WO2021232275A1 - 一种热作模具钢及其制备方法 - Google Patents

一种热作模具钢及其制备方法 Download PDF

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WO2021232275A1
WO2021232275A1 PCT/CN2020/091225 CN2020091225W WO2021232275A1 WO 2021232275 A1 WO2021232275 A1 WO 2021232275A1 CN 2020091225 W CN2020091225 W CN 2020091225W WO 2021232275 A1 WO2021232275 A1 WO 2021232275A1
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work die
forging
hot work
die steel
temperature
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French (fr)
Inventor
黄进峰
张津
张�诚
赵超
连勇
李建强
张程
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University of Science and Technology Beijing USTB
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University of Science and Technology Beijing USTB
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Priority to PCT/CN2020/091225 priority Critical patent/WO2021232275A1/zh
Priority to EP20767457.3A priority patent/EP3940105A4/en
Priority to US17/021,404 priority patent/US11180820B1/en
Publication of WO2021232275A1 publication Critical patent/WO2021232275A1/zh
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D17/00—Pressure die casting or injection die casting, i.e. casting in which the metal is forced into a mould under high pressure
    • B22D17/20—Accessories: Details
    • B22D17/22—Dies; Die plates; Die supports; Cooling equipment for dies; Accessories for loosening and ejecting castings from dies
    • B22D17/2209—Selection of die materials
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21D—WORKING OR PROCESSING OF SHEET METAL OR METAL TUBES, RODS OR PROFILES WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21D37/00—Tools as parts of machines covered by this subclass
    • B21D37/10—Die sets; Pillar guides
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D23/00—Casting processes not provided for in groups B22D1/00 - B22D21/00
    • B22D23/06—Melting-down metal, e.g. metal particles, in the mould
    • B22D23/10—Electroslag casting
    • 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
    • C21D1/19—Hardening; Quenching with or without subsequent tempering by interrupted quenching
    • 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
    • C21D1/25—Hardening, combined with annealing between 300 degrees Celsius and 600 degrees Celsius, i.e. heat refining ("Vergüten")
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    • C21—METALLURGY OF IRON
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    • 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
    • C21D1/26—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
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/78—Combined heat-treatments not provided for above
    • 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
    • C21D6/02—Hardening by precipitation
    • 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 of ferrous metals or ferrous alloys 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
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/0068—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for particular articles not mentioned below
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B9/00—General processes of refining or remelting of metals; Apparatus for electroslag or arc remelting of metals
    • C22B9/16—Remelting metals
    • C22B9/18—Electroslag remelting
    • 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
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
    • 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
    • C22C38/18—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
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21D—WORKING OR PROCESSING OF SHEET METAL OR METAL TUBES, RODS OR PROFILES WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21D37/00—Tools as parts of machines covered by this subclass
    • B21D37/01—Selection of materials
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22C—FOUNDRY MOULDING
    • B22C9/00—Moulds or cores; Moulding processes
    • B22C9/06—Permanent moulds for shaped castings
    • B22C9/061—Materials which make up the mould
    • 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
    • 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
    • C21D2211/008—Martensite
    • 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
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/005—Heat treatment of ferrous alloys containing Mn
    • 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
    • C21D6/008—Heat treatment of ferrous alloys containing Si

Definitions

  • the application relates to the field of hot work die steel, and in particular to a hot work die steel and a preparation method thereof.
  • Hot work die steel is mainly used to press solid or liquid metal above the recrystallization temperature into molds for workpieces, such as hot forging dies, hot extrusion dies, and die-casting dies.
  • Hot-work die steel has poor service conditions. Its cavity is in direct contact with high-temperature workpieces, and the local temperature can reach 600-700°C. At the same time, it also bears strong high-temperature load, high-temperature strain fatigue, and thermal fatigue. Insufficient high-temperature strength will cause the mold to soften, deform, and collapse, while the lack of high-temperature fatigue resistance and thermal fatigue resistance will cause cracks and peeling of the mold. Therefore, the high-temperature strength, high-temperature fatigue, and cold-heat of the hot-work die steel will be fully improved. Fatigue and other properties are the core and key indicators to improve the life of hot work die steel.
  • H13 steel has good strength and toughness and thermal fatigue resistance below 550°C, but the strength and thermal stability above 600°C
  • the tensile strength at 700°C is only 260 ⁇ 320MPa.
  • the decrease in high temperature strength also leads to the deterioration of its thermal fatigue resistance.
  • the tendency of hot cracking at high temperature increases, which makes it difficult to meet the high temperature service conditions of hot work die steel.
  • the prior art usually uses increased carbon and alloy content to prepare hot work die steels, such as high-alloy tungsten-molybdenum hot work die steel (3Cr2W8V), etc.
  • the alloy content is as high as Above 10%, the high temperature strength at 700°C can be increased to 300 ⁇ 400MPa, but its room temperature toughness is only 11 ⁇ 13J, and its resistance to cold and heat fatigue is poor. It often fails early due to mold cracks, regardless of safety in use or cost. Processing and other applications are very limited.
  • the purpose of this application is to provide a hot work die steel and a preparation method thereof, so that the hot work die steel has good ductility and high temperature application stability.
  • the specific technical solutions are as follows:
  • the first aspect of the application provides a hot work die steel, the chemical composition mass percentage of which is:
  • the tensile strength of the hot work die steel at 700°C is 560-700 MPa
  • the room temperature hardness value of the hot work die steel after being kept at 700°C for 3 to 5 hours is 32 to 38HRC;
  • the hot work die steel has an elongation rate of 14% to 16% at room temperature, a reduction of area of 48% to 65%, and a room temperature impact toughness of 52 to 63J.
  • the hot work die steel further contains at least one of the following chemical components:
  • Zr 0.01 to 0.03 wt%
  • Co 0.10 to 0.50 wt%
  • B 0.001 to 0.005 wt%
  • Re 0.01 to 0.10 wt%
  • Ti 0.02 to 0.06 wt%
  • Y 0.01 to 0.1 wt%.
  • the S content is less than 0.02 wt%, and the P content is less than 0.02 wt%.
  • the carbides in the hot work die steel are nano-sized needle-shaped MC alloy carbides.
  • the nano-sized needle-shaped MC alloy carbide is: V 0.5-0.8 Mo 0.5-0.6 Cr 0.15-0.3 W 0.06-0.14 Nb 0.01-0.02 C.
  • the tensile strength of the hot work die steel at 700° C. is 600-700 MPa.
