WO2024109880A1 - 一种纳米析出物强化超高强钢及其制造方法 - Google Patents

一种纳米析出物强化超高强钢及其制造方法 Download PDF

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WO2024109880A1
WO2024109880A1 PCT/CN2023/133642 CN2023133642W WO2024109880A1 WO 2024109880 A1 WO2024109880 A1 WO 2024109880A1 CN 2023133642 W CN2023133642 W CN 2023133642W WO 2024109880 A1 WO2024109880 A1 WO 2024109880A1
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steel
nano
precipitates
temperature
present
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French (fr)
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刘刚
李自刚
杨阿娜
唐骜
王巍
温识博
张华伟
温东辉
宋凤明
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宝山钢铁股份有限公司
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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
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21B—ROLLING OF METAL
    • B21B1/00—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations
    • B21B1/02—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling heavy work, e.g. ingots, slabs, blooms, or billets, in which the cross-sectional form is unimportant ; Rolling combined with forging or pressing
    • B21B1/026—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
    • 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
    • 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
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C21D8/0263—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment following hot rolling
    • 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
    • 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
    • C22C38/04—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
    • C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
    • 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
    • C22C38/14—Ferrous alloys, e.g. steel alloys containing 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
    • 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
    • C22C38/24—Ferrous alloys, e.g. steel alloys containing chromium 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
    • C22C38/28—Ferrous alloys, e.g. steel alloys containing chromium 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
    • C22C38/32—Ferrous alloys, e.g. steel alloys containing chromium 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
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of manganese
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21B—ROLLING OF METAL
    • B21B1/00—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations
    • B21B1/02—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling heavy work, e.g. ingots, slabs, blooms, or billets, in which the cross-sectional form is unimportant ; Rolling combined with forging or pressing
    • B21B2001/028—Slabs
    • 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
    • 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
    • C21D2211/004—Dispersions; Precipitations

Definitions

  • the present invention relates to the technical field of high-strength steel, and in particular to a nano-precipitate reinforced ultra-high-strength steel and a manufacturing method thereof.
  • Hot-rolled ultra-high-strength steel for engineering machinery with a yield strength of 960MPa is mainly used to manufacture components such as crane booms and pump truck feeder booms, which places high demands on the strength, plasticity, low-temperature toughness and fatigue performance of the steel plate.
  • Traditional 960MPa ultra-high-strength steel is generally produced by offline quenching and tempering heat treatment or online quenching + tempering process to obtain tempered martensite structure.
  • the plasticity of tempered martensite is low, and it is easy to crack during subsequent bending, hole expansion and other processing.
  • High-temperature tempering can improve the plasticity of ultra-high-strength steel, but the strength will be significantly reduced.
  • Chinese patent CN103014538B discloses an ultra-high strength steel with a yield strength of 960 MPa, which is prepared by an online quenching + 510-550°C tempering process, and its structure is tempered martensite.
  • Chinese patent CN102134680A discloses a method for producing high-strength steel with a yield strength of 960 MPa, which is designed with a lower carbon content and has a higher Cr content, C: 0.07-0.09%, Cr: 1.05-1.15%.
  • the patent does not contain Nb, Ti, V microalloying elements, and has a higher Cr content.
  • Chinese patent CN102560274A has developed a 1000MPa yield strength ultra-high strength steel through offline heat treatment, the structure is tempered martensite structure. Its main components are Cr: 0.30-0.50%; Mo: 0.30-0.50%; Ni: 0.20-0.50%; V: 0.030-0.050%.
  • Chinese patent CN102505096A obtains a tempered martensitic ultra-high strength steel by online quenching + 460-520°C tempering.
  • the present invention provides a nano-precipitate reinforced ultra-high strength steel and a manufacturing method thereof.
  • the microstructure of the ultra-high strength steel is a tempered More preferably, the steel has a yield strength of ⁇ 1000MPa, a tensile strength of ⁇ 1050MPa, an elongation A 50 of ⁇ 19%, and an impact energy of ⁇ 90J at -60°C.
  • a first aspect of the present invention provides a steel having the following chemical composition by weight: C: 0.15-0.21%, Si ⁇ 0.50%, Mn: 0.60-1.60%, Ti: 0.051-0.15%, V: 0.040-0.12%, Cr: 0.20-1.20%, B: 0.0005-0.0030%, Al: 0.02-0.06%, Ca: 0.0005-0.004%, N ⁇ 0.005%, P ⁇ 0.020%, S ⁇ 0.0050%, O ⁇ 0.0040%, the balance including Fe and other unavoidable impurities, and the following conditions must be met at the same time:
  • NPI (Mo + W + 2.3 * Cr) / (Ti + V), and the value before the percentage sign of the corresponding element weight percentage is entered during the calculation;
  • the balance of the above steel chemical composition is Fe and other inevitable impurities.
  • the steel further includes one or more elements selected from the group consisting of Nb: 0-0.060%, Mg: 0-0.003%, Ni: 0-0.30%, Cu: 0-0.40%, Mo: 0-0.40%, and W: 0-0.30%.
  • the microstructure of the steel of the present invention is tempered troostite and nano-precipitates
  • the original austenite grain size of the tempered troostite i.e. the original austenite grain size
  • the nano-precipitates include TiC and VC precipitates
  • the size of the nano-precipitates is 2-5 nanometers.
