JP2003193202A - High elasticity metastable austenitic stainless steel sheet and production method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a metastable austenitic stainless steel sheet which has a high Young's modulus of ≥200,000 N/mm<SP>2</SP>in both the T direction and the L direction. <P>SOLUTION: The steel sheet has a chemical composition containing, by mass, 0.01 to 0.20% C, 12.0 to 20.0% Cr, 4.0 to 12.0% Ni, and 0.01 to 0.20% N, and in which the valule of Md (N) defined as Md (N) =580-520C-2Si-16Mn-16 Cr-23Ni-26Cu-300N-10Mo reaches 0 to 125. The steel sheet has a fine austenite single phase structure having a mean particle diameter of ≤5 μm, a dual-phase structure of fine austenite+martensite where a part of the fine austenite phase is transformed into martensite, or a metallic structure obtained by subjecting these structures to cold rolling. The steel sheet is produced by using a method where a cold rolled steel sheet having the above chemical composition containing ≥60 vol.% martensite is heated at 550 to 850°C to inversely transform the martensite into austenite. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to various applications which require high strength and a large longitudinal elastic modulus (Young's modulus), such as a railroad car's sharpening or horizontal breaking material,
Car antennas, various blades such as doctor blades, printer rail shafts, golf club heads, small springback springs, springs that require damping,
The present invention relates to a high-strength metastable austenitic stainless steel sheet having high elasticity, which can be suitably used for a tact switch that requires repulsive force as a push button switch, a pressing spring of a VTR cassette, a bearing seal material, and the like, and a method for manufacturing the same. .

[0002]

2. Description of the Related Art As a means for increasing the longitudinal elastic modulus of a metal material, a method of theoretically depositing a precipitate having a high elasticity and utilizing the phenomenon that the elastic modulus is improved according to its volume ratio, There is a method of controlling the texture using a single crystal. However, it is quite difficult to commercialize them industrially.

On the other hand, as an example in which the longitudinal elastic modulus is improved by an industrial method, there is known a method of using work-induced martensite produced by cold rolling using SUS301 series metastable austenitic stainless steel. (The Japan Institute of Metals, Vol. 33, No. 5, p. 511-515). However, according to this method, the longitudinal elastic modulus in the direction perpendicular to the cold rolling direction (T direction) is greatly improved, while the longitudinal elastic modulus in the cold rolling direction (L direction) is not so much increased or is decreased. Tend. For example SUS301 3 / modulus of longitudinal elasticity of 4H material although about 200000N / mm ² in the T direction is obtained, the L direction is about 170000~180000N / mm ^2. That is, the method of increasing elasticity using metastable austenitic stainless steel has a drawback that the longitudinal elastic coefficient can be sufficiently improved only in a specific direction within the steel sheet, and a stable high elastic modulus is not always obtained. The current situation is not.

[0004]

It is desirable that the high-strength stainless steel sheets used for the above-mentioned various applications should stably obtain a high longitudinal elastic modulus of 200,000 N / mm ² or more in both the T and L directions of the steel sheet. Be done. It is an object of the present invention to industrially stably produce and provide such a high-elasticity / high-strength stainless steel sheet using metastable austenitic stainless steel.

[0005]

As a result of various studies, the inventors of the present invention have positively utilized the micronization phenomenon of the structure that occurs when the work-induced martensite undergoes the reverse transformation to austenite at high temperature. It has been found that even with such metastable austenitic stainless steel, it is possible to realize a highly elastic stainless steel sheet with little anisotropy as described above.

