KR101289518B1 - Austenite stainless steel sheet and method for producing same - Google Patents

Abstract

Austenitic stainless steel sheet for springs having high strength and excellent formability, C: 0.01 to 0.15%, Si: 3.0% or less, Mn: 3.0% or less, Cr: 10.0 to 30.0%, Ni: 4.0 to 20.0%, N : It contains 0.4% or less, has a chemical composition which consists of remainder Fe and an impurity, The austenite amount (gamma) s (%) of a steel plate surface part and the austenite amount (gamma) c (%) of a plate thickness center part are ((gamma) s + (gamma) c) / 2. <55, and also satisfies [gamma] s / [gamma] c> 0.1, and has a metal structure whose balance is mainly processed organic martensite structure.

Description

Austenitic stainless steel sheet and its manufacturing method {AUSTENITE STAINLESS STEEL SHEET AND METHOD FOR PRODUCING SAME}

TECHNICAL FIELD The present invention relates to an austenitic stainless steel sheet and a method for manufacturing the same, and more particularly, to an austenitic stainless steel sheet for spring having high strength and excellent moldability and a method for producing the same.

Spring materials used as leaf springs, springs, housings, plate springs, dome switches, etc. in electronic devices, nuclear power plants, automotive parts, etc., have high strength for thinning the material and excellent molding for processing into predetermined product shapes. Sex is required.

The material applied to these uses until now was SUS301 (AISI301) stainless steel which belongs to metastable austenitic stainless steel. Since SUS301 stainless steel is transformed into a hardened organic martensite having a hardened portion at the time of cold working, high strength can be obtained relatively easily, and local strain is suppressed by the TRIP (transformation organic plasticity) effect. Therefore, excellent moldability can also be obtained. Such a spring material is disclosed by following patent documents 1-3, for example.

In patent document 1, C: 0.03% or less (In this specification, unless otherwise indicated, "%" with respect to a chemical composition means "mass%."), Si: 1.0% or less, Mn: 2.5% or less, Ni: 4.0 to 10.0%, Cr: 13.0 to 20.0%, N: 0.06 to 0.30%, S: 0.01% or less, O: 0.007% or less, M value = 330- (480 × C)-(2 × Si) A stainless steel having excellent molding processability, wherein-(10 × Mn)-(14 × Ni)-(5.7 × Cr)-(320 × N) is 30 or more, is disclosed.

In patent document 2, C: 0.08% or less, Si: 3.0% or less, Mn: 4.0% or less, Ni: 4.0-10.0%, Cr: 13.0-20.0%, N: 0.06-0.30%, O: 0.007% or less The stainless steel which is excellent in the spring property and the fatigue property of a process part which the said M value is 40 or more is disclosed.

Patent Document 3 includes C: 0.03% or less, Si: more than 1.0% and 3.0% or less, Mn: 4.0% or less, Ni: 4.0 to 10.0%, Cr: 13.0 to 20.0%, N: 0.30% or less, and S: 0.01%. Hereinafter, the stainless steel which contains O: 0.007% or less and excellent in the formability and fatigue property which M value exists in the range of 30-100 is disclosed.

All of the stainless steels disclosed in Patent Literatures 1 to 3 are subjected to cold rolling after hot rolling at a rolling rate of 50% or more, and then relatively low temperature and short time to generate fine uniform recrystallized particles having an average crystal grain size of 10 μm or less. It manufactures by carrying out finish annealing and temper rolling at the end. That is, these are all trying to acquire predetermined intensity | strength characteristic by utilizing crystal grain refinement which is a reinforcement mechanism with little moldability deterioration. However, in recent years, since the strength required for the spring material is improving, the stainless steel disclosed in Patent Documents 1 to 3 may be insufficient in the strength required for the product.

Patent Document 4 below describes a high-strength spring material based on low C and high N SUS301L, specifically, C: 0.03% or less, Si: 1.0% or less, Mn: 2.0% or less, Cr: 16.0 to 18.0%, Ni: 6.0 to 8.0%, N: 0.25% or less, Nb: 0 to 0.30%, and having an area ratio of 50% or more and less than 100% of recrystallized particles having an average particle diameter of 5 μm or less, and unrecrystallized part 0 Stainless steel having a martensite of 40% or more of area ratio and residual austenite or martensite single-phase structure obtained by performing temper rolling of 30% or more of reduction ratio to a stainless steel having a structure composed of more than 50% and 50% or less. Steel is disclosed.

