JP6150819B2 - High strength austenitic stainless steel and method for producing the same - Google Patents

Description

  The present invention relates to a high-strength austenitic stainless steel for springs and a method for producing the same, and more particularly to a high-strength austenitic stainless steel for springs and a method for producing the same that have improved strength by controlling alloy design and production conditions.

  Austenitic stainless steel has excellent physical properties such as formability, corrosion resistance and weldability, and is the most commonly used stainless steel. In particular, one of the characteristics of austenitic stainless steel is that it involves a phase transformation during processing. Ultimately, if the austenite phase is an element that stabilizes the austenite phase and does not maintain a sufficiently high alloy state, the austenite phase has a very high probability of being transformed into a martensite phase without diffusion during plastic deformation addition. I can say that.

  Among them, one of typical steels is 301 series stainless steel, and the steel having unstable phase stability as described above has a very high degree of work hardening due to the amount of plastic deformation. For example, when the yield strength of the heat-treated material is around 300 MPa, when cold-rolled to 80% or more, it becomes 1800 MPa or more, and it is observed that work hardening progresses considerably. Therefore, the 301 series having a large rolling reduction is used as a material that requires high elastic stress and high strength, such as an automobile gasket or spring.

  On the other hand, the use of such a full hard material requires various strength characteristics depending on the shape and application part of the spring and gasket, and there are parts that require high tensile strength up to 2200 MPa as required. . However, it is not easy to obtain a tensile strength of 2200 MPa or more even at a high cold reduction rate when steel is manufactured by a conventional continuous casting method using a conventional 301 series material. Accordingly, in order to ensure high strength characteristics of 2200 MPa or more even in austenitic stainless steel used for high strength springs, it is necessary to develop additional elemental technologies such as components and process control.

  As described above, the present invention has been devised in order to solve the above-mentioned problems, and its purpose is to provide an austenitic stainless steel for high-strength springs having a cold reduction rate of 80% or more and a tensile strength of 2200 MPa or more. The purpose is to provide steel.

  In addition, the present invention uses the control of the content of substitutional alloy elements and the strip casting casting method for the purpose of controlling the alloy design and manufacturing conditions of austenitic stainless steel for high-strength springs. An object of the present invention is to provide a method for producing a high-strength austenitic stainless steel having a tensile strength of 2200 MPa or more with an increase.

  In order to achieve the above object, according to one aspect of the present invention, by weight, C: 0.05-0.15, N: 0.05-0.09%, Cr: 15-18, Ni : 6 to 8, Si: more than 1.0 to 1.5%, Mo: 0.5 to 0.9, Mn: 0.4 to 1.2, Cu: 1.5% or less, the balance is Provided is a high-strength austenitic stainless steel containing Fe and other inevitable impurities and having an Md30 range of 25 to 30 ° C. according to the following formula 1.

  Formula (1): Md30 (° C.) = 551-462 (C + N) -9.2Si-8.1Mn-13.7Cr-29Ni-18.5Mo-29Cu-68Nb

  According to another aspect of the present invention, by weight, C: 0.05-0.15, N: 0.05-0.09%, Cr: 15-18, Ni: 6-8, Si: 1 Over 0.0 to 1.5%, Mo: 0.5 to 0.9, Mn: 0.4 to 1.2, Cu: 1.5% or less, the balance contains Fe and other inevitable impurities The present invention provides a high-strength austenitic stainless steel produced by strip-casting a stainless steel having an Md30 range of 25 to 30 ° C. represented by the following formula 1.

  Formula (1): Md30 (° C.) = 551-462 (C + N) -9.2Si-8.1Mn-13.7Cr-29Ni-18.5Mo-29Cu-68Nb

  The content of delta ferrite remaining during solidification when the stainless steel is cast by strip casting is 5% or more.

  Further, the content of delta ferrite remaining during solidification when the stainless steel is cast by strip casting is 10% or less.

  Further, when the stainless steel is cold-rolled at a reduction rate of 80%, the tensile strength is 2200 MPa or more and the hardness is ensured to be 570 Hv or more.

  Moreover, the grain size of the cold rolled structure of the stainless steel is 8.5 or more.

