WO2023153185A1 - Acier inoxydable austénitique et procédé de production d'acier inoxydable austénitique - Google Patents

Acier inoxydable austénitique et procédé de production d'acier inoxydable austénitique Download PDF

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WO2023153185A1
WO2023153185A1 PCT/JP2023/001836 JP2023001836W WO2023153185A1 WO 2023153185 A1 WO2023153185 A1 WO 2023153185A1 JP 2023001836 W JP2023001836 W JP 2023001836W WO 2023153185 A1 WO2023153185 A1 WO 2023153185A1
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stainless steel
austenitic stainless
mass
phase
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太一朗 溝口
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日鉄ステンレス株式会社
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    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/60—Ferrous alloys, e.g. steel alloys containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur

Definitions

  • the present invention relates to austenitic stainless steel and a method for producing austenitic stainless steel.
  • Metastable austenitic stainless steel represented by SUS301 is known as an austenitic stainless steel used for applications requiring corrosion resistance and strength. Such austenitic stainless steels are used, for example, as materials for spring products such as cylinder head gaskets for automobile engines or structural members such as frame materials for automotive batteries.
  • Patent Document 1 discloses a method for producing a spring material having a martensite phase in which precipitates composed of a Cu-rich phase are dispersed. A method of subjecting a spring steel plate to aging treatment has been proposed.
  • Cu-rich phase precipitation is effective in increasing the strength of stainless steel. Therefore, according to the method described in Patent Document 1, the steel plate for spring is subjected to aging treatment to precipitate a Cu-rich phase, thereby reducing the processing load in the manufacturing process of the steel plate for spring, and the spring, which is the final product. It is possible to increase the strength of the material. However, since an aging treatment process is required, there is a problem in the productivity of the spring material.
  • An object of one aspect of the present invention is to realize an austenitic stainless steel with high productivity while simultaneously reducing the processing load during manufacturing and increasing the strength of the final product.
  • an austenitic stainless steel has C: more than 0.03% and 0.15% or less and Si: 0.1% or more and 2.0% by mass.
  • Mn 0.3% or more and 2.5% or less
  • P 0.04% or less
  • S 0.015% or less
  • Cr 16.0% 18.5% or more
  • Cu 1.5% or more and 4.0% or less
  • N 0.005% or more and 0.25% or less
  • the balance being Fe and unavoidable impurities, 20% by volume or more and a Cu-rich phase with a number density of 1.0 ⁇ 10 3 ⁇ m ⁇ 3 or more and a major axis of 30 nm or less
  • the balance consists of a deformation-induced martensite phase and an unavoidable formation phase, and the following ( 1)
  • a method for producing austenitic stainless steel according to an aspect of the present invention comprises: 0% or less, Mn: 0.3% or more and 2.5% or less, P: 0.04% or less, S: 0.015% or less, Ni: 3.0% or more and less than 6.0%, Cr: 16 0% or more and 18.5% or less, Cu: 1.5% or more and 4.0% or less, N: 0.005% or more and 0.25% or less, the balance being Fe and unavoidable impurities, and the following (1)
  • the content (% by mass) of each element contained in the austenitic stainless steel is substituted for the symbol of the element in the formula (1), and 0 is substituted for the non-additive element.
  • an austenitic stainless steel with high productivity while achieving both reduction in processing load during production and high strength of the final product.
  • FIG. 2 shows an EBSD grain boundary map and a TEM image of an austenitic stainless steel according to one embodiment
  • FIG. 2 is a diagram showing the relationship between 0.2% proof stress (YS18%) and reference strength (HV60%) of austenitic stainless steel according to an example and a comparative example;
  • Austenitic stainless steel according to one embodiment of the present invention is stainless steel containing 20% by volume or more of an austenitic phase.
  • austenitic stainless steel refers to austenitic stainless steel according to one embodiment of the present invention unless otherwise specified.
  • Austenitic stainless steel may be, for example, a steel strip.
  • Austenitic stainless steel contains a deformation-induced martensite phase, which is part of the austenite phase transformed by the deformation-induced transformation plasticity (TRIP) phenomenon.
  • the proportion of the deformation-induced martensite phase is preferably 5% by volume or more, more preferably 10% by volume or more, and 15% by volume or more. is more preferable, and 20% by volume or more is more preferable.
  • the austenitic stainless steel preferably has a deformation-induced martensitic phase ratio of less than 80% by volume, more preferably 75% by volume or less. As long as the austenitic stainless steel contains at least 20% by volume of the austenite phase, the proportion of the deformation-induced martensite phase may decrease as the proportion of the deformation-induced martensite phase increases.
