WO2023246465A1 - 一种用于630℃以上的马氏体耐热钢及其制备方法 - Google Patents

一种用于630℃以上的马氏体耐热钢及其制备方法 Download PDF

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WO2023246465A1
WO2023246465A1 PCT/CN2023/097809 CN2023097809W WO2023246465A1 WO 2023246465 A1 WO2023246465 A1 WO 2023246465A1 CN 2023097809 W CN2023097809 W CN 2023097809W WO 2023246465 A1 WO2023246465 A1 WO 2023246465A1
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heat
resistant steel
temperature
tempering
martensitic
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PCT/CN2023/097809
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French (fr)
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朱琳
霍洁
李晓
陈楚
郭秀斌
伊鹏跃
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中国第一重型机械股份公司
天津重型装备工程研究有限公司
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Publication of WO2023246465A1 publication Critical patent/WO2023246465A1/zh

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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
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/18—Hardening; Quenching with or without subsequent tempering
    • 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
    • C21D1/28—Normalising
    • 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
    • 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
    • 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
    • C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous alloys
    • 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
    • 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
    • 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
    • C21D8/06—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires
    • 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
    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
    • 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
    • C22C38/005—Ferrous alloys, e.g. steel alloys containing rare earths, i.e. Sc, Y, Lanthanides
    • 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
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • 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
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing 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
    • C22C38/06—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
    • 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
    • C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
    • 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
    • C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
    • 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
    • C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
    • 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
    • C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel with niobium or tantalum
    • 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
    • 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
    • C22C38/52—Ferrous alloys, e.g. steel alloys containing chromium with nickel with cobalt
    • 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
    • C22C38/54—Ferrous alloys, e.g. steel alloys containing chromium with nickel with boron
    • 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 invention belongs to the technical field of metal materials, and specifically relates to a martensitic heat-resistant steel used above 630°C and a preparation method thereof.
  • thermal power generation technology is currently developing in the direction of high parameters, secondary reheating, cleanliness and efficiency, and making full use of advanced ultra-supercritical coal-fired power generation technology.
  • thermal power generation is upgraded from subcritical to ultra-supercritical conditions, 68g of coal can be saved per kilowatt hour of electricity, and coal consumption in power supply can be reduced by 21%.
  • China can save 232 million tons of coal every year and reduce 510 million tons of CO 2 emissions annually.
  • martensitic heat-resistant steel materials in large castings and forgings of high-parameter steam turbines is still a technical bottleneck that restricts the improvement of power plant parameters.
  • 630°C steam turbine rotor forgings there are currently no mature products at home and abroad, and there are a large number of 620°C steam turbine rotors. Rely on imports.
  • the present invention aims to provide a martensitic heat-resistant steel for use above 630°C and a preparation method thereof, which has comprehensive properties such as high-temperature strength, impact resistance, permanent creep resistance and oxidation resistance. Good, suitable for ultra-supercritical steam turbine rotors with operating temperatures of 630°C and above.
  • the present invention has conducted a large number of experimental studies and developed a The new martensitic heat-resistant steel, by adding tantalum element, uses high-temperature stable fine chromium-tantalum nitride instead of MX as the precipitation strengthening phase.
  • the invention provides a martensitic heat-resistant steel for use above 630°C.
  • its components include: C: 0.01%-0.14%, Si: 0.05%-0.50%, Mn: 0.05%- 0.70%, Cr: 8.5%-13%, W: 2.0%-3.5%, Mo: 0.1%-0.7%, Nb: 0.03%-0.07%, V: 0.1%-0.3%, Co: 2.8%-5% , Cu: 0.8%-1.5%, Ni: 0.1%-0.5%, B: 0.01%-0.015%, N: 0.01%-0.08%, Ta: 0.2%-0.5%, Zr: 0.1%-0.5%, Ce +Y: 0.01%-0.3%, the remaining components are Fe and inevitable impurities.
  • a martensitic heat-resistant steel used above 630°C the composition in terms of mass percentage includes: C: 0.01%-0.14%, Si: 0.05%-0.50%, Mn: 0.05%-0.70% , Cr: 8.5%-13%, W: 2.0%-3.5%, Mo: 0.1%-0.7%, Nb: 0.03%-0.07%, V: 0.1%-0.3%, Co: 2.8%-5%, Cu : 0.8%-1.2%, Ni: 0.1%-0.5%, B: 0.01%-0.015%, N: 0.01%-0.08%, Ta: 0.28%-0.45%, Zr: 0.1%-0.5%, Ce+Y :0.1%-0.2%, the remaining components are Fe and inevitable impurities.
  • the microstructure of the heat-resistant steel is a complete tempered martensite structure and a precipitated phase
  • the precipitated phase includes dispersed M23C6 carbide, CrTaN phase, Laves phase and nanoscale dispersion-strengthened Cu. Mutually.
  • the invention is used for martensitic heat-resistant steel above 630°C.
  • Ta element in addition to adding a small amount of V and Nb elements, 0.2%-0.5% Ta element is also added.
  • An appropriate amount of Ta element will form a CrTaN phase that is not easy to coarsen, thereby avoiding the easy formation and The formation of the coarsened Cr(V, Nb)N phase.
  • the coarsening of this phase will deteriorate the durability and also avoid the coarsening caused by the transformation of MX to Cr(Nb, V)N during the long-term service of this steel. Sudden drop in performance;
  • the present invention controls the carbon content at a lower level and forms finely dispersed M23C6 through the lower C content, which plays a dispersion strengthening effect; by adding a certain amount of Cu element to suppress It can control the formation of high-temperature ferrite, and at the same time, the precipitation of nano-scale copper-rich phase can make up for the lack of V and Nb, play the role of precipitation strengthening, and improve the lasting strength of heat-resistant steel; add an appropriate amount of B element to replace the C of M23C6 The position of the element forms M23(C,B)6, thereby reducing the coarsening rate of M23C6 near the original austenite grain boundary and significantly improving the creep strength; using an appropriate amount of W element improves the lasting strength; using a small amount of Ni element, A higher Co content is used to improve the matrix toughness; through a reasonable element ratio, the formation of high-temperature ferrite can be greatly avoided, providing a larger temperature window for the forging and heat treatment processes in actual production.
  • the invention also provides a method for preparing martensitic heat-resistant steel above 630°C, which includes the following steps:
  • Step S1 Weigh the raw materials according to the content of each component in the component ratio, smelt it in a vacuum induction furnace, and pour it into an ingot, and strictly control the content of impurity elements.
  • the component ratio is based on mass percentage, including: C: 0.01%-0.14%, Si: 0.05%-0.50%, Mn: 0.05%-0.70%, Cr: 8.5%-13%, W: 2.0%-3.5%, Mo: 0.1%-0.7%, Nb: 0.03% -0.07%, V: 0.1%-0.3%, Co: 2.8%-5%, Cu: 0.8%-1.5%, Ni: 0.1%-0.5%, B: 0.01%-0.015%, N: 0.01%-0.08 %, Ta: 0.2%-0.5%, Zr: 0.1%-0.5%, Ce+Y: 0.01%-0.3%, the remaining components are Fe and inevitable impurities;
  • Step S2 Perform high-temperature homogenization treatment on the ingot obtained in step S1, keep it warm, and then cool it to room temperature with the furnace to obtain a billet;
  • Step S3 Forge the blank obtained in step S2 by rounding, piercing or drawing.