  Furthermore, according to still another aspect of the present invention, a pair of rolls rotating in opposite directions, an edge dam provided so as to form a molten steel pool on both sides thereof, and an inert nitrogen on an upper surface of the molten steel pool Strip casting apparatus including meniscus shield for supplying gas, and by weight, C: 0.05 to 0.15, N: 0.05 to 0.09%, Cr: 15 to 18, Ni: 6 to 8, Si: more than 1.0 to 1.5%, Mo: 0.5 to 0.9, Mn: 0.4 to 1.2, Cu: 1.5% or less, the balance is Fe and others High strength that contains inevitable impurities and controls the content of delta ferrite remaining at the time of solidification to be 5% or more by casting an austenitic stainless steel having an Md30 range of 25-30 ° C. according to the following formula 1 Of austenitic stainless steel To provide a production method.

  Formula (1): Md (30 ° C.) = 551-462 (C + N) -9.2Si-8.1Mn-13.7Cr-29Ni-18.5Mo-29Cu-68Nb

  In addition, when the stainless steel having a cast structure obtained by the strip casting is cold-rolled at a reduction rate of 80%, a tensile strength of 2200 MPa or more and a hardness of 570 Hv or more are ensured. To manufacture.

  Moreover, the grain size of the cold rolled structure of the stainless steel is 8.5 or more.

  As described above, according to the present invention, it is possible to obtain a high-strength austenitic stainless steel for a spring having a tensile strength of 2200 MPa through control of alloy design and manufacturing conditions. In addition, according to the present invention, there is an effect that austenitic stainless steel for high-strength springs can be obtained by utilizing the control of the content of substitutional alloy elements and the strip casting method.

FIG. 3 is a schematic view of an apparatus for explaining a strip casting process according to the present invention. It is a graph which shows the example of the change of the process induction martensite production amount by processing when changing Md30 temperature through component control of an austenite and a ferrite stabilization element. It is the photograph which compared the microstructure of the cold rolling coil by the normal continuous casting process, and the cold rolling structure of the coil manufactured by the strip casting method. It is the graph which showed the change of the tensile strength which is a mechanical characteristic according to the Md30 temperature changing (8 degreeC, 28 degreeC, 48 degreeC) according to the cold reduction rate. It is the graph which showed the change of the tensile strength which is a mechanical characteristic according to the Md30 temperature changing (8 degreeC, 28 degreeC, 48 degreeC) according to the cold reduction rate. It is the graph which showed the change of the tensile strength which is a mechanical property at the time of optimizing a component by Md30 temperature around 28 degreeC in order to strengthen the work hardening ability through component control.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. Also, the singular forms used herein include the plural forms unless the context clearly indicates the contrary.

    As used herein, the term “comprising” embodies specific characteristics, regions, integers, steps, operations, elements and / or components, and other specific properties, regions, integers, steps, operations, It is not meant to exclude the presence or addition of elements, ingredients and / or groups.

 Further, although not defined separately, all terms including technical terms and scientific terms used herein have the same meaning as commonly understood by those having ordinary knowledge in the technical field to which the present invention belongs. Usually, the terms defined in the dictionary used are further interpreted as having a meaning consistent with the relevant technical literature and the presently disclosed content, and are not interpreted as ideal or very formal meaning unless defined. .

  FIG. 1 is a schematic view of an apparatus for explaining a conventionally known strip casting process. This strip casting process is a process for manufacturing thin hot strips directly from molten steel, omitting the hot rolling process, greatly reducing production costs, capital investment costs, energy consumption, pollution gas emissions, etc. It is a new steel process that can be done.

  As shown in FIG. 1, a twin roll type thin plate casting machine used in a general strip casting process accommodates molten steel in a ladle 1 and flows it into a turn dish 2 along a nozzle. The flowing molten steel is supplied between the edge dams 5 provided at both ends of the casting roll 6, that is, through the molten steel injection nozzle 3 between the casting rolls 6, and solidification is started. At this time, in the molten metal part between the rolls, in order to prevent oxidation, the molten metal surface is protected by the meniscus shield 4, and a suitable gas is injected to adjust the atmosphere appropriately. A thin plate 8 is manufactured while passing through a roll nip 7 where both rolls meet, and after rolling through a rolling mill 9 while being drawn, it is wound by a winding facility 10 through a cooling process.