  • Austenitic stainless steels also contain Cu-rich phases.
  • the Cu-rich phase is a phase containing 60 atom % or more of Cu (copper), such as an ⁇ -Cu phase.
  • Austenitic stainless steel contains at least a Cu-rich phase with a number density of 1.0 ⁇ 10 3 ⁇ m ⁇ 3 or more and a major axis of 30 nm or less.
  • the major diameter means the diameter of the maximum length among the diameters of the Cu-rich phase precipitated in the form of particles.
  • the austenitic stainless steel may contain a Cu-rich phase with a major axis of more than 30 nm.
  • the Cu-rich phase may be dispersed in the austenite phase, may be dispersed in the deformation-induced martensite phase, or may be dispersed in the inevitable formation phase described later.
  • the Cu-rich phase may be determined by structural observation using a transmission electron microscope (TEM).
  • TEM transmission electron microscope
  • a TEM sample including an arbitrary cross section of austenitic stainless steel is prepared, and a predetermined range of the cross section is observed using a TEM.
  • the number of rich phases can be measured. Further, the number density per volume can be calculated by calculating the volume based on the thickness of the TEM sample used for the number measurement and the area of the range where the number measurement was performed.
  • a measured thickness of the TEM sample may be used, or an estimate of the thickness based on the method by which the TEM sample was made may be used. Examples of the method for producing a TEM sample include, but are not limited to, electropolishing.
  • the strength of austenitic stainless steel increases as the precipitated Cu-rich phase becomes finer and more abundant.
  • the amount and size of the Cu-rich phase as described above are effective in increasing the strength of the austenitic stainless steel.
  • Austenitic stainless steel does not precipitate a Cu-rich phase during production such as cold rolling before final annealing, and keeps the strength low to reduce the working load. By precipitating a Cu-rich phase in the final annealing step, the strength of the manufactured austenitic stainless steel is increased. Manufacturing processes such as the finish annealing process will be described later.
  • the austenitic stainless steel may contain unavoidably formed phases other than the austenite phase, the strain-induced martensite phase and the Cu-rich phase.
  • Inevitably formed phases are not particularly limited, but include, for example, delta ferrite phases and phases containing carbides, nitrides and/or oxides.
  • Phases containing carbides, nitrides and/or oxides include, for example, phases containing carbides and/or nitrides of Cr, Ti and/or Nb, and oxidation of Si, Ti, Al, Mg and/or Ca. phases containing substances.
  • Austenitic stainless steel preferably has an average crystal grain size of 10.0 ⁇ m or less.
  • the strength of austenitic stainless steel increases as the crystal grains become finer. Further, in austenitic stainless steel, it is common that ductility decreases as strength increases. However, by refining grains, it is possible to achieve both strength improvement and ductility improvement in austenitic stainless steel.
  • the average grain size may be measured using the EBSD (Electron Back Scattering Diffraction) method.
  • EBSD Electro Back Scattering Diffraction
  • grain sizes in multiple fields of view may be calculated by the EBSD method, and the average value of the grain sizes calculated in the multiple fields of view may be used as the average grain size.
  • the average crystal grain size may be measured using a method other than the EBSD method.
  • a method other than the EBSD method for example, a method of exposing grain boundaries by nitric acid electrolytic treatment as shown in JIS G0551 and measuring by an intercept method or the like may be used.
  • Austenitic stainless steel is, in mass%, C: more than 0.03% and 0.15% or less, Si: 0.1% or more and 2.0% or less, Mn: 0.3% or more and less than 2.5%, P : 0.04% or less, S: 0.015% or less, Ni: 3.0% or more and less than 6.0%, Cr: 16.0% or more and 18.5% or less, Cu: 1.5% or more3. 8% or less and N: 0.005% or more and 0.25% or less.
  • the balance of the austenitic stainless steel may consist of Fe (iron) and unavoidable impurities. The significance of the content of each element contained in the austenitic stainless steel will be described below.
  • (C) C is an austenite forming element that facilitates the formation of an austenite phase, has a high solid-solution strengthening action, and is also an effective element for obtaining strength.
  • Austenitic stainless steel contains more than 0.03% by mass and not more than 0.15% by mass of C. If the C content is more than 0.03% by mass, an austenitic stainless steel exhibiting sufficient solid-solution strengthening action and having good strength can be obtained.
  • Si Si
  • the austenitic stainless steel contains 0.1% by mass or more and 2.0% by mass or less of Si, preferably 0.2% by mass or more and 1.0% by mass or less of Si.