That is, the above-mentioned object is C: 0.
01 to 0.20%, Cr: 12.0 to 20.0%, Ni: 4.0 to 12.0%,
A steel sheet containing N: 0.01 to 0.20% and having a chemical composition such that the value of Md (N) defined by the following formula (1) is 0 to 125, preferably C: 0.01 to 0.20%, Cr: 12.0 to 20.0
%, Ni: 4.0 to 12.0%, N: 0.01 to 0.20%, Si: 4.0%
Below, Mn: 5.0% or less, P: 0.040% or less, S: 0.020%
Below, O: 0.02% or less, Mo: 0 (no addition) to 5.0%, C
u: 0 (no additive) to 3.0%, Ti: 0 (no additive) to 0.50%,
Nb: 0 (no addition) to 0.50%, Al: 0 (no addition) to 0.20
%, B: 0 (no addition) to 0.015%, REM: 0 (no addition) to 0.
20%, Y: 0 (no addition) ~ 0.20%, Ca: 0 (no addition) ~
0.10%, Mg: 0 (no addition) to 0.10%, the balance consisting of Fe and inevitable impurities, and Md defined by the following formula (1)
A steel sheet having a chemical composition such that the value of (N) is 0 to 125, having a fine austenite single-phase structure with an average grain size of 5 μm or less,
Or, the fine austenite phase with an average grain size of 5 μm or less exhibits a fine austenite + martensite two-phase structure in which part of the fine austenite phase is transformed into martensite, and the longitudinal elastic moduli in the T direction and the L direction of the steel sheet are both 200,000 N / mm ² or more. Achieved by a highly elastic metastable austenitic stainless steel sheet. Md (N) = 580-520C-2Si-16Mn-16Cr-23Ni-26Cu-300N-10Mo ... (1)

Here, Mo, Cu, Ti, Nb, Al, B, R
The lower limit of EM, Y, Ca, and Mg was set to 0 (no addition) because these elements, unlike Si, Mn, N, etc., usually do not come from raw materials in a general steelmaking process. Therefore, in the case of no addition, it is considered to be 0% (below the detection limit by a general analytical method). In addition to austenite and martensite, a small amount of precipitates and inclusions (generally 1 vol% or less) may be present.
The T direction of the steel sheet is a direction perpendicular to the rolling direction, and the L direction is a direction parallel to the rolling direction. The content of each element expressed in mass% is substituted in the places of C, Si, Mn, Cr, Ni, Cu, N, Mo on the right side of the equation (1). In addition, in this specification, a "steel strip" is contained in a "steel plate."

According to the present invention, a steel sheet having the above chemical composition, which is a cold-worked austenite single phase structure,
It has a cold-worked austenite + martensite two-phase structure or a cold-worked martensite single-phase structure, has a hardness of Hv350 or more, and has a longitudinal elastic modulus in the T and L directions of the steel sheet. A highly elastic metastable austenitic stainless steel sheet having a total of 200,000 N / mm ² or more is provided.

Further, in particular, the present invention provides a steel sheet having a fine structure obtained by the method of cold rolling a steel sheet having any one of the following structures i) and ii). i) Fine austenite single-phase structure with an average grain size of 5 μm or less. ii) Fine austenite + martensite two-phase structure in which part of the fine austenite phase having an average grain size of 5 μm or less is transformed into martensite.

Further, the present invention provides the following method as a method for producing a metastable austenitic stainless steel sheet having high elasticity as described above. That is, a metastable austenitic stainless cold-rolled steel sheet having the above chemical composition and containing 60 vol% or more of martensite is prepared, and the cold-rolled steel sheet is heated to a temperature of 550 to 850 ° C to austenite the martensite. Average particle size by reverse transformation to
Provided is a manufacturing method in which a fine austenite single-phase structure having a size of 5 μm or less is formed, and a heat treatment (reverse transformation process) is performed to cool the state to normal temperature. In addition, the holding time of 550 to 850 ℃ is soaked to 0 to 1
Providing a manufacturing method of 80 seconds. Here, "reverse transformation process"
Means a series of processes including a heating process and a cooling process.

In the present invention, after the above reverse transformation treatment,
i) A manufacturing method in which final cold rolling is performed at a reduction rate of 90% or less, ii)
A method for aging at 250 to 540 ° C, iii) A method for final cold rolling at a reduction rate of 90% or less, and further aging at 250 to 540 ° C.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, a highly elastic stainless steel sheet having a longitudinal elastic modulus in the T direction and the L direction of 200,000 N / mm ² or more is realized by using metastable austenitic stainless steel. For that purpose, the phenomenon of micronization of the structure that occurs when the work-induced martensite undergoes reverse transformation to austenite at high temperature is positively utilized (described above). However,
The desired high-elasticity steel sheet cannot be obtained simply by reverse-transforming the work-induced martensite. For that purpose, it is necessary to devise the chemical composition and the metal structure. Hereinafter, matters for specifying the present invention will be described.