  At this time, an important technique in the twin roll type thin plate casting process for directly manufacturing a thin plate having a thickness of 10 mm or less from the molten steel is to introduce the molten steel through an injection nozzle between internal water-cooled twin rolls rotating in the opposite direction at a high speed. A thin plate having a desired thickness is supplied without being cracked and the yield is improved.

  Such a strip casting process uses a twin roll type strip caster by casting a liquid steel directly to a plate having a thickness of 1 to 5 mm while applying a very fast cooling rate to the cast plate. A hot rolled coil is manufactured. The twin roll type strip caster supplies molten steel between twin rolls and side dams rotating in opposite directions, and releases a large amount of heat through the water-cooled roll surface. It is characterized by casting. At this time, a solidified cell is formed on the roll surface at a rapid cooling rate, and a thin hot-rolled sheet having a thickness of 1 to 5 mm is manufactured by in-line rolling performed continuously after casting. In the embodiment of the present invention, a thin plate of 2 mm or less is manufactured.

  In the strip casting process, since a thin object of about 2 mm is usually directly cast, the slab manufacturing by continuous casting and the hot rolling process can be omitted. In particular, for steel types in which surface defects occur during hot rolling, application of the strip casting method is particularly advantageous. However, the 301 series is a steel type in which defects frequently occur during hot rolling, and this application is advantageous. Moreover, in order to manufacture a high-strength steel material, in addition to the problem of surface defects, it can have further great advantages.

Austenitic stainless steel is solidified into an austenitic phase after a delta ferrite phase is formed at the initial stage of solidification in order to ensure stability in solidification during normal continuous casting. At this time, the amount of delta ferrite remaining at the time of casting is around 1 to 10% for each steel type according to the theoretical empirical formula (δ _Cal ), but the presence of such a delta ferrite phase in the structure is It affects work hardening during downstream (Down STREAM) rolling.

  After normal slab casting, the delta ferrite phase remaining in the slab is heated for more than 2 hours in a reheating furnace for hot rolling. Since the austenite phase is decomposed by the solid phase transformation, the hot rolling is similarly performed at a high temperature, so that the delta ferrite phase present in the cast structure of the slab is almost decomposed. . In fact, it can be seen that the delta ferrite content of the hot rolled coil of austenitic stainless steel is less than 0.5%.

On the other hand, the strip casting process uses a water-cooled roll to cast a thin plate of about 2 mm directly from molten steel, so it is a cast structure like a slab by the existing continuous casting method, and the content of delta ferrite is 1 to It appears high in the range of 10%. In general, the delta ferrite phase not only deteriorates high-temperature workability and corrosion resistance, but also has magnetism, so it has the disadvantage of limiting the use of the final product. When producing high-strength steel with a high rate, it can contribute to activating work hardening while reducing the particle size by being present in a small amount during cold rolling.

  The increase in material strength is a phenomenon that appears when various strengthening devices act in a complex manner. In a metastable austenitic stainless steel such as the 301 series, as described above, it can be said that the generation of a work organic martensite phase according to the amount of deformation is the most important reason for improving work hardening. However, on the other hand, the effect of solid solution strengthening by addition of alloy elements is also important, but here also the effect of interstitial elements such as C and N and the effect of substitutional elements such as Si and Mo Appears in various ways. Generally, the strength is improved by controlling interstitial elements such as C and N from an economic aspect, but substitutional elements can act more effectively in high strength steel with a high rolling reduction. .

  Hereinafter, first, the composition range of the austenitic stainless steel used in one embodiment of the present invention and the reason for limiting the composition range will be examined in detail.

  First, the present invention is, by weight, Cr: 15.0-18%, Ni: 6-8%, N: 0.05-0.09%, C: 0.05-0.15%, Mn: It is composed of alloy components of 0.4 to 1.2%, Mo: 0.5 to 0.9%, Si: more than 1.0 to 1.5%, Cu: 1.5% or less. The Md30 temperature satisfies the range of 25 to 30 ° C. The Md30 temperature is represented by the following formula (1).