  • the yield strength of the steel of the present invention is ⁇ 1000MPa
  • the tensile strength is ⁇ 1050MPa
  • the elongation A50 is ⁇ 19%
  • the -60°C impact energy is ⁇ 90J.
  • the properties of the steel meet at least one of the following: the yield strength is 1000-1115MPa, the tensile strength is 1050-1172MPa, the elongation A50 is 19-25%, and the -60°C impact energy is 90-129J.
  • each element in the steel composition of the present invention is in weight percentage.
  • the role of each element is as follows:
  • Carbon It has a solid solution strengthening effect and can adjust the strength and plasticity of martensite structure.
  • tempering is used to further adjust the strength, plasticity and toughness; a high C content will lead to an increase in the overall C equivalent, which is easy to crack during welding.
  • the C content of the present invention is in the range of 0.15-0.21%.
  • Silicon A certain amount of Si can play a good deoxidation role and can inhibit The precipitation of carbides improves the toughness of steel. Too high Si content easily produces red iron scale, so the silicon content of the present invention is ⁇ 0.50%.
  • Mn can improve the hardenability of steel when it is above 0.6%, but when it exceeds 1.6%, it is easy to produce segregation and inclusions such as MnS, which deteriorates the toughness of martensitic high-strength steel. Therefore, the Mn content in the steel of the present invention is 0.60-1.60%, preferably 1.20-1.60%.
  • Titanium is a microalloying element, which can form a large number of nano-scale precipitates with elements such as C and N through controlled rolling and controlled cooling processes. During heat treatment, it can strongly inhibit the growth of austenite grains, and on the other hand, it can retain a large number of nano-precipitates after heat treatment, which plays a precipitation strengthening role.
  • the titanium content in the steel of the present invention is 0.051-0.15%, preferably 0.051-0.09%, so as to reduce the manufacturing cost while ensuring the strength of the steel.
  • Vanadium is a microalloying element that can form nano-scale precipitates with C. A large amount of nano-scale VC precipitates will be produced during heat treatment and tempering.
  • the vanadium content in the steel of the present invention is 0.040-0.12%, preferably 0.04-0.08%, so as to reduce the manufacturing cost while ensuring the strength of the steel.
  • Niobium is a microalloying element that can form nano-scale precipitates with C element, inhibiting the growth of austenite grains during hot rolling, thereby refining the structure after phase transformation.
  • the niobium content in the steel of the present invention is 0-0.060%, preferably less than 0.03%.
  • Magnesium A trace amount of Mg will form fine MgO precipitate particles by controlling the steelmaking and continuous casting processes during steelmaking, so that TiN adheres to MgO to form a composite precipitate MgO-TiN, thereby modifying the shape of cubic TiN and making the composite precipitate close to a spherical shape. At the same time, it can control the growth of harmful TiN and reduce the number of large particles of TiN. The maximum size of TiN can be reduced from the conventional 8-10 microns to less than 5 microns, thereby improving the toughness and plasticity of the steel.
  • the Mg content in the steel of the present invention is 0-0.003%.
  • Chromium Cr element above 0.2% can improve the hardenability of steel and is conducive to the formation of full martensite structure during quenching. Cr will form Cr carbide during tempering, which has the effect of resisting tempering softening. If the Cr content exceeds 1.20%, large sparks will appear during welding, affecting the welding quality. Therefore, the Cr content in the steel of the present invention is 0.20-1.20%, preferably 0.20-0.80%.
  • Molybdenum A certain amount of Mo element can improve the hardenability of steel and is conducive to the formation of full martensite structure during quenching. Mo reacts with C to form carbide particles during high temperature tempering, which has the effect of resisting high temperature tempering softening and softening of welded joints. Too high Mo content will lead to an increase in carbon equivalent and deteriorate welding performance. At the same time, Mo is a precious metal, and a large amount of use will increase the cost. Therefore, the steel of the present invention The Mo content is 0 to 0.40%, preferably 0.25% or less.
  • the W element can improve the hardenability of steel, form carbide particles during tempering, and has a significant effect of resisting temper softening, and also has the effect of resisting temper brittleness.
  • the W content in the steel of the present invention is 0 to 0.30%, preferably less than 0.22%.
  • Nickel A certain amount of Ni element has the effect of refining the martensitic structure and improving the toughness of steel. Too high Ni content will lead to an increase in carbon equivalent and deteriorate welding performance. At the same time, Ni is a precious metal, and a large amount of use will increase the cost. Therefore, the Ni content in the steel of the present invention is 0 to 0.30%, preferably less than 0.20%.
  • the Cu element can produce a certain precipitation strengthening effect during tempering.
  • adding a certain amount of Cu element can improve the corrosion resistance of ultra-high strength steel for engineering machinery.
  • the Cu content in the steel of the present invention is 0 to 0.40%, preferably less than 0.25%.
  • the boron content in the steel of the present invention is 0.0005-0.0030%, preferably 0.0005-0.0020%.
  • Aluminum above 0.02% can be used as a deoxidizer on the one hand, and on the other hand, a small amount of Al 2 O 3 formed can refine the grains when the slab is heated, thereby refining the microstructure of the steel plate after rolling.