  • the Si content is 0.1% by mass or more, deoxidizing action and solid solution strengthening action are effectively exhibited in the austenitic stainless steel. More preferably, the Si content is 0.2% by mass or more.
  • Si is a ferrite-forming element that facilitates the formation of a ferrite phase.
  • the ⁇ ferrite phase causes edge splitting or splitting in hot rolling.
  • the Si content is 2.0% by mass or less, preferably less than 1.5% by mass, and preferably 1.0% by mass or less.
  • Mn manganese
  • Mn manganese
  • the austenitic stainless steel contains 0.3 mass % or more and 2.5 mass % or less of Mn, preferably 0.5 mass % or more and 2.0 mass % or less of Mn. If the content of Mn is 0.3% by mass or more, it is easy to secure the amount of precipitation of the Cu-rich phase, and if the content of Mn is 0.5% by mass or more, it is more preferable. Moreover, excessive addition of Mn causes deterioration of the hot workability of the austenitic stainless steel. Therefore, the content of Mn is set to 2.5% by mass or less, preferably 2.0% by mass or less.
  • the austenitic stainless steel may contain P of 0.04% by mass or less. If the P content is 0.04% by mass or less, the adverse effect on material properties such as ductility can be reduced in the austenitic stainless steel.
  • the austenitic stainless steel may contain 0.015% by mass or less of S. If the S content is 0.015% by mass or less, the adverse effects on material properties such as ductility can be reduced in the austenitic stainless steel.
  • Ni Ni (nickel) is an austenite-generating element and an element effective for maintaining the austenite phase.
  • the austenitic stainless steel contains 3.0% by mass or more and less than 6.0% by mass of Ni, preferably 3.5% by mass or more and 5.5% by mass or less of Ni, and 4.0% by mass or more and 5 More preferably, it contains less than 0.0% by mass of Ni.
  • the Ni content is 3.0% by mass or more, the austenite phase is well formed and maintained. More preferably, the Ni content is 4.5% by mass or more.
  • Ni is an expensive element, and when added in excess, it stabilizes the austenite phase and reduces the amount of deformation-induced martensite phase produced. Therefore, the Ni content is less than 6.0% by mass, preferably 5.5% by mass or less, and more preferably less than 5.0% by mass.
  • Cr Cr (chromium) is an effective element for ensuring the corrosion resistance of austenitic stainless steel.
  • the austenitic stainless steel contains 16.0% by mass or more and 18.5% by mass or less of Cr, preferably 16.5% by mass or more and 18.0% by mass or less of Cr. If the Cr content is 16.0% by mass or more, good corrosion resistance of the austenitic stainless steel can be ensured. More preferably, the Cr content is 16.5% by mass or more.
  • the Cr content is 18.5% by mass or less, preferably 18.0% by mass or less.
  • Cu is an austenite-forming element and an element effective for maintaining the austenite phase. It is also effective in increasing the strength of austenitic stainless steel by precipitation of Cu-rich phases. Cu is an element that effectively acts also for crystal grain refinement. This is probably because the Cu-rich phase exhibits an inhibitory effect on grain growth. In addition, Cu reduces the work hardening of the austenite phase in a solid solution state, so that the rolling load in the manufacturing process of the austenitic stainless steel can be reduced.
  • the austenitic stainless steel contains 1.5% by mass or more and 4.0% by mass or less of Cu, preferably 2.0% by mass or more and 3.5% by mass or less of Cu, and more than 2.0% by mass. It is more preferable to contain 0.5% by mass or less of Cu.
  • the Cu content is 1.5% by mass or more, the austenite phase is well formed and maintained, and the Cu-rich phase is well precipitated. More preferably, the Cu content is 2.0% by mass or more, and even more preferably more than 2.0% by mass.
  • the Cu content is 4.0% by mass or less, preferably 3.5% by mass or less.
  • N nitrogen
  • Austenitic stainless steel has a N content of 0.005% by mass or more in order to generate an austenitic phase. With such a content of N, an austenitic phase is effectively formed.
  • the N content is 0.25% by mass or less, preferably 0.20% by mass or less.
  • the austenitic stainless steel contains, by mass%, Mo: 1.0% or less, W: 1.0% or less, V: 0.5% or less, and B: 0.0001% or more and 0.0001% or less. 01% or less, Co: 0.8% or less, Sn: 0.1% or less, Ca: 0.03% or less, Mg: 0.03% or less, Ti: 0.5% or less, Nb: 0.5% Below, Al: 0.3% or less, Sb: 0.5% or less, Zr: 0.5% or less, Ta: 0.03% or less, Hf: 0.03% or less, and REM (rare earth metal): 0.5% or less. It may further contain one or more selected from 2% or less.