  Formula (1): Md30 (° C.) = 551-462 (C + N) -9.2Si-8.1MN-13.7Cr-29Ni-18.5Mo-29Cu-68Nb

  More preferably, Cr is 16 to 17 wt%, Ni is 6 to 7 wt%, and Mo is 0.6 to 0.8 wt%. Usually, in the case of Si, it is an element that can improve the solid solution strengthening ability of austenitic stainless steel. However, there may be a problem that hot workability deteriorates when excessively added. Therefore, Si is controlled to at least 1.5% to 1.5%, and the optimum Si range is 1.1 to 1.3 wt%.

  In the present invention, the alloy design is well known as a component of austenitic stainless steel, and the detailed reason is omitted. However, in the present invention, a feature of the alloy design is that the alloy components are optimized by controlling Md30.

  The austenitic stainless steel used in the present invention is a steel characterized by a metastable microstructure at room temperature so that the austenitic phase subjected to processing by an external force is accompanied by a phase transformation on the processed organic martensite. It is a set steel grade. A typical index indicating the metastability of such austenitic stainless steel is represented by Md30 and can be represented by the following formula (1).

  Formula (1): Md (30 ° C.) = 551-462 (C + N) -9.2Si-8.1MN-13.7Cr-29Ni-18.5Mo-29Cu-68Nb

  C, N, Mn, Ni, Cu, etc. are elements that stabilize the austenite phase during component adjustment by the above formula, and Si, Cr, Mo, Nb, etc. stabilize the ferrite phase or martensite phase. It is an element, and the phase stability on steel comes to be determined by the combination of these elements. In the present invention, the Md30 (° C.) value is controlled to 25 to 30 or less.

  FIG. 2 is a graph showing an example of the amount of processed organic martensite produced during treatment when the Md30 temperature is varied by controlling the components of austenite and ferrite stabilizing elements.

  FIG. 2 shows the degree of phase stability due to a change in Md30 temperature, and shows a tendency that the amount of processed organic martensite generated increases as the Md30 temperature increases. However, such a phenomenon shows a slightly different behavior as the rolling reduction increases. However, in the case of a very metastable material having an Md30 temperature exceeding 45 ° C., 50% of the cold rolling reduction peaked. It can be seen that no further phase transformation has occurred.

  That is, it turns out that the transformation into the processed organic martensite phase is abruptly performed at the initial reduction rate, and does not contribute to the work hardening according to the reduction rate higher than that. On the other hand, in the raw material whose Md30 is 25-30, the strength continuously increases while the phase transformation continues until the cold rolling reduction reaches 80%. Therefore, in order to produce the high-strength steel that is the object of the present invention, it is necessary to ensure the conditions under which the phase transformation is continuously performed in accordance with the increase in the cold rolling reduction ratio. Then, such a condition of Md30 is set to 25-30. In FIG. 2, an experiment was conducted using a value of 27.4 ° C. representative of such a value of Md30.

  When the temperature of Md30 is less than 25, the degree of work hardening associated with cold reduction is not large, and when the temperature of Md30 exceeds 30, as shown in FIG. The effect of the rolling reduction is not so great since no further phase transformation takes place with a certain amount peaked. On the other hand, in order to increase the work hardening amount, the control of the production process can also play an important role in addition to the promotion of such phase transformation. In the present invention, a strip casting method is employed in place of the conventional continuous casting process in order to manufacture a high-strength austenite coil.

  The strip casting process of the present invention is a method of forming a thin plate of about 2 mm directly from molten steel using a water-cooled roll, as described in FIG. 1, and the sheet cast by this method is reheated. And a desired sheet form can be obtained by cold rolling immediately without a hot rolling process.

  From the aspect of manufacturing high-strength steel, the alloy component system is an index of work hardening ability separately from the manufacturing process, but the microstructure in the material varies depending on the influence of the process. The microstructure is determined according to the size of grain boundaries, precipitates, second phase, potential, twin, etc. In such a metastable austenitic stainless steel, the most of the continuous cast structure and the strip casting structure. It can be said that there is a big difference in the content of the delta ferrite phase. In the continuous casting structure, the delta ferrite phase generated during solidification is almost decomposed in the long heating process of reheating the slab, while the strip casting structure is not included in the material. There will be more. The presence of such a delta ferrite phase serves as a role of enhancing work hardening from the aspect of manufacturing a very high strength steel corresponding to the cold rolling reduction.