  • the temperature during the forging process is lower than the final forging temperature, return to the furnace for heating and then forge. After forging, the furnace is cooled to room temperature;
  • Step S4 Perform normalizing and two tempering heat treatments on the forged rod obtained in step S3 to obtain chromium-tantalum nitride reinforced martensitic heat-resistant steel; wherein the first tempering temperature is lower than the second tempering temperature.
  • the temperature of the high-temperature homogenization treatment is 1160-1200°C, and the holding time is 4-8 hours.
  • step S3 the initial forging temperature in the forging process is 1160-1200°C, and the final forging temperature is 850-950°C.
  • step S4 includes the following steps:
  • Step S401 Normalizing.
  • the normalizing process is to heat the forged rod to 1050-1150°C and keep it warm, and then air-cool to room temperature;
  • Step S402 First tempering.
  • the first tempering process is to heat the forged rod to 600-700°C, keep it warm, and then air-cool to room temperature;
  • Step S403 Second tempering.
  • the second tempering process is to heat the forged rod to 680-780°C, keep it warm, and then air-cool it to room temperature.
  • the heating rate is less than or equal to 100°C/h, and the heat preservation time is 1-10 h.
  • step S402 the heat preservation time is 5-10 hours.
  • step S403 the heat preservation time is 5-10 hours.
  • the preparation process of the martensitic heat-resistant steel above 630°C provided by the present invention is achieved by accurately controlling the time and temperature of high-temperature homogenization treatment, forging temperature, normalizing temperature and time, and secondary tempering.
  • Process parameters such as temperature and time ensure that the obtained microstructure is a complete tempered martensite structure and precipitated phases.
  • the precipitated phases include finely dispersed M23C6 carbide, CrTaN phase, a small amount of fine Laves phase and nanoscale dispersion.
  • Strengthened Cu phase It ensures the excellent room temperature strength, high temperature strength, durable creep resistance and oxidation resistance of heat-resistant steel, and is suitable for ultra-supercritical steam turbine rotors above 630°C.
  • Figure 1 is a cast structure diagram of heat-resistant steel in Example 1 of the present invention.
  • Figure 2 is the homogenized structure of the heat-resistant steel in Example 1 of the present invention.
  • Figure 3 shows the quenched and tempered structure of the heat-resistant steel in Example 1 of the present invention.
  • the invention provides a martensitic heat-resistant steel for use above 630°C.
  • its components include: C: 0.01%-0.14%, Si: 0.05%-0.50%, Mn: 0.05%-0.70 %, Cr: 8.5%-13%, W: 2.0%-3.5%, Mo: 0.1%-0.7%, Nb: 0.03%-0.07%, V: 0.1%-0.3%, Co: 2.8%-5%, Cu: 0.8%-1.5%, Ni: 0.1%-0.5%, B: 0.01%-0.015%, N: 0.01%-0.08%, Ta: 0.2%-0.5%, Zr: 0.1%-0.5%, Ce+Y: 0.01%-0.3%, and the remaining components are Fe and inevitable impurities.
  • the heat-resistant steel provided by the present invention has a lower C content and a higher Co content, and is added with reinforcing elements such as Ta and Cu as well as Ce+Y rare earth elements.
  • the heat-resistant steel provided by the present invention does not add V and Nb elements, and can avoid the formation of the Cr(V, Nb)N phase that is easily formed and coarsened during the durability process. The coarsening of this phase will deteriorate the durability performance.
  • Ta element 0.2%-0.5% is added in the present invention.
  • An appropriate amount of Ta element will form a CrTaN phase that is not easy to coarsen, which can avoid the coarsening of MX to Cr(Nb, V)N during long-term service. A sudden drop in performance caused by changes.
  • the heat-resistant steel provided by the present invention forms finely dispersed M 23 C 6 through a lower C content, which plays a dispersion strengthening effect; 0.8%-1.5% Cu element is added.
  • the Cu element acts as an austenite-forming element to suppress high temperatures.
  • the precipitation of nanoscale copper-rich phases can make up for the lack of V and Nb, play a role in precipitation strengthening, and improve the lasting strength of heat-resistant steel; an appropriate amount of B element can replace M 23 C 6
  • the position of the C element forms M 23 (C,B) 6 , thereby reducing the M 23 C 6 coarsening rate near the original austenite grain boundary and significantly improving the creep strength; using an appropriate amount of W element improves the lasting strength ;
  • Use a small amount of Ni element and a higher Co content to improve the toughness of the matrix.
  • the heat-resistant steel provided by the invention has the characteristics of high strength, resistance to persistent creep, and oxidation resistance.
  • the room temperature yield strength of the martensitic heat-resistant steel prepared by the invention is greater than 660MPa, the tensile strength is greater than 850MPa, and the elongation is more than 16%.
  • the area shrinkage is more than 50%, and the impact energy is more than 20J.
  • the yield strength at 630°C is greater than 280Mpa, the tensile strength is greater than 380Mpa, the elongation is more than 22%, the area shrinkage is more than 62%, the creep rupture time at 650°C and 180MPa is more than 3500h, and it can withstand 650°C oxidation weight gain (400h) 0.3mg/ m2 or less, excellent overall performance.
  • C An important precipitation strengthening element, M23C6 and MX dispersion strengthening, improving long-lasting creep performance; C is a strong austenite stabilizing element, which can reduce the formation of ⁇ -ferrite; improve hardenability and precipitation strengthening; Carbon Too high content can lead to excessive consumption of solid solution elements (such as Cr, W) and reduce grain boundary resistance. The corrosion ability will deteriorate the welding performance and have a negative impact on the durable creep performance; too low will cause insufficient strengthening and reduce the strength and hardness. Therefore, the mass percentage of C in the present invention is controlled at 0.01%-0.14%.
  • Si It is beneficial to improve the strength and steam corrosion resistance of the material matrix; as the Si content increases, the oxidation resistance increases sharply; the increased Si content will promote the formation of high-temperature ferrite and reduce the formation temperature of high-temperature ferrite, which is beneficial to The forging temperature range will have adverse effects. At the same time, too high Si content is detrimental to the impact toughness of the material. The lasting strength of the material decreases as the Si content increases. Therefore, the mass percentage of Si in the present invention is controlled at 0.05%-0.50%.
  • Mn Improves strength, improves thermal processing performance, and can also stabilize P, S, etc.
  • Mn does not play a significant role; when the content is higher than 1%, a second phase may appear in the structure, which is harmful to the impact toughness of the material. Therefore, the mass percentage of Mn in the present invention is controlled at 0.05%-0.70%.
  • Cr The most critical element to resist corrosion and oxidation. Cr element itself has excellent resistance to creep deformation. It is also the main element in heat-resistant steel to improve its resistance to steam oxidation and corrosion, and can improve the high-temperature strength of steel. When there is enough Cr, it can react with O to form a Cr2O3 protective film on the surface of the alloy matrix, preventing the diffusion of O atoms and metal ions, thus delaying the oxidation process. In addition, Cr is also an important precipitation strengthening element, which can form M23C6 precipitation strengthening with C. When the Cr content is too high, delta ferrite will be produced and the high-temperature thermal strength will be reduced, because the Cr element content range is set at 9-13%.
  • W A typical solid solution strengthening element.
  • the solid solution strengthening effect is more obvious than that of Mo element. It can stabilize the fine distribution of M23C6 and promote its precipitation strengthening.
  • the increase of W element can significantly improve the high temperature strength and creep performance of heat-resistant steel.
  • the W element below 2.0% cannot meet the long-term creep requirements of heat-resistant steel at temperatures of 630°C and above.
  • W exceeds 3.5% it will lead to the formation of high-temperature ferrite.
  • the mass percentage of W in the present invention is controlled at 2.0%-3.5%.