  • the austenitic stainless steel preferably contains one or more selected from Mo of 1.0% by mass or less, W of 1.0% by mass or less, and V of 0.5% by mass or less.
  • B B (boron) is an element that improves hot workability, and is an element that is effective in reducing the occurrence of edge splitting and double cracking in hot rolling.
  • the austenitic stainless steel preferably contains 0.0001% by mass or more and 0.01% by mass or less of B. If the B content is 0.0001% by mass or more, it is effective in improving hot workability and reducing edge splitting and split cracking in hot rolling. However, excessive addition of B to an austenitic stainless steel containing Cr causes deterioration of corrosion resistance due to precipitation of Cr 2 B. Therefore, the content of B is preferably 0.01% by mass or less.
  • Co Co
  • Co Co
  • Co is an effective element for ensuring the corrosion resistance of austenitic stainless steel. It also contributes to reducing the coarsening of the Cu-rich phase and maintaining it fine. In order to obtain such an effect, it is preferable to contain 0.10% by mass or more of Co. However, Co is an expensive element, and from the viewpoint of cost reduction, the Co content is preferably 0.8% by mass or less.
  • Sn Sn (tin) is an effective element for ensuring the corrosion resistance of austenitic stainless steel.
  • the Sn content is preferably 0.1% by mass or less.
  • Al, Ca, Mg, Ti Al (aluminum), Ca (calcium), Mg (magnesium) and Ti (titanium) are all deoxidizing elements.
  • the austenitic stainless steel is selected from 0.3 wt% or less Al, 0.03 wt% or less Ca, 0.03 wt% or less Mg, and 0.5 wt% or less Ti as a deoxidizing agent. It is preferable to include one or more of
  • Nb Nb niobium
  • the austenitic stainless steel preferably contains 0.5% by mass or less of Nb.
  • the austenitic stainless steel contains up to 0.5% by weight Sb, up to 0.5% by weight Zr, up to 0.03% by weight Ta, up to 0.03% by weight Hf, and up to 0.2% by weight It preferably contains one or more selected from REM.
  • the austenitic stainless steel has an Md30 value of 10.0 or more and 80.0 or less, preferably 20.0 or more and 70.0 or less, as indicated by the following formula (1).
  • Md 30 551-462(C+N)-9.2Si-8.1Mn-29Ni-10.6Cu-13.7Cr-18.5Mo (1)
  • the content (% by mass) of each element contained in the austenitic stainless steel is substituted for the symbol of the element in the formula (1), and 0 is substituted for the non-additive element.
  • the value of Md30 is the temperature at which 50% of the structure of the austenitic stainless steel transforms into the martensitic phase when 30% tensile strain is applied to the austenitic stainless steel of the austenitic single phase. (°C). Therefore, the value of Md30 can be used as an indicator of the stability of the austenite phase. In addition, the value of Md30 can also be used as an index that influences the likelihood of the TRIP phenomenon occurring in austenitic stainless steel.
  • the value of Md30 of the austenitic stainless steel according to one embodiment of the present invention is preferably 10.0 or more and 80.0 or less.
  • the higher the value of Md 30 the easier the transformation from the austenite phase to the deformation-induced martensite phase occurs, and the application of mild cold-rolling strain can provide high strength and ensure excellent ductility. Further, even when the austenitic stainless steel is subjected to forming processing, the portion to which processing strain is imparted, such as a bent portion, tends to obtain higher strength due to the TRIP phenomenon.
  • Md30 which is an index of the stability of the austenite phase
  • Md30 which is an index of the stability of the austenite phase
  • the coefficient of Cu is set smaller than the coefficient of Ni in the component regression equation of Md 30 .
  • Many of the component regression equations of Md 30 based on conventional knowledge are based on the results of austenitic stainless steels that are not Ni-saving types.
  • the Ni-saving type composition of the present invention it has been found that the influence of Cu on the stabilization of the austenite phase is clearly smaller than the conventional knowledge.
  • a method for producing an austenitic stainless steel according to an embodiment of the present invention includes, in mass%, C: more than 0.03% and 0.15% or less, Si: 0.1% or more and 2.0% or less, Mn: 0 .3% or more and 2.5% or less, P: 0.04% or less, S: 0.015% or less, Ni: 3.0% or more and less than 6.0%, Cr: 16.0% or more and 18.5% Below, Cu: 1.5% or more and 4.0% or less and N: 0.005% or more and 0.25% or less, the balance being Fe and unavoidable impurities, Md 30 represented by the above formula (1) is 10.0 or more and 80.0 or less. Also, the method for producing austenitic stainless steel includes a finish annealing step.