  • Al content exceeding 0.06% is prone to Al oxide inclusion defects.
  • the Al content in the steel of the present invention is 0.02-0.06%, preferably 0.02-0.04%.
  • Ca A trace amount of Ca can purify molten steel during steelmaking, optimize the shape and size of inclusions such as MnS, and improve the toughness of steel.
  • the Ca content in the steel of the present invention is 0.0005-0.004%, preferably 0.0015-0.0035%.
  • N content in the steel is strictly controlled to be below 0.0050%, preferably below 0.0030% through the refining process, and on the other hand, a trace amount of rare earth elements is added, and a specific steelmaking superheat and molten steel solidification process are combined to effectively reduce the size and amount of TiN formed.
  • P, S and O are impurity elements in steel, which affect the plasticity and toughness of steel.
  • the present invention strictly controls the content of the above elements in steel to P ⁇ 0.020%, S ⁇ 0.0050%, O ⁇ 0.0040%; preferably, at least one of the following is satisfied: P ⁇ 0.012%, S ⁇ 0.0035%, O ⁇ 0.0035%.
  • the steel composition of the present invention also needs to meet the following requirements:
  • NPI (Mo + W + 2.3 * Cr) / (Ti + V), and the value before the percentage sign of the corresponding element weight percentage is entered during the calculation.
  • NPI is 7-15, and NPI within this numerical range can achieve better steel properties, such as higher strength and greater elongation;
  • Mo, W and Cr are all strong carbide-forming elements that can inhibit the diffusion of carbon.
  • the precipitated TiC and VC are large in size, reaching 6-15nm, and the strengthening effect of the precipitates is relatively weak, and the strength of the steel can only be increased by 50-100MPa.
  • the 6-15nm TiC will partially dissolve, and the VC will completely dissolve, making it difficult to exert the strengthening effect of nano-precipitates on the steel.
  • the present invention can inhibit the growth of TiC by adding a certain amount of Mo, W and/or Cr elements in combination, especially when 5 ⁇ NPI ⁇ 26, and control the dissolution rate of TiC within a suitable range, so that the average size of TiC is at the micro-nano level of 2-5mm. And then the steel is heated and quenched at 900°C, and then tempered and kept at 500-600°C for 10-30min, VC and TiC precipitate for the second time, and the addition of Mo, W and/or Cr can control the precipitates of VC and TiC to a micro-nano size range of about 2-5nm. If NPI is too low, VC and TiC will coarsen, and if NPI is too high, VC and TiC will not precipitate sufficiently. Therefore, in the present invention, NPI is controlled to be 5-26; and
  • Ti+V ⁇ 0.11% can give full play to the precipitation strengthening effect of TiC and VC in the heat treatment process.
  • Ti+V ⁇ 0.11% sufficient micro-nano precipitate strengthening effect can be achieved.
  • the micro-nano precipitates of TiC and VC of the present invention can produce a precipitation strengthening effect of 180-280MPa by combining NPI and heat treatment process.
  • the amount of Ti+V in the steel is 0.12-0.24%.
  • the present invention also relates to a method for manufacturing the above steel, which comprises the following steps:
  • steel is smelted and refined by converter or electric furnace, and then cast to form ingot;
  • the ingot is placed in a heating furnace at 1220-1300°C for heating, and after the core temperature of the ingot reaches the furnace temperature, the ingot is kept warm for a period of >30 minutes, for example, 30-200 minutes, preferably 100-200 minutes;
  • the ingot is rolled to a target thickness by single-stand reciprocating rolling or multi-stand hot continuous rolling to obtain a steel plate, wherein the final rolling temperature is 820-920°C;
  • the hot-rolled steel plate is cooled to 560-680°C at a cooling rate of 10-30°C/s to obtain ferrite and pearlite structures, and a large number of TiC precipitates with a size of 6-15 nm are generated in the ferrite;
  • Quenching heat treatment heating the steel plate to Ac 3 + (20-50) °C, keeping the temperature for 5-10 min, and then rapidly cooling to room temperature at a cooling rate of ⁇ 150 °C/s, such as 170-300 °C/s, preferably 190-250 °C/s;
  • the superheat of molten steel in the converter is controlled within 15°C, and the amount of secondary cooling water in continuous casting is appropriately increased to increase the solidification rate of molten steel, thereby forming fine MgO precipitates.
  • TiN can attach to MgO to form a composite precipitate MgO-TiN, thereby modifying the shape of cubic TiN, and the composite precipitate is close to spherical.
  • the composite precipitate is relatively dispersed, which is conducive to controlling the growth of harmful TiN and reducing the number of large particles of TiN.
  • the maximum size of TiN can be reduced from the conventional 8-10 microns to less than 5 microns, which is conducive to improving the toughness and plasticity of steel.
  • controlling the heating temperature at 1220-1300°C and the core holding time >30min can ensure that the TiC precipitated during continuous casting is fully dissolved.
  • the heating temperature exceeds 1300°C, the austenite grains will grow excessively, resulting in weakened intergranular bonding and easy cracking during rolling.
  • the finishing rolling temperature is 820-920°C
  • the austenite grains can be refined by austenite recrystallization.
  • the steel plate is cooled to 560-680°C at a cooling rate of 10-30°C/s to obtain ferrite+pearlite+nanoprecipitates, and the size of the precipitated TiC is 6-15nm.