  • the second aspect of the present application provides a method for preparing the hot work die steel described in any of the above aspects, including the following steps:
  • Electroslag remelting step remove the oxide scale of the electrode rod, and then put it into a vacuum electroslag remelting device for secondary refining, and keep the water temperature of the water cooling system of the electroslag remelting device not higher than 70°C. Electroslag remelting the electrode rod to obtain an electroslag steel ingot, wherein the melting rate is 7-12kg/min, and the cooling water temperature of the crystallizer is maintained at 40-50°C;
  • Homogenizing annealing step heating the electroslag steel ingot to 1200-1250°C and holding it for 15-23h;
  • Forging step cooling the electroslag steel ingot to a forging heating temperature of 1150 to 1200°C for forging, with an initial forging temperature of 1130 to 1160°C, and a final forging temperature of ⁇ 850°C to obtain a steel ingot;
  • Annealing step after forging Put the steel ingot into an annealing furnace when the temperature is lower than 500°C, heat it to 830 ⁇ 890°C at a heating rate of not more than 100°C/h, and then carry out heat preservation.
  • the holding time is [120min+r(mm) ) ⁇ 2min/mm] or [120min+d(mm)/2 ⁇ 2min/mm], and then cooled with the furnace at a rate of 20 ⁇ 40°C/h to below 500°C, and then air-cooled out of the annealing furnace to obtain the annealed steel ingot ;
  • Fine-grain heat treatment step heat the annealed steel ingot to 930 ⁇ 1150°C for the first heat preservation, and the heat preservation time is [(15 ⁇ 40)min+r(mm) ⁇ 2min/mm] or [(15 ⁇ 40) min+d(mm)/2 ⁇ 2min/mm], after water cooling to 400 ⁇ 500°C in 1 ⁇ 2min, then air cooling to 250 ⁇ 280°C for the second heat preservation, heat preservation time is 5 ⁇ 10h; then at 660 Keep for 5 ⁇ 10h at a temperature of ⁇ 700°C;
  • Quenching and tempering treatment steps heat the insulated steel ingot to 980 ⁇ 1100°C and then keep it warm.
  • the heat preservation time is [(15 ⁇ 40)min+r(mm) ⁇ 2min/mm] or [(15 ⁇ 40)min+d( mm)/2 ⁇ 2min/mm], then cooled to 50 ⁇ 150°C, and then tempered and kept at a temperature of 580 ⁇ 660°C for 6 ⁇ 16h to obtain the hot work die steel;
  • r is the radius of the material
  • d is the thickness of the material.
  • the raw material further includes at least one of the following components: Zr: 0.01 ⁇ 0.03wt%, Co: 0.10 ⁇ 0.50wt%, B: 0.001 ⁇ 0.005wt%, Re: 0.01 ⁇ 0.10 wt%, Ti: 0.02 to 0.06 wt%, and Y: 0.01 to 0.1 wt%.
  • the forging step specifically includes:
  • Forming and forging using a precision forging machine where the forging heating temperature is 900 ⁇ 1050°C, the initial forging temperature is 850 ⁇ 950°C, and the final forging temperature is ⁇ 800°C;
  • a hydraulic hammer or hydraulic press is used for forming and forging, wherein the forging heating temperature is 1150-1200°C, the initial forging temperature is 1130-1160°C, and the final forging temperature is ⁇ 850°C.
  • the holding time of annealing after forging is 6-8h.
  • alloy degree refers to the total content of other elements in steel except iron and carbon.
  • the hot work die steel provided by this application compared with traditional hot work die steel, has a tensile strength of 560-700 MPa at 700°C, which is more than twice that of H13 steel and about 1.5 times that of 3Cr2W8V Above, the operating temperature is increased to about 700°C compared with the 600°C currently used H13 steel, and the increase is as high as 100°C, thereby improving the application stability of hot work die steel at higher temperatures, and the application has good room temperature ductility And high temperature fatigue resistance, thereby increasing the application range of hot work die steel.
  • the heat treatment method of hot work die steel provided in this application can make the tensile strength of the hot work die steel at 700 °C reach 560 ⁇ 700MPa, the room temperature hardness value after being kept at 700°C for 3 ⁇ 5h is 32 ⁇ 38HRC, and this application has good room temperature ductility, and its room temperature ductility is better than the current H13 steel and low-carbon low-alloy hot mold steel It is equivalent, and it also has good resistance to high temperature strain fatigue, thereby increasing the application range of hot work die steel.
  • Figure 1 is the heat treatment process flow chart of the hot work die steel of the application
  • Example 2 is a schematic diagram of the tensile strength of the hot work die steel of Example 5 and the H13 steel of Comparative Example 1 as a function of temperature;
  • Figure 3a is an electron micrograph of the hot work die steel of Example 5 of the application at room temperature
  • Figure 3b is an electron micrograph of the hot work die steel in Example 5 of the application after being stretched at 700°C;
  • Figure 3c is a partial enlarged view of Figure 3b;
  • Figure 4a is an electron micrograph of H13 steel of Comparative Example 1 at room temperature
  • Figure 4b is an electron micrograph of the H13 steel of Comparative Example 1 after being stretched at 700°C;
  • Figure 4c is a partial enlarged view of Figure 4b;
  • Figure 5a is a carbide microscopic morphology diagram of the hot work die steel in Example 5 of the application after being stretched at 700°C;
  • Figure 5b is a selected area electron diffraction pattern diagram of the hot work die steel in Example 5 of the application after being stretched at 700°C;
  • Fig. 5c is a high-resolution image of the MC alloy carbide after being stretched at 700°C of the hot work die steel in Example 5 of the application;
  • FIG. 6 is an analysis diagram of the carbide composition of the hot work die steel in Example 5 of the application.
  • H13 steel to improve the room temperature and low temperature toughness and high temperature strength of hot work die steels
  • it is usually by increasing the content of carbon and alloys to promote the formation of high melting point carbides to solid solution strengthening and Carbide dispersion strengthening method improves the high temperature strength of hot work die steel.
  • it has a certain effect on the high temperature strength of 600 °C, but at higher temperatures, such as 700 °C, its strengthening effect is limited. This is mainly because when the temperature exceeds 600 At °C, the coherent relationship between the M 2 C or MC carbides and the matrix is destroyed, and it turns into non-coherent M 6 C or M 23 C 6 carbides that are easy to grow, resulting in a significant reduction in the strengthening effect. Therefore, the existing design principles and methods of increasing the carbon content and high alloying to increase the high temperature strength have reached the limit to increase the high temperature strength of hot work die steel, and will lead to a sharp decline in plastic toughness, high temperature fatigue, and cold and heat fatigue.
  • this application provides a hot work die steel and a preparation method thereof.