  • Mo W and Mo composite addition can improve the toughness and plasticity of the material, have good hot workability and improve impact performance.
  • Co is an austenite stabilizing element that inhibits the formation of ⁇ -ferrite, improves the high-temperature strength of the material, and inhibits the coarsening of M23C6; the mass percentage of Co in the present invention is controlled at 2.8%-5%.
  • Cu element can inhibit the formation of ⁇ -ferrite.
  • the addition of Cu is beneficial to improving the solid solution strengthening effect of W and improving the high-temperature creep strength of W-containing martensitic heat-resistant steel.
  • the presence of Cu itself in the form of nano-Cu-rich particles can also play a precipitation strengthening role.
  • the mass percentage of Cu in the present invention is controlled at 0.5%-1.5%.
  • Ni a typical austenite-forming element that can improve toughness and balance the Cr equivalent of the material; in the present invention, the mass percentage of Ni is controlled at 0.1%-0.5%.
  • the B element can replace the position of the C element in M23C6 to form M23(C,B)6.
  • M23(C,B)6 has a slow aging rate and good durability, thereby reducing The coarsening rate of M23C6 near the original austenite grain boundary inhibits the coarsening of M23C6 and improves the creep strength of steel;
  • B can purify the grain boundary and form M23(C0.85B0.15)6 carbon boride; while too high
  • the B content will reduce high-temperature plasticity and increase the risk of forging cracking. Therefore, the mass percentage of B in the present invention is controlled at 0.01%-0.015%.
  • N It can form fine dispersed second phase particles with V, Nb, and Ta, which significantly improves the high-temperature durability strength of the material; however, when the N content is too high, it combines with the B element to form coarse BN particles, seriously weakening the strength and toughness of the steel. The B element used for grain boundary strengthening will also be consumed, seriously damaging the high-temperature durable strength of steel. Therefore, the mass percentage of N in the present invention is controlled at 0.01%-0.08%.
  • Ta As the Cr element content in this steel increases to about 12%, during long-term aging and use at 600-650°C, the Cr in the matrix will aggregate toward MX and further form Cr(Nb, V)N, thereby consuming The Cr element in the matrix also causes the coarsening of the precipitated phase, further promoting the generation of Cr(Nb, V)N. 12Cr is more likely to form coarse chromium vanadium or chromium niobium nitride phase than 9Cr steel, which is not conducive to pinning dislocations. and laths, thereby affecting the lasting strength of the steel.
  • Adding an appropriate amount of Ta element will inhibit the transformation of MX into Cr(Nb, V)N, and instead form a phase dominated by CrTaN.
  • This CrTaN phase is less likely to be coarse than the Cr(Nb, V)N phase.
  • the mass percentage of Ta is controlled at 0.2%-0.5%.
  • Zr The tendency of austenite grains to grow becomes smaller as the Zr content increases, and will reduce the size of inclusions. Therefore, the mass percentage of Zr in the present invention is controlled at 0.1%-0.5%.
  • Rare earth elements are rare earth elements. Adding a small amount can improve the high temperature mechanical properties and corrosion resistance of heat-resistant steel. The addition of mixed rare earth elements can exert a synergistic effect, purify and strengthen grain boundaries, control the number and shape of inclusions, thereby improving high-temperature strength and antioxidant properties. The present invention combines rare earth elements The addition amount is 0.01%-0.3%.
  • a martensitic heat-resistant steel for use above 630°C has components in terms of mass percentage: C: 0.01%-0.14%, Si: 0.05%-0.50%, Mn: 0.05%-0.70% , Cr: 8.5%-13%, W: 2.0%-3.5%, Mo: 0.1%-0.7%, Nb: 0.03%-0.07%, V: 0.1%-0.3%, Co: 2.8%-5%, Cu : 0.8%-1.2%, Ni: 0.1%-0.5%, B: 0.01%-0.015%, N: 0.01%-0.08%, Ta: 0.28%-0.45%, Zr: 0.1%-0.5%, Ce+Y :0.1%-0.2%, the remaining components are Fe and inevitable impurities.
  • the invention also provides a method for preparing martensitic heat-resistant steel above 630°C, which includes the following steps:
  • Step S1 Weigh the raw materials according to the content of each component in the component ratio, smelt it in a vacuum induction furnace, and pour it into an ingot, and strictly control the content of impurity elements.
  • the component ratio is based on mass percentage, including: C: 0.01%-0.14%, Si: 0.05%-0.50%, Mn: 0.05%-0.70%, Cr: 8.5%-13%, W: 2.0%-3.5%, Mo: 0.1%-0.7%, Nb: 0.03% -0.07%, V: 0.1%-0.3%, Co: 2.8%-5%, Cu: 0.8%-1.5%, Ni: 0.1%-0.5%, B: 0.01%-0.015%, N: 0.01%-0.08 %, Ta: 0.2%-0.5%, Zr: 0.1%-0.5%, Ce+Y: 0.01%-0.3%, the remaining components are Fe and inevitable impurities;
  • Step S2 Perform high-temperature homogenization treatment on the ingot obtained in step S1, keep it warm, and then cool it to room temperature with the furnace to obtain a billet;
  • Step S3 Forge the blank obtained in step S2 by rounding, piercing or drawing.
  • the temperature during the forging process is lower than the final forging temperature, return to the furnace for heating and then forge. After forging, the furnace is cooled to room temperature;
  • Step S4 Perform normalizing and two tempering heat treatments on the forged rod obtained in step S3 to obtain chromium-tantalum nitride reinforced martensitic heat-resistant steel; wherein the first tempering temperature is lower than the second tempering temperature.
  • the purpose of the high-temperature homogenization treatment is to eliminate the segregation of high-temperature ferrite, precipitated phases and alloy elements in the ingot. If the high-temperature homogenization temperature is too high, it will lead to severe grain coarsening and the formation of high-temperature ferrite. If the temperature is too low, it will not be able to effectively eliminate precipitated phases such as delta ferrite and M3B2 and element segregation in the casting structure. After extensive experimental research, the high-temperature homogenization temperature is controlled to 1160-1200°C. The holding time is controlled at 4-8 hours. A holding time that is too short is not enough to eliminate high-temperature ferrite, precipitated phases, element segregation, etc. in the ingot. A time that is too long may cause overheating, overburning, and coarse grains.
  • step S3 defects can be compacted, grains refined, and uniform Structure and other purposes (the quenched and tempered structure of the heat-resistant steel in Example 1 is shown in Figure 3), thereby laying a good foundation for improving the comprehensive performance of the heat-resistant steel.
  • the initial forging temperature is higher than 1200°C, high-temperature ferrite will be formed, increasing the risk of forging cracks.
  • an excessively high initial forging temperature will cause serious grain coarsening, making it more difficult to control the grain size in the subsequent forging process. If there are excessively large grains and mixed crystals after forging, it will affect the final mechanical properties on the one hand, and also affect the flaw detection on the other hand.
  • the present invention controls the initial forging temperature to be 1160-1200°C and the final forging temperature to be 850-950°C.
  • the steel has good plasticity.
  • the initial forging temperature of the present invention is about 100°C higher than that of similar steels, greatly increasing the forging temperature range.
  • step S4 includes the following steps:
  • Step S401 Normalizing.
  • the normalizing process is to heat the forged rod to 1050-1150°C and keep it warm, and then air-cool to room temperature;
  • Step S402 First tempering.
  • the first tempering process is to heat the forged rod to 600-700°C, keep it warm, and then air-cool to room temperature;
  • Step S403 Second tempering.
  • the second tempering process is to heat the forged rod to 680-780°C, keep it warm, and then air-cool it to room temperature.