  • the steel plate is heated to Ac 3 + (20-50)°C, and the holding time is controlled to be 5-10 minutes.
  • the present invention controls the dissolution rate of TiC within a suitable range during the heat treatment process by adding a certain amount of Mo, W and/or Cr to make 5 ⁇ NPI ⁇ 26, so that the size of TiC is controlled at the micro-nano level of 2-5nm. During this period, the nano-scale TiC can strongly inhibit the growth of austenite, refine the austenite and the structure after quenching.
  • the steel plate obtains tempered troostite structure during tempering (500-600°C for 10-30min), VC and TiC precipitate secondary during tempering, and the precipitates of VC and TiC are controlled in the micro-nano size range of about 2-5nm.
  • the comprehensive nano-precipitation of TiC and VC can produce a precipitation strengthening effect of 180-280MPa.
  • the steel of the present invention obtains a microstructure of tempered troostite + nano-precipitates through a process of high-temperature tempering after quenching, and a large amount of nano-precipitates ensure that the strength can still reach more than 1000MPa after high-temperature tempering.
  • the purity of molten steel is purified by rare earth elements, the size and shape of inclusions are controlled, the crack initiation caused by inclusions during deformation is reduced, and the plasticity of the steel plate is improved.
  • the present invention obtains a steel having a microstructure of tempered troostite + nano-precipitates through controlled rolling, controlled cooling and heat treatment processes.
  • the steel of the present invention has a large amount of nano-precipitates of TiC and VC, which ensures that the steel plate has a strength of more than 1000MPa after high-temperature tempering.
  • the tempered troostite obtained by high-temperature tempering improves the plasticity of the steel plate.
  • the purity of molten steel is purified by rare earth elements, the size and shape of inclusions are controlled, the crack initiation caused by inclusions during deformation is reduced, and the plasticity of ultra-high strength steel is further improved.
  • the present invention obtains steel with a microstructure of tempered troostite + nano-precipitates, combines rare earth to purify molten steel, and controls the size and shape of inclusions to obtain ultra-high-strength steel with higher plasticity and toughness.
  • FIG1 is a metallographic structure photograph of ultra-high strength steel after rapid heat treatment in Example 3 of the present invention, taken using an optical microscope;
  • FIG2 is a metallographic structure photograph of the ultra-high strength steel after rapid heat treatment in Example 3 of the present invention, taken using a scanning electron microscope.
  • Table 1 shows the composition and corresponding NPI of the embodiments and comparative examples of the present invention, and the balance of the steel is Fe and unavoidable impurities.
  • the steels of the embodiments and comparative examples are all prepared by the above-mentioned preparation method of the present invention, and the process parameters are shown in Table 2.
  • the corresponding properties of the steels of each embodiment and comparative example are shown in Table 3.
  • Comparative Examples 1-4 are manufactured by substantially the same method as Example 3 of the present invention, except that the NPI of Comparative Examples 1 and 2 is not within the numerical range defined in the present invention, the Ti+V of Comparative Example 3 is not within the range defined in the present invention, and the Cr content in Comparative Example 4 is not within the range defined in the present invention.
  • the average austenite grain size was measured according to GB/T 6394-2017 “Method for determination of average grain size of metals”.
  • the polished samples were corroded with picric acid, and more than 10 microstructure photographs were taken with an optical microscope to calculate the average austenite grain size.
  • nano-precipitates was observed by transmission electron microscopy (TEM) with thin film samples and the size of nano-precipitates was counted.
  • TEM transmission electron microscopy
  • Figures 1 and 2 respectively show optical microscope and scanning electron microscope photos of Example 3 of the present invention.
  • the steel of Example 3 of the present invention has a tempered troostite structure after heat treatment.
  • the microstructure of the steel of Example 3 after heat treatment has a large number of micro-nano precipitates.
  • the steels of Examples 1 to 8 of the present invention are obtained by adding Mo, V and/or Cr to steel containing specific amounts of Ti and V and satisfying the above-mentioned NPI, so that the microstructure of the steel is tempered troostite + nano-precipitates with a size of 2-5 nm, thereby comprehensively improving the strength, plasticity and toughness of the steel.
  • the present invention adopts controlled rolling and controlled cooling and offline heat treatment process, and controls from the perspectives of chemical composition design, parent material structure, heating rate, holding time and cooling rate, so that the steel has In addition to ultra-high strength, it also has good elongation and low-temperature impact toughness.