  • the high temperature strength of the material is determined by the stability of the high temperature coherent relationship between carbide and the matrix, and this is regarded as carbon and
  • the application maintains the low-to-medium carbon design (C content is 0.20 ⁇ 0.32%), and obtains the quenched dislocation martensite fine-grained structure through the fine-grain heat treatment step to ensure the toughness and fatigue resistance of the material after tempering Therefore, the service life of the new hot work die steel is ensured from the organizational structure.
  • This application provides a hot work die steel whose chemical composition mass percentage is:
  • the tensile strength of the hot work die steel at 700°C is 560-700 MPa, preferably 600-700 MPa, and more preferably 650-690 MPa;
  • the room temperature hardness value of the hot work die steel after being kept at 700°C for 3 to 5 hours is 32 to 38 HRC.
  • This application does not specifically limit the holding time, for example, it can be 3 to 5 hours, specifically, it can be 3 hours, 4 hours, or 3 hours. 5h, preferably 4h.
  • the elongation rate of the hot work die steel at room temperature is 14% to 16%; the reduction of area is 48% to 65%; and the room temperature impact toughness is 52 to 63J.
  • C carbon
  • the inventor’s research found that carbon (C), as an important element in hot work die steel, determines the hardness and strength of martensite formed during quenching, and plays a key role in the secondary hardening of tempering, and it also plays a key role in the strength of hot work die steel. And toughness have important effects.
  • the quenched structure of low carbon steel is usually dislocation martensite, which not only has high toughness, but also has a certain plastic deformation ability, which can avoid and reduce the formation of quenching cracks; while the acicular martensite formed by medium and high carbon steel is Explosive formation, not only the stress is very high, but also the twin martensite has low toughness and cannot be plastically deformed, and it is easy to produce micro-cracks during quenching.
  • the carbon content design needs to maintain the low-to-medium carbon level, the carbon content in the matrix is below 0.25wt%, and the full lath martensite structure can be obtained after quenching, but considering the actual preparation, Mo, W, V, etc.
  • the carbon content in the hot work die steel of the present application is controlled to 0.20 ⁇ 0.32wt%, so as to improve the toughness and fatigue performance of the material, and it is more in line with actual production. Demand, in order to facilitate the mass production of hot work die steel.
  • the inventor’s research also found that the main function of silicon (Si) and manganese (Mn) is to also deoxidize in steel, and have a certain solid solution strengthening effect and an effect of improving hardenability.
  • the solid solution strengthening effect of Si is better.
  • a small amount of Si can obtain a good solid solution strengthening effect.
  • excessive Si will rapidly reduce the toughness of the material; and Mn is an austenitizing element, and excessive Mn will cause After the material is quenched, the retained austenite is retained in the structure. Too much retained austenite is not conducive to the high-temperature performance of the material. Therefore, the content of Si and Mn in this application is controlled as follows: Si ⁇ 0.5wt%, Mn ⁇ 0.5wt%.
  • Cr chromium
  • Cr is a carbide forming element, which can form a variety of carbides with carbon, such as Cr 7 C 3 , Cr 23 C 6, but these mismatch carbide and the matrix is large, it is difficult to maintain coherent relationship to a high temperature, it is easy to grow rough, high Cr content is not conducive to hot work die steel, high-temperature strength at high temperatures, so the In the application, the content of Cr is controlled to be 1.5-2.8wt%.
  • Tungsten (W) and molybdenum (Mo) can not only improve the hardenability of the material, but also can form a large number of high melting point W 2 C and Mo 2 C carbides in the material, and can also be dissolved in the carbide VC to form alloy carbides, resulting in Secondary hardening effect, and can inhibit the accumulation and growth of carbides, thereby improving high-temperature strength.
  • W and Mo can be too high, the mismatch between the carbide and the matrix will be too large at high temperature and the coherent relationship will be lost. It will also promote the formation of M 6 C and other easy-to-grow coarse carbides, leading to the disappearance of the high-temperature strengthening effect.
  • the content of Mo, W and V are matched with each other to form a low temperature that can maintain a coherent relationship with the matrix at high temperatures.
  • the degree of mismatch MC type alloy carbide improves the high temperature strength of the hot work die steel.
  • Vanadium (V) is a strong carbide forming element.
  • the carbide particles formed are finely distributed and dispersed, and need to be above 1200 °C to be completely dissolved in austenite, so it has the effect of refining austenite grains, and the formed MC-type alloy carbides have a good degree of mismatch with the matrix, but excessively high vanadium content is likely to form coarse primary carbides, resulting in a significant decrease in the plasticity and toughness of the steel.
  • the inventor unexpectedly discovered during research that by controlling the content of V to 0.15-0.7wt%, not only can the combined effects of W, Mo, and V elements be used, the high-temperature coherent relationship between the MC-type alloy carbide and the matrix can be maintained to 700°C. Thereby, the high-temperature strength and thermal stability of the hot-work die steel can be significantly improved, and the plasticity and toughness of the hot-work die steel can also be improved.
  • Nickel (Ni) can effectively increase the hardenability of steel and improve the low-temperature toughness. However, adding too much will not only increase the cost, but also reduce the critical point Ac1 of the hot work die steel, which is detrimental to the red hardness. It is applied to control the content of Ni to Ni: 0.5 to 1.6% wt.
  • Niobium can preferentially combine with C to form strong carbides, which can control grain growth during high-temperature austenitization and play a role in grain refinement.
  • the content is too high, it will form a primary carbonization when the material is solidified. Too many materials and large size are not conducive to the improvement of the impact toughness and fatigue properties of the hot work die steel. Therefore, the content of Nb is controlled to 0.01-0.1 wt% in this application to maximize the effect of grain refinement.
  • the hot work die steel further contains at least one of the following chemical components:
  • Zr 0.01 to 0.03 wt%
  • Co 0.10 to 0.50 wt%
  • B 0.001 to 0.005 wt%
  • Re 0.01 to 0.10 wt%
  • Ti 0.02 to 0.06 wt%
  • Y 0.01 to 0.1 wt%.
  • the inventor’s research also found that, without being limited to any theory, when the hot work die steel contains at least one of the above-mentioned Zr, Co, B, Re, Ti and Y, the high temperature stability and purity of the hot work die steel can be further improved. Degree and grain size, this may be due to:
  • Zirconium has a strong deoxidation and denitrification element effect in the steelmaking process. Therefore, adding a small amount of Zr can combine Zr with oxygen and nitrogen during the smelting process to form finely dispersed oxides and nitrides in the matrix. Conducive to refine the grain structure.
  • the Zr element can also combine with the impurity element S to form sulfides, avoiding the hot brittleness of the steel. Therefore, in order to obtain a finer and purer steel, the Zr content is controlled to 0.01-0.03%wt in this application.