  • the forged rods are placed at room temperature. into the heating furnace, the heating rate is less than or equal to 100°C/h.
  • the holding time is controlled to 1-10h.
  • the function of the first tempering is to promote the precipitation of CrTaN and fix the N element into the CrTaN phase. Because around 650°C is the temperature range where CrTaN is most likely to precipitate in 12% Cr steel. Tempering at this temperature can form a very fine and dispersed CrTaN phase. This CrTaN phase is less likely to grow than other MX, Cr23C6, Laves and other precipitated phases. If the tempering temperature is too high, a large amount of carbides will precipitate, making the horse The laths of the lath structure are broadened and the dislocation density is reduced, resulting in a serious decrease in strength.
  • the tempering temperature is too low to promote the precipitation of CrTaN. If the holding time is too long, the performance will soften; if the holding time is too short, it will be insufficient for heat penetration and element diffusion. Therefore, control the tempering temperature to 600-700°C and the holding time to 5-10h.
  • the function of the second tempering is to form a complete tempered martensite group.
  • the tempering temperature is too high, and the strength is insufficient; the tempering temperature is too low, the impact is too low, and the holding time is too long, which will cause the size of the precipitated phase to grow, and neither the strength nor the impact value meet the performance requirements; If the holding time is too short, the forging will not be sufficiently heated and tempered martensite will form. Therefore, control the tempering temperature to 680-780°C and the holding time to 5-10h.
  • the above-mentioned normalizing temperature can completely eliminate precipitated phases such as M23C6, M3B2, Laves, etc., so that the alloy elements are completely dissolved in the matrix, and the grain size is controlled within level 2 without forming ⁇ - ferrite.
  • the first low-temperature tempering can promote the precipitation of CrTaN and fix the N element into the CrTaN phase.
  • the second high-temperature tempering tempers the newly transformed martensite to ensure that the final structure is all uniform tempered martensite. + Precipitated phase, the proportions of tempered martensite and precipitated phase are 98% and 2% respectively.
  • the precipitated phase is finely dispersed and distributed on lath boundaries and grain boundaries, which plays a very good strengthening role.
  • the structure of the heat-resistant steel after the above heat treatment is a complete tempered martensite structure + precipitated phase.
  • the precipitated phase is mainly fine and dispersed M23C6, CrTaN, a small amount of fine Laves phase and nano-scale dispersion-strengthened Cu phase.
  • the room temperature yield strength of the heat-resistant steel after the above heat treatment is greater than 660MPa, the tensile strength is greater than 850MPa, the elongation is greater than 16%, the section shrinkage is greater than 50%, and the impact energy is greater than 20J.
  • the yield strength at 630°C is greater than 280Mpa, the tensile strength is greater than 380Mpa, the elongation is more than 22%, the area shrinkage is more than 62%, the creep rupture time at 650°C and 180MPa is more than 3500h, and it can withstand 650°C oxidation weight gain (400h) 0.3mg/ m2 or less. Excellent performance.
  • This embodiment provides a martensitic heat-resistant steel used above 630°C and a preparation method thereof.
  • the chemical components of this embodiment include, in terms of weight percentage: C: 0.05%, Si: 0.30%, Mn: 0.50%, Cr: 12.0%, W: 3.0%, Mo: 0.2%, Nb: 0.05, V : 0.2%, Co: 4.5%, Ni: 0.2%, Cu: 1.0%, B: 0.01%, N: 0.045%, Ta: 0.32%, Zr: 0.3%, Ce+Y: 0.15%, the remaining components are Fe and unavoidable impurities.
  • Preparation methods of heat-resistant steel include:
  • Step S1 According to the proportion of alloy components, smelt and pour into ingots in a vacuum induction furnace, strictly Control the content of impurity elements;
  • Step S2 Perform high-temperature homogenization treatment on the ingot obtained in step S1, and then cool it to room temperature in the furnace to obtain a billet; wherein, the high-temperature homogenization temperature is 1180°C, and the holding time is 5 hours;
  • Step S3 Forge the blank obtained in step S2 by rounding, piercing or drawing.
  • the initial forging temperature is 1180°C and the final forging temperature is 950°C. If the forging temperature is lower than the final forging temperature during the forging process, it needs to be returned to the furnace and heated before forging;
  • Step S4 Perform normalizing and twice tempering heat treatment on the forged rod obtained in step S3 to obtain chromium-tantalum nitride reinforced martensitic heat-resistant steel; wherein, the normalizing temperature is 1100°C, the holding time is 5h; the first tempering temperature is 650°C °C, the first tempering and holding time is 6h; the second tempering temperature is 740°C, and the second tempering and holding time is 6h.
  • Example 1-4 and Comparative Example 1-2 The chemical composition of the steel in Example 1-4 and Comparative Example 1-2 is shown in Table 1.
  • the process steps of Example 2-4 are the same as those in Example 1.
  • the specific process parameters are shown in Table 2.
  • the chemical composition of the steel in Example 1-4 and Comparative Example 1-2 is shown in Table 1.
  • the properties of 2 are shown in Table 3 and Table 4, and the metallographic structures of Examples 1-4 and Comparative Examples 1-2 are shown in Table 5.
  • Comparative Example 1 Cu, Ta, Zr and rare earth elements were not added to its chemical composition; in Comparative Example 2, Ta element was not added to its chemical composition; the specific chemical composition is shown in Table 1.
  • the process steps of Comparative Example 1-2 are the same as those of Embodiment 1.
  • the specific process parameters are shown in Table 2.
  • the various performance indicators are shown in Table 3 in comparison with those of Embodiment 1-4. It can be seen from Table 3 that compared with the comparative example, the performance of the embodiment is more excellent.