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Abstract

一种纳米析出物强化超高强钢及其制造方法，该超高强钢的成分重量百分比为：C 0.15～0.21％，Si≤0.50％，Mn 0.60～1.60％，Ti 0.051～0.15％，V 0.040～0.12％，Cr 0.20～1.20％，B 0.0005～0.0030％，Al 0.02～0.06％，Ca0.0005～0.004％，N≤0.005％，P≤0.020％，S≤0.0050％，O≤0.0040％，纳米析出物控制指数NPI为5～26，Ti+V≥0.11％，余量为Fe及不可避免杂质。本发明还提供了上述超高强钢的制造方法。

Description

一种纳米析出物强化超高强钢及其制造方法 技术领域
本发明涉及高强钢技术领域，特别涉及一种纳米析出物强化超高强钢及其制造方法。
背景技术
屈服强度960MPa级的工程机械热轧超高强钢主要应用于制造起重机吊臂和泵车布料杆等部件，对钢板的强度、塑性、低温韧性和疲劳性能都提出了较高的要求。传统960MPa级超高强钢一般采用离线调质热处理或在线淬火+回火工艺生产，得到回火马氏体组织。回火马氏体的塑性较低，在后续进行折弯、扩孔等加工时容易开裂。例如，传统工艺生产的960MPa级超高强钢，冷弯性能只能满足D＝5-6a、90度，延伸率≤16％。采用高温回火可以提高超高强钢的塑性，但强度会明显下降。
中国专利CN103014538B公开了一种屈服强度为960MPa的超高强钢，通过在线淬火+510-550℃回火工艺制备，其组织为回火马氏体。
中国专利CN102134680A公开了一种屈服强度960MPa级高强钢的生产方法，采用较低的碳含量设计且具有较高的Cr含量，C：0.07～0.09％，Cr：1.05～1.15％。该专利不含Nb、Ti、V微合金元素，Cr含量较高。
中国专利CN102560274A通过离线热处理开发了一种屈服强度1000MPa级超高强钢，组织为回火马氏体组织。其主要成分为Cr：0.30～0.50％；Mo：0.30～0.50％；Ni：0.20～0.50％；V：0.030～0.050％。
中国专利CN102505096A通过在线淬火+460-520℃回火得到一种回火马氏体超高强钢。
发明内容
为了解决现有技术存在的上述技术问题，本发明提供一种纳米析出物强化超高强钢及其制造方法。优选地，该超高强度钢的显微组织为回火索 氏体+大量纳米析出物。更优选地，该钢的屈服强度≥1000MPa，抗拉强度≥1050MPa，延伸率A50≥19％，-60℃冲击功≥90J。
本发明的第一方面提供一种钢，其化学成分重量百分比为：C：0.15～0.21％，Si≤0.50％，Mn：0.60～1.60％，Ti：0.051～0.15％，V：0.040～0.12％，Cr：0.20～1.20％，B：0.0005～0.0030％，Al：0.02～0.06％，Ca：0.0005～0.004％，N≤0.005％，P≤0.020％，S≤0.0050％，O≤0.0040％，余量包含Fe及其它不可避免杂质，且，需同时满足：
通过下式计算获得的纳米析出物控制指数NPI为5～26：NPI＝(Mo+W+2.3*Cr)/(Ti+V)，计算时代入相应元素重量百分比百分号前的数值；
Ti+V≥0.11％。
优选地，上述钢化学成分的余量为Fe及其它不可避免杂质。
优选地，上述钢还包含Nb：0～0.060％、Mg：0～0.003％、Ni：0～0.30％、Cu：0～0.40％、Mo：0～0.40％、W：0～0.30％中的一种以上元素。
优选地，本发明所述钢的显微组织为回火索氏体和纳米析出物，回火索氏体的原奥晶粒尺寸(即原始奥氏体晶粒尺寸)为5-10微米，纳米析出物包括TiC和VC析出物，所述纳米析出物的尺寸为2-5纳米。
优选地，本发明所述钢的屈服强度为≥1000MPa，抗拉强度为≥1050MPa，延伸率A50≥19％，-60℃冲击功≥90J。更优选地，钢的性能满足以下中的至少一项：屈服强度为1000-1115MPa，抗拉强度为1050-1172MPa，延伸率A50为19-25％，-60℃冲击功为90-129J。
如无特别说明，本发明的钢组分中各元素的含量为重量百分比。在本发明所述钢的成分设计中，各元素的作用如下：
碳：具有固溶强化作用，能调整马氏体组织的强度和塑韧性。经试验，再加热淬火后低碳马氏体的抗拉强度与C含量的关系如下：Rm＝2510×C+790(经验公式，计算时代入钢中C的重量百分比百分号前的数值，单位：MPa)，淬火后通过回火进一步调整强度、塑性和韧性；C含量较高会导致整体C当量的提高，焊接时容易产生裂纹，本发明的C含量范围为0.15～0.21％。
硅：一定量的Si可以起到较好的脱氧作用，同时能在回火过程中抑制 碳化物的析出、改善钢的韧性。Si太高容易产生红铁皮，因此，本发明的硅含量≤0.50％。