[Alloy Element] C is an austenite forming element and is extremely effective in strengthening martensite.
Further, there is an action of lowering the reverse transformation start temperature, which contributes to the formation of fine reverse transformation austenite grains in the reverse transformation treatment. To make full use of these effects,
It is necessary to contain 0.01% by mass or more of C. The content of 0.018 mass% or more is preferable, and the content of 0.05 mass% or more is more preferable. However, as the C content increases, Cr carbides tend to precipitate at grain boundaries during the cooling process of reverse transformation treatment and aging treatment, which causes intergranular corrosion and deterioration of fatigue properties. This can be avoided industrially to some extent by controlling the heat treatment conditions, but even considering this point, the upper limit of the C content should be 0.20% by mass.

Cr is an essential element for ensuring the corrosion resistance of stainless steel. At least 10.0 mass% of Cr must be contained in order to provide the corrosion resistance required for the above various uses. However, if a large amount of Cr is contained in excess of 20.0% by mass, the toughness of the steel sheet will decrease. Further, in order to sufficiently generate martensite, it becomes necessary to add a large amount of austenite forming elements such as C, N, Ni, Mn and Cu.
This not only increases the cost of the steel sheet, but also stabilizes austenite more than necessary at room temperature, making it difficult to increase strength.
Therefore, the upper limit of the Cr content is set to 20.0 mass%.

Ni is an austenite forming element,
It is an essential element for optimizing the amount of work-induced martensite produced in cold rolling. Further, like C, it has the effect of lowering the reverse transformation temperature, and therefore contributes to the refinement of the reverse transformation austenite. However, excessive addition of Ni makes it difficult to form work-induced martensite. Considering these points, the Ni content is specified to be 4.0 to 12.0 mass%. In addition,
It is more preferable to set it in the range of more than 4.0 to 12.0 mass%.

N is an austenite forming element, and C
As well as strengthening martensite, it lowers the reverse transformation start temperature and contributes to the refinement of austenite. In order to exert its effect effectively, it is necessary to add 0.01% by mass or more of N. However, excessive addition of N causes the generation of blowholes during steelmaking, which causes surface defects on the steel material. Further, in the cooling process of the reverse transformation treatment, precipitation of Cr nitrides at the grain boundaries is promoted, which causes intergranular corrosion and deterioration of fatigue properties. Therefore, the N content is set to 0.20 mass% or less.

Si is a ferrite-forming element, which hardens martensite and also forms a solid solution in the austenite phase to harden it, contributing to the improvement of strength after cold rolling. In addition, strain aging improves age hardening ability.
However, addition of a large amount of Si causes various problems in manufacturing, such as inducing hot cracking. Therefore, when Si is added, it is desirable to add Si in an amount of 4.0 mass% or less.

Mn is an austenite forming element,
Like Ni, it contributes to the optimization of the amount of work-induced martensite in cold rolling and, like C, lowers the reverse transformation temperature and contributes to the refinement of austenite. But the excess M
The addition of n makes it difficult to form work-induced martensite in cold rolling, and makes it impossible to refine the structure using reverse transformation. Therefore, when Mn is added, it is desirable to add it in a range of 5.0 mass% or less.

Mo has the effect of improving the corrosion resistance of the stainless steel sheet and finely dispersing the carbonitride during the reverse transformation. Further, since Mo suppresses the crystal grain growth by its own drag effect, the addition of Mo is very effective in the present invention which aims at the refinement of the structure by utilizing the reverse transformation. However, the addition of a large amount of Mo promotes the formation of δ-ferrite at high temperature, which is not preferable. Mo is an expensive element. Therefore, when Mo is added, it is desirable to add it in the range of 5.0 mass% or less.