The stainless steel disclosed in Patent Document 4 is formed into a metal structure containing a processed organic martensite structure by temper rolling, and then molded into a predetermined shape, and further subjected to an aging treatment, whereby fine chromium nitride is formed on the martensite. To precipitate. By utilizing the precipitation strengthening at that time, the strength can be increased without adding a new process.

Patent Document 1: Japanese Patent Application Laid-Open No. 4-214841 Patent Document 2: Japanese Patent Application Laid-open No. H5-279802 Patent Document 3: Japanese Patent Application Laid-open No. Hei 5-117813 Patent Document 4: Japanese Patent No.4321066

However, in order to reduce the size of the product and to improve the performance, spring materials are still required to further improve the strength and formability. For this reason, even the stainless steel disclosed by patent document 4 may not fully satisfy the performance calculated | required by the latest product.

In one aspect, the present invention contains C: 0.01 to 0.15%, Si: 3.0% or less, Mn: 3.0% or less, Cr: 10.0 to 30.0%, Ni: 4.0 to 20.0%, and N: 0.40% or less. , The balance of Fe and impurities, and the amount of austenite γs (%) of the steel plate surface portion and the amount of austenite γc (%) at the center of the plate thickness of the steel sheet are (γ s + γ c) / 2 ≦ 55, It is an austenitic stainless steel sheet characterized by satisfying [gamma] s / [gamma] c> 0.10 and having a metal structure whose balance is mainly processed organic martensite structure.

Here, the austenite content γs (%) of the steel plate surface portion means the volume fraction (%) of austenite contained in the region (referred to as steel plate surface portion) from the outermost surface of the steel sheet to a depth position of 10 μm in the plate thickness direction. . On the other hand, the amount of austenite γc (%) at the center of the plate thickness is an area (plate thickness) from a surface in which one surface of the steel sheet is cut to half of the original plate thickness by mechanical polishing and chemical polishing (plate thickness in a direction of 10 μm in thickness). It means the volume fraction (%) of austenite included in the center).

In the austenitic stainless steel sheet of the present invention, the chemical composition is in place of a part of Fe,

1) at least one of Mo: 3.0% or less and Cu: 3.0% or less, and / or

2) Ti: 0.50% or less, Nb: 0.50% or less and V: 1.0% or less may further include one or two or more selected from the group consisting of.

From another aspect, the present invention, after hot rolling to a steel material having the chemical composition, and then cold rolling and annealing the obtained hot rolled steel sheet to form a cold-rolled annealing material, the reduction ratio (%) / 10 to this cold-rolled annealing material It is a manufacturing method of an austenitic stainless steel sheet characterized by performing temper rolling by the above-mentioned number of passes.

In the said method, it is preferable that the cold-rolled annealing material before temper rolling has an average grain size of 5 micrometers or less of austenite particle | grains.

According to the present invention, an austenitic stainless steel sheet having a high strength and excellent moldability and a manufacturing method thereof are provided.

BRIEF DESCRIPTION OF THE DRAWINGS Explanatory drawing which shows an example of the processing process which the austenitic stainless steel plate which concerns on this invention receives after temper rolling.
2 is an explanatory diagram showing an example of the relationship between the distribution of the austenite content in the plate thickness direction after temper rolling and the formability;
3 is an explanatory diagram showing a moldability evaluation method.

The present invention will be described in more detail with reference to the accompanying drawings.

The austenitic stainless steel sheet according to the present invention is a cold rolled steel sheet subjected to temper rolling. As shown in Fig. 1, the austenitic stainless steel sheet is subjected to temper rolling, then subjected to molding to obtain a desired shape, and then subjected to aging treatment as necessary, to a product (for example, various springs). do.

MEANS TO SOLVE THE PROBLEM This inventor thought that by increasing content of C which is a solid solution strengthening element, the processed organic martensite structure produced by temper rolling will strengthen, and the steel can be made high. The problem of the lack of strength described above can be solved by the superposition of the strengthening of the martensite phase due to the increase of the C content and the precipitation strengthening utilizing Cr ₂ N.