  • Co Co
  • Co can form a continuous solid solution with iron, which can hinder and delay the precipitation and aggregation of carbides in other alloys during the tempering process, thereby significantly improving the thermal strength of the material, but cobalt will reduce the Martensite Due to the hardenability of bulk steel, it is not suitable to add excessive amounts. Therefore, the content of cobalt is controlled to 0.10 to 0.50 wt% in this application.
  • Boron (B) has a very strong ability to improve hardenability within a certain content range, but it does not improve the hardenability much when it exceeds 0.005wt% in steel, and B plays a role in strengthening the grain boundary in steel.
  • the high temperature strength of the material is significantly improved, so the B content is controlled to 0.001 to 0.005 wt% in this application.
  • rhenium (Re) can control the form of sulfide in steel, and at the same time has the effects of deoxidation, desulfurization, improving lateral performance and low temperature toughness, and also has a dispersion hardening effect in low-sulfur steel. Therefore, in order to deoxidize steel To desulfurize and purify molten steel and improve the strength and toughness of steel, the content of Re is controlled to be 0.01 to 0.10 wt% in this application.
  • Titanium (Ti) can preferentially combine with C to form strong carbides, which can control grain growth during high-temperature austenitization and play a role in grain refinement.
  • the content is too high, it will form a primary carbonization when the material is solidified. Too many materials and large size are not conducive to the improvement of the impact toughness and fatigue properties of the hot work die steel. Therefore, the content of Ti is controlled to 0.02-0.06% by weight in this application to play its role in grain refinement.
  • the trace amount of yttrium (Y) in the steel can segregate at the grain boundary at high temperature, so that the grain boundary can be strengthened at high temperature and the high temperature strength can be improved. Therefore, the content of Y is controlled to 0.01-0.1wt% in this application.
  • S and P are not good for the toughness of the material. This may be due to the fact that in addition to the formation of sulfide inclusions and lower plasticity, S also easily forms (Fe+FeS) eutectic in a sulfur-containing atmosphere , Cracking occurs, so its content should be reduced as much as possible; too high P content will lead to a decrease in low temperature toughness and an increase in cold brittle transition temperature, so its content should also be reduced as much as possible to avoid or reduce the adverse effects on plasticity. However, when the content of S and P in the steel is lower, the cost of removing these elements will be higher. In order to ensure the excellent performance of the hot work die steel, it can also reduce its production cost as much as possible to facilitate large-scale production. Therefore, this application controls the S content to be less than 0.02wt% and the P content to be less than 0.02wt%.
  • the tempered sorbite structure retains the characteristics of laths, and the interior of the laths is distributed with high-density nano-level MC alloy carbonization It shows that in the hot work die steel of the present application, nano-carbides have higher thermal stability.
  • the carbides in the hot work die steel are nano-sized needle-shaped MC alloy carbides, which are multi-element carbides.
  • Alloy carbide, after atom probe analysis, the nano-level needle-shaped MC alloy carbide is: V 0.5 ⁇ 0.8 Mo 0.5 ⁇ 0.6 Cr 0.15 ⁇ 0.3 W 0.06 ⁇ 0.14 Nb 0.01 ⁇ 0.02 C, not limited to any theory , This kind of carbide can maintain a higher temperature coherent relationship with the matrix, so as to realize the high temperature and high strength of the hot work die steel under the low alloy degree.
  • the hot work die steel provided by this application has a tensile strength of 560-700 MPa at 700°C and a room temperature hardness value after heat preservation at 700°C for 3 to 5 hours. It is 32 to 38HRC, so it can increase the temperature of hot work die steel from the existing 600 °C to about 700 °C, the increase rate is as high as 100 °C, so as to improve the application stability of hot work die steel at higher temperatures, and, This application has good room temperature ductility, thereby increasing the application range of hot work die steel.
  • This application also provides a method for preparing hot work die steel as described in any of the above embodiments, including the following steps:
  • the raw materials are prepared according to the following mass percentages: C: 0.20 ⁇ 0.32wt%, Si: ⁇ 0.5wt%, Mn: ⁇ 0.5wt%, Cr: 1.5 ⁇ 2.8wt%, Mo: 1.5 ⁇ 2.5wt%, W: 0.5 ⁇ 1.2 wt%, Ni: 0.5 to 1.6 wt%, V: 0.15 to 0.7 wt%, Nb: 0.01 to 0.1 wt%, the balance is iron, and then the raw materials are subjected to arc smelting, refining outside the furnace, vacuum degassing, and forging
  • the billet is an electrode rod.
  • the preparation process of the electrode rod is well-known to those skilled in the art, and there is no particular limitation in this application.
  • the electrode rod can be prepared by the following process: after mixing the above-mentioned raw materials, they are sequentially subjected to electric arc smelting (EAF) and out-of-furnace refining (LF), vacuum degassing (VD), forging into electrode rods in a forging furnace.
  • EAF electric arc smelting
  • LF out-of-furnace refining
  • VD vacuum degassing
  • This application has no special restrictions on the above-mentioned arc smelting, out-of-furnace refining, vacuum degassing, and forging, as long as the purpose of the application can be achieved.
  • the arc smelting furnace temperature can be no less than 1690°C, and the gas content in the molten steel can be controlled.
  • the content of impurity elements is: [nitrogen(N)]+[hydrogen(H)]+[oxygen(O)] ⁇ 150ppm;
  • the heating temperature of the refining outside the furnace is 1600 ⁇ 1700°C, and the refining process can produce high alkalinity Reduced slag, and enhanced desulfurization by controlling the temperature;
  • the vacuum degassing time is 15-20 minutes, the heating temperature is 1560-1675°C, and the absolute vacuum degree is 50-100 Pa.
  • the melting rate can be 7-12kg/min
  • the cooling water temperature of the crystallizer is maintained at 40-50°C
  • the deoxidizer can be aluminum.
  • the electroslag remelting process is filled with inert gas, such as argon.
  • the electroslag steel ingot is cooled to a forging heating temperature of 1150 to 1200°C for forging, the initial forging temperature is 1130 to 1160°C, and the final forging temperature is greater than or equal to 850°C to obtain a steel ingot.
  • the forging heating temperature of the present application is increased by about 50° C. compared with the heating temperature of the existing die steel, so as to increase the high-temperature solid solubility of carbon and alloy elements, and make the structure and crystal grain fine after forging.
  • the holding time is [120min+r(mm) ⁇ 2min/mm ] Or [120min+d(mm)/2 ⁇ 2min/mm], the specific holding time can be determined by the size of the material, preferably 6-8 hours, and then cooled to 500°C with the furnace at a rate of 20-40°C/h Next, the annealing furnace is air-cooled to obtain an annealed steel ingot.
  • r is the material radius and d is the material thickness.