Cu is an austenite forming element,
Decrease reverse transformation temperature. It also has an age hardening effect during reverse transformation. However, excessive addition of Cu deteriorates the hot workability and causes the occurrence of ear cracks. Therefore, when Cu is added, it is desirable to add Cu in an amount of 3.0 mass% or less.

Ti is effective in increasing the strength during reverse transformation, but addition of a large amount thereof causes surface flaws in the steelmaking slab. For this reason, when Ti is added, it is desirable to add Ti in an amount of 0.50% by mass or less. Nb has an action of suppressing grain growth of the reverse transformation austenite phase, but addition of a large amount thereof causes deterioration of hot workability due to increase in high temperature strength. Therefore, Nb
When added, it is desirable to add 0.50 mass% or less.

Al is an element effective for deoxidation during steel making, and has an effect of significantly reducing A ₂ type inclusions which adversely affect press formability. However, even if it is contained in an amount of more than 0.20 mass%, the effect is saturated, and there is a problem such as an increase in surface defects. Therefore, when Al is added, it is desirable to add Al in an amount of 0.20% by mass or less.

B has a function of improving hot workability,
In particular, the effect of preventing the occurrence of edge cracks during hot rolling due to S is great. When B is added, it is desirable to add it in the range of 0.015% by mass or less.

REM (rare earth element), Y, Ca and Mg are elements effective for improving hot workability and oxidation resistance. When these elements are added, it is desirable to add them in the range of 0.20 mass% or less for REM and Y and 0.10 mass% or less for Ca and Mg. In addition, V which has the effect of increasing the strength of the reverse transformation austenite phase itself and suppressing grain growth
May be contained in the range of 0.5 mass% or less.

P is an element having a large solid solution strengthening ability,
Since it may adversely affect the toughness, it is limited to 0.040 mass% or less. S causes adverse effects such as promoting the occurrence of edge cracks in hot rolling, and is therefore limited to 0.020 mass% or less. O forms an oxide-based non-metallic inclusion to reduce the cleanliness of steel and adversely affects press formability and bendability, so O is limited to 0.02 mass% or less.

[Md (N) Value] In the present invention, a work-induced martensite is produced by cold rolling, and this is subjected to reverse transformation to obtain a fine austenite structure. As described below, the cold-rolled steel sheet subjected to the reverse transformation treatment needs to have a total martensite content in the steel sheet of 60% by volume or more.
Further, if hardened martensite exceeding about 20% by volume is generated in the cooling process of the reverse transformation treatment, the desired high elasticity cannot be stably obtained. Therefore, in the present invention, by using the austenite stability index Md (N) defined by the equation (1),
Its value is specified as 0 to 125. That is, the Md (N) value is
For steel grades less than 0, the above desirable structure cannot be obtained unless cold rolling is performed at a low temperature, which is very difficult industrially.For steel grades over 125, a large amount of martens of more than about 20% by volume is used in the cooling process of the reverse transformation treatment. Even if the average grain size of the remaining reverse transformed austenite is 5 μm or less due to the formation of sites, 20
It becomes difficult to stably obtain a high longitudinal elastic modulus of 0000 N / mm ² or more.

[Metal Structure] It is a well-known phenomenon that the tensile strength and the yield strength (or proof stress) of a metal material are improved when the crystal grains are refined. However, a technique for positively utilizing the refinement of crystal grains has not been established as a means for improving the longitudinal elastic modulus of a steel sheet. As a cause thereof, the average crystal grain size is at a level of several μm, and it is not always easy to realize a structural state with little directionality.
It can be argued that research on microstructures at the level of several μm has not been sufficiently conducted. The inventors have paid attention to the reverse transformation of martensite, and have realized a very fine and isotropic microstructure state in a metastable austenitic steel grade, thereby significantly increasing the longitudinal elastic modulus of the steel sheet in both T-steel and L-directions. Succeeded in improving.