Abstract

本发明公开了用于630℃以上的马氏体耐热钢及其制备方法，属于金属材料技术领域。耐热钢按质量百分比计，包括：C:0.01％-0.14％、Si:0.05％-0.50％、Mn:0.05％-0.70％、Cr:8.5％-13％、W:2.0％-3.5％、Mo:0.1％-0.7％，Nb:0.03％-0.07％、V:0.1％-0.3％、Co:2.8％-5％、Cu：0.8％-1.5％、Ni:0.1％-0.5％、B:0.01％-0.015％、N:0.01％-0.08％、Ta:0.2％-0.5％、Zr:0.1％-0.5％、Ce+Y:0.01％-0.3％，其余成分为Fe和不可避免的杂质。本发明的耐热钢综合性能良好。

Description

一种用于630℃以上的马氏体耐热钢及其制备方法
相关申请的交叉引用
本申请要求于2022年6月22日提交中国专利局，申请号为2022107134571，发明名称为“一种用于630℃以上的马氏体耐热钢及其制备方法”的中国专利申请的优先权，其全部内容通过引用结合在本申请中。
技术领域
本发明属于金属材料技术领域，具体涉及一种用于630℃以上的马氏体耐热钢及其制备方法。
背景技术
为实现节能减排目标，目前火力发电技术向高参数、二次再热和清洁高效的方向发展，并充分利用先进超超临界燃煤发电技术。例如，火力发电从亚临界状态升高到超超临界条件，每度电可节煤68g，供电煤耗可降低21％，我国每年可节约2.32亿吨煤，年减排5.1亿吨CO2。然而，目前应用于高参数汽轮机大型铸锻件马氏体耐热钢材料仍是制约电站参数提升的技术瓶颈，特别是应用于630℃汽轮机转子锻件目前国内外均无成熟产品，620℃汽轮机转子大量依赖进口。
因此，为攻克关键核心技术，高性能、高可靠性的耐热钢材料与产品的国产化迫在眉睫，机组参数的提高对材料性能要求也进一步提高，尤其对高应力高温度条件下的强韧性及持久性能要求更加苛刻。目前，国内外研究主要通过添加W、Co、B、N这些元素来进一步提高耐热钢的高温持久性能和抗氧化性能。但是，调整W、Co、B、Nb、N等元素对耐热钢高温持久性能和抗氧化性能的提高也是有限的，目前急需开拓一种新型的强化方式来进一步优化耐热钢的高温性能和抗氧化性能。
发明内容
鉴于上述分析，本发明旨在提供一种用于630℃以上的马氏体耐热钢及其制备方法，其高温强度、抗冲击性、抗持久蠕变和抗氧化性能等综合性能 良好，适用于工作温度为630℃及以上超超临界汽轮机转子。
针对超临界条件下，电站汽轮机组用耐热钢的选材需要，本发明进行了大量的实验研究，从控制10-12％Cr钢中氮化物析出相的微观形态的角度出发，开发了一种新型马氏体耐热钢，通过增加钽元素，利用高温稳定的细小铬钽氮化物代替MX作为析出强化相。
本发明的目的主要是通过以下技术方案实现的：
本发明提供了一种用于630℃以上的马氏体耐热钢，按质量百分比计，其成分包括：：C:0.01％-0.14％、Si:0.05％-0.50％、Mn:0.05％-0.70％、Cr:8.5％-13％、W:2.0％-3.5％、Mo：0.1％-0.7％，Nb:0.03％-0.07％、V:0.1％-0.3％、Co:2.8％-5％、Cu：0.8％-1.5％、Ni:0.1％-0.5％、B:0.01％-0.015％、N:0.01％-0.08％、Ta:0.2％-0.5％、Zr：0.1％-0.5％、Ce+Y：0.01％-0.3％，其余成分为Fe和不可避免的杂质。
进一步的，一种用于630℃以上的马氏体耐热钢，按质量百分比计，其成分包括：C:0.01％-0.14％、Si:0.05％-0.50％、Mn:0.05％-0.70％、Cr:8.5％-13％、W:2.0％-3.5％、Mo：0.1％-0.7％，Nb:0.03％-0.07％、V:0.1％-0.3％、Co:2.8％-5％、Cu：0.8％-1.2％、Ni:0.1％-0.5％、B:0.01％-0.015％、N:0.01％-0.08％、Ta:0.28％-0.45％、Zr：0.1％-0.5％、Ce+Y：0.1％-0.2％，其余成分为Fe和不可避免的杂质。
进一步的，所述耐热钢的显微组织为完全的回火马氏体组织和析出相，所述析出相包括弥散分布的M23C6型碳化物、CrTaN相、Laves相以及纳米级弥散强化的Cu相。
与现有技术相比，本发明的一种用于630℃以上的马氏体耐热钢，
一方面，除添加少量V、Nb元素外，还添加了0.2％-0.5％的Ta元素，适量的Ta元素会形成一种不易粗化的CrTaN相，从而避免了在持久过程中极易形成并粗化的Cr(V、Nb)N相的形成，此相的粗化会恶化持久性能，也避免本钢在长时服役过程中，因MX向Cr(Nb，V)N转变粗化而造成的性能的骤降；
另一方面，本发明通过控制碳含量在一个较低水平，通过较低的C含量形成细小弥散的M23C6，起到弥散强化作用；通过添加一定量的Cu元素抑 制高温铁素体的形成，同时纳米级的富铜相的析出可以弥补V、Nb的缺失，起到析出强化的作用，提高耐热钢的持久强度；添加适量的B元素，替换M23C6的C元素的位置，形成M23(C,B)6，从而减少原奥氏体晶界附近的M23C6粗化速率，显著提高蠕变强度；采用适量的W元素，提高了持久强度；采用少量Ni元素，采用较高的Co含量以提高基体韧性；通过合理的元素配比，能够极大的避免高温铁素体的形成，为实际生产中的锻造与热处理过程提供了更大的温度窗口。
本发明还提供了一种630℃以上的马氏体耐热钢的制备方法，包括如下步骤：
步骤S1：按照成分配比中的各组分含量称取原料，在真空感应炉中熔炼、浇注成铸锭，并严格控制杂质元素含量，所述成分配比按质量百分比计，包括：C:0.01％-0.14％、Si:0.05％-0.50％、Mn:0.05％-0.70％、Cr:8.5％-13％、W:2.0％-3.5％、Mo：0.1％-0.7％，Nb:0.03％-0.07％、V:0.1％-0.3％、Co:2.8％-5％、Cu：0.8％-1.5％、Ni:0.1％-0.5％、B:0.01％-0.015％、N:0.01％-0.08％、Ta:0.2％-0.5％、Zr：0.1％-0.5％、Ce+Y：0.01％-0.3％，其余成分为Fe和不可避免的杂质；
步骤S2：将步骤S1得到的铸锭进行高温均质化处理，保温，然后随炉冷却至室温得到坯料；
步骤S3：对步骤S2得到的坯料，通过归圆、墩或拔的手段进行锻造，当锻造过程中的温度低于终锻温度时，回炉加热后再锻造，锻后炉冷至室温；
步骤S4：对步骤S3得到的锻棒进行正火及两次回火热处理得到铬钽氮化物增强马氏体耐热钢；其中，第一次回火温度低于第二次回火温度。
进一步地，所述步骤S2中，所述高温均质化处理的温度为1160-1200℃，保温时间为4-8h。
进一步地，所述步骤S3中，所述锻造过程中的始锻温度为1160-1200℃，终锻温度为850-950℃。
进一步地，所述步骤S4包括如下步骤：
步骤S401：正火，正火工艺为将所述锻棒升温加热至1050-1150℃并保温，然后空冷至室温；
步骤S402：第一次回火，第一次回火工艺为将所述锻棒升温加热至600-700℃，并保温，然后空冷至室温；
步骤S403：第二次回火，第二次回火工艺为将所述锻棒升温加热至680-780℃，并保温，然后空冷至室温。
进一步地，所述步骤S401中，升温速率小于等于100℃/h，保温时间为1-10h。
进一步地，所述步骤S402中，保温时间为5-10h。
进一步地，所述步骤S403中，保温时间为5-10h。