  • the method for manufacturing austenitic stainless steel may include a general manufacturing process for austenitic stainless steel for processes other than the final annealing process.
  • An example of a method for producing an austenitic stainless steel according to one embodiment of the present invention is shown below, but the present invention is not limited to this.
  • a slab is produced by continuously casting molten steel whose composition is adjusted. Then, the slab produced by continuous casting is heated to 1100° C. or higher and 1300° C. or lower, and then hot rolled to produce a hot rolled steel strip.
  • the precipitation rate of the Cu-rich phase from the less strained austenite phase after hot rolling is slow. Therefore, the finishing temperature and coiling temperature of the hot-rolled steel strip after hot rolling may be the same conditions as in the general method for producing austenitic stainless steel.
  • the coiling temperature of the hot-rolled steel strip after hot rolling is preferably 850° C. or lower, more preferably 650° C. or lower.
  • the hot-rolled steel strip that has been hot-rolled may be pickled.
  • the hot-rolled steel strip may be annealed before pickling, or may be pickled without annealing.
  • the annealing temperature is preferably in the range of 900° C. or higher and 1150° C. or lower. It is more preferable to operate at a temperature within the range, but is not limited to the above range. Then, the pickled hot-rolled steel strip is cold-rolled to a predetermined thickness to obtain a cold-rolled steel strip.
  • the cold rolling process should be performed at a rolling reduction and a rate such that the strain-induced martensite phase in the cold-rolled steel strip accounts for 20% by volume or more of the total. It is preferable to carry out by rolling temperature. By performing such a cold rolling process, a Cu-rich phase can be effectively precipitated in the steel strip in the subsequent finish annealing process.
  • the value of Md30 is adjusted to 10.0 or more and 80.0 or less.
  • An austenitic stainless steel having such a value of Md 30 precipitates a Cu-rich phase in the amount specified in one embodiment of the present invention, regardless of the amount of deformation-induced martensitic phase in the cold-rolled steel strip.
  • increasing the rolling reduction in the cold-rolling process, controlling the temperature in the cold-rolling process to be low, etc. as necessary are more effective for the precipitation of the Cu-rich phase.
  • the rolling reduction in the cold rolling step is preferably 40% or more, more preferably 50% or more, It is more preferably 60% or more.
  • the temperature in the cold rolling step is preferably 90° C. or lower, more preferably 60° C. or lower.
  • the cold-rolled steel strip is subjected to finish annealing.
  • the finish annealing step is carried out under conditions that promote the precipitation of the Cu-rich phase.
  • a Cu-rich phase is effective in increasing the strength of austenitic stainless steel. Therefore, the strength of the hot-rolled steel strip and the cold-rolled steel strip before precipitation of the Cu-rich phase is rather low, and the rolling load in the cold rolling process can be reduced. Then, the Cu-rich phase is precipitated in the final annealing step, so that the austenitic stainless steel after the final annealing has high strength.
  • the precipitation of the Cu-rich phase is also effective in refining the recrystallized grains of the austenite phase. Therefore, the precipitation of the Cu-rich phase can be used to control the average crystal grain size to 10.0 ⁇ m or less.
  • the method for producing austenitic stainless steel according to one embodiment of the present invention, it is possible to achieve both a reduction in the processing load during production and an increase in the strength of the final product at a high level.
  • the productivity of the austenitic stainless steel is also good because the additional step of the aging treatment is not required for the precipitation of the Cu-rich phase unlike the conventional method.
  • the finish annealing temperature in the finish annealing step is preferably 750°C or higher and 980°C or lower, and preferably 800°C or higher and 925°C or lower so that the Cu-rich phase is effectively precipitated in the austenitic stainless steel. If the final annealing temperature is less than 750°C, recrystallization of the structure will be insufficient. Moreover, when the temperature of the final annealing exceeds 980° C., the Cu-rich phase dissolves, so the amount of the Cu-rich phase remaining after the final annealing becomes insufficient.
  • the Cu-rich phase that precipitates from the deformation-induced martensite phase is particularly likely to dissolve in the austenite phase if it is held at a temperature of 850°C or higher for a long time in the final annealing. Therefore, when the maximum temperature reached in the final annealing step is 850°C or higher, it is preferable to shorten the heating time at 850°C or higher. Specifically, when the maximum temperature reached in the final annealing step is 850° C. or higher, the heating time at 850° C. or higher is set to 30 seconds or less, preferably 15 seconds or less.
