EP4257717A1 - Acier inoxydable austénitique haute entropie et son procédé de préparation - Google Patents

Acier inoxydable austénitique haute entropie et son procédé de préparation Download PDF

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EP4257717A1
EP4257717A1 EP22897547.0A EP22897547A EP4257717A1 EP 4257717 A1 EP4257717 A1 EP 4257717A1 EP 22897547 A EP22897547 A EP 22897547A EP 4257717 A1 EP4257717 A1 EP 4257717A1
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entropy
stainless steel
ingot
follows
austenitic stainless
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English (en)
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Tongde SHEN
Kangkang WEN
Baoru SUN
Xuecheng CAI
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Yanshan University
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Yanshan University
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    • 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
    • C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
    • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
    • C22F1/16—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of other metals or alloys based thereon
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21B—ROLLING OF METAL
    • B21B3/00—Rolling materials of special alloys so far as the composition of the alloy requires or permits special rolling methods or sequences ; Rolling of aluminium, copper, zinc or other non-ferrous metals
    • B21B3/02—Rolling special iron alloys, e.g. stainless steel
    • 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
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/26—Methods of annealing
    • 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
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/56—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering characterised by the quenching agents
    • C21D1/60—Aqueous agents
    • 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
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/74—Methods of treatment in inert gas, controlled atmosphere, vacuum or pulverulent material
    • C21D1/76—Adjusting the composition of the atmosphere
    • 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
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/004—Heat treatment of ferrous alloys containing Cr and Ni
    • 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
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/021—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips involving a particular fabrication or treatment of ingot or slab
    • 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
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0226—Hot rolling
    • 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
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0236—Cold rolling
    • 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
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C21D8/0273—Final recrystallisation annealing
    • 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
    • C22C1/00—Making non-ferrous alloys
    • C22C1/02—Making non-ferrous alloys by melting
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C30/00—Alloys containing less than 50% by weight of each constituent
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C33/00—Making ferrous alloys
    • C22C33/04—Making ferrous alloys by melting
    • 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
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
    • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
    • C22F1/002—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working by rapid cooling or quenching; cooling agents used therefor
    • 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
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/001—Austenite

Definitions

  • the invention belongs to the field of materials, specifically, the technical field of stainless steel materials, in particular to high-entropy austenitic stainless steels and their preparation methods.
  • austenitic stainless steels are widely used in many industrial fields such as aviation, aerospace, marine, and nuclear industries due to their good corrosion and oxidation resistance.
  • excellent strength and high-plasticity are difficult to achieve simultaneously in all commercial stainless steels.
  • austenitic stainless steels have a good plasticity and low strength
  • ferritic stainless steels and martensitic stainless steels have slightly higher strength and a moderate plasticity
  • precipitation hardening stainless steels have the highest strength and poorest plasticity in all stainless steels.
  • the austenitic stainless steels commonly used in the market are 201-, 301-, 304-, 316-type, and other stainless steels with low strength and a good plasticity and their derived materials.
  • the weight content of chemical elements in these austenitic stainless steels is: C ⁇ 0.15%, Si ⁇ 2.0%, Mn ⁇ 2.0% (in 201- and 202-type stainless steels: 5.0% ⁇ Mn ⁇ 10.5%), P ⁇ 0.045%, S ⁇ 0.03%, N ⁇ 0.025%, 15.0% ⁇ Cr ⁇ 28.0%, 3.5% ⁇ Ni ⁇ 36.0% (the content of Cr and Ni is dependent on the type of steels).
  • Others are trace doping elements such as Cu, Nb, W, Ta, B, and Al, as well as iron and other unavoidable impurities.
  • High-entropy alloys have excellent properties that are difficult to achieve in conventional alloys, such as high hardness, strength, oxidation resistance, corrosion resistance, fatigue resistance, high-temperature softening resistance, creep resistance, wear resistance, unique magnetism, and excellent low-temperature mechanical properties.