与现有技术相比，本发明提供的630℃以上的马氏体耐热钢的制备过程中通过精确控制高温均质化处理的时间和温度、锻造温度、正火温度和时间以及二次回火温度和时间等工艺参数保证获得的显微组织为完全的回火马氏体组织和析出相，析出相包括细小弥散分布的M23C6型碳化物，CrTaN相，少量细小的Laves相以及纳米级的弥散强化的Cu相。保证了耐热钢的优良的室温强度、高温强度以及抗持久蠕变、抗氧化性能，适用于630℃以上超超临界汽轮机转子。
本发明的其他特征和优点将在随后的说明书中阐述，并且，部分的从说明书中变得显而易见，或者通过实施本发明而了解。本发明的目的和其他优点可通过在所写的说明书以及附图中所特别指出的内容来实现和获得。
附图说明
图1为本发明实施例1中耐热钢的铸态组织图；
图2为本发明实施例1中耐热钢的均质化组织；
图3为本发明实施例1中耐热钢的调质态组织。
具体实施方式
下面结合附图来具体描述本发明的优选实施例，其中，附图构成本发明的一部分，并与本发明的发明内容一起用于阐释本发明的原理。
本发明提供了一种用于630℃以上的马氏体耐热钢，按质量百分比计，其成分包括：C:0.01％-0.14％、Si:0.05％-0.50％、Mn:0.05％-0.70％、Cr:8.5％-13％、W:2.0％-3.5％、Mo：0.1％-0.7％，Nb:0.03％-0.07％、V:0.1％-0.3％、Co:2.8％-5％、Cu：0.8％-1.5％、Ni:0.1％-0.5％、B:0.01％-0.015％、N: 0.01％-0.08％、Ta:0.2％-0.5％、Zr：0.1％-0.5％、Ce+Y：0.01％-0.3％，其余成分为Fe和不可避免的杂质。
一般情况下，9-12％Cr钢经过长时服役后，会形成粗大的铬钒或铬铌氮化物相，即CrVN与CrNbN。与现有技术相比，本发明提供的耐热钢C含量较低，Co含量较高，添加了Ta，Cu等强化元素以及Ce+Y稀土元素。本发明提供的耐热钢未添加V、Nb元素，能够避免在持久过程中极易形成并粗化的Cr(V、Nb)N相的形成，此相的粗化会恶化持久性能。
本发明中添加了0.2％-0.5％的Ta元素，适量的Ta元素会形成一种不易粗化的CrTaN相，能够避免在长时服役过程中，因MX向Cr(Nb，V)N转变粗化而造成的性能的骤降。
本发明提供的耐热钢通过较低的C含量形成细小弥散的M23C6，起到弥散强化作用；添加0.8％-1.5％的Cu元素，Cu元素一方面作为奥氏体形成元素抑制高温铁素体的形成，另一方面纳米级的富铜相的析出可以弥补V、Nb的缺失，起到析出强化的作用，提高耐热钢的持久强度；适量的B元素能够替换M23C6的C元素的位置，形成M23(C,B)6，从而减少原奥氏体晶界附近的M23C6粗化速率，显著提高蠕变强度；采用适量的W元素，提高了持久强度；采用少量Ni元素，采用较高的Co含量以提高基体韧性。通过合理的元素配比，还能够极大的避免高温铁素体的形成，这为实际生产中的锻造与热处理过程提供了更大的温度窗口。
本发明提供的耐热钢具有高强度、抗持久蠕变、抗氧化等特点，本发明制备的马氏体耐热钢的室温屈服强度大于660MPa，抗拉强度大于850MPa，延伸率16％以上，断面收缩率50％以上，冲击功20J以上。630℃的屈服强度大于280Mpa，抗拉强度大于380Mpa，延伸率22％以上，断面收缩率62％以上，650℃、180MPa蠕变断裂时间大于3500h，耐650℃氧化增重(400h)0.3mg/m2以下，综合性能优异。
具体来说，上述用于630℃以上的马氏体耐热钢，各组分的作用如下：
C：重要的沉淀强化元素，M23C6及MX弥散强化，提高持久蠕变性能；C是强烈的奥氏体稳定化元素，可减少δ-铁素体的生成；提高淬透性，析出强化；碳含量过高，可导致消耗固溶元素(如Cr、W)过多，降低晶界抗 腐蚀能力，劣化焊接性能，且对持久蠕变性能产生负面影响；过低会造成强化不足，降低强度硬度，因此本发明中C的质量百分比控制在0.01％-0.14％。
Si：对提高材料基体的强度和抗蒸汽腐蚀性能有利；Si含量升高，抗氧化性急剧提高；提高的Si含量会促进高温铁素体的生成，降低高温铁素体的形成温度，这对锻造温度区间会有不利的影响，同时过高的Si含量对材料的冲击韧性不利，材料的持久强度随着Si含量的增加而降低。因此本发明中Si的质量百分比控制在0.05％-0.50％。
Mn：提高强度，提高热加工性能，也可稳定P、S等。当含量低于0.2％时，Mn起不到明显作用；含量高于1％时，组织中可能会出现第二相，对材料的冲击韧性有害。因此本发明中Mn的质量百分比控制在0.05％-0.70％。
Cr：最关键的抗腐蚀和氧化元素。Cr元素本身具有优异的抗蠕变变形能力，也是耐热钢中提高抗蒸汽氧化和腐蚀能力的主要元素，而且可以提高钢的高温强度。在Cr足够多的情况下，能够和O反应在合金基体表面形成Cr2O3保护膜，阻止O原子和金属离子的扩散，从而延缓氧化过程。此外，Cr还是重要的沉淀强化元素，可与C生成M23C6沉淀强化。当Cr含量过高时，将产生δ铁素体，降低高温热强度，因为将Cr元素含量范围定在9-13％。
W：典型的固溶强化元素，固溶强化效果比Mo元素明显，可以稳定M23C6的细小分布，促进其析出强化；W元素的增加能够显著提高耐热钢的高温强度和蠕变性能。低于2.0％的W元素不能满足630℃及以上温度耐热钢长时蠕变的要求，W超过3.5％时会导致高温铁素体的生成，同时W含量的增加，耐热钢焊接性能会逐渐恶化。因此，本发明中W的质量百分比控制在2.0％-3.5％。
Mo：W、Mo复合添加能够改善材料的韧性和塑性，热加工性好，冲击性能提高。
Co：是奥氏体稳定元素，抑制δ-铁素体的形成，提高材料的高温强度，并抑制M23C6的粗化；本发明中Co的质量百分比控制在2.8％-5％。
Cu：Cu元素可以抑制δ-铁素体的形成。同时，Cu的加入有利于提高W的固溶强化作用，能提高含W的马氏体耐热钢的高温蠕变强度。Cu本身以纳米富Cu颗粒存在也能起到析出强化作用。当Cu含量较低时，主要以固 溶方式存在，强化效果相对较弱，当Cu含量较高时，会严重降影响高温塑性。因此，本发明中Cu的质量百分比控制在0.5％-1.5％。
Ni：典型的奥氏体形成元素，能够提高韧性，平衡材料的Cr当量；本发明中Ni的质量百分比控制在0.1％-0.5％。
B：对于高Cr马氏体耐热钢，B元素能够替换M23C6的C元素的位置，形成M23(C,B)6，M23(C,B)6熟化速率慢，持久性能良好，从而减少了原奥氏体晶界附近的M23C6粗化速率，抑制M23C6的粗化，提高钢的蠕变强度；B能净化晶界，形成M23(C0.85B0.15)6碳硼化物；而过高的B含量会降低高温塑性，增加锻造开裂的风险。因此，本发明中B的质量百分比控制在0.01％-0.015％。
N：可以与V，Nb，Ta形成细小弥散第二相颗粒，显著提高材料的高温持久强度；但是当N含量过高时，与B元素结合成粗大的BN颗粒，严重弱化钢的强韧性，还将消耗用于晶界强化的B元素，严重损害钢的高温持久强度。因此，本发明中N的质量百分比控制在0.01％-0.08％。
Ta：本钢中随着Cr元素含量提高至12％左右，在600-650℃长时时效及使用时，基体中的Cr会向MX聚集并进一步形成Cr(Nb，V)N，从而消耗了基体的Cr元素，也造成析出相的粗化，更加促进了Cr(Nb，V)N的生成，12Cr比9Cr钢更容易形成粗大的铬钒或铬铌氮化物相，不利于钉扎位错和板条，从而影响钢的持久强度。而添加适量的Ta元素，会抑制MX向Cr(Nb，V)N的转变，而是形成以CrTaN为主的相，此种CrTaN相，相较于Cr(Nb，V)N相不容易粗化，会以细小弥散的析出相存在，起到析出强化的作用，从而解决Cr元素含量提高所带来的问题。Ta含量过高则很难完全固溶于基体中，以富Ta颗粒存在，给冶炼增加难度。因此，本发明中，Ta的质量百分比控制在0.2％-0.5％。