  • d is the material thickness.
  • the above r can be used to calculate the holding time.
  • the steel ingot is a cube, the above d can be used to calculate the holding time.
  • the specific calculation method is determined by the actual shape of the material; The steel ingot is cooled to a lower temperature (such as lower than 500°C) and then annealed to avoid the coarsening of the crystal grains caused by the high temperature holding for too long.
  • Figure 1 is the heat treatment process flow chart of the hot working die steel of the application.
  • the annealed steel ingot is heated to 930 ⁇ 1150°C for the first heat preservation, and the heat preservation time is [(15 ⁇ 40)min+r( mm) ⁇ 2min/mm] or [(15 ⁇ 40)min+d(mm)/2 ⁇ 2min/mm], the specific holding time can be determined by the material size, the above process is the normalizing process, and then within 1 ⁇ 2min
  • the internal water is cooled to 400 ⁇ 500°C, it is air-cooled to 250 ⁇ 280°C for the second heat preservation, and the heat preservation time is 5 ⁇ 10h; then it is kept at the temperature of 660 ⁇ 700°C for 5 ⁇ 10h;
  • r is the material radius and d is the material thickness.
  • d is the material thickness.
  • the above r can be used to calculate the holding time.
  • the steel ingot is a cube, the above d can be used to calculate the holding time.
  • the specific calculation method is determined by the actual shape of the material.
  • the holding time is [(15 ⁇ 40)min+r(mm) ⁇ 2min/mm] or [(15 ⁇ 40)min+d(mm)/2 ⁇ 2min/mm], and then cooled to 50-150°C; and then tempered and kept at a temperature of 580-660°C for 6-16h to obtain the hot work die steel.
  • the heating temperature is increased by 30-50° C. compared with the quenching heating temperature of the existing hot work die steel, and the purpose is to increase the solid solubility of alloying elements.
  • the present application has no special restrictions on the cooling method of the quenching and tempering treatment step, for example, it can be air cooling, water cooling or oil cooling.
  • tempering at 580-660°C can make the hot-working die steel form nano-level low-mismatch MC-type alloy carbides, and further improve the thermal stability of the material.
  • the raw material may also include at least one of the following ingredients:
  • Zr 0.01 to 0.03 wt%
  • Co 0.10 to 0.50 wt%
  • B 0.001 to 0.005 wt%
  • Re 0.01 to 0.10 wt%
  • Ti 0.02 to 0.06 wt%
  • Y 0.01 to 0.1 wt%.
  • the forging step may specifically include:
  • Forming and forging using a precision forging machine where the forging heating temperature is 900-1050°C, the initial forging temperature is 850-950°C, and the final forging temperature is ⁇ 800°C; or, hydraulic hammer or hydraulic press is used for forming and forging, where the forging heating temperature is 1150 ⁇ 1200°C, the initial forging temperature is 1130 ⁇ 1160°C, and the final forging temperature is ⁇ 850°C, so as to obtain forgings with suitable shape and size.
  • the precision forging machine can be a precision forging machine produced by GFM Company in Austria.
  • the heat treatment method of hot work die steel provided in this application can make the tensile strength of the hot work die steel at 700 °C reach 560 ⁇ 700 MPa, the room temperature hardness value after being kept at 700°C for 3 to 5 hours is 32 to 38 HRC, and the present application has good room temperature ductility, thereby increasing the application range of hot work die steel.
  • the raw materials are prepared according to the following mass percentages:
  • the balance is iron, and the raw materials are forged into electrode rods through arc smelting, refining, vacuum degassing, and forging in a forging furnace.
  • the electroslag ingot is heated to 1200°C for 23h.
  • the electroslag steel ingot is cooled to a forging heating temperature of 1150°C for forging.
  • the initial forging temperature is 1130°C and the final forging temperature is 850°C to obtain a steel ingot with a radius of 40mm and a length of 100mm.
  • the steel ingot into the annealing furnace when the temperature is lower than 500°C, heat it to 830°C at a heating rate of 80°C/h, and keep it warm for 200min, and then cool it to 450°C with the furnace at a rate of 20°C/h
  • the annealing furnace is air-cooled to obtain an annealed steel ingot.
  • the holding time is 2h. After water cooling to 400°C within 1 min, it is air-cooled to 250°C for the second heat preservation. The holding time is 10h; then at 660°C. Keep the temperature for 10h.
  • the raw materials are prepared according to the following mass percentages:
  • the balance is iron, and the raw materials are forged into electrode rods through arc smelting, refining, vacuum degassing, and forging in a forging furnace.
  • the electroslag ingot is heated to 1230°C for 20 hours.
  • the electroslag steel ingot is cooled to a forging heating temperature of 1170°C for forging, the initial forging temperature is 1150°C, and the final forging temperature is 860°C to obtain a steel ingot with a radius of 40mm and a length of 100mm.
  • the steel ingot into the annealing furnace when the temperature is lower than 500°C, heat it to 850°C at a heating rate of 90°C/h, and then heat it for 200min, and then cool it with the furnace to 480°C at a rate of 30°C/h
  • the annealing furnace is air-cooled to obtain an annealed steel ingot.
  • the holding time is 2h. After water cooling to 450°C within 1.5 minutes, it is air-cooled to 260°C for the second heat preservation. The holding time is 6h; then at 660°C. Keep the temperature at °C for 5h.
  • the insulated steel ingot is heated to 1020°C and held for 1.5 hours, then cooled to 100°C; then tempered and held at 620°C for 10 hours to obtain hot working die steel.
  • the raw materials are prepared according to the following mass percentages:
  • the electroslag ingot is heated to 1250°C for 15h.
  • the electroslag steel ingot is cooled to a forging heating temperature of 1200°C for forging.
  • the initial forging temperature is 1160°C and the final forging temperature is 870°C to obtain a steel ingot with a radius of 40mm and a length of 100mm.
  • the steel ingot into the annealing furnace when the temperature is lower than 500°C, heat it to 900°C at a heating rate of 100°C/h, and then heat it for 200min, and then cool it with the furnace to 490°C at a rate of 40°C/h
  • the annealing furnace is air-cooled to obtain an annealed steel ingot.
  • the holding time is 2h. After water cooling to 500°C within 2min, it is air-cooled to 280°C for the second heat preservation. The holding time is 6h; then at 680°C. Keep the temperature for 5h.
  • the insulated steel ingot is heated to 1020°C and held for 1.5 hours, and then cooled to 150°C; and then tempered and held at 635°C for 6 hours to obtain hot working die steel.
  • the raw materials are prepared according to the following mass percentages:
  • the electroslag ingot is heated to 1250°C for 15h.