  • the term "heating time at 850° C. or higher" refers to the total time of the plurality of heating times when the final annealing step is divided into multiple times for heating to 850° C. or higher.
  • Austenitic stainless steel has a C content of 0.15% or less, so Cr carbides do not necessarily precipitate during cooling.
  • the average cooling rate from 700°C to 500°C is preferably 20°C/second or more, more preferably 50°C/second or more, and 75°C/second or more. more preferably.
  • intermediate annealing and intermediate rolling may be performed as necessary. Further, in order to further increase the strength of the steel strip after finish annealing, skin pass rolling may be performed as necessary.
  • the temperature of the intermediate annealing is preferably 980° C. or higher and 1150° C. or lower in order to avoid precipitation of the Cu-rich phase when priority is given to reducing the rolling load. In order to increase the strength by repeating the precipitation treatment, it is preferable that the temperature of the intermediate annealing is the same as that of the finish annealing. In addition, the temperature of the intermediate annealing is not limited to the above range.
  • An austenitic stainless steel according to an embodiment of the present invention has a relatively low strength in the manufacturing process to reduce the rolling load and achieves high strength after manufacturing.
  • Such properties of austenitic stainless steel can be expressed, for example, by the relationship between 0.2% proof stress (YS18%, MPa) and reference strength (HV60%).
  • 0.2% proof stress (YS18%) is an indicator of the strength of austenitic stainless steel.
  • the 0.2% yield strength (YS18%) indicates the 0.2% yield strength when the austenitic stainless steel is further subjected to temper rolling with an elongation of 18% after finish annealing.
  • the 0.2% yield strength can be evaluated using a method conforming to JIS Z2241.
  • the reference strength (HV60%) is an index that hypothetically indicates the strength of the austenitic stainless steel before precipitation of the Cu-rich phase in the final annealing process.
  • the reference strength (HV60%) although the chemical composition of the austenitic stainless steel is the same, the manufacturing method is partially changed from the manufacturing method according to the embodiment of the present invention, and after hot rolling, annealing at 1050 ° C. is performed. It shows the Vickers hardness when cold rolling is applied at a rolling reduction of 60%. That is, the reference strength (HV60%) does not indicate the strength of the austenitic stainless steel according to one embodiment of the present invention, but may be the strength of a steel strip produced for evaluation, for example. Vickers hardness can be measured based on the Vickers hardness test method conforming to JIS Z2244.
  • the austenitic stainless steel which achieves both a reduction in the processing load during manufacturing and a high strength of the final product, has a relationship between the 0.2% proof stress (YS18%) and the reference strength (HV60%). satisfies the following formula (2).
  • Austenitic stainless steel has very high strength and corrosion resistance. Therefore, austenitic stainless steel is suitable as a material for spring products that require high strength and corrosion resistance, such as cylinder head gaskets, spiral springs, springs for electronic device parts, automotive battery frame materials, structural materials, and metal packings. is. ⁇ summary ⁇
  • the austenitic stainless steel according to aspect 2 of the present invention in aspect 1 above, contains Mo: 1.0% or less, W: 1.0% or less, V: 0.5% or less, and B: 0.5% by mass. 0001% or more and 0.01% or less, Co: 0.8% or less, Sn: 0.1% or less, Ca: 0.03% or less, Mg: 0.03% or less, Ti: 0.5% or less, Nb : 0.5% or less, Al: 0.3% or less, Sb: 0.5% or less, Zr: 0.5% or less, Ta: 0.03% or less, Hf: 0.03% or less and REM ( rare earth metal): may further contain one or more selected from 0.2% or less.
  • the austenitic stainless steel according to aspect 3 of the present invention in aspect 1 or 2 above, may have an average crystal grain size of 10.0 ⁇ m or less.
  • the method for producing an austenitic stainless steel according to aspect 4 of the present invention comprises, in % by mass, C: more than 0.03% and 0.15% or less, Si: 0.1% or more and 2.0% or less, Mn: 0.1% or less; 3% or more and 2.5% or less, P: 0.04% or less, S: 0.015% or less, Ni: 3.0% or more and less than 6.0%, Cr: 16.0% or more and 18.5% or less , Cu: 1.5% or more and 4.0% or less and N: 0.005% or more and 0.25% or less, the balance being Fe and unavoidable impurities, Md 30 represented by the following formula (1)
  • the content (% by mass) of each element contained in the austenitic stainless steel is substituted for the symbol of the element in the formula (1), and 0 is substituted for the non-additive element.
  • Austenitic stainless steels according to each of the examples and comparative examples of the present invention were produced by the following method.