锰：Mn元素在0.6％以上可以提高钢的淬透性，但含量超过1.6％容易产生偏析和MnS等夹杂物，恶化马氏体高强钢的韧性。因此，本发明的钢中Mn含量为0.60～1.60％，优选为1.20-1.60％。
钛：Ti为微合金元素，通过控轧控冷工艺可以与C、N等元素形成大量纳米级析出物。在热处理时一方面能强烈抑制奥氏体晶粒的长大，另一方面在热处理后可以保留大量纳米析出物，起到析出强化作用。本发明的钢中钛含量为0.051～0.15％，优选为0.051-0.09％，以在保证钢强度的同时降低制造成本。
钒：V为微合金元素，能与C元素形成纳米级析出物。在热处理回火时会产生大量纳米级VC析出物。本发明的钢中钒含量为0.040～0.12％，优选为0.04-0.08％，以在保证钢强度的同时降低制造成本。
铌：Nb为微合金元素，能与C元素形成纳米级析出物，在热轧时抑制奥氏体晶粒长大，进而细化相变后的组织。本发明的钢中铌含量为0～0.060％，优选为0.03％以下。
镁：微量的Mg在炼钢时通过控制炼钢和连铸工艺会形成细小的MgO析出物小颗粒，使TiN依附于MgO形成复合析出物MgO-TiN，从而对立方型TiN的形状进行改性，复合析出物接近球型。同时能控制有害的TiN长大，使大颗粒的TiN数量减少。TiN的最大尺寸从常规的8-10微米可以降低至5微米以下，从而改善钢的韧性和塑性。本发明的钢中Mg含量为0～0.003％。
铬：Cr元素在0.2％以上可以提高钢的淬透性，有利于在淬火时形成全马氏体组织。Cr在回火过程中会形成Cr的碳化物，具有抗回火软化的作用。Cr含量超过1.20％在焊接时会出现较大的火花，影响焊接质量。因此，本发明的钢中Cr含量为0.20～1.20％，优选为0.20-0.80％。
钼：一定量的Mo元素可以提高钢的淬透性，有利于在淬火时形成全马氏体组织。Mo在高温回火时与C反应形成碳化物颗粒，具有抗高温回火软化和焊接接头软化的作用。Mo含量太高会导致碳当量提高，恶化焊接性能。同时Mo属于贵金属，大量使用会提高成本。因此，本发明的钢 中Mo含量为0～0.40％，优选为0.25％以下。
钨：W元素可以提高钢的淬透性，在回火时形成碳化物颗粒，具有明显的抗回火软化作用，同时具有抗回火脆性的作用。本发明的钢中W含量为0～0.30％，优选为0.22％以下。
镍：一定量的Ni元素具有细化马氏体组织、改善钢的韧性的作用。Ni含量太高会导致碳当量提高，恶化焊接性能。同时Ni属于贵金属，大量使用会提高成本。因此，本发明的钢中Ni含量为0～0.30％，优选为0.20％以下。
铜：Cu元素在回火时可以产生一定的沉淀强化作用。此外添加一定量的Cu元素可以提高工程机械用超高强钢的耐腐蚀性。本发明的钢中Cu含量为0～0.40％，优选为0.25％以下。
硼：微量的B可以提高钢的淬透性，提高钢的强度。但超过0.0030％的B容易产生偏析，形成碳硼化合物，严重恶化钢的韧性。因此，本发明的钢中硼含量为0.0005～0.0030％，优选为0.0005～0.0020％。
铝：0.02％以上的Al一方面可以作为脱氧剂，另一方面形成的少量Al2O3可在板坯加热时细化晶粒，进而细化轧制后钢板的微观组织。但Al含量超过0.06％容易产生Al的氧化物夹杂缺陷。本发明的钢中Al含量为0.02～0.06％，优选为0.02-0.04％。
钙：微量的Ca元素可以在钢冶炼过程中起到净化钢水的作用，优化MnS等夹杂物的形状和尺寸，改善钢的韧性。Ca含量超过0.004％容易形成尺寸较大的Ca的化合物，反而会恶化韧性。因此，本发明的钢中Ca含量为0.0005～0.004％，优选为0.0015-0.0035％。
氮：由于本发明的钢中添加了较多的Ti，而Ti容易与N形成立方结构的大颗粒TiN，恶化钢板的塑性和韧性。在本发明中，一方面通过精炼工艺将钢中N的含量严格控制在0.0050％以下，优选为0.0030％以下，另一方面采用微量的稀土元素添加，并配合特定的炼钢过热度和钢水凝固工艺，可以有效降低形成的TiN的尺寸和数量。
磷、硫和氧：P、S和O是钢中的杂质元素，影响钢的塑性、韧性。本发明严格控制钢中上述元素的含量为P≤0.020％，S≤0.0050％，O≤0.0040％；优选满足以下中的至少一项：P≤0.012％，S≤0.0035％，O≤ 0.0035％。
特别是，本发明的钢成分还需要满足：
①通过下式计算获得的纳米析出物控制指数NPI为5～26：NPI＝(Mo+W+2.3*Cr)/(Ti+V)，计算时代入相应元素重量百分比百分号前的数值。优选地，NPI为7-15，NPI在该数值范围内可以实现更佳的钢性能，例如更高的强度和更大的延伸率；