  • C. T. Liu et al. introduced a design scheme for strengthening FeCoNiTiAl high-entropy alloys with L1 2 -type multicomponent intermetallic nano-sized precipitates (MCINP). By introducing L1 2 -type MCINP into the multi-principal alloy matrix, the strength of the material is greatly improved, and a good tensile uniform elongation is maintained [ Science 362 (2018) 933 - 937 ].
  • the strength is improved by introducing high-density nano-sized precipitates.
  • dislocations will shear the nano-sized precipitates, so that the stress concentration occurs on the grain boundary, thus maintaining its high-plasticity. Therefore, the introduction of fine and high-density nano-sized precipitates in the matrix alloy plays a critical role in simultaneously achieving good strength and toughness.
  • the above-mentioned high-entropy alloy contains expensive strategic metal, cobalt, makes it difficult to apply in large quantities.
  • composition of high-entropy austenitic stainless steels in this invention is mainly designed based on the following ideas:
  • the addition of Cr element can improve the strength of stainless steels while ensuring their corrosion resistance, high Cr content is helpful for the application in the service environment of nuclear materials (supercritical water, liquid lead-bismuth alloy, etc.).
  • Ni element can widen the phase region formed by nano-sized precipitates and inhibit the formation of other harmful intermetallic compounds to avoid brittleness.
  • Al element can endow the alloy with good oxidation and corrosion resistance, and promote the generation of nano-sized precipitates so that the nano-sized precipitates and the matrix maintain a high degree of coherence.
  • Ti element can refine the grains and homogenize the structure, and form nano-sized precipitates with Ni and Al to improve the strength of stainless steels. Moreover, Ti replaces expensive elements such as Cu, Co, Nb, and Mo to reduce production costs without destroying the microstructure of nano-sized precipitates.
  • the volatilization of Mn in the melting process brings inconvenience to the preparation of the alloy, and causes great waste; the presence of Cu may cause segregation of the material and bring inhomogeneity to the structure. Therefore, the alloy in the invention needs to remove these two elements.
  • the variation rules of the content of each element in the alloy the content of Ti and Al is determined by the content of the other three elements.
  • the content of Cr and Ni is higher than that of Ti and Al, the content of Ti and Al needs to be reduced appropriately.
  • the content of Cr and Ni is lower than that of Ti and Al, it is necessary to increase the content of Ti and Al.
  • the content of Cr element increases, it is necessary to increase the content of Ni element at the same time because, on the one hand, this can ensure that the matrix has an austenitic structure, on the other hand, this can ensure that there are enough Ni atoms to form nano-sized precipitates.
  • the purpose of the invention is to provide high-strength, high-plasticity, and high-entropy austenitic stainless steels and their preparation methods.
  • the technical methods used in the invention are as follows:
  • a high-entropy austenitic stainless steel is characterized in that the elemental composition in atomic percentage is as follows: Cr: 5 - 30%; Ni: 5 - 50%; Ti: 1 - 15%; Al: 1 - 15%; the balance element is Fe.
  • the elemental composition is as follows: Cr: 5 - 19%; Ni: 5 - 29%; Ti: 6 - 15%; Al: 5 - 15%; the balance element is Fe.
  • the size of nano-sized precipitates in the high-entropy stainless steel is below 30 nm, and the number density of nano-sized precipitates is above 5.0 ⁇ 10 21 m -3 .
  • a preparation method for high-entropy austenitic stainless steels is introduced, the specific steps are as follows: mixing the raw materials according to the desired atomic content, obtaining an ingot by melting and casting in a vacuum argon arc furnace, performing a solution/homogenization treatment for the cast ingot, cold-rolling and recrystallizing (1) or hot-rolling, cold-rolling, and recrystallizing (2) the recrystallized ingot, and finally carrying out aging treatment to obtain a high-entropy austenitic stainless steel.
  • the cold rolling process of (1) is as follows: the reduction in thickness per pass is no more than 0.2 mm, and the total reduction in thickness is 60% - 70%.