Specifically, in the steel sheet adjusted to the above chemical composition, one of the following microstructure states was realized. a) Fine austenite single-phase structure with an average grain size of 5 μm or less b) Fine austenite + martensite two-phase structure in which part of the fine austenite phase with an average grain size of 5 μm or less is transformed into martensite, of which martens in the structure of b) The site has a smaller block that constitutes martensite, and has a different morphology from ordinary martensite. This point is identified by electron microscopy. The structures a) and b) are the average grain size generated in the high temperature austenite single phase region.
It is derived from a fine austenite phase of 5 μm or less. The martensite in the structure of b) is work-induced martensite, hardened martensite, or a mixed phase of both of them, but when hardened martensite is present, its content is within 20% by volume or less. Permissible.

If cold rolling is performed on a steel sheet having the structure of a) or b) as a base, the high elastic properties can be further improved and the strength can be improved. In that case, when the cold rolling rate increases to some extent, work-induced martensite is formed, and therefore the following three patterns of microstructure appear. c) Cold-worked austenite single phase structure d) Cold-worked austenite + martensite 2
Phase structure e) Cold-worked martensite single-phase structure Of these, the martensite in d) and e) is mainly work-induced martensite, but may contain 20% by volume or less of quenched martensite.

Whether the structures c) to e) are caused by the above a) or b) can be examined by electron microscope observation when the cold rolling ratio is relatively low. However, as a result of the detailed study by the inventors, in the steel sheet having the chemical composition defined above and exhibiting the metal structures of c) to e), the hardness is Hv350 or more, and the hardness in the T direction and the L direction is If both the longitudinal elastic moduli are 200,000 N / mm ² or more, it can be said that the metal structure of the steel sheet is generated from the structure of a) or b).

In these fine structures, the frequency of grain boundaries per unit volume is extremely high. Therefore, the deformation strain due to the deformation in the elastic deformation region is easily piled up at the grain boundary, and the dislocations due to the deformation strain interfere with each other at a close distance. Due to the interference of the dislocations, the stress generated when a certain elastic deformation is applied macroscopically becomes high. That is, the elastic modulus increases.

[Longitudinal elastic modulus in both T and L directions is 200,000 N / mm ² or more] From a steel sheet, a tensile test piece in the T direction and L
When a tensile test piece in each direction is sampled and subjected to a tensile test, it is necessary that each longitudinal elastic modulus is 200,000 N / mm ² or more, that the steel sheet has properties that are extremely suitable for the various applications. It becomes a condition.

[Hardness of Hv350 or More] It is desirable to secure a hardness of Hv350 or more in order to widen the range of use in the various applications mentioned above. Such high hardness is obtained by combining the reverse transformation treatment with the subsequent final cold rolling or aging treatment (described later).

Next, the manufacturing conditions of the metastable austenitic stainless steel sheet having high elasticity as described above will be described.

[Starting Material for Reverse Transformation] As a starting material, a metastable austenitic stainless cold-rolled steel sheet containing 60% by volume or more of martensite is prepared. This starting material is obtained by cold rolling an annealed steel sheet that has undergone solution treatment. Within the chemical composition range defined in the present invention, there may be up to about 20% by volume of quenched martensite after solution treatment. This quenched martensite itself also becomes austenite in the reverse transformation treatment,
According to the research conducted by the inventors, it was found that the presence of the processing-induced martensite greatly contributes to the refinement of the structure. That is, in order to obtain a fine austenite structure having an average grain size of 5 μm or less, in the stage before the reverse transformation treatment, the processing-induced martensite is present, and the total martensite amount is 60% by volume or more. ,is necessary. Those with a low Md (N) value exhibit an austenite single-phase structure after solution treatment, but in this case, 60% by volume was obtained by cold rolling.
It is necessary to generate the above-mentioned processing-induced martensite. The term "cold rolled steel sheet" as used herein means one that has not been subjected to heat treatment after being subjected to cold rolling.