  • the electroslag steel ingot is cooled to a forging heating temperature of 1200°C for forging.
  • the initial forging temperature is 1160°C and the final forging temperature is 870°C to obtain a steel ingot with a radius of 40mm and a length of 100mm.
  • the steel ingot into the annealing furnace when the temperature is lower than 500°C, heat it to 900°C at a heating rate of 100°C/h, and then heat it for 200min, and then cool it with the furnace to 490°C at a rate of 40°C/h
  • the annealing furnace is air-cooled to obtain an annealed steel ingot.
  • the annealed steel ingot is heated to 1100°C for the first heat preservation.
  • the holding time is 2h. After water cooling to 500°C within 2min, it is air-cooled to 270°C for the second heat preservation.
  • the holding time is 6h; then at 700°C. Keep the temperature for 5h.
  • the insulated steel ingot is heated to 1050°C and held for 1 hour, then cooled to 100°C; and then tempered and held at 640°C for 6 hours to obtain hot working die steel.
  • the raw materials are prepared according to the following mass percentages:
  • the balance is iron, and the raw materials are forged into electrode rods by arc smelting, refining, vacuum degassing, and forging in a forging furnace.
  • the electroslag ingot is heated to 1230°C for 20 hours.
  • the electroslag steel ingot is cooled to a forging heating temperature of 1180°C for forging.
  • the initial forging temperature is 1140°C and the final forging temperature is 870°C to obtain a steel ingot with a radius of 40mm and a length of 100mm.
  • the steel ingot into the annealing furnace when the temperature is lower than 500°C, heat it to 850°C at a heating rate of 95°C/h, and keep it warm.
  • the holding time is 200min, and then it is cooled to 485°C with the furnace at a rate of 35°C/h.
  • the annealing furnace is air-cooled to obtain an annealed steel ingot.
  • the holding time is 2h. After water cooling to 430°C within 1min, it is air-cooled to 270°C for the second heat preservation. The holding time is 6h; then at 680°C. Keep the temperature for 5h.
  • W is 1.00wt%
  • Ni is 1.22wt%
  • V is 0.60wt%
  • Nb 0.02wt% and contains Zr: 0.01wt%
  • Co 0.20wt%
  • B 0.001wt%
  • Re 0.05wt %
  • Ti 0.04wt%
  • Y 0.02wt%
  • the rest are the same as in Example 5.
  • Cr is 1.50wt%
  • W is 1.00wt%
  • Ni is 1.22wt%
  • V is 0.60wt%
  • Nb 0.02wt%
  • Zr 0.03wt%
  • Co 0.40wt%
  • B 0.005 Except for wt%, Re: 0.10 wt%, Ti: 0.06 wt%, and Y: 0.10 wt%, the rest is the same as in Example 5.
  • This comparative example is H13 hot work die steel, its specifications are: radius 40mm, length 100mm, and its heat treatment process includes the following steps:
  • Tempering Heat the quenched steel ingot to 590°C, hold it for 2h, then heat it to 620°C, and hold it for 2h.
  • This comparative example is 3Cr2W8V hot work die steel, its specifications are: radius 40mm, length 100mm, and its heat treatment process includes the following steps:
  • Tempering Heat the quenched steel ingot to 610°C, hold it for 2h, then heat it to 630°C, and hold it for 2h.
  • the room temperature Rockwell hardness (HRC) of the hot work die steels of Examples 1 and 5 and Comparative Examples 1 and 2 were tested at different temperatures for 4 hours. The test results are shown in Table 3.
  • the room temperature tensile properties and impact toughness (U-shaped notch) of the hot work die steels of Examples 1 and 5 and Comparative Examples 1 and 2 were tested.
  • the test results include elongation (A), reduction of area (Z) and room temperature impact toughness (A ku ), as shown in Table 4.
  • Example 1 is improved by nearly 2 times.
  • Examples 2 to 5 are improved by more than 2 times; compared to comparative example 2, examples 1 and 2 are improved by nearly 1.5 times, and examples 3 to 5 are improved by more than 1.5 times, indicating that the hot work die steel of the present application is excellent The high temperature strength.
  • Figure 2 is a schematic diagram of the tensile strength of the hot work die steel prepared in Example 5 of the application and the H13 steel of Comparative Example 1 with temperature.
  • the tensile strength of the H13 steel rapidly decreases after the temperature exceeds 600°C, °C tensile strength is only 292MPa, while the hot work die steel of the present application decreases slowly as the temperature rises.
  • the tensile strength at temperatures above 650°C is higher than that of H13 steel, even if the tensile strength reaches about 700°C 700MPa, which is about twice as high as that of H13 steel.
  • Figure 3a is an electron micrograph of the hot work die steel of Example 5 of this application at room temperature (25°C);
  • Figure 3b is an electron micrograph of the hot work die steel of Example 5 of this application after being stretched at 700°C;
  • Figure 3c is Figure 3b is a partial enlarged view.
  • Fig. 4a is an electron micrograph of the H13 steel of Comparative Example 1 at room temperature
  • Fig. 4b is an electron micrograph of the H13 steel of Comparative Example 1 after being stretched at 700° C.
  • Fig. 4c is a partial enlarged view of Fig. 4b.
  • the hot work die steel of the present application and Comparative Example 1 has a tempered sorbite structure that retains lath characteristics at room temperature; Figure 3b and Figure 4b are compared, and Figure 3c and Compared with Figure 4c, after stretching at 700°C, the hot work die steel of the present application still retains the characteristics of the slats, and high-density nano-level MC alloy carbides are distributed inside the slats, while the H13 steel of Comparative Example 1 completely loses the plate.
  • the characteristics of the article are that the carbides are coarsened and spheroidized, which indicates that the nano-carbides in the hot work die steel of the present application have higher thermal stability and do not grow up at 700°C. Therefore, the hot work die steel of the present application has excellent properties.
  • the thermal stability is that the carbides are coarsened and spheroidized, which indicates that the nano-carbides in the hot work die steel of the present application have higher thermal stability and do not grow up at 700°C. Therefore, the hot work die steel of the present application has excellent properties.
  • the thermal stability is that the carbides are coarsened and spheroidized, which indicates that the nano-carbides in the hot work die steel of the present application have higher thermal stability and do not grow up at 700°C. Therefore, the hot work die steel of the present application has excellent properties. The thermal stability.
  • Figure 5a is a carbide microscopic morphology of the hot work die steel in Example 5 of the application after being stretched at 700°C, which is specifically a TEM bright-field image.
  • the carbide is a nanoscale needle-shaped MC Type alloy carbide.
  • Figure 5b is the selected area electron diffraction pattern of the hot work die steel in Example 5 of the application after being stretched at 700°C.