  FIG. 3 is a photograph comparing the microstructure of a cold rolled coil produced by a normal continuous casting process with the cold rolled structure of a coil produced by a strip casting method.

  In FIG. 3, the upper part is a microstructure produced by strip casting, and the grain size is about 8.5-9. On the other hand, in the case of the fine structure after the continuous casting and hot rolling steps displayed at the bottom, the crystal grain size is about 7-8. In this way, the strength of the material manufactured by strip casting is increased compared to the material manufactured by continuous casting with the same component system. The reason is that the grain size is reduced due to the difference in the content of residual delta ferrite. Therefore, in the case of the present invention, it is advantageous for the application of a high-strength material such as a spring by improving the strength and hardness characteristics.

As shown in FIG. 3, when comparing the microstructure of the cold-rolled coils produced by continuous casting and strip casting, compared to the case of strip casting material (top), a continuous cast material (bottom) Thus, the particle size of the delta ferrite phase in the structure is small, suggesting that the delta ferrite phase can serve as a solid solution strengthening similar to the second phase.

  4 and 5 are graphs respectively showing changes in tensile strength and hardness, which are mechanical characteristics depending on the cold rolling reduction, due to changes in Md30 temperature (8 ° C., 28 ° C., 48 ° C.). As shown in FIG. 4, the tensile strength of all materials having different Md30 temperatures tends to increase in proportion to the increase in the cold rolling reduction.

  On the other hand, in the case of FIG. 5, as the cold rolling reduction increases, the hardness of each of the materials having different Md30 temperatures similarly increases in proportion to the cold rolling reduction, When the Md30 temperature is high (48.7 ° C.), it indicates that the degree of improvement in hardness is slight at a certain rolling reduction or more. This indicates that the work hardening effect due to the formation of work-induced martensite is large at the initial rolling reduction, but shows that there is a limit to the improvement in hardness after this production is saturated. It can be confirmed that it is necessary to set the Md30 condition for the increase.

  According to FIG. 4, when the Md30 value for the steel of the present invention is 27.4 ° C. in the range of 25-30 (test piece: C901 steel type), it can be seen that the tensile strength value increases to 2200 MPa. This shows that the cold rolling reduction was measured at about 78%, which is 80% or less, so that when the cold rolling reduction is measured at 80%, it can be further increased in proportion. However, in the case of the remaining steel types, the value of Md30 is out of the range of the present invention, and in this case, it can be seen that the value of tensile strength remains below 2200 MPa.

  FIG. 6 is a graph showing that the mechanical properties can be improved by optimizing the components around 28 ° C. in which the Md30 temperature is in the range of 25 to 30 in order to enhance the work hardening ability by controlling the components. FIG.

  Based on the results of FIG. 6, in the example (C901 steel type) in which the component was controlled at an Md30 temperature of about 28 ° C. in the range of 25 to 30 in order to enhance the work hardening ability by the component control, the reduction rate was 80%. It can be confirmed that the tensile strength increases substantially to 2200 MPa. However, this production uses a strip casting method, and the cast sheet is a 2 mm sheet. At this time, the content of residual delta ferrite of 2 mm material cast by strip casting is 5% or more, and after the heat treatment and pickling process of the coil, the delta ferrite phase of 1% or more over the entire width of the plate. Exists.

  As shown in FIG. 3, the delta ferrite phase has a continuous cast material particle size of 7.5 by refining the slab by continuous casting and refining the particle size of the parts that have undergone hot rolling and annealing pickling. On the other hand, the strip casting material shows around 8.5.

  In the present invention, an austenitic stainless steel having metastable characteristics through addition of Md30 and a substitutional alloy element can be used to obtain an effect of improving strength by using a strip casting process.

(Example)
Hereinafter, examples in which changes in mechanical properties were investigated by component and process control using 15-18% Cr austenitic stainless steel of the present invention will be described.

      Table 1 shows an example of component changes when the Md30 temperature is varied by controlling the components of austenite and ferrite stabilizing elements. First, as shown in FIG. 4 and FIG. 5, when the Md30 temperature is changed (about 8 ° C., 28 ° C., 48 ° C.), the mechanical properties (tensile strength and hardness) due to the cold reduction rate change.