[Reverse Transformation Treatment] In the reverse transformation treatment, the martensite present in the steel sheet is heated to a temperature range where all the martensite undergoes reverse transformation to austenite. However, even in such a temperature range, if the reaction temperature is lower than 550 ° C., the reaction of the reverse transformed austenite is remarkably slow, which is not suitable for industrial production. On the other hand, 850
If the temperature exceeds ℃, the rate of grain growth of the reverse transformed austenite formed is high, so it is extremely difficult to control the microstructure to an average grain size of 5 μm or less. Therefore, the heating temperature of the reverse transformation treatment is specified to be 550 to 850 ° C. The holding time in this temperature range is preferably 0 to 180 seconds for soaking.
Here, 0 second soaking refers to the case where cooling is started immediately after the central portion of the plate thickness of the material reaches this temperature range. In the cooling process of the reverse transformation treatment, up to 20% of hardened martensite is allowed to be formed.

[Final Cold Rolling / Aging Treatment] The steel sheet that has undergone the reverse transformation treatment is left as it is for 2000 in both T and L directions.
It exhibits a longitudinal elastic modulus of 00 N / mm ² or more, and by further performing "final cold rolling", "aging treatment", or "final cold rolling + aging treatment" on the basis of this, the above High elasticity characteristics can be further improved. The strain in the final cold rolling and the accumulation of solute atoms in the aging treatment suppress the movement of mobile dislocations during elastic deformation and contribute to the improvement of the longitudinal elastic modulus. At the same time, the strength (hardness) is also improved.

In general, excessive cold rolling brings about anisotropy of the material, but in the microstructured steel sheet utilizing the reverse transformation of the present invention, the anisotropy hardly occurs even at a very high cold rolling rate. Therefore, the cold rolling rate of the final cold rolling can be increased to about 90%. The reason for this is that the austenite produced by the reverse transformation process has a relatively random orientation with no texture, and the work-induced martensite produced when such a fine austenitic steel sheet is cold-rolled. It is possible that the site will also be relatively non-directional.

Regarding the aging treatment temperature, if it is less than 250 ° C., the contribution to the improvement of the longitudinal elastic modulus is small, and if it exceeds 540 ° C., C which is dissolved in supersaturation after the reverse transformation is dissolved even if the heating time is short. Form Cr carbides and precipitate in large amounts at grain boundaries and in the grains, leading to a decrease in material strength and a decrease in corrosion resistance. Therefore, the aging temperature is specified to be 250 to 540 ° C.
It is desirable that the aging treatment time is soaking 0.5 to 120 minutes.

[0040]

[Examples] Table 1 shows the chemical component values (% by mass) of the test materials and the Md (N) values obtained by the above equation (1). Steel No. in Table 1
1 to 8 are "invention steels" having a chemical composition within the range specified by the present invention, and steel Nos. 9 to 13 are "comparative steels". These steels are melted using a vacuum melting furnace, forged and hot rolled, and then the plate thickness is 3.0mm.
As a hot-rolled sheet of No. 1, hot-rolled sheet was annealed at 1050 ° C. for 60 seconds, pickled, and then cold-rolled to obtain a cold-rolled steel sheet having a sheet thickness of 0.8 mm. The cold-rolled steel sheet was subjected to reverse transformation treatment at various temperatures for 60 seconds soaking. After the reverse transformation treatment, final cold rolling or aging treatment (soaking for 60 minutes) was appropriately performed to obtain a steel sheet sample having the following four types of manufacturing history. [History 1] Reverse transformation treatment as it is [History 2] Reverse transformation treatment → final cold rolling [History 3] Reverse transformation treatment → aging treatment [History 4] Reverse transformation treatment → final cold rolling → aging treatment

For each sample, the average grain size, hardness, and longitudinal elastic modulus in the T and L directions of reverse transformed austenite were measured. The average grain size of the reverse transformed austenite was measured by measuring the grain size of the center portion of the plate thickness in the L-section using an optical microscope or an electron microscope for the samples of history 1 and 3. In the samples of History 2 and 4, the reverse-transformed austenite crystal grains were flattened by the final cold rolling. Therefore, the crystal grain size was converted by approximating the area by the regular hexagonal approximation.
For those for which the final cold rolling rate was large and the crystal grain size could not be measured, the austenite average grain size measured in advance after the reverse transformation treatment and before the final cold rolling was displayed. The longitudinal elastic modulus was obtained from the slope of the stress-displacement graph by attaching a strain gauge to a JIS 13B tensile test piece. Table 2 shows the experimental conditions and measurement results.