  • the process of hot rolling and cold rolling of (2) is as follows: carrying out hot rolling at 800 - 1150 °C, the reduction in thickness per pass is no more than 0.5 mm, and the temperature is guaranteed to be within the range of 800 - 1150 °C during the hot rolling process.
  • the temperature of the specimen during the hot rolling is lowered, the specimen can be placed back into a furnace and remained within the rolling temperature range for 5 - 15 min, and the total reduction in thickness should be 50% - 60%, the cold rolling reduction in thickness per pass is no more than 0.2 mm, and the total reduction in thickness is 60% - 70%.
  • recrystallization is as follows: keeping the ingot rolled by (1) or (2) at 1140 - 1160 °C for 1 - 3 min. If the volume of the ingot is large, the recrystallization time can be increased.
  • the heating rate for the recrystallization process is 10 - 20 °C/min.
  • the weight of pure Ti is 30 - 40 g, which is not used as raw material and does not participate in melting.
  • the vacuum argon arc melting process is repeated at least four times.
  • the specific operation of the solution/homogenization treatment is as follows: heating the ingot to 1140 - 1160 °C under a vacuum better than 1.0 ⁇ 10 -3 Pa, then remaining at this temperature for 1 - 2.5 h, and finally quenching the ingot in water or cooling the ingot in air.
  • the heating rate of the solution/homogenization treatment is 10 - 20 °C/min.
  • the specific operation of the aging treatment is as follows: ageing the recrystallized ingot at 500 - 600 °C for 0.5 - 1.5 h and then quenching in water or cooling in air.
  • the heating rate of the aging treatment is 5 - 15 °C/min.
  • the beneficial effects of the invention provides a high-entropy austenitic stainless steel, whose composition is expressed by atomic percentage of each element: Cr: 5 - 30%; Ni: 5 - 50%; Ti: 1 - 15%; Al: 1 - 15%; the rest are Fe and other unavoidable impurity elements (C, N, O, etc.) introduced during melting or heat treatment.
  • the component of stainless steel is so simple that only five alloying elements (Fe, Cr, Ni, Ti, and Al) are used.
  • the invented stainless steel reduces some precious metals and trace doping elements and minimizes the addition of alloying elements. By adjusting the atomic proportion of each component, the number of nano-sized precipitates is maximized so that the prepared high-entropy austenitic stainless steels have both high strength and high plasticity.
  • the strength and corrosion resistance of the stainless steels are improved by adding Cr.
  • the addition of Ni can be used to broaden the phase region for the formation of nano-sized precipitates and inhibit the generation of harmful intermetallic compounds.
  • the addition of Al endows the material with high oxidation and corrosion resistance, and contributes to the formation of nano-sized precipitates.
  • Ti element refines the grain and homogenizes the microstructure, and forms nano-sized precipitates with Ni and Al to improve the strength of stainless steels. At the same time, Ti replaces expensive Cu, Co, Nb, and Mo to reduce production costs and does not destroy the microstructure of nano-sized precipitates.
  • the stainless steels take the Fe-Cr-Ni phase as the matrix.
  • the content of Ti and Al is adjusted to form nano-sized precipitates to strengthen the matrix.
  • the content of Cr element increases, it is necessary to increase the content of Ni element because, on the one hand, it is necessary to ensure that the matrix has an austenitic structure, on the other hand, it is necessary to ensure that enough Ni atoms form nano-sized precipitates.
  • the content of Ti and Al should be reduced appropriately to prevent the formation of brittle intermetallic compounds, and vice versa.
  • the content of each element is 5 - 19% Cr; 5 - 29% Ni; 6 - 15% Ti; 5 - 15% Al; the rest is iron.
  • the amount of Cr and Ni is reduced, and the production cost is further reduced.
  • the invention also provides a preparation process for the high-strength, high-plasticity, and high-entropy austenitic stainless steels, which simplifies the heat treatment process, reduces the production cost and has a broad application prospect.