  • the (200) plane of the ⁇ matrix is parallel to the (200) of the MC carbide, while The [001] direction of the ⁇ matrix is parallel to the [011] direction of the MC carbide, indicating that the MC carbide still maintains a good BN orientation relationship with the ⁇ matrix after 700°C.
  • Figure 5c is a high-resolution image of the MC alloy carbide of the hot work die steel in Example 5 of the application after being stretched at 700°C. As shown in Figure 5c, the carbide/matrix interface still maintains a high degree of coherence, indicating the application The hot work die steel has good high temperature stability.
  • Figure 6 is a carbide composition analysis diagram of the hot work die steel of Example 5 of the application.
  • the atom probe analysis result shows that the dashed box represents the carbides from the region in the composition analysis, and the carbides are multi-element alloys.
  • Carbide V 0.5 ⁇ 0.8 Mo 0.5 ⁇ 0.6 Cr 0.15 ⁇ 0.3 W 0.06 ⁇ 0.14 Nb 0.01 ⁇ 0.02 C
  • this special carbide can maintain a higher temperature coherent relationship with the matrix, so as to achieve high temperature under low alloying degree high strength.
  • the inventor believes that this application can maintain a high-temperature coherent relationship between the carbides of the hot work die steel and the matrix through the mutual cooperation of the components and the innovative heat treatment process, and realize the carbide/matrix interface error
  • the adjustment of the degree of coordination keeps the stability of the coherent relationship between the carbide and the matrix up to 700°C, thereby improving the high-temperature tensile strength of the hot-work die steel.

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Abstract

一种热作模具钢及其制备方法，其中热作模具钢的化学成分质量百分比为：C：0.20～0.32wt％、Si：≤0.5wt％、Mn：≤0.5wt％、Cr：1.5～2.8wt％、Mo：1.5～2.5wt％、W：0.5～1.2wt％、Ni：0.5～1.6wt％、V：0.15～0.7wt％、Nb：0.01～0.1wt％，余量为铁，合金度为5～7％；锻造后经过细晶热处理，具有良好的热稳定性及室温塑韧性。

Description

一种热作模具钢及其制备方法 技术领域
本申请涉及热作模具钢领域，具体涉及一种热作模具钢及其制备方法。
背景技术
热作模具钢主要用于将再结晶温度以上固态或液态金属压制成工件的模具，例如热锻模、热挤压模、压铸模等。热作模具钢服役条件恶劣，其模腔与高温工件直接接触，局部温度可达600～700℃，同时，还承受强烈高温载荷、高温应变疲劳、冷热疲劳等作用。高温强度不足会导致模具发生软化、变形、塌陷，而抗高温应变疲劳、冷热疲劳性能的不足则导致模具发生龟裂、剥落，因此全面提升热作模具钢的高温强度、高温疲劳、冷热疲劳等性能是提高热作模具钢寿命的核心与关键指标。
现有的应用较广泛的热作模具钢为中合金铬系H13钢(4Cr5MoSiV1)，H13钢在550℃以下具有良好的强韧性配合和抗热疲劳性能，但超过600℃时强度与热稳定性急剧下降，700℃抗拉强度仅260～320MPa，高温强度的降低也导致其抗热疲劳性能的恶化，高温发生热裂倾向增大，难以满足热作模具钢高温服役工况。
为了提高热作模具钢的使用温度和高温强度，现有技术通常会采用提高碳和合金含量而制备热作模具钢，例如高合金钨钼系热作模具钢(3Cr2W8V)等，其合金含量高达10％以上，700℃高温强度可提高到300～400MPa，但其室温韧性仅为11～13J，抗冷热疲劳性能差，常常由于模具发生龟裂而早期失效，无论从使用安全性，还是成本加工等，应用范围均十分有限。
因此亟需一种具有高温高强度，同时兼具良好室温塑韧性和抗疲劳性能的热作模具钢。
发明内容
本申请的目的在于提供一种热作模具钢及其制备方法，以使热作模具钢具有良好的塑韧性高温应用稳定性。具体技术方案如下：
本申请的第一方面提供了一种热作模具钢，其化学成分质量百分比为：
C：0.20～0.32wt％、Si：≤0.5wt％、Mn：≤0.5wt％、Cr：1.5～2.8wt％、Mo：1.5～2.5wt％、W：0.5～1.2wt％、Ni：0.5～1.6wt％、V：0.15～0.7wt％、Nb：0.01～0.1wt％，余量为铁，合金度为5～7％；
所述热作模具钢在700℃时的抗拉强度为560～700MPa；
所述热作模具钢在700℃下保温3～5h后的室温硬度值为32至38HRC；
所述热作模具钢在室温下的延伸率为14％～16％，断面收缩率为48％～65％，室温冲击韧性为52～63J。
在本申请的一种实施方案中，所述热作模具钢还含有以下化学成分中的至少一种：
Zr：0.01～0.03wt％、Co：0.10～0.50wt％、B：0.001～0.005wt％、Re：0.01～0.10wt％、Ti：0.02～0.06wt％、以及Y：0.01～0.1wt％。
在本申请的一种实施方案中，所述热作模具钢中，S含量小于0.02wt％，P含量小于0.02wt％。