[0042]

[Table 1]

[0043]

[Table 2]

Each of the examples of the present invention had excellent high elastic properties in which the longitudinal elastic modulus was 200,000 N / mm ² or more in both the T and L directions. Among them, those subjected to the final cold rolling or the aging treatment were further improved in the longitudinal elastic modulus and the hardness. On the other hand, Comparative Examples Nos. 21 and 24 had an austenite average grain size of 5 because the reverse transformation temperature was too high.
Since the reverse transformation temperature of Nos. 22 and 23 was too low, the reverse transformation to austenite did not occur sufficiently, and in any case, a longitudinal elastic modulus of 200,000 N / mm ² or more was stably obtained. I couldn't do that. In Comparative Examples Nos. 25 to 29, the chemical compositions of steels were out of the regulation of the present invention, and none of them could stably obtain the longitudinal elastic modulus of 200,000 N / mm ² or more. Of these, Nos. 26 and 28 had a high Md (N) value of more than 125, and therefore a large amount of quenched martensite was produced in excess of 20% by volume after the reverse transformation treatment. High elasticity is not obtained even though the diameter is 5 μm or less.

[0045]

Industrial Applicability According to the present invention, it is possible to industrially stably provide and provide a metastable austenitic stainless steel sheet having a high longitudinal elastic modulus of 200,000 N / mm ² or more in both T and L directions. It became possible. The steel sheet according to the present invention is used for a railroad vehicle's railroad hull, horizontal rail material, car antenna,
Various blades such as doctor blades, printer rail shafts, golf club heads, small springback springs, springs that require vibration damping, tactile switches that require repulsive force as a push button switch, VT
It achieves the high elasticity characteristics desired for various applications such as the pressing spring of the R cassette and the bearing sealing material, and contributes to the performance improvement in terms of materials in these applications.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Naoto Hiramatsu             4976 Nomura-Minami-cho, Shinnanyo-shi, Yamaguchi Nissin             Within Steel Co., Ltd. F-term (reference) 4K037 EA01 EA02 EA05 EA06 EA12                       EA13 EA15 EA16 EA17 EA18                       EA19 EA20 EA21 EA22 EA23                       EA25 EA27 EA28 EA31 EA36                       EB02 EB06 EB07 EB08 EB09                       FJ04 FJ05

Claims (10)