      4 and 5, the tensile strength and hardness tend to increase in proportion to each of the materials having different Md30 temperatures in accordance with the increase of the cold rolling reduction, but when the Md30 temperature is high (about 48 ° C.), Above a certain rolling reduction, the degree of strength improvement is slight. This indicates that the effect of work hardening due to the formation of processed organic martensite is large at the initial rolling reduction, but indicates that there is a limit to the improvement in strength after the generation of this is saturated. And appropriate Md30 conditions for increased hardness are required. In the present invention, the temperature range of Md30 is set to 25 to 30.

FIG. 6 shows an example (C901 steel type) in which the component control is performed at an Md30 temperature of about 28 ° C. in order to enhance the work hardening ability by the component control, and the tensile strength reaches approximately 2200 MPa with a reduction rate of 80%. Shown to reach. Of course, in the case of the above steel types, the content of residual delta ferrite is 5% or more as a thin plate of 2 mm material, and even after the heat treatment and pickling process of the coil, there is 1% or more delta ferrite phase over the entire width of the plate. To do.

      When comparing the quality characteristics of the material that has undergone the continuous casting process in the present invention and the material of the present invention in the strip casting process, it is as follows in terms of securing the intrinsic component system; the Cr content is 16. It is around 5%, and the Ni content is around 6.5%. The austenite stabilizing element Mn is about 0.6%, and the substitutional alloy elements Mo and Si have the characteristics of about 0.7% and 1.1% or more, respectively.

      As a condition for such component design, the theoretical delta ferrite content during solidification must be designed to be 5% or more, and the Md30 temperature, which is an indicator of metastability, is set within the range of 25-30. It is desirable. And in order to ensure the quality characteristics of full hard materials with a tensile strength of 2200 MPa or more and a hardness of 570 Hv or more, it must be cast around 2 mm using the strip casting method. Is around 8.5 and the cold rolling reduction must be 80% or more.

      From Table 1 above, in the case of Invention Steel 1 to Invention Steel 7 which is the range of the steel of the present invention, it is shown that the range of Md30 which is the range of the present invention is 25 to 30 ° C., and Comparative Steel 1 to Comparison Steel 9 shows a comparative example showing Md30 outside the scope of the present invention. As can be seen from Table 1 above, when the range of Md30 is substantially controlled to 25 to 30 and is manufactured by applying the strip casting process, the tensile strength value is 2200 MPa or more and the hardness value is 570 Hv. This is shown above.

      As described above, the technical idea of the present invention has been specifically described on the basis of the above-described preferred embodiments. However, the above-described embodiments are for explanation and not for limitation. In addition, those skilled in the art of the present invention can understand that various modifications are possible within the scope of the technical idea of the present invention. The scope of the right of the invention described above is determined by the following claims, and is not restricted by the description of the specification, and all modifications and changes belonging to the equivalent scope of the claims are within the scope of the present invention. Belongs.

DESCRIPTION OF SYMBOLS 1 Ladle 2 Turn dish 3 Molten steel injection nozzle 4 Meniscus shield 5 Edge dam 6 Casting roll 7 Roll nip 8 Thin plate 9 Rolling machine 10 Winding equipment

Claims (16)

By mass%, C: 0.05 to 0.15%, N: 0.05 to 0.09%, Cr: 15 to 18%, Ni: 6 to 8%, Si: more than 1.0 to 1.5 %, Mo: 0.5-0.9%, Mn: 0.4-1.2%, Cu: 1.5% or less, and Nb: 0% , and the balance consisting of Fe and other inevitable impurities Become
The range of Md30 which consists of following formula (1) is 25-30 degreeC, and in following formula (1), C, N, Si, Mn, Cr, Ni, Mo, Cu, and Nb contain each element High-strength austenitic stainless steel that represents mass% of the proportion.
Formula (1): Md30 (° C.) = 551-462 (C + N) -9.2Si-8.1Mn-13.7Cr-29Ni-18.5Mo-29Cu-68Nb Delta Blow wells containing chromatic amount calculated by the following equation as [delta] _Cal is characterized by at least 5%, atomic symbol represents the mass% of the content of that element in the formula, Ti is 0% , high strength austenitic stainless steel according to claim 1.