Zr：奥氏体晶粒的长大倾向随Zr含量的增加而变小，并会降低夹杂物的尺寸。因此，本发明中Zr的质量百分比控制在0.1％-0.5％。
稀土元素：Ce+Y为稀土元素，少量添加可以提高耐热钢高温力学性能及耐蚀性能。混合稀土元素加入可以发挥协同作用，纯化、强韧化晶界，控制夹杂物的数量与形态，从而提高高温强度及抗氧化性能，本发明综合稀土 添加量为0.01％-0.3％。
优选的，一种用于630℃以上的马氏体耐热钢，按质量百分比计，其成分包括：C:0.01％-0.14％、Si:0.05％-0.50％、Mn:0.05％-0.70％、Cr:8.5％-13％、W:2.0％-3.5％、Mo：0.1％-0.7％，Nb:0.03％-0.07％、V:0.1％-0.3％、Co:2.8％-5％、Cu：0.8％-1.2％、Ni:0.1％-0.5％、B:0.01％-0.015％、N:0.01％-0.08％、Ta:0.28％-0.45％、Zr：0.1％-0.5％、Ce+Y：0.1％-0.2％，其余成分为Fe和不可避免的杂质。
本发明还提供了一种630℃以上的马氏体耐热钢的制备方法，包括如下步骤：
步骤S1：按照成分配比中的各组分含量称取原料，在真空感应炉中熔炼、浇注成铸锭，并严格控制杂质元素含量，所述成分配比按质量百分比计，包括：C:0.01％-0.14％、Si:0.05％-0.50％、Mn:0.05％-0.70％、Cr:8.5％-13％、W:2.0％-3.5％、Mo：0.1％-0.7％，Nb:0.03％-0.07％、V:0.1％-0.3％、Co:2.8％-5％、Cu：0.8％-1.5％、Ni:0.1％-0.5％、B:0.01％-0.015％、N:0.01％-0.08％、Ta:0.2％-0.5％、Zr：0.1％-0.5％、Ce+Y：0.01％-0.3％，其余成分为Fe和不可避免的杂质；
步骤S2：将步骤S1得到的铸锭进行高温均质化处理，保温，然后随炉冷却至室温得到坯料；
步骤S3：对步骤S2得到的坯料，通过归圆、墩或拔的手段进行锻造，当锻造过程中的温度低于终锻温度时，回炉加热后再锻造，锻后炉冷至室温；
步骤S4：对步骤S3得到的锻棒进行正火及两次回火热处理得到铬钽氮化物增强马氏体耐热钢；其中，第一次回火温度低于第二次回火温度。
具体的，上述步骤S2中，高温均质化处理的目的是对铸锭中的高温铁素体、析出相及合金元素的偏析进行消除。高温均质化温度过高会导致晶粒严重粗化以及高温铁素体的形成，过低会无法有效消除铸造组织中的δ铁素体、M3B2等析出相及元素偏析。经过大量实验研究，控制高温均质化温度为1160-1200℃。保温时间控制在4-8h，保温时间过短不足以消除铸锭中的高温铁素体、析出相及元素偏析等，时间过长可能引起过热过烧，晶粒粗大。
具体的，通过上述步骤S3的锻造可以达到压实缺陷，细化晶粒，均匀 组织等目的(实施例1中耐热钢的调质态组织如图3所示)，从而为提高耐热钢的综合性能打下良好的基础。当始锻温度高于1200℃，会形成高温铁素体，增加锻造开裂的风险，而且过高的始锻温度会造成晶粒粗化严重，对后续锻造过程中的晶粒度控制增加难度，而锻后如存在晶粒过大以及混晶的情况，一方面影响最终的力学性能，另一方面也很影响探伤。因此，本发明控制始锻温度为1160-1200℃，终锻温度为850-950℃，在本发明给出的锻造温度区间内，该钢具有良好的塑性。与现有技术相比，本发明始锻温度比同类钢高出100℃左右，大大增大锻造温度区间。
具体的，上述步骤S4包括如下步骤：
步骤S401：正火，正火工艺为将锻棒升温加热至1050-1150℃并保温，然后空冷至室温；
步骤S402：第一次回火，第一次回火工艺为将锻棒升温加热至600-700℃，并保温，然后空冷至室温；
步骤S403：第二次回火，第二次回火工艺为将锻棒升温加热至680-780℃，并保温，然后空冷至室温。
具体的，上述S401中，考虑到大件热处理时过快的升温速率会导致内外温差巨大，过快的升温速率可能导致热裂，因此，根据实际大件的热处理规律，室温下将锻棒放入加热炉中，升温速率小于等于100℃/h。
具体的，上述S401中，保温时间过长会使晶粒严重粗化，过短不足以使得锻件热透。因此，控制保温时间为1-10h。
具体的，上述S402中，第一次回火的作用是促进CrTaN析出，将N元素固定至CrTaN相中。因为650℃左右是12％Cr钢中CrTaN最容易析出的温度区间。在此温度下回火，可以形成非常细小弥散的CrTaN相，此CrTaN相相对其他MX，Cr23C6，Laves等析出相都更不容易长大；回火温度过高会析出大量的碳化物，使得马氏体组织板条宽化，位错密度降低，导致强度严重下降。回火温度过低不足于促进CrTaN的析出。保温时间过长性能软化，过短不足于热透及元素扩散。因此，控制回火温度600-700℃，保温时间为5-10h。
具体的，上述S403中，第二次回火的作用是形成完全的回火马氏体组 织，获得良好的综合性能；回火温度过高，强度不足；回火温度过低，冲击过低，保温时间过长，会导致析出相尺寸长大，强度和冲击值均不满足性能要求；保温时间过短，锻件不足以热透及形成回火马氏体。因此，控制回火温度680-780℃，保温时间为5-10h。
需要说明的是，上述的正火温度可以将M23C6，M3B2，Laves等析出相完全消除，使得合金元素完全固溶在基体中，且将晶粒度控制在2级以内，同时不会形成δ-铁素体。第一次低温回火能够促进CrTaN析出，将N元素固定至CrTaN相中，第二次高温回火将新转变的马氏体进行回火，从而保证最终组织全部为均匀的回火马氏体+析出相，回火马氏体和析出相的占比分别为98％和2％，析出相细小弥散的分布于板条界及晶界上，起到很好的强化作用。
经过上述热处理的耐热钢的组织为完全的回火马氏体组织+析出相，析出相主要为细小弥散分布的M23C6，CrTaN，少量细小的Laves相以及纳米级的弥散强化的Cu相。
需要说明的是，经过上述热处理的耐热钢的室温屈服强度大于660MPa，抗拉强度大于850MPa，延伸率16％以上，断面收缩率50％以上，冲击功20J以上。630℃的屈服强度大于280Mpa，抗拉强度大于380Mpa，延伸率22％以上，断面收缩率62％以上，650℃、180MPa蠕变断裂时间大于3500h，耐650℃氧化增重(400h)0.3mg/m2以下。性能优异。
下面将以具体的实施例与对比例来展示本发明钢的成分和工艺参数精确控制的优势。
实施例1
本实施例提供了一种用于630℃以上的马氏体耐热钢及其制备方法。
本实施例的化学成分以重量百分含量计，包含：C:0.05％、Si:0.30％、Mn:0.50％、Cr:12.0％、W:3.0％、Mo：0.2％，Nb：0.05，V：0.2％，Co:4.5％、Ni:0.2％、Cu:1.0％，B:0.01％、N:0.045％、Ta:0.32％、Zr：0.3％、Ce+Y：0.15％、其余成分为Fe和不可避免杂质。
耐热钢的制备方法包括：
步骤S1：按合金成分比例，在真空感应炉中熔炼、浇注成铸锭，严格 控制杂质元素含量；
步骤S2：将步骤S1得到的铸锭进行高温均质化处理，然后随炉冷却至室温得到坯料；其中，高温均质化温度1180℃，保温时间5h；