  • Austenitic stainless steel having the chemical composition shown in Table 1 was melted, and the production method according to one example of the present invention (invention examples C1 to C8) or the production method according to the comparative example (comparative examples D1 and D2), From hot rolling to finish annealing, a cold-rolled annealed material was obtained.
  • the conditions of each manufacturing method are shown in Table 2 below.
  • the time for reaching 850°C or higher was adjusted as shown in Table 2.
  • the heating was adjusted so that the temperature began to decrease when the final annealing temperature reached 850 ° C., but for convenience, in Table 2, the time to reach 850 ° C. or higher is described as "1 second". are doing.
  • a TEM sample was produced by an electropolishing method from the cold-rolled annealed material produced under each condition. A plane parallel to the rolling direction of the cold-rolled and annealed material in the TEM sample was observed in three fields of view in a range of 400 nm ⁇ 400 nm. Cu-rich phases were determined from the contrast of the TEM image, and the number of Cu-rich phases was counted. The thickness of the TEM sample was assumed to be 150 nm, and the number density per unit volume was determined. When the Cu-rich phase coarsened, it became observed in a clear shape instead of contrast. Cu-rich phases with longer diameters greater than 30 nm were excluded from the measurements.
  • the base material Cr concentration is the average value of the Cr concentration of the entire cold-rolled annealed material, and indicates the Cr content (% by mass) contained in the cold-rolled annealed material. If the number density of the Cr carbides was 50/ ⁇ m ⁇ 3 or more, it was evaluated as “ ⁇ ”, and if it was less than 50 ⁇ m ⁇ 3 , it was evaluated as “ ⁇ ”.
  • Crystal grain size The average grain size was evaluated using the EBSD method. A cross section parallel to the rolling direction and perpendicular to the rolling surface of the cold-rolled annealed material manufactured under each condition was mechanically polished and then electrolytically polished. After that, EBSD analysis was performed on a 40 ⁇ m ⁇ 40 ⁇ m range of the cross section with a step interval of 0.2 ⁇ m in a field of view with a magnification of 2000 times.
  • misorientation in the orientation relationship satisfying the ⁇ 3 correspondence grain boundary except for annealing twins with misorientation of 1° or less, boundaries with misorientation of 2° or more are regarded as grain boundaries, and the area of each grain is S ( ⁇ m 2 ), and the diameter of a circle having the same area as the crystal grain was defined as D ( ⁇ m), and the crystal grain size was calculated by the following formula (3). This was performed for 5 fields of view, and the average of the grain sizes obtained in the 5 fields of view was calculated as the average grain size.
  • Crystal grain size ⁇ (D ⁇ S) ⁇ /40 ⁇ 40 (3) (Amount of martensite phase)
  • the amount of martensite phase (% by volume) is as it is when the plate thickness is 1.5 mm or more, and when the plate thickness is less than 1.5 mm, the material after cold rolling or temper rolling is adjusted so that the total is 1.5 mm or more. Later materials were layered. These materials were measured with a ferrite scope (Fischer FMP30, electromagnetic induction method), and the value obtained by dividing the measured value by 0.7475 was taken as the amount of martensite phase.
  • the amount (% by volume) of the austenite phase was regarded as a value obtained by subtracting the amount of the martensite phase from 100% by volume of the entire matrix of the austenitic stainless steel.
  • the amounts of Cu-rich phases and unavoidably formed phases in austenitic stainless steel may be calculated as extraneous numbers because their ratios are small and accurate measurement is difficult.
  • Table 3 shows the amount of precipitated Cu-rich phase and the grain size of the cold-rolled annealed material obtained under the conditions shown in Table 2 for the invention steel A2.
  • 0.2% yield strength (YS18%) under each condition and the amount of martensite phase after cold rolling (before finish annealing) and after temper rolling at which the elongation is 18% after finish annealing. are also shown in Table 3 below.
  • the cold-rolled annealed materials produced under the respective conditions of invention examples C1 to C8 have a Cu-rich phase precipitation amount within the specified range of the present invention, and have a fine average grain size of 10.0 ⁇ m or less. Indicated. On the other hand, precipitation of the Cu-rich phase was not observed in any of the cold-rolled annealed materials produced under the conditions of Comparative Examples D1 and D2.
  • the EBSD grain boundary map is shown on the left side of FIG. 1, and the TEM imaged image is shown on the right side of FIG.
  • the TEM imaged image is shown on the right side of FIG.
  • precipitation of a Cu-rich phase indicated as “Cu” in FIG. 1 was observed in the austenitic stainless steel according to one embodiment of the present invention.
  • the 0.2% yield strength (YS18%) is preferably 1134 MPa or more based on the above formula (2).