At this time, if the amount of processed organic martensite is small and a large amount of austenite remains, predetermined strength cannot be obtained. Therefore, the average value of the amount of austenite γs (%) of the steel plate surface portion and the amount of austenite γc (%) at the center of the plate thickness, that is, the value of (γ s + γ c) / 2 (hereinafter referred to as the average amount of austenite To 55 or less). γs and γc are as defined above.

This inventor also considered that the control of the plate thickness direction distribution of the amount of austenite is effective in order to improve the moldability which falls by high strength. 2 is an explanatory diagram showing an example of the relationship between the distribution of the austenite content in the plate thickness direction after temper rolling and formability.

As shown in Fig. 2, even if the average amount of austenite after temper rolling is the same, the moldability can be greatly improved by changing the distribution in the plate thickness direction of the amount of austenite after temper rolling. Specifically, by increasing the amount of austenite remaining in the steel sheet surface portion after temper rolling, the processed organic martensite transformation occurs in the steel sheet surface portion that is most deformed at the time of subsequent molding, thereby exhibiting a sufficient TRIP effect. This results in excellent moldability.

Further, the austenitic stainless steel, when aged, N is the solubility limit by loading a small maten Xi-form, can be, to take advantage of limitations Ganghwado since fine Cr ₂ N is precipitated. In this way, the austenitic stainless steel according to the present invention can have high strength and excellent moldability.

On the other hand, since the processing heat generation of the steel sheet in the temper rolling increases as the amount of reduction per one pass increases, the temperature of the surface of the steel sheet cooled by the rolling oil is significantly lower than the temperature of the sheet thickness center part, As the amount of martensite produced on the surface of the steel sheet is significantly increased during rolling, the amount of austenite on the surface of the steel sheet is greatly reduced.

That is, when temper rolling with a small number of passes as in the conventional method, the amount of austenite remaining on the surface of the steel sheet is remarkably smaller than the amount of austenite remaining at the center of the plate thickness, so that the subsequent The sufficient TRIP effect accompanying process organic martensite transformation is not acquired, and moldability falls.

On the other hand, when the number of passes of temper rolling is increased to reduce the amount of rolling reduction per pass and the work heat is suppressed, the amount of austenite remaining in the steel sheet surface portion after temper rolling can be increased. Thereby, distribution of the plate thickness direction of the amount of austenite suitable for subsequent shaping | molding can be achieved.

Specifically, the austenite content γs (%) of the steel plate surface portion after temper rolling and the austenite content γc (%) at the center of the plate thickness have a plate thickness direction distribution of the amount of austenite satisfying the condition of γs / γc≥0.10. When it achieves, a sufficient TRIP effect will be exhibited in the steel plate surface part which deform | transforms the greatest at the time of subsequent shaping | molding, and moldability improves.

Even if the number of rolling reductions per pass is reduced by increasing the number of passes in temper rolling, since the temperature of the steel plate surface is lower than that of the plate thickness center, the amount of martensite is greater in the steel plate surface area than in the plate thickness center, so that the amount of austenite Less is inevitable. However, when the amount of austenite of the steel plate surface part is 1/10 or more of the amount of austenite of the plate thickness center part, it turned out that moldability sufficient for practical use is ensured.

As described above, the present invention is directed to "significantly high strength by superposition of the strengthening of the martensite phase by the increase of the C content and precipitation strengthening by the Cr ₂ N, and optimization of the plate thickness direction distribution of the austenite amount. By achieving excellent moldability, thereby obtaining an austenitic stainless steel sheet that satisfies the requirement as a material for a spring component to be compact and lightweight ''.

Next, the chemical composition, metal structure, and manufacturing method of the austenitic stainless steel sheet according to the present invention will be described.

(1) chemical composition

C: 0.01 ~ 0.15%

C is a solid solution strengthening element and is very effective for strengthening the martensite phase produced by cold working, so the C content is at least 0.01%. However, when the amount of C is excessive, coarse carbides are produced in the manufacturing process, and moldability and corrosion resistance deteriorate. Therefore, the C content is 0.15% or less. C content is preferably 0.03% or more.