步骤S3：对步骤S2得到的坯料，通过归圆、墩或拔手段进行锻造，始锻温度为1180℃，终锻温度为950℃，锻造过程中低于终锻温度需回炉加热后再锻造；
步骤S4：对步骤S3得到的锻棒进行正火及两次回火热处理得到铬钽氮化物增强马氏体耐热钢；其中，正火温度1100℃，保温时间5h；第一次回火温度650℃，第一次回火保温时间6h；第二次回火温度740℃，第二次回火保温时间6h。
实施例1-4与对比例1-2的钢的化学成分见表1，实施例2-4工艺步骤与实施例1相同，具体工艺参数见表2，实施例1-4与对比例1-2的性能见表3和表4，实施例1-4与对比例1-2的金相组织见表5。
对比例1，其化学成分中未添加Cu，Ta，Zr及稀土元素；对比例2，其化学成分中未添加Ta元素；具体化学成分如表1所示。对比例1-2工艺步骤与实施例1相同，具体工艺参数见表2，其各项性能指标与实施例1-4对比如表3所示。由表3可以看出，实施例与对比例相比，其各项性能更加优异。
表1实施例和对比例的化学成分wt％

表2实施例和对比例的具体工艺参数
表3实施例和对比例的室温性能

表4实施例和对比例的630℃性能
表5实施例和对比例的金相组织
以上所述仅为本发明较佳的具体实施方式，但本发明的保护范围并不局限于此，任何熟悉本技术领域的技术人员在本发明揭露的技术范围内，可轻易想到的变化或替换，都应涵盖在本发明的保护范围之内。

Claims (10)

  1. 一种用于630℃以上的马氏体耐热钢，其中，按质量百分比计，其成分包括：C:0.01％-0.14％、Si:0.05％-0.50％、Mn:0.05％-0.70％、Cr:8.5％-13％、W:2.0％-3.5％、Mo：0.1％-0.7％，Nb:0.03％-0.07％、V:0.1％-0.3％、Co:2.8％-5％、Cu：0.8％-1.5％、Ni:0.1％-0.5％、B:0.01％-0.015％、N:0.01％-0.08％、Ta:0.2％-0.5％、Zr：0.1％-0.5％、Ce+Y：0.01％-0.3％，其余成分为Fe和不可避免的杂质。
  2. 根据权利要求1所述的用于630℃以上的马氏体耐热钢，其中，按质量百分比计，其成分包括：C:0.01％-0.14％、Si:0.05％-0.50％、Mn:0.05％-0.70％、Cr:8.5％-13％、W:2.0％-3.5％、Mo：0.1％-0.7％，Nb:0.03％-0.07％、V:0.1％-0.3％、Co:2.8％-5％、Cu：0.8％-1.2％、Ni:0.1％-0.5％、B:0.01％-0.015％、N:0.01％-0.08％、Ta:0.28％-0.45％、Zr：0.1％-0.5％、Ce+Y：0.1％-0.2％，其余成分为Fe和不可避免的杂质。
  3. 根据权利要求1或2所述的用于630℃以上的马氏体耐热钢，其中，所述耐热钢的显微组织为完全的回火马氏体组织和析出相，所述析出相包括弥散分布的M23C6型碳化物、CrTaN相、Laves相以及纳米级弥散强化的Cu相。
  4. 一种如权利要求1-3任一项所述的630℃以上的马氏体耐热钢的制备方法，其中，包括如下步骤：
    步骤S1：按照成分配比中的各组分含量称取原料，在真空感应炉中熔炼、浇注成铸锭，并严格控制杂质元素含量，所述成分配比按质量百分比计，包括：C:0.01％-0.14％、Si:0.05％-0.50％、Mn:0.05％-0.70％、Cr:8.5％-13％、W:2.0％-3.5％、Mo：0.1％-0.7％，Nb:0.03％-0.07％、V:0.1％-0.3％、Co:2.8％-5％、Cu：0.8％-1.5％、Ni:0.1％-0.5％、B:0.01％-0.015％、N:0.01％-0.08％、Ta:0.2％-0.5％、Zr：0.1％-0.5％、Ce+Y：0.01％-0.3％，其余成分为Fe和不可避免的杂质；
    步骤S2：将步骤S1得到的铸锭进行高温均质化处理，保温，然后随炉冷却至室温得到坯料；
    步骤S3：对步骤S2得到的坯料，通过归圆、墩或拔的手段进行锻造， 当锻造过程中的温度低于终锻温度时，回炉加热后再锻造，锻后炉冷至室温；
    步骤S4：对步骤S3得到的锻棒进行正火及两次回火热处理得到铬钽氮化物增强马氏体耐热钢；其中，第一次回火温度低于第二次回火温度。
  5. 根据权利要求4所述的630℃以上的马氏体耐热钢的制备方法，其中，所述步骤S2中，所述高温均质化处理的温度为1160-1200℃，保温时间为4-8h。
  6. 根据权利要求4所述的630℃以上的马氏体耐热钢的制备方法，其中，所述步骤S3中，所述锻造过程中的始锻温度为1160-1200℃，终锻温度为850-950℃。
  7. 根据权利要求4所述的630℃以上的马氏体耐热钢的制备方法，其中，所述步骤S4包括如下步骤：
    步骤S401：正火，正火工艺为将所述锻棒升温加热至1050-1150℃并保温，然后空冷至室温；
    步骤S402：第一次回火，第一次回火工艺为将所述锻棒升温加热至600-700℃，并保温，然后空冷至室温；
    步骤S403：第二次回火，第二次回火工艺为将所述锻棒升温加热至680-780℃，并保温，然后空冷至室温。
  8. 根据权利要求7所述的630℃以上的马氏体耐热钢的制备方法，其中，所述步骤S401中，升温速率小于等于100℃/h，保温时间为1-10h。
  9. 根据权利要求7所述的630℃以上的马氏体耐热钢的制备方法，其中，所述步骤S402中，保温时间为5-10h。
  10. 根据权利要求7所述的630℃以上的马氏体耐热钢的制备方法，其中，所述步骤S403中，保温时间为5-10h。
PCT/CN2023/097809 2022-06-22 2023-06-01 一种用于630℃以上的马氏体耐热钢及其制备方法 WO2023246465A1 (zh)

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US4850187A (en) * 1986-02-05 1989-07-25 Hitachi, Ltd. Gas turbine having components composed of heat resistant steel
JPH09184050A (ja) * 1995-12-28 1997-07-15 Kansai Electric Power Co Inc:The フェライト系鉄基合金の製造方法、フェライト系耐熱鋼の製造方法およびフェライト系耐熱鋼
JPH1192881A (ja) * 1997-09-22 1999-04-06 Natl Res Inst For Metals ラスマルテンサイト組織のフェライト系耐熱鋼と その製造方法
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US4850187A (en) * 1986-02-05 1989-07-25 Hitachi, Ltd. Gas turbine having components composed of heat resistant steel
JPH09184050A (ja) * 1995-12-28 1997-07-15 Kansai Electric Power Co Inc:The フェライト系鉄基合金の製造方法、フェライト系耐熱鋼の製造方法およびフェライト系耐熱鋼
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