  • the 0.2% proof stress (YS18%) of the cold-rolled annealed materials of the invention steel A2 manufactured under the respective conditions of invention examples C1 to C8 was 1134 MPa or more.
  • the 0.2% proof stress (YS18%) of the cold-rolled annealed materials manufactured under the respective conditions of Comparative Examples D1 and D2 was lower than 1134 MPa.
  • Table 4 below shows the Cu-rich phase precipitation amount and grain size after finish annealing of the cold-rolled and annealed materials produced from the invention steels A1 to A15 or the comparative steels B1 to B4 under the production conditions shown in invention example C2. show.
  • the 0.2% proof stress (YS18%) and reference strength (HV60%) under these conditions are also shown in Table 4 below.
  • the cold-rolled and annealed materials of the invention steels A1 to A15 had a precipitation amount of the Cu-rich phase within the specified range of the present invention, and exhibited a fine average crystal grain size of 10 ⁇ m or less.
  • the 0.2% proof stress (YS18%) showed good values satisfying the above formula (2).
  • Fig. 2 shows a plot of the relationship between the 0.2% proof stress (YS18%) and the reference strength (HV60%) under each condition in Table 4.
  • an example of the present invention is indicated by a white circle, and a comparative example is indicated by a black arrowhead.
  • the higher the upper left plot the better the balance between the workability before the finish annealing and the high strength after the finish annealing.
  • the amount of precipitated Cr carbides is 50/ ⁇ m ⁇ 3 or more, and although the corrosion resistance of the cold-rolled annealed material is not at a problem level, it is an amount that can have a slight effect. Precipitation of Cr carbide was observed.
  • the cold-rolled annealed material manufactured by the manufacturing method according to one embodiment of the present invention using the austenitic stainless steel having the composition according to one embodiment of the present invention is It was shown that both the reduction of the processing load and the increase in strength of the product are compatible.

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Abstract

La présente invention vise à réaliser un acier inoxydable austénitique qui soit hautement productif et à l'aide duquel il soit possible d'obtenir tant une réduction de la charge de traitement en cours de production qu'une augmentation de la résistance mécanique d'un produit final. La présente invention concerne à cet effet un acier inoxydable austénitique comprenant : 20 % en volume ou plus d'une phase austénitique contenant plus de 0,03 % et jusqu'à 0,15 % de C, 0,1 à 2,0 % de Si, 0,3 à 2,5 % de Mn, 0,04 % ou moins de P, 0,015 % ou moins de S, 3,0 à 6,0 % de Ni, 16,0 à 18,5 % de Cr, 1,5 à 4,0 % de Cu et 0,005 à 0,25 % de N, le reste étant constitué de Fe et des impuretés inévitables ; et une phase riche en Cu ayant un nombre volumique supérieur ou égal 1,0 × 103 par μm-3 et un grand diamètre inférieur ou égal à 30 nm, le reste étant constitué d'une phase martensitique induite par le traitement et d'une phase inévitablement formée, la valeur de Md30 étant de 10,0 à 80,0.
PCT/JP2023/001836 2022-02-10 2023-01-23 Acier inoxydable austénitique et procédé de production d'acier inoxydable austénitique WO2023153185A1 (fr)

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Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2009041072A (ja) * 2007-08-09 2009-02-26 Nisshin Steel Co Ltd Ｎｉ節減型オーステナイト系ステンレス鋼
JP2010189719A (ja) * 2009-02-18 2010-09-02 Nisshin Steel Co Ltd 時効硬化型ばね用ステンレス鋼板
WO2016047734A1 (fr) * 2014-09-25 2016-03-31 新日鐵住金株式会社 Tôle d'acier inoxydable austénitique et procédé de production de ladite tôle
JP2017206725A (ja) * 2016-05-17 2017-11-24 Ｊｆｅスチール株式会社 フェライト系ステンレス鋼およびその製造方法

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2009041072A (ja) * 2007-08-09 2009-02-26 Nisshin Steel Co Ltd Ｎｉ節減型オーステナイト系ステンレス鋼
JP2010189719A (ja) * 2009-02-18 2010-09-02 Nisshin Steel Co Ltd 時効硬化型ばね用ステンレス鋼板
WO2016047734A1 (fr) * 2014-09-25 2016-03-31 新日鐵住金株式会社 Tôle d'acier inoxydable austénitique et procédé de production de ladite tôle
JP2017206725A (ja) * 2016-05-17 2017-11-24 Ｊｆｅスチール株式会社 フェライト系ステンレス鋼およびその製造方法

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