Si: 3.0% or less

Si is a solid solution strengthening element, contributes to the high strength of the steel, and is also used as a deoxidizer in the solvent. However, when the Si content is excessive, coarse Si compounds are produced in the manufacturing process, and these coarse Si compounds cause deterioration of hot workability and cold workability. For this reason, Si content is 3.0% or less, Preferably it is 2.8% or less.

Mn: 3.0% or less

Mn is used as a deoxidation material at the time of a solvent. In addition, Mn is an austenite stabilizing element and contains an appropriate amount in consideration of the balance with other elements. However, when the Mn content is excessive, coarse Mn compounds are produced in the manufacturing process, the coarse Mn compounds become the starting point of destruction, and the moldability is deteriorated. Therefore, Mn content is 3.0% or less, Preferably it is 2.8% or less.

Cr: 10.0-30.0%

Cr is a basic element of stainless steel, and by containing 10.0% or more, Cr forms a passivation film on the surface of steel materials and shows the effect | action which improves corrosion resistance. In addition, when the steel is aged, it precipitates as fine Cr ₂ N, thereby contributing to the improvement of strength of the steel. However, since Cr is a ferrite generating element, when Cr content is excessive, (delta) ferrite will generate | occur | produce at high temperature, and the hot workability of steel will remarkably deteriorate. Therefore, Cr content is 10.0% or more and 30.0% or less, Preferably they are 12.0% or more and 25.0% or less.

Ni: 4.0-20.0%

Ni is a basic element of austenitic stainless steel and contains 4.0% or more of Ni in order to stably obtain an austenite phase having an excellent strength-ductility balance at room temperature. However, when the Ni content is excessive, the austenite phase becomes too stable and the processed organic martensite transformation is suppressed, so that high strength cannot be obtained. Therefore, Ni content is 4.0% or more and 20.0% or less, Preferably they are 4.5% or more and 18.0% or less.

N: 0.40% or less

N, like C, is a solid solution strengthening element and contributes to improving the strength of steel. In addition, when the steel is aged, it is also precipitated as fine Cr ₂ N, which contributes to the high strength of the steel. However, when N content is excessive, it will become easy to cause an edge crack at the time of hot working. Therefore, N content is 0.40% or less, Preferably it is 0.05% or more and 0.30% or less.

The austenitic stainless steel according to the present invention may further contain the following optional additional elements as necessary.

One or both of Mo: 3.0% or less and Cu: 3.0% or less

Since both Mo and Cu are elements which precipitate fine intermetallic compounds during the aging treatment and contribute to the strength increase of the steel sheet, they may be included as necessary. However, when the Mo content or the Cu content is excessive, δ ferrite is likely to be formed at high temperatures and precipitates at grain boundaries, which may significantly degrade hot workability. Therefore, Mo content and Cu content are all 3.0% or less, Preferably they are all 2.8% or less.

One or two or more selected from Ti: 0.5% or less, Nb: 0.5% or less and V: 1.0% or less

Ti, Nb and V are precipitated as fine carbides or nitrides in the manufacturing process, suppress the grain growth of the crystals by the pinning effect, and contribute to the strength increase of the steel sheet by precipitation strengthening, You may make it contain as needed. However, when the content of these elements becomes excessive, coarse carbides and nitrides are formed, and these become breakpoints upon deformation and significantly deteriorate formability. Therefore, Ti content and Nb content are made into 0.5% or less, and V content is made into 1.0% or less. Preferably, the Ti content and the Nb content are 0.4% or less, and the V content is 0.8% or less.

Remainder other than the above-mentioned is Fe and an impurity. Representative impurities include P: 0.05% or less, S: 0.03% or less.

(2) metallographic

[Austenitic Distribution in Plate Thickness]

MEANS TO SOLVE THE PROBLEM As a result of performing various tests, the present inventors found that the amount of austenite (gamma) s (%) of a steel plate surface part and the amount of austenite (gamma) c (%) of a center part of a plate | board thickness satisfy following formula (1) and formula (2), and remainder In the case of mainly processed organic martensite structure, it was found that an austenitic stainless steel sheet having high strength and formability was obtained.