The high-strength austenitic stainless steel according to claim 2, wherein the delta ferrite content is 10% or less.   The high-strength austenitic stainless steel according to any one of claims 1 to 3, wherein the tensile strength is 2200 MPa or more, the hardness is 570 Hv or more, and the thickness is 2 mm or less.   The high-strength austenitic stainless steel according to any one of claims 1 to 4, wherein the Si is 1.1 to 1.3% by mass.   The high content according to any one of claims 1 to 5, wherein the Cr is 16 to 17%, Ni is 6 to 7%, and Mo is 0.6 to 0.8%. Strength austenitic stainless steel. By mass%, C: 0.05 to 0.15%, N: 0.05 to 0.09%, Cr: 15 to 18%, Ni: 6 to 8%, Si: more than 1.0 to 1.5 %, Mo: 0.5-0.9%, Mn: 0.4-1.2%, Cu: 1.5% or less, and Nb: 0% , and the balance consisting of Fe and other inevitable impurities Become
Stainless steel having a Md30 range of 25 to 30 ° C. composed of the following formula (1) is cast by strip casting. In the following formula (1), C, N, Si, Mn, Cr, Ni, Mo, Cu, and Nb represent mass% of the content ratio of each element.
A method for producing high-strength austenitic stainless steel.
Formula (1): Md30 (° C.) = 551-462 (C + N) -9.2Si-8.1Mn-13.7Cr-29Ni-18.5Mo-29Cu-68Nb And wherein the delta Blow wells containing chromatic amount remaining during solidification when the stainless steel was cast by strip casting is 5% or more, the delta ferrite content was calculated as [delta] _Cal by the following equation, the following The manufacturing method according to claim 7, wherein the element symbol represents mass% of the content ratio of the element, and Ti is 0% .

The manufacturing method according to claim 8, wherein the delta ferrite content is 10% or less.   The stainless steel cast by the strip casting has a tensile strength of 2200 MPa or more, a hardness of 570 Hv or more, and a thickness of 2 mm or less when cold-rolled at 80% reduction. The manufacturing method according to any one of claims 7 to 9.   The manufacturing method according to any one of claims 7 to 10, wherein the Si is 1.1 to 1.3% by mass%.   12. The mass% according to claim 7, wherein the Cr is 16 to 17%, Ni is 6 to 7%, and Mo is 0.6 to 0.8%. Production method. A pair of rolls rotating in opposite directions;
An edge dam provided to form a molten steel pool on both sides,
In a strip casting apparatus including a meniscus shield for supplying inert nitrogen gas to the upper surface of the molten steel pool,
By mass%, C: 0.05 to 0.15%, N: 0.05 to 0.09%, Cr: 15 to 18%, Ni: 6 to 8%, Si: more than 1.0 to 1.5 %, Mo: 0.5-0.9%, Mn: 0.4-1.2%, Cu: 1.5% or less, and Nb: 0% , and the balance consisting of Fe and other inevitable impurities from now, to control as delta Blow wells containing chromatic amount range of Md30 remains during solidification by casting austenitic stainless steel is 25 to 30 ° C. consisting of the following formula (1) is equal to or greater than 5% The delta ferrite content is calculated as δ _Cal by the following formula (2) , and in the following formulas (1) and (2) , C, N, Si, Mn, Cr, Ni, Mo, Cu, Nb , Ti and table the weight percent of the content of each element, Ti is 0%, the high strength austenitic Method of manufacturing a stainless steel.
Formula (1): Md30 (° C.) = 551-462 (C + N) -9.2Si-8.1Mn-13.7Cr-29Ni-18.5Mo-29Cu-68Nb
Formula (2) ...

  The cast structure stainless steel obtained by the strip casting is a thin plate having a tensile strength of 2200 MPa or more, a hardness of 570 Hv or more, and a thickness of 2 mm or less when cold-rolled at a reduction rate of 80%. The method for producing high-strength austenitic stainless steel according to claim 13.    The method for producing a high-strength austenitic stainless steel according to claim 13 or 14, wherein the Si is 1.1 to 1.3% by mass.   The high content according to any one of claims 13 to 15, wherein the Cr is 16 to 17%, Ni is 6 to 7%, and Mo is 0.6 to 0.8%. A method for producing high strength austenitic stainless steel.

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