stainless steel.

Claims (10)

1. By weight, C: 0.02 to 0.15%, N: 0.1 to 0.3%, Si: 0.2 to 0.7, Mn: 2.0 to 5.0%, Cr: 17.0 to 19.0%, Ni: 2.5 to 5.0%, Cu: 1.0 to 3.0 %, including the remainder Fe and unavoidable impurities,

   Austenitic stainless steel with improved resistance to softening at high temperatures satisfying the following formula (1).

   Formula (1): -30≤ 551-462*(C+N)-9.2*Si-8.1*Mn-13.7*Cr-29*(Ni+Cu) ≤30

   (Here, C, N, Si, Mn, Cr, Ni, and Cu mean weight% of each element)
2. The method of claim 1,

   Austenitic stainless steel with improved resistance to high temperature softening with an average grain diameter of 10 μm or less.
3. The method of claim 1,

   Ca: 0.001 to 0.003%, B: 0.001 to 0.005%, P: 0.1% or less (excluding 0), and S: 0.01% or less (excluding 0) Austenite with improved resistance to softening at high temperature further comprising at least one of series stainless steel.
4. According to claim 1,

   Austenitic stainless steel with improved high temperature softening resistance with a yield strength of 450 MPa or more.
5. The method of claim 1,

   Austenitic stainless steel with improved resistance to high temperature softening with hardness of 450 Hv or higher at a temperature of 500 °C or higher.
6. The method of claim 1,

   Austenitic stainless steel with improved high temperature softening resistance with an elongation of 35% or more.
7. By weight, C: 0.02 to 0.15%, N: 0.1 to 0.3%, Si: 0.2 to 0.7, Mn: 2.0 to 5.0%, Cr: 17.0 to 19.0%, Ni: 2.5 to 5.0%, Cu: 1.0 to 3.0 %, including the remaining Fe and unavoidable impurities, and hot rolling and hot annealing of a slab satisfying the following formula (1);

   cold-rolling the hot-rolled annealed material to a total reduction ratio of 50% or more; and

   Heat-treating the cold-rolled material at 900°C to 1000°C;

   Formula (1): -30≤ 551-462*(C+N)-9.2*Si-8.1*Mn-13.7*Cr-29*(Ni+Cu) ≤30

   (Here, C, N, Si, Mn, Cr, Ni, and Cu mean weight% of each element)
8. 8. The method of claim 7,

   A method of manufacturing austenitic stainless steel with improved resistance to high temperature softening, with a total rolling reduction of 70% or more during cold rolling.
9. 8. The method of claim 7,

   The hot rolling is a method of manufacturing an austenitic stainless steel having improved resistance to high temperature softening performed at 1,050 to 1,300°C.
10. 8. The method of claim 7,

    After hot rolling, the step of solution heat treatment at 1050 to 1200 ℃; Method for producing austenitic stainless steel with improved resistance to high temperature softening further comprising.

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