Equation (1): (γ s + γ c) / 2 ≦ 55

Equation (2): γ s / γ c ≥ 0.10

First, as shown in Formula (1), the average austenite content which is an average value of the austenite content γs of the steel plate surface part and the austenite content γc in the center of the plate thickness is set to 55% or less, and the balance is mainly high-strength processed organic martensitic By high strength, high strength steel is obtained. The average amount of austenite is preferably 50% or less, more preferably 45% or less, still more preferably 40% or less, and most preferably 35% or less. The lower limit of the average amount of austenite is not specifically defined. However, when the austenite is extremely small, a sufficient TRIP effect may not be obtained on the surface of the steel sheet during molding, so it is preferably 5% or more, more preferably 7.5 More than%

Next, as shown in formula (2), the ratio (γs / γc ratio) of the austenite amount γs of the steel plate surface portion to the amount of austenite γc at the center of the plate thickness is 0.10 or more, so that at the time of forming the plate, Even on the surface of the steel sheet subjected to large deformation, the TRIP effect associated with the processing organic martensite transformation of austenite is sufficiently exhibited, and excellent moldability is obtained. The γs / γc ratio is preferably 0.2 or more, more preferably 0.3 or more, still more preferably 0.5 or more, and most preferably 0.6 or more.

In this invention, high strength and excellent moldability can be made compatible by the amount of austenite of a steel plate surface part, and the amount of austenite of a plate thickness center part satisfy | filling both Formula (1) and Formula (2).

Remainder other than austenite of a metal structure mainly consists of a process organic martensite phase. This processed organic martensite is produced by temper rolling a steel sheet annealed after cold rolling. Therefore, the austenitic stainless steel sheet of the present invention is a temper rolled material.

The term "consisting mainly of the processed organic martensite phase" means that the processed organic martensite occupies 50% by volume or more of the remainder other than austenite. In the austenitic stainless steel sheet produced according to the method of the present invention described below, the metal structure is substantially austenite and processed organic martensite, and other phases include fine precipitates (carbide, nitride, carbonitride) and the like. But the amount is very small. Complete martensite single-phase tissues with γs = γc = 100% are not subjects of the present invention.

As described above, the amount of austenite is higher in the plate thickness center than in the steel plate surface portion, and therefore, even in the austenitic stainless steel sheet according to the present invention, which has increased the austenite amount in the steel plate surface portion, γs <γc (that is, γs / γc). The relationship of <1) is established.

Crystal grain size of the austenitic particles before temper rolling: 5 μm or less

Refinement of crystal grains is known as a reinforcement method with a small deterioration in ductility of steel, and is an effective reinforcement method also in stainless steel as the object of the present invention. In addition, by decreasing the grain size and increasing the density of the grain boundaries, there is also an effect of dispersing the strain concentrated on the grain boundaries during molding, thereby suppressing the occurrence of cracks. Then, in this invention, it is preferable to make the crystal grain diameter of the austenite particle of the steel plate (cold rolled annealing material) before temper rolling into 5 micrometers or less.

(3) Manufacturing method

According to the present invention, after hot rolling to a steel material having the above-described chemical composition, it is cold rolled and annealed to the obtained hot rolled steel sheet to form a cold rolled annealing material, and a pass rate (%) / 10 or more passes to the cold rolled annealing material. By carrying out temper rolling by collection | recovery, the austenitic stainless steel plate which concerns on this invention mentioned above can be manufactured.

What is necessary is just to perform hot rolling, cold rolling, and annealing all by the conventional method. It is preferable to perform cold rolling dividing about 1 to 3 times so that a total rolling reduction may be about 30 to 90%, and annealing is performed when the predetermined total rolling reduction is obtained. Cold rolling and annealing of several passes can also be performed repeatedly. It does not specifically limit about the pass | cover recovery of cold rolling performed before temper rolling.

It is preferable to increase the total reduction ratio of cold rolling and to form a fine metal structure in which the average crystal grain size of the austenite particles of the cold rolled annealing material to be used for the next temper rolling is 5 µm or less, in particular, since the moldability becomes good.

