WO2023153184A1 - 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

Info

Publication number
WO2023153184A1
WO2023153184A1 PCT/JP2023/001835 JP2023001835W WO2023153184A1 WO 2023153184 A1 WO2023153184 A1 WO 2023153184A1 JP 2023001835 W JP2023001835 W JP 2023001835W WO 2023153184 A1 WO2023153184 A1 WO 2023153184A1
Authority
WO
WIPO (PCT)
Prior art keywords
less
stainless steel
austenitic stainless
mass
phase
Prior art date
Application number
PCT/JP2023/001835
Other languages
English (en)
Japanese (ja)
Inventor
太一朗 溝口
Original Assignee
日鉄ステンレス株式会社
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by 日鉄ステンレス株式会社 filed Critical 日鉄ステンレス株式会社
Publication of WO2023153184A1 publication Critical patent/WO2023153184A1/fr

Links

Images

Classifications

    • 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.
  • N since the precipitation temperature of the Cu-rich phase and the precipitation temperature of Cr carbide are relatively close, it is preferable to use N without excessively increasing the amount of C in order to reduce the deterioration of corrosion resistance due to precipitation of Cr carbide. I focused on that. Reducing the amount of C in the austenitic stainless steel is also preferable for achieving the desired reduction in processing load.
  • the austenitic stainless steel according to one aspect of the present invention has C: 0.005% or more and 0.03% 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
  • Ni 3.0% or more and less than 6.0%
  • Cr 16.0% 18.5% or less
  • Cu 1.5% or more and 4.0% or less
  • N 0.08% 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 an austenitic stainless steel comprises: C: 0.005% or more and 0.03% or less; Si: 0.1% or more 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, and N: 0.08% or more and 0.25% or less, the balance being Fe and unavoidable impurities.
  • a method for producing an austenitic stainless steel having an Md30 value of 0.0 or more and 80.0 or less represented by the formula comprising a finish annealing step of performing finish annealing at a temperature of 750°C or more and 980°C or less. , When the maximum temperature reached in the final annealing step is 850 ° C. or higher, the time to heat at 850 ° C. or higher is within 30 seconds, and in the final annealing step, the average temperature from 700 ° C. to 500 ° C.
  • 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 steels may be, for example, steel sheets or strips.
  • 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. phase 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: 0.005% or more and 0.03% 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: 0.08% 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 0.005% by mass or more and 0.03% by mass or less of C. When the C content is 0.005% by mass or more, an austenitic stainless steel having a sufficient solid-solution strengthening effect and 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. From the viewpoint of reducing the formation of the ⁇ ferrite phase, the Si content is 2.0% by mass or less, 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
  • nitrogen is an austenite forming element, and is an element having a solid-solution strengthening effect and an effect of improving corrosion resistance. Since the austenitic stainless steel has a C content of 0.03% by mass or less in order to ensure corrosion resistance of the weld zone, the N content is 0.08% by mass or more, and 0.10% by mass or more. is preferably 0.11% by mass or more, and even more preferably 0.12% by mass or more. Such an N content is effective in ensuring the strength and corrosion resistance required for austenitic stainless steel.
  • 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 0.0 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 0.0 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 stability of the austenite phase
  • Md30 which is an index of 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: 0.005% to 0.03%, Si: 0.1% to 2.0%, 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: 0.08% or more and 0.25% or less, the balance being Fe and unavoidable impurities, Md 30 represented by the above formula (1) is 0.0 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 0.0 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 0.03% by mass or less, so precipitation of Cr carbide during cooling is unlikely to occur. Therefore, the cooling rate after finish annealing may be the same as in a general stainless steel manufacturing method. From the viewpoint of productivity, it can be said that a faster cooling rate is preferable, but the average cooling rate from 700 ° C. to 500 ° C. may be a relatively slow speed of 1 ° C./sec or more, for example. Taking this into consideration, 5° C./second or more is preferable. Also, considering the flatness of the steel sheet, the cooling rate is preferably less than 75° C./second, more preferably 50° C./second or less.
  • 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 used for spring products that require high strength and corrosion resistance, such as cylinder head gaskets, spiral springs, springs for electronic device parts, train vehicle members, automotive battery frame materials, structural materials, and metal packings. It is suitable as a material for In particular, austenitic stainless steel is excellent in corrosion resistance (weldability) even when welded. Therefore, the austenitic stainless steel according to one embodiment of the present invention is suitable even for applications in which a relatively large number of welded structures are used, such as train vehicle members or automotive battery frame materials manufactured for welding. Available.