  • the solution /homogenization treatment method in the invention can make the alloy elements fully dissolve into the austenite matrix so that the alloy composition is more uniform.
  • the high-temperature and short-time recrystallization treatment can achieve uniform and coarse equiaxed grains, ensure the good plasticity of the alloy, and greatly improve the production efficiency and save the cost.
  • the rolling process of hot rolling followed by cold rolling is helpful to solve the difficulties in rolling large ingots.
  • Hot rolling can eliminate the cracks caused by rolling at the initial stage, help subsequent cold rolling and reduce the risk.
  • Through the subsequent aging treatment it is helpful to form the nano-sized strengthened precipitates, thereby improving the strength and plasticity of stainless steels.
  • the stainless steels prepared by the preparation method of the invention are superior to most commercial stainless steel due to their good strength and plasticity and are suitable for most of the service fields of stainless steels.
  • each raw reagent material is commercially available, and the unspecified experimental method and condition are those well known in the field, or according to those recommended by the instrument manufacturers.
  • This embodiment provides a high-entropy austenitic stainless steel with a chemical composition of Fe 47 Cr 16 Ni 26 Ti 6 Al 5 (atomic ratio) or Fe 48.56 Cr 15.39 Ni 28.24 Ti 5.32 Al 2.5 (weight ratio).
  • the influence of the introduction of unavoidable and very few impurity elements (C, N, O, etc.) during the melting process and heat treatment process on the properties of the material can be ignored.
  • the preparation steps of the high-entropy austenitic stainless steels are as follows: According to the design proportion of elements, the raw elemental materials with a purity >_ 99.9% were weighed and mixed. The argon arc furnace was vacuumed to a pressure below 5.0 ⁇ 10 -3 Pa and then filled with argon to a pressure of 5.0 ⁇ 10 3 Pa. When the oxygen content and nitrogen content in the furnace were lower than 0.002% within 180 min, 30 g of pure Ti was melted first to remove oxygen and then the arc melting was started. A 60 ⁇ 10 ⁇ 5 mm 3 flake ingot was obtained by the arc melting for 6 times.
  • the ingot was placed in a furnace for solution and homogenization treatment.
  • the ingot was heated to 1150 °C at a rate of 15 °C/min, remained at 1150 °C for 120 min, and then quenched in water.
  • Cold rolling deformation was performed for the ingot after the solution/homogenization treatment.
  • the rolling process was as follows: the reduction in thickness per pass was no more than 0.2 mm, and the total reduction in thickness was 66.7%.
  • the rolled ingot was heated to 1150 °C at a rate of 10 °C/min and recrystallized at 1150 °C for 1.5 min.
  • the recrystallized ingot was heated to 600 °C at a rate of 10 °C/min, remained at 600 °C for 1 h, and then quenched in water to complete the aging treatment.
  • the conventional Cu K ⁇ radiation was used as the X-ray source for x-ray diffraction.
  • the diffraction pattern was shown in FIG. 1 , where the diffraction peaks can be indexed as the (111), (200), (220), (311), (222) diffraction peaks of a face-centered structure, so the obtained structure was austenitic. Because the size of the nano-sized precipitates was too small, they did not exhibit any visible diffraction peak on the X-ray diffraction patterns.
  • This embodiment provides a high-entropy austenitic stainless steel with a chemical composition of Fe 47 Cr 16 Ni 26 Ti 6 Al 5 (atomic ratio) or Fe 48.56 Cr 15.39 Ni 28.24 Ti 5.32 Al 2.5 (weight ratio).
  • the influence of the introduction of unavoidable and very few impurity elements (C, N, O, etc.) during the melting process and heat treatment process on the properties of the material can be ignored.