Mo、W和Cr都是强的碳化物形成元素，可以抑制碳元素的扩散。钢在560-680℃下长时间卷取时，析出的TiC和VC尺寸较大，达到6-15nm，析出物强化作用相对较弱，钢强度只能提高50-100MPa。并且在随后的热处理过程中，在钢加热到900℃下保温5-10min时，6-15nm的TiC会部分溶解，VC则全部溶解，由此难以发挥纳米析出物对钢的强化效果。本发明通过组合添加一定量的Mo、W和/或Cr元素，尤其是当5≤NPI≤26时，可以抑制TiC的长大，并控制TiC的溶解速度在合适的范围内，使TiC的平均尺寸在2-5mm的微纳米级别。并且随后钢在900℃下加热并淬火，再在500-600℃回火保温10-30min时，VC和TiC二次析出，Mo、W和/或Cr的添加可以将VC和TiC的析出物控制在2-5nm左右的微纳米尺寸范围。NPI太低则VC和TiC粗化，NPI太高则VC和TiC析出不充分。因此在本发明中，控制NPI为5～26；以及
②Ti+V≥0.11％；
Ti+V≥0.11％可以充分发挥TiC和VC在热处理过程的析出强化作用，当Ti+V≥0.11％时，能实现足够的微纳米析出物强化作用。再优选结合NPI和热处理工艺，本发明TiC和VC的微纳米析出物可以产生180～280MPa的析出强化作用。优选地，钢中Ti+V的量为0.12-0.24％。
本发明还涉及上述钢的制造方法，其包括如下步骤：
1)冶炼、铸造
按上述成分采用转炉或电炉炼钢、精炼，铸造形成铸坯；
2)加热
将铸坯置于1220～1300℃的加热炉中加热，待铸坯芯部温度到炉温后开始保温，保温时间>30min，例如30-200min，优选100-200min；
3)轧制
采用单机架往复轧制或多机架热连轧将铸坯轧至目标厚度，获得钢板，其中终轧温度为820～920℃；
4)冷却
将热轧后的钢板以10～30℃/s的冷速冷却至560～680℃，得到铁素体和珠光体组织，在铁素体中产生大量6～15nm大尺寸TiC析出物；
5)淬火+回火热处理
淬火热处理，将钢板加热到Ac3+(20～50)℃，保温时间5～10min，再以≥150℃/s，例如170-300℃/s，优选190-250℃/s的冷速快速冷却至室温；
回火处理，将钢板加热到500～600℃，保温10～30min，最后空冷至室温；其中，Ac3为奥氏体转变结束温度；Ac3＝955-350C-25Mn+51Si+106Nb+100Ti+68Al-11Cr-33Ni-16Cu+67Mo，计算时代入相应元素的重量百分比百分号前的数值。
在本发明的超高强钢的制造方法中：
在炼钢环节添加Mg元素时，将转炉中钢水的过热度控制在15℃以内，同时适度提高连铸二冷水量，以提高钢水的凝固速度，从而形成细小的MgO析出物。TiN可以依附于MgO形成复合析出物MgO-TiN，从而对立方型TiN的形状进行改性，复合析出物接近球型。同时复合析出物较为分散，有利于控制有害的TiN长大，使大颗粒TiN的数量减少，TiN的最大尺寸从常规的8-10微米可以降低至5微米以下，这有利于改善钢的韧性和塑性。
在铸坯加热步骤中，控制加热温度在1220～1300℃、芯部保温时间>30min可以保证连铸期间析出的TiC充分固溶。加热温度超过1300℃时会导致奥氏体晶粒过度长大，造成晶间结合力减弱，在轧制时容易产生裂纹。
在本发明的制造方法中，精轧终轧温度为820～920℃，通过奥氏体再结晶，可以细化奥氏体晶粒。热轧后钢板以10-30℃/s的冷速冷至560～680℃，得到铁素体+珠光体+纳米析出物，此时析出的TiC的尺寸为6-15nm。
在热处理步骤中，将钢板加热到Ac3+(20～50)℃，保温时间控制在5～10min，本发明通过组合添加一定量的Mo、W和/或Cr使5≤NPI≤26，可以在热处理过程中控制TiC的溶解速度在合适的范围内，使TiC的尺寸控制在2～5nm的微纳米级别。在此期间，纳米级的TiC能强烈抑制奥氏体的长大，细化奥氏体和淬火后的组织。
钢板在回火(500～600℃保温10～30min)时得到回火索氏体组织，VC和TiC在回火时二次析出，VC和TiC的析出物控制在2～5nm左右的微纳米尺寸范围。TiC和VC的综合纳米析出可以产生180～280MPa的析出强化作用。
本发明的钢通过淬火后高温回火的工艺得到回火索氏体+纳米析出物的微观组织，大量的纳米析出物保证了高温回火后仍能达到1000MPa以上的强度。通过稀土元素净化钢水纯净度，控制夹杂物的尺寸和形状，减少了变形时夹杂物造成的裂纹萌生，提高了钢板的塑性。
本发明的有益效果如下：
本发明通过控轧控冷和热处理工艺，得到微观组织为回火索氏体+纳米析出物的钢。本发明的钢具有大量TiC和VC的纳米析出物，保证了高温回火后钢板具有1000MPa以上的强度。高温回火得到的回火索氏体提高了钢板的塑性。通过稀土元素净化钢水纯净度，控制夹杂物的尺寸和形状，减少了变形时夹杂物造成的裂纹萌生，进一步提高了超高强钢的塑性。
与现有技术相比，本发明通过获得微观组织为回火索氏体+纳米析出物的钢，并结合稀土净化钢水，控制夹杂物的尺寸和形状，得到了具有更高塑性和韧性的超高强钢。
附图说明
图1为本发明实施例3快速热处理后超高强钢采用光学显微镜拍摄的金相组织照片；
图2为本发明实施例3快速热处理后超高强钢采用扫描电镜拍摄的金相组织照片。
具体实施方式
下面结合实施例和附图对本发明做进一步说明。
表1示出本发明实施例和对比例的成分和相应的NPI，钢的余量为Fe和不可避免杂质。实施例和对比例的钢均使用本发明上述制备方法制得，其工艺参数如表2所示。各实施例和对比例的钢对应的性能如表3所示。