  • the austenitic stainless steel according to aspect 1 of the present invention has, in mass %, C: 0.005% or more and 0.03% or less, Si: 0.1% or more and 2.0% or less, Mn: 0.3% or more 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: Contains 1.5% or more and 4.0% or less and N: 0.08% or more and 0.25% or less, the balance being Fe and unavoidable impurities, 20% by volume or more of the austenitic phase, and a number density of 1 .0 ⁇ 10 3 ⁇ m ⁇ 3 or more and a Cu-rich phase with a major axis of 30 nm or less, and the balance consists of a deformation-induced martensite phase and an unavoidable formation phase, and the value of Md 30 shown by the following formula (1) is 0.0 or more and 80.0 or less: Md 30 shown by the following formula
  • 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, by mass %, C: 0.005% or more and 0.03% or less, Si: 0.1% or more and 2.0% or less, Mn: 0.1% or more, and 0.03% 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: 0.08% or more and 0.25% or less, the balance being Fe and unavoidable impurities, Md 30 represented by the following formula (1)
  • the heating time at 850° C. or higher is 30 seconds or less, and the average cooling rate from 700° C. to 500° C. after the finish annealing is 1° C./second or more in the final annealing step.
  • 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.
  • 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.
  • 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 ⁇ .
  • 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.
  • a cold-rolled annealed material having a plate thickness of 1.5 mm was subjected to TIG tanning welding at an electrode diameter of 1.6 mm, a welding speed of 70 cm/min, and a welding current of 90 A under the conditions of an Ar gas seal.
  • a 10 mm ⁇ 10 mm area including the weld was used as an evaluation surface, and #600 polishing was applied to remove the influence of the film, and the corrosion resistance of the evaluation surface was evaluated using the electrochemical reactivation rate as an index.
  • the reactivation rate was measured according to JIS G0580. Specifically, in a 0.5 mol/L sulfuric acid and 0.01 mol/L potassium thiocyanate aqueous solution at a liquid temperature of 30°C, polarization was performed from the spontaneous potential to 0.3 V (vs SCE) at a sweep rate of 100 mV/min ( hereinafter referred to as the “outward route”). After reaching 0.3 V (vs SCE), the potential was swept in the direction opposite to the forward trip, and after reactivation of the hot-rolled material, the sweep was terminated at a potential at which the anode current became 0 again (hereinafter, "return trip"). .
  • the ratio (ir/ia) of the maximum current density ia on the outward trip and the maximum current density ir on the return trip was calculated as the reactivation rate.
  • Such an evaluation method is strict as a sensitization determination method for evaluating corrosion resistance, so even if the reactivation rate is, for example, about 1.5%, it is considered that there is no problem in the actual environment. be done.
  • the cold-rolled annealed material according to one example of the present invention may have fine crystal grains, it is difficult to evaluate corrosion resistance. It can be said that it has Therefore, the corrosion resistance of the weld zone was evaluated as "O" (good) when the reactivation rate was 1% or less, and as "x" (poor) when the reactivation rate exceeded 1%.
  • 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 1094 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 1094 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 1094 MPa.
  • Table 4 below shows the Cu-rich phase precipitation amount and grain size after finish annealing of the cold-rolled and annealed materials manufactured from the invention steels A1 to A15 or the comparative steels B1 to B5 under the manufacturing conditions shown in invention example C2. show.
  • the 0.2% proof stress (YS18%), reference strength (HV60%), and corrosion resistance of the weld 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 10.0 ⁇ m or less.
  • the 0.2% proof stress (YS18%) showed good values satisfying the above formula (2).
  • the cold-rolled and annealed material of comparative steel B1 had poor corrosion resistance at the weld.
  • the cold-rolled annealed materials of comparative steels B2 to B5 do not satisfy the above formula (2) in terms of 0.2% proof stress (YS18%), and have a good balance between workability before finish annealing and high strength after finish annealing. Austenitic stainless steel was not obtained.
  • 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 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. It was also shown that such a cold-rolled annealed material is excellent in corrosion resistance of welded parts and suitable for applications in which many weldings are performed.

Landscapes

  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Heat Treatment Of Sheet Steel (AREA)
  • Heat Treatment Of Steel (AREA)

Abstract

La présente invention permet d'obtenir un acier inoxydable austénitique ayant une productivité élevée tout en réduisant la charge de traitement pendant la production et en augmentant la résistance du produit final. L'acier inoxydable austénitique contient, en % en masse, de 0,005 à 0,03 % de C, de 0,1 à 2,0 % de Si, de 0,3 à 2,5 % de Mn, une proportion inférieure ou égale à 0,04 % de P, une proportion inférieure ou égale à 0,015 % de S, de 3,0 à 6,0 % de Ni, de 16,0 à 18,5 % de Cr, de 1,5 à 4,0 % de Cu, et de 0,08 à 0,25 % de N, le reste comprenant du Fe et des impuretés inévitables, comprend une proportion supérieure ou égale à 20 % en volume d'une phase austénitique, et une phase riche en Cu présentant un nombre volumique supérieur ou égal à 1,0×103•μm-3 et un grand axe inférieur ou égal à 30 nm, le reste comprenant des phases de martensite induites par déformation et des phases de formation inévitables, et présente une valeur Md30 de 0,0 à 80,0.
PCT/JP2023/001835 2022-02-10 2023-01-23 Acier inoxydable austénitique et procédé de production d'acier inoxydable austénitique WO2023153184A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
JP2022-019593 2022-02-10
JP2022019593 2022-02-10