  • the preparation steps of the high-entropy austenitic stainless steel are as follows: According to the design proportion of elements, the raw elemental materials with a purity >_ 99.9% were weighed and mixed. The argon arc furnace was vacuumed to a pressure below 5.0 ⁇ 10 -3 Pa and then filled with argon to a pressure of 5.0 ⁇ 10 3 Pa. When the oxygen content and nitrogen content in the furnace were lower than 0.002% within 180 min, 30 g of pure Ti was melted first to remove oxygen and then the arc melting was started. A 60 ⁇ 10 ⁇ 5 mm 3 flake ingot was obtained by the arc melting for 6 times.
  • the ingot was placed in a furnace for solution and homogenization treatment.
  • the ingot wash heated to 1150 °C at a rate of 15 °C/min, remained at 1150 °C for 120 min, and then cooled in air.
  • hot rolling and the subsequent cold rolling were performed.
  • the rolling process was as follows: the hot rolling temperature was 1150 °C, and the temperature was guaranteed to be in the range of 800 - 1150 °C during the hot rolling process. If the temperature was reduced during the hot rolling, the ingot can be put back into the furnace and remained at the desired rolling temperature for 5 - 15 min.
  • the reduction in thickness per rolling pass was no more than 0.5 mm, and the total reduction in thickness was 50% during the hot rolling.
  • the reduction in thickness per rolling pass was no more than 0.2 mm, and the total reduction in thickness was 66.7%.
  • the rolled ingot was heated to 1140 °C at a rate of 15 °C/min and recrystallized at 1140 °C for 1.5 min.
  • the recrystallized ingot was heated to 550 °C at a rate of 15 °C/min, remained at 550 °C for 1.5 h, and then cooled in the air to complete the aging treatment.
  • the material was characterized by transmission electron microscopy.
  • the transmission electron microscopy and element distribution image was shown in FIG. 2 .
  • a large number of spherical nano-sized precipitates were distributed in the stainless steel matrix, whose composition was Ni-Ti-Al.
  • the crystal structure was face-centered cubic.
  • the average size and number density of the nano-sized precipitates were 14.4 nm and 1.68 ⁇ 10 22 m -3 , respectively.
  • This embodiment provides a high-entropy austenitic stainless steel with a chemical composition of Fe 39 Cr 20 Ni 30 Ti 6 Al 5 (atomic ratio) or Fe 40.33 Cr 19.25 Ni 32.6 T 5.32 Al 2.5 (weight ratio).
  • the influence of the introduction of unavoidable and very few impurity elements (C, N, O, etc.) during the melting process and heat treatment process on the properties of the material can be ignored.
  • the preparation steps of the high-entropy austenitic stainless steel are as follows: According to the design proportion of elements, the raw elemental materials with a purity >_ 99.9% were weighed and mixed. The argon arc furnace was vacuumed to a pressure below 5.0 ⁇ 10 -3 Pa and then filled with argon to a pressure of 5.0 ⁇ 10 3 Pa. When the oxygen content and nitrogen content in the furnace were lower than 0.002% within 180 min, 35 g of pure Ti was melted first to remove oxygen and then the arc melting was started. A 60 ⁇ 10 ⁇ 5 mm 3 flake ingot was obtained by the arc melting for 5 times.
  • the ingot was placed in a furnace for solution/homogenization treatment.
  • the ingot was heated to 1150 °C at a rate of 15 °C/min, remained at 1150 °C for 120 min, and then quenched in water.
  • cold rolling was performed.
  • the cold rolling process was as follows: the reduction in thickness per rolling pass was no more than 0.2 mm, and the total reduction in thickness was 66.7%.
  • the cold-rolled ingot was heated to 1145 °C at a rate of 18 °C/min and recrystallized at 1145 °C for 1.5 min.
  • the recrystallized ingot was heated to 600 °C at a rate of 12 °C/min, remained at 600 °C for 1 h, and then quenched in water to complete the aging treatment.
  • This embodiment provides a high-entropy austenitic stainless steel with a chemical composition of Fe 31 Cr 24 Ni 34 Ti 6 Al 5 (atomic ratio) or Fe 32 . 08 Cr 23.12 Ni 36.98 Ti 5.32 Al 2.5 (weight ratio).