对比例1-4与本发明实施例3采用基本相同的方法制造，所不同的是，对比例1和2的NPI不在本发明限定的数值范围内，对比例3的Ti+V不在本发明限定的范围内，对比例4中的Cr含量不在本发明限定的范围内。
表3中钢的屈服强度、抗拉强度、延伸率按照GB/T 228.1-2021“金属材料拉伸试验第1部分：室温试验方法”进行测试。-60℃冲击功参照GB/T 229-2020《金属材料夏比摆锤冲击试验方法》进行测定。
奥氏体平均晶粒尺寸参照GB/T 6394-2017《金属平均晶粒度测定方法》进行测量，采用苦味酸对磨平的样品进行腐蚀，采用光学显微镜进行拍摄10张以上显微组织照片并统计奥氏体晶粒平均尺寸。
纳米析出物尺寸采用透射电镜(TEM)用薄膜样品观察，统计纳米析出物尺寸。
图1和图2分别给出了本发明实施例3的光学显微镜和扫描电镜照片。从图1可以看出，本发明实施例3的钢热处理后具有回火索氏体组织。从图2可以看出，实施例3的钢热处理后的微观组织中具有大量微纳米析出物。
从图1、图2的金相照片上可以看出，成品钢板的金相组织为均一的等轴状回火索氏体，且组织细密，回火索氏体的原始奥氏体平均晶粒尺寸6微米左右。在图2中可以看到本发明的钢中存在大量颗粒状的碳化物析出物，且90％以上的TiC和TiV析出物尺寸在2-5nm。
本发明实施例1-8的钢通过在含特定量的Ti和V的钢中添加Mo、V和/或Cr并使它们之间满足上述NPI，可获得微观组织为回火索氏体+尺寸为2-5nm的纳米析出物的钢，由此综合改善了钢的强度、塑性和韧性。
从表3可以看出，与对比例1-4相比，本发明通过控制元素钢的组成，可以获得强度、塑性和韧性获得明显提升的钢。
综上所述，本发明采用控轧控冷和离线热处理工艺，从化学成分设计、母材组织、加热速度、保温时间和冷却速度等角度进行控制，使钢在具有 超高强度的同时，还具有良好的延伸率和低温冲击韧性等。
表2
表3
注：-60℃冲击功试验结果中三列分别代表三个平行试样的测试结果。

Claims (6)

  1. 一种钢，其化学成分重量百分比为：C：0.15～0.21％，Si≤0.50％，Mn：0.60～1.60％，Ti：0.051～0.15％，V：0.040～0.12％，Cr：0.20～1.20％，B：0.0005～0.0030％，Al：0.02～0.06％，Ca：0.0005～0.004％，N≤0.005％，P≤0.020％，S≤0.0050％，O≤0.0040％，余量包含Fe及其它不可避免杂质，且，需同时满足：
    通过下式计算获得的纳米析出物控制指数NPI为5～26：NPI＝(Mo+W+2.3*Cr)/(Ti+V)，计算时代入相应元素重量百分比百分号前的数值；
    Ti+V≥0.11％。
  2. 如权利要求1所述的钢，其特征在于，余量为Fe及其它不可避免杂质。
  3. 如权利要求1或2所述的钢，其特征在于，所述钢还包含选自Nb、Mg、Ni、Cu、Mo、W中的一种以上，其中，以重量百分比计，Nb：0～0.060％、Mg：0～0.003％、Ni：0～0.30％、Cu：0～0.40％、Mo：0～0.40％、W：0～0.30％。
  4. 如权利要求1-3中任一项所述的钢，其特征在于，所述钢的显微组织为回火索氏体和纳米析出物；回火索氏体的原奥晶粒尺寸为5-10微米，纳米析出物包括TiC和VC析出物，所述纳米析出物的尺寸为2-5纳米。
  5. 如权利要求1-4中任一项所述的钢，其特征在于，所述钢的屈服强度为≥1000MPa，抗拉强度为≥1050MPa，延伸率A50≥19％，-60℃冲击功≥90J。
  6. 如权利要求1～5中任一项所述的钢的制造方法，其特征在于，所述方法包括如下步骤：
    1)冶炼、铸造
    按权利要求1-3中任一项所述成分采用转炉或电炉炼钢、精炼，铸造形成铸坯；
    2)加热
    将所述铸坯置于1220～1300℃的加热炉中加热，待铸坯芯部温度到炉温后开始保温，保温时间>30min；
    3)轧制
    采用单机架往复轧制或多机架热连轧将所述铸坯轧至目标厚度，获 得钢板，其中终轧温度为820～920℃；
    4)冷却
    将热轧后的钢板以10～30℃/s的冷速冷却至560～680℃的轧制卷取温度；
    5)淬火+回火热处理
    淬火热处理，将钢板加热到Ac3+(20～50)℃，保温5～10min，再以≥150℃/s的冷速快速冷却至室温；
    回火热处理，将钢板加热到500～600℃，保温10～30min，最后空冷至室温；其中，Ac3为奥氏体转变结束温度；Ac3＝955-350C-25Mn+51Si+106Nb+100Ti+68Al-11Cr-33Ni-16Cu+67Mo，计算时代入相应元素的重量百分比百分号前的数值。
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