[Quick Rolling Condition]

In this invention, temper rolling is performed strongly in order to utilize the strengthening by process organic martensite to the maximum. The total reduction ratio is preferably at least 40%, more preferably at least 50%, most preferably at least 60%. The upper limit of the total rolling reduction is not particularly specified, but is usually less than 100%, preferably 90% or less.

When such strong temper rolling is performed with a small number of passes, as described above, the processed organic martensite in the steel plate surface portion proceeds, and the amount of austenite in this portion is reduced, and the amount of austenite at the center of the plate thickness is c. The ratio (γ c / γ s ratio) ≥ 0.1 of the amount of austenite γ s to the surface portion of the steel sheet is not satisfied, resulting in deterioration of formability.

MEANS TO SOLVE THE PROBLEM As a result of investigating the relationship between the path | pass number at the time of temper rolling, and the austenite distribution in a plate thickness direction, as shown in Formula (3), it is temper-rolled by the number of passes | passes which become total reduction ratio (%) / 10 or more. By doing this, it was confirmed that the γc / γs ratio was 0.10 or more. Therefore, temper rolling is performed by the number of passes of the total rolling reduction (%) / 10 or more in temper rolling. For example, when the total reduction ratio of temper rolling is 65%, the number of passes is 7 or more.

Equation (3): number of tempered rolling passes ≥ tempered rolling total reduction rate (%) / 10

Preferably, the reduction ratio in each pass of temper rolling is made about the same. Therefore, it is preferable that the reduction ratio in each pass of temper rolling be 10% or less. Since increasing the number of passes blindly deteriorates the work efficiency, it is desirable that the number of passes be in the range from the smallest number of passes for satisfying the total reduction ratio (%) / 10 to two more passes.

&Lt; Example 1 >

Table 1 shows the chemical components of the stainless steel used in this example. Steels A to F are inventive steels that satisfy the components defined in the present invention, and steels G to M are comparative steels that do not satisfy the components specified in the present invention.

Table 2 shows the manufacturing conditions and test results of the steel sheet manufactured using steels A to M. Steel sheets 1-8 are steel sheets which satisfy the provisions of the present invention, and steel sheets 9-18 are comparative steel sheets which do not satisfy the provisions of the present invention.

The steel having the chemical composition shown in Table 1 was dissolved in a normal air melting furnace to obtain 17 kg of steel ingot. After hot rolling and annealing the steel ingot to form a hot rolled steel sheet with a thickness of 6.0 mm, cold rolling and annealing were repeated one to three times with this hot rolled steel sheet to obtain a cold rolled annealing material with a thickness of 0.8 to 4.0 mm. The cold rolling annealing material was subjected to temper rolling by plural passes, and finally to a thin plate having a thickness of 0.4 mm. Temper rolling was performed on the conditions that the reduction ratio of each path | pass is equal.

Using the test piece collected from the steel sheet before and after this temper rolling, the grain size, austenite amount, formability, and tensile strength were investigated with the following method. Moreover, some steel sheets performed the aging treatment for 1 minute at 300 degreeC after temper rolling. The tensile strength of these steel sheets used the value after aging treatment.

(Average grain size after annealing)

The crystal grain size of the austenitic particles was calculated from the nominal particle diameter of the austenitic particles from a scanning micrograph after corrosion of the test piece cross section taken from the cold rolled annealing material before temper rolling.

(Austenite content)

The amount of austenite was calculated from the steel plate surface portion of the test piece taken from the steel sheet after temper rolling and the plate thickness center surface cut by mechanical polishing and chemical polishing. The integrated intensity ratio by X-ray diffraction measurement and the scanning microscope photograph after the etching were used for calculation. In Table 2, austenite content of the steel plate surface part is described by (gamma) s and austenite amount of the plate thickness center surface as (gamma) c.

(Moldability)

3 is an explanatory diagram showing a moldability evaluation method. The shallow drawing process as shown in FIG. 3 was given to the test piece of 100 mm <^2> collected from the steel plate after temper rolling. Thereafter, the edge portion was observed with an optical microscope, and ◎ that no cracks were observed at all, 것을, no continuous cracks were confirmed, and that the continuous cracks were confirmed or broken were ×.