  • the influence of the introduction of unavoidable and very few impurity elements (C, N, O, etc.) during the melting process and heat treatment process on the properties of the material can be ignored.
  • the preparation steps of the high-entropy austenitic stainless steel are as follows: According to the design proportion of elements, the raw elemental materials with a purity >_ 99.9% were weighed and mixed. The argon arc furnace was vacuumed to a pressure below 5.0 ⁇ 10 -3 Pa and then filled with argon to a pressure of 5.0 ⁇ 10 3 Pa. When the oxygen content and nitrogen content in the furnace were lower than 0.002% within 180 min, 40 g of pure Ti was melted first to remove oxygen and then the arc melting was started. A 60 ⁇ 10 ⁇ 5 mm 3 flake ingot was obtained by the arc melting for 5 times.
  • the ingot was placed in a furnace for solution/homogenization treatment.
  • the ingot was heated to 1150 °C at a rate of 15 °C/min, remained at 1150 °C for 120 min, and then quenched in water.
  • cold rolling deformation was performed for the ingot.
  • the cold rolling process was as follows: the reduction in thickness per pass was no more than 0.2 mm, and the total reduction in thickness was 66.7%.
  • the cold-rolled ingot was heated to 1155 °C at a rate of 10 °C/min and recrystallized at 1155 °C for 1.5 min.
  • the recrystallized ingot was heated to 600 °C at a rate of 10 °C/min, remained at 600 °C for 1 h, and then quenched in water to complete the aging treatment.
  • This embodiment of the invention provides a high-entropy austenitic stainless steel with a chemical composition of Fe 42 Cr 16 Ni 28 Ti 7 Al 7 (atomic ratio) or Fe 43.88 Cr 15.56 Ni 30.75 Ti 6.27 Al 3.53 (weight ratio).
  • the influence of the introduction of unavoidable and very few impurity elements (C, N, O, etc.) during the melting process and heat treatment process on the properties of the material can be ignored.
  • the preparation steps of the high-entropy austenitic stainless steel are as follows: According to the design proportion of elements, the raw elemental materials with a purity >_ 99.9% were weighed and mixed. The argon arc furnace was vacuumed to a pressure below 5.0 ⁇ 10 -3 Pa and then filled with argon to a pressure of 5.0 ⁇ 10 3 Pa. When the oxygen content and nitrogen content in the furnace were lower than 0.002% within 180 min, 35 g of pure Ti was melted first to remove oxygen and then the arc melting was started. A 60 ⁇ 10 ⁇ 5 mm 3 flake ingot was obtained by the arc melting for 6 times.
  • the ingot was placed in a furnace for solution and homogenization treatment.
  • the ingot was heated 1150 °C at a rate of 15 °C/min, remained at 1150 °C for 120 min, and then quenched in water.
  • cold rolling deformation was performed for the ingot.
  • the cold rolling process was as follows: the reduction in thickness per pass was no more than 0.2 mm, and the total reduction in thickness was 66.7%.
  • the cold-rolled ingot was heated to 1160 °C at a rate of 20 °C/min and recrystallized at 1160 °C for 1.5 min.
  • the recrystallized ingot was heated to 600 °C at a rate of 10 °C/min, remained at 600 °C for 1 h, and then quenched in water to complete the aging treatment.
  • the embodiment of the invention provides a high-entropy austenitic stainless steel with a chemical composition of Fe 49 Cr 16 Ni 28 Ti 4 Al 3 (atomic ratio) or Fe 49.9 Cr 15.17 Ni 29.98 Ti 3.49 Al 1.48 (weight ratio).
  • the influence of the introduction of unavoidable and very few impurity elements (C, N, O, etc.) during the melting process and heat treatment process on the properties of the material can be ignored.