Publications (1)

Publication Number Publication Date
WO2023153184A1 true WO2023153184A1 (fr) 2023-08-17

Family

ID=87564041

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/JP2023/001835 WO2023153184A1 (fr) 2022-02-10 2023-01-23 Acier inoxydable austénitique et procédé de production d'acier inoxydable austénitique

Country Status (1)

Country Link
WO (1) WO2023153184A1 (fr)

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH04191352A (ja) * 1990-11-26 1992-07-09 Nisshin Steel Co Ltd 耐ヘタリ性に優れた内燃機関のガスケット用材料
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
JP2022064692A (ja) * 2020-10-14 2022-04-26 日鉄ステンレス株式会社 オーステナイト系ステンレス鋼およびオーステナイト系ステンレス鋼の製造方法

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH04191352A (ja) * 1990-11-26 1992-07-09 Nisshin Steel Co Ltd 耐ヘタリ性に優れた内燃機関のガスケット用材料
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
JP2022064692A (ja) * 2020-10-14 2022-04-26 日鉄ステンレス株式会社 オーステナイト系ステンレス鋼およびオーステナイト系ステンレス鋼の製造方法

Similar Documents

Publication Publication Date Title
KR100957664B1 (ko) 오스테나이트·페라이트계 스테인레스 강판
KR101779305B1 (ko) 오스테나이트계 스테인리스 강판 및 그 제조 방법
KR101289518B1 (ko) 오스테나이트계 스테인리스 강판 및 그 제조 방법
EP2617852A1 (fr) Feuille d'acier laminée à chaud à haute résistance possédant une excellente aptitude au cintrage et procédé de production
KR20180109865A (ko) Nb함유 페라이트계 스테인리스 열연 강판 및 그 제조 방법과, Nb함유 페라이트계 스테인리스 냉연 강판 및 그 제조 방법
WO2013099136A1 (fr) Tôle d'acier laminée à chaud à haute résistance et son procédé de fabrication
EP2578714B1 (fr) Tôle d'acier haute résistance laminée à chaud, et son procédé de production
CN115003839A (zh) 钢板及其制造方法
WO2019176283A1 (fr) Feuille d'acier inoxydable martensitique, son procédé de fabrication et élément de ressort
JP3357226B2 (ja) 耐リジング性と表面性状に優れたＦｅ−Ｃｒ合金
JP4754362B2 (ja) 耐食性、耐力、低温靱性が良好なオーステナイト系ステンレス熱間圧延鋼材およびその製造方法
WO2018114865A1 (fr) Objet comprenant un acier inoxydable duplex et utilisation correspondante
JP2022045505A (ja) フェライト系ステンレス鋼板およびその製造方法ならびに排気部品
JP3247244B2 (ja) 耐食性と加工性に優れたＦｅ−Ｃｒ−Ｎｉ系合金
CN105164295A (zh) 点焊性优异的高强度低比重钢板
WO2023153184A1 (fr) Acier inoxydable austénitique et procédé de production d'acier inoxydable austénitique
EP1354975B1 (fr) Tôle d'acier inoxydable pour éléments de construction soudés et procédé pour leur fabrication
JP7440805B2 (ja) 鋼材
JP2001271143A (ja) 耐リジング性に優れたフェライト系ステンレス鋼及びその製造方法
WO2023153185A1 (fr) Acier inoxydable austénitique et procédé de production d'acier inoxydable austénitique
JP2022064692A (ja) オーステナイト系ステンレス鋼およびオーステナイト系ステンレス鋼の製造方法
EP4265764A1 (fr) Tôle d'acier à haute résistance ayant une excellente aptitude au façonnage, et son procédé de fabrication
EP3670692B1 (fr) Acier inoxydable ferritique
JP2004137554A (ja) 加工性に優れた鋼板及びその製造方法
JPS5949301B2 (ja) 加工性に優れたフエライト系ステンレス鋼

Legal Events

Date Code Title Description
121 Ep: the epo has been informed by wipo that ep was designated in this application

Ref document number: 23752652

Country of ref document: EP

Kind code of ref document: A1