[Claims] 1. In mass%, C: 0.01 to 0.20%, Cr: 12.
0 to 20.0%, Ni: 4.0 to 12.0%, N: 0.01 to 0.20%, and the value of Md (N) defined by the following formula (1) is 0 to
It has a chemical composition of 125 and has a fine austenite single-phase structure with an average grain size of 5 μm or less, or a fine austenite + martensite two-phase structure in which a part of the fine austenite phase with an average grain size of 5 μm or less is transformed into martensite. , The longitudinal elastic modulus of the steel sheet in both the T and L directions is 200,000 N /
Highly elastic metastable austenitic stainless steel sheet with a size of mm ² or more. Md (N) = 580-520C-2Si-16Mn-16Cr-23Ni-26Cu-300N-10Mo ... (1) 2. C: 0.01 to 0.20% and Cr: 12.% by mass.
0 to 20.0%, Ni: 4.0 to 12.0%, N: 0.01 to 0.20%, and the value of Md (N) defined by the following formula (1) is 0 to
It has a chemical composition of 125 and exhibits a cold-worked austenite single-phase structure, a cold-worked austenite + martensite two-phase structure, or a cold-worked martensite single-phase structure with a hardness of Hv350. The above is the T of the steel plate.
A highly elastic metastable austenitic stainless steel sheet having a longitudinal elasticity coefficient of 200,000 N / mm ² or more in both the L and L directions. Md (N) = 580-520C-2Si-16Mn-16Cr-23Ni-26Cu-300N-10Mo ... (1) 3. The steel sheet according to claim 2, wherein the metallographic structure is a fine structure obtained by a method of cold rolling a steel sheet exhibiting any of the structures i) and ii) below. i) Fine austenite single-phase structure with an average grain size of 5 μm or less. ii) Fine austenite + martensite two-phase structure in which part of the fine austenite phase having an average grain size of 5 μm or less is transformed into martensite. 4. The chemical composition in mass% is C: 0.01 to 0.20.
%, Cr: 12.0 to 20.0%, Ni: 4.0 to 12.0%, N: 0.01
~ 0.20%, Si: 4.0% or less, Mn: 5.0% or less, P: 0.04
0% or less, S: 0.020% or less, O: 0.02% or less, Mo: 0
(No addition) ~ 5.0%, Cu: 0 (No addition) ~ 3.0%, Ti: 0
(No addition) ~ 0.50%, Nb: 0 (No addition) ~ 0.50%, A
l: 0 (no addition) to 0.20%, B: 0 (no addition) to 0.015%,
REM: 0 (no additive) to 0.20%, Y: 0 (no additive) to 0.20
%, Ca: 0 (no addition) to 0.10%, Mg: 0 (no addition) to 0.
The balance consists of Fe and inevitable impurities at 10%.
The steel sheet according to claim 1, wherein the value of Md (N) defined by the formula (1) is 0 to 125. Md (N) = 580-520C-2Si-16Mn-16Cr-23Ni-26Cu-300N-10Mo ... (1) 5. C: 0.01 to 0.20% and Cr: 12.% by mass.
0 to 20.0%, Ni: 4.0 to 12.0%, N: 0.01 to 0.20%, and the value of Md (N) defined by the following formula (1) is 0 to
Prepare a metastable austenitic stainless cold-rolled steel sheet having a chemical composition of 125 and containing 60% by volume or more of martensite, and heat the cold-rolled steel sheet to a temperature of 550 to 850 ° C to convert martensite to austenite. By performing reverse transformation into a fine austenite single-phase structure with an average grain size of 5 μm or less, heat treatment (reverse transformation treatment) to cool from that state to room temperature is performed, and the longitudinal elastic moduli in the T and L directions of the steel sheet are both 200,000 N / A method for producing highly elastic metastable austenitic stainless steel sheets of mm ² or more. Md (N) = 580-520C-2Si-16Mn-16Cr-23Ni-26Cu-300N-10Mo ... (1) 6. The chemical composition of the cold-rolled steel sheet subjected to reverse transformation treatment, in mass%, is C: 0.01 to 0.20%, Cr: 12.0 to 20.0.
%, Ni: 4.0 to 12.0%, N: 0.01 to 0.20%, Si: 4.0%
Below, Mn: 5.0% or less, P: 0.040% or less, S: 0.020%
Below, O: 0.02% or less, Mo: 0 (no addition) to 5.0%, C
u: 0 (no additive) to 3.0%, Ti: 0 (no additive) to 0.50%,
Nb: 0 (no addition) to 0.50%, Al: 0 (no addition) to 0.20
%, B: 0 (no addition) to 0.015%, REM: 0 (no addition) to 0.
20%, Y: 0 (no addition) ~ 0.20%, Ca: 0 (no addition) ~
0.10%, Mg: 0 (no addition) to 0.10%, the balance consisting of Fe and inevitable impurities, and Md defined by the following formula (1)
The method according to claim 5, wherein the value of (N) is 0 to 125. Md (N) = 580-520C-2Si-16Mn-16Cr-23Ni-26Cu-300N-10Mo ... (1) 7. The production method according to claim 5, wherein the holding time at 550 to 850 ° C. in the reverse transformation treatment is soaking for 0 to 180 seconds. 8. The production method according to claim 5, wherein after the reverse transformation treatment, final cold rolling is performed at a reduction rate of 90% or less. 9. The production method according to claim 5, wherein an aging treatment is performed at 250 to 540 ° C. after the reverse transformation treatment. 10. The production method according to claim 5, wherein after the reverse transformation treatment, final cold rolling is performed at a reduction rate of 90% or less, and further aging treatment is performed at 250 to 540 ° C.