  • the preparation steps of the high-entropy austenitic stainless steel are as follows: According to the design proportion of elements, the raw elemental materials with a purity >_ 99.9% were weighed and mixed. The argon arc furnace was vacuumed to a pressure below 5.0 ⁇ 10 -3 Pa and then filled with argon to a pressure of 5.0 ⁇ 10 3 Pa. When the oxygen content and nitrogen content in the furnace were lower than 0.002% within 180 min, 30 g of pure Ti was melted first to remove oxygen and then the arc melting was started. A 60 ⁇ 10 ⁇ 5 mm 3 flake ingot was obtained by the arc melting for 6 times.
  • the ingot was placed in a furnace for solution and homogenization treatment.
  • the ingot was heated to 1150 °C at a rate of 15 °C/min, remained at 1150 °C for 120 min, and then quenched in water.
  • cold rolling deformation was performed for the ingot.
  • the cold rolling process was as follows: the reduction in thickness per pass was no more than 0.2 mm, and the total reduction in thickness was 66.7%.
  • the cold-rolled ingot was heated to 1150 °C at a rate of 10 °C/min and recrystallized at 1150 °C for 1.5 min.
  • the recrystallized ingot was heated to 600 °C at a rate of 10 °C/min, remained at 600 °C for 1 h, and then quenched in water to complete the aging treatment.
  • Embodiment 1 820 ⁇ 10 1220 ⁇ 15 35.5 ⁇ 2.6 0.67 Embodiment 2 810 ⁇ 5 1215 ⁇ 12 33.2 ⁇ 3.5 0.67 Embodiment 3 980 ⁇ 22 1340 ⁇ 24 22.4 ⁇ 4.5 0.73 Embodiment 4 1210 ⁇ 18 1510 ⁇ 22 10.2 ⁇ 1.6 0.80 Embodiment 5 1050 ⁇ 20 1425 ⁇ 35 16.7 ⁇ 1.5 0.74 Embodiment 6 680 ⁇ 20 1165 ⁇ 30 37.8 ⁇ 2.2 0.56
  • FIG. 3 is an engineering stress-strain curve of high-entropy austenitic stainless steel measured at room temperature at a strain rate of 1 ⁇ 10 -3 s -1 .
  • the yield strength, tensile strength, and fracture elongation of the high-entropy austenitic stainless steel are shown in Table 1.
  • the figure shows that the yield strength, ultimate tensile strength, and fracture elongation of the optimized high-entropy austenitic stainless steel are 820 MPa, 1220 MPa, and 37 %, respectively.
  • FIG. 4 is a comparison of the yield strength R eL and fracture elongation E of commercial stainless steels and the high-entropy austenitic stainless steels of the invention. This figure shows that the high-entropy austenitic stainless steels of the invention have yield strength higher than those of most commercial stainless steels and maintain a high plasticity.
  • the product of yield strength and fracture elongation is 14.5 - 30.3 GPa%, which is higher than those (2.62 - 17.2 GPa%) of commercial stainless steels.
  • FIG. 5 is a comparison of the tensile strength R m and the fracture elongation E of commercial stainless steels and the high-entropy austenitic stainless steels of the invention. This figure shows that the high-entropy austenitic stainless steels of the invention maintain a high plasticity and high tensile strength.
  • the product of tensile strength and fracture elongation is 18.0 - 46.1 GPa%, which is higher than those (2.9 - 42.8 GPa%) of commercial stainless steels.
  • FIG. 6 is a comparison of the yield strength and the product of strength and plasticity [ultimate tensile strength (UTS) ⁇ fracture elongation] of commercial stainless steels and the high-entropy austenitic stainless steels of the invention.
  • UTS timate tensile strength
  • FIG. 6 shows that the yield strength and the product of strength and elongation of the high-entropy austenitic stainless steels of the invention are higher than those of commercial stainless steels.
  • the high-entropy austenitic stainless steels maintain a high plasticity and high-strength, and their comprehensive performance is better than that of commercial stainless steels.

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EP22897547.0A 2021-11-23 2022-10-31 Acier inoxydable austénitique haute entropie et son procédé de préparation Pending EP4257717A1 (fr)

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