(The tensile strength)

Tensile strength was measured based on JISZ 2241 using the JIS-13B tension test piece extract | collected from the steel plate after temper rolling or the aging treatment. Along with the measured value, a thing with a tensile strength exceeding 1500 N / mm <^2> was represented by (circle) and the thing below.

The steel sheets 1-8 in Table 2 are steel sheets of this invention, and have the outstanding moldability and high strength. In addition, by comparing the steel sheets 1, 2, by the fine precipitation of Cr ₂ N at the time of aging, in particular it has been confirmed that high strength is obtained. Moreover, it was confirmed that the steel sheets 3 and 4 whose crystal grain diameter after annealing are 5 micrometers or less especially obtained high strength and excellent moldability.

Steel sheets 9-18 are comparative examples in which the chemical composition or the manufacturing conditions were out of the range defined by the present invention.

The steel sheets 9 to 11 have a γs / γc of less than 0.1, and high strength is obtained, but formability is not preferable. In addition, when comparing steel plate 7 and steel plate 10, or steel plate 8 and steel plate 11, although steel plate 7, 8 has both high strength and formability, steel plate 10 and 11 are high strength, but moldability is not preferable, Even in the case of producing the same at the same rough rolling ratio, it was confirmed that the distribution of the amount of austenite was changed by the number of rolling passes, and the characteristics were greatly changed.

The steel sheet 12 has a C content and an N content exceeding the scope of the present invention, and coarse carbonitrides are produced, and thus formability is remarkably undesirable.

The steel plate 13 has C content below the range of this invention, and its strength is small also after an aging treatment. Moreover, since γs / γc is less than 0.1, moldability is also undesirable.

The steel sheet 14 has a low Cr content and a Ni content exceeding the scope of the present invention, and since the average value of γs and γc exceeds 55, even after aging treatment.

Since the Cr content and Ni content are less than the range of this invention and (gamma) s / (gamma) c is less than 0.1, the steel plate 15 does not have moldability.

The steel sheet 16 has a low Si content and a Mn content exceeding the scope of the present invention, and the average value of γs and γc exceeds 55, even after aging treatment. In addition, coarse Si compounds and Mn compounds are produced, and moldability is also undesirable.

Since steel content 17 and Mo content and Cu content exceed the range of this invention, and the average value of (gamma) s and (gamma) c exceeds 55, even after an aging treatment, strength is small. Moreover, coarse intermetallic compound is produced | generated and moldability is also unpreferable.

In addition, in the steel plate 18, Ti content exceeds the range of this invention, coarse TiN is produced | generated and moldability is undesirable.

Claims (5)

By mass%, C: 0.01-0.15%, Si: greater than 0% and 3.0% or less, Mn: greater than 0% and 3.0% or less, Cr: 10.0-30.0%, Ni: 4.0-20.0%, N: greater than 0% 0.40% The austenitic amount γ s (%) and the austenite content γ c (%) at the center of the plate thickness are (γ s + γ c) / 2 ≦ 55 while containing a chemical composition composed of the balance Fe and impurities. And austenite-based stainless steel sheet, which satisfies [gamma] s / [gamma] c> 0.10 and has a metal structure whose balance is mainly a processed organic martensite structure. The method according to claim 1,
The austenitic stainless steel sheet as described above, wherein the chemical composition has at least one of Mo: 3.0% or less or Cu: 3.0% or less by mass% instead of a part of Fe. The method according to claim 1 or 2,
Austenitic stainless steel having the chemical composition of one or two or more selected from the group consisting of Ti: 0.50% or less, Nb: 0.50% or less, and V: 1.0% or less by mass% instead of a part of Fe. Grater. After hot rolling to the steel material which has the chemical composition of Claim 1 or 2, it cold-rolls and anneales to the obtained hot-rolled steel sheet, and makes it a cold-rolled annealing material, and collect | recovers the pass rate (%) / 10 or more in this cold-rolled annealing material A tempering rolling is carried out by a method for producing an austenitic stainless steel sheet. The method of claim 4,
The method whose average crystal grain size of the austenite grains of the cold rolled annealing material before temper rolling is 5 micrometers or less.

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