在本申请的一种实施方案中，所述热作模具钢在700℃经拉伸后，其回火索氏体组织仍保留有板条特征。
在本申请的一种实施方案中，所述热作模具钢在700℃经拉伸后，所述热作模具钢中的碳化物为纳米级针状MC型合金碳化物。
在本申请的一种实施方案中，所述纳米级针状MC型合金碳化物为：V 0.5～0.8Mo 0.5～0.6Cr 0.15～0.3W 0.06～0.14Nb 0.01～0.02C。
在本申请的一种实施方案中，所述热作模具钢在700℃时的抗拉强度为600～700MPa。
本申请的第二方面提供了一种上述任一方面所述的热作模具钢的制备方法，包括以下步骤：
熔炼步骤：按以下质量百分比配制原料：
C：0.20～0.32wt％、Si：≤0.5wt％、Mn：≤0.5wt％、Cr：1.5～2.8wt％、Mo：1.5～2.5wt％、W：0.5～1.2wt％、Ni：0.5～1.6wt％、V：0.15～0.7wt％、Nb：0.01～0.1wt％，余量为铁，
将所述原料经电弧熔炼、炉外精炼、真空脱气、锻造炉中锻造为电极棒；
电渣重熔步骤：将所述电极棒去除氧化皮，然后放入真空电渣重熔装置中进行二次精炼，并保持电渣重熔装置的水冷系统水温不高于70℃，对所述电极棒电渣重熔得到电渣钢锭，其中，熔化速度为7～12kg/min，结晶器冷却水水温保持在40～50℃；
均质化退火步骤：将所述电渣钢锭加热至1200～1250℃，保温15～23h；
锻造步骤：将所述电渣钢锭降温至锻造加热温度1150～1200℃进行锻造，始锻温度为1130～1160℃，终锻温度≥850℃，得到钢锭；
锻后退火步骤：将所述钢锭在温度低于500℃时放入退火炉，以不大于100℃/h的加热速率加热到830～890℃后进行保温，保温时间为[120min+r(mm)×2min/mm]或[120min+d(mm)/2×2min/mm]，然后再以20～40℃/h的速率随炉冷至500℃以下出退火炉空冷，得到退火后的钢锭；
细晶热处理步骤：将退火后的钢锭加热至930～1150℃后进行第一次保温，保温时间为[(15～40)min+r(mm)×2min/mm]或[(15～40)min+d(mm)/2×2min/mm]，在1～2min内水冷至400～500℃后，再空冷至250～280℃进行第二次保温，保温时间为5～10h；然后在660～700℃温度下保温5～10h；
调质处理步骤：将保温后的钢锭加热到980～1100℃后保温，保温时间为[(15～40)min+r(mm)×2min/mm]或[(15～40)min+d(mm)/2×2min/mm]，然后冷却至50～150℃，再在580～660℃温度下回火保温，保温时间6～16h，得到所述热作模具钢；
其中，r为材料半径，d为材料厚度。
在本申请的一种实施方案中，所述原料还包含以下成分的至少一种：Zr：0.01～0.03wt％、Co：0.10～0.50wt％、B：0.001～0.005wt％、Re：0.01～0.10wt％、Ti：0.02～0.06wt％、以及Y：0.01～0.1wt％。
在本申请的一种实施方案中，锻造步骤具体包括：
利用精锻机成形锻造，其中，锻造加热温度为900～1050℃，始锻温度为850～950℃，终锻温度≥800℃；
或者，利用液压锤或油压机成形锻造，其中，锻造加热温度为1150～1200℃，始锻温度为1130～1160℃，终锻温度≥850℃。
在本申请的一种实施方案中，锻后退火的保温时间为6～8h。
本申请中，术语“合金度”是指：钢中除铁、碳以外的其他元素的总含量。
本申请提供的一种热作模具钢，与传统热作模具钢相比，由于其在700℃时的抗拉强度为560～700MPa，为H13钢的约2倍以上，为3Cr2W8V的约1.5倍以上，使用温度较现用H13钢的600℃提升至约700℃，提升幅度高达100℃，从而提升热作模具钢在更高温度下的应 用稳定性，并且，本申请具有良好的室温塑韧性和抗高温疲劳性能，从而提高了热作模具钢的应用范围。
本申请提供的一种热作模具钢的热处理方法，通过控制各原料的添加比例以及合理的锻造和热处理工艺，能够使所制得的热作模具钢在700℃时的抗拉强度达到560～700MPa，在700℃下保温3～5h后的室温硬度值为32～38HRC，并且，本申请具有良好的室温塑韧性，其室温塑韧性优于现用H13钢，与低碳低合金热模钢相当，同时还具有良好的抗高温应变疲劳性能，从而提高了热作模具钢的应用范围。
当然，实施本申请的任一产品或方法并不一定需要同时达到以上所述的所有优点。
附图说明
为了更清楚地说明本申请和现有技术的技术方案，下面对实施例和现有技术中所需要使用的附图作简单地介绍，显而易见地，下面描述中的附图仅仅是本申请的一些实施例，对于本领域普通技术人员来讲，在不付出创造性劳动的前提下，还可以根据这些附图获得其他的技术方案。
图1为本申请热作模具钢的热处理工艺流程图；
图2为本申请实施例5的热作模具钢及对比例1的H13钢抗拉强度随温度变化的示意图；
图3a为本申请实施例5的热作模具钢在室温时的电镜照片；
图3b为本申请实施例5的热作模具钢经700℃拉伸后的电镜照片；
图3c为图3b的局部放大图；
图4a为对比例1的H13钢在室温时的电镜照片；
图4b为对比例1的H13钢经700℃拉伸后的电镜照片；
图4c为图4b的局部放大图；
图5a为本申请实施例5的热作模具钢经700℃拉伸后的碳化物显微形貌图；
图5b为本申请实施例5的热作模具钢经700℃拉伸后的选区电子衍射花样图；
图5c为本申请实施例5的热作模具钢经700℃拉伸后的MC型合金碳化物的高分辨率图像；
图6为本申请实施例5的热作模具钢的碳化物成分分析图。
具体实施方式
为使本申请的目的、技术方案、及优点更加清楚明白，以下参照附图和实施例，对本申请进一步详细说明。显然，所描述的实施例仅仅是本申请一部分实施例，而不是全部的实施例。基于本申请中的实施例，本领域普通技术人员在没有做出创造性劳动前提下所获得的所有其他技术方案，都属于本申请保护的范围。
现有技术虽然也有对H13钢加以改进，从而提高提高热作模具钢室温低温韧性与高温强度，但通常是通过提高碳和合金的含量，从而促进高熔点碳化物的形成，以固溶强化及碳化物弥散强化的方式提高热作模具钢的高温强度，虽对600℃高温强度具有一定的提升效果，但在更高温度下，如700℃，其强化效果有限，这主要因为当温度超过600℃时，M 2C或MC碳化物与基体的共格关系遭到破坏，转变为易于长大的非共格M 6C或M 23C 6碳化物，导致强化效果大幅减弱。因此，现有的以提高碳含量、高合金化提高高温强度的设计原理与方法，提升热作模具钢高温强度已到极限，且会导致塑韧性、高温疲劳、冷热疲劳等急剧下降。
有鉴于此，本申请提供了一种热作模具钢及其制备方法，从整体上而言，发明人基于碳化物与基体高温共格关系稳定性决定材料高温强度的发现，将此作为碳与合金元素选择、以及确定热加工热处理参数的依据，通过以W、Mn、Mo、V、Cr、Ni、Nb的多元合金化设计及热处理工艺优化，实现碳化物/基体界面错配度的调控，获得弥散分布的纳米级低错配度MC型合金碳化物，使碳化物与基体的共格关系稳定性可保持至700℃，阻碍位错运动与索氏体板条的再结晶，从而获得高温高强度；同时，本申请保持中低碳设计(C含量为0.20～0.32％)，并通过细晶热处理步骤，获得淬火位错马氏体细晶组织以保证回火后材料韧性及抗疲劳性能，因此从组织结构上保证了新型热作模具钢的使用寿命。
本申请提供了一种热作模具钢，其化学成分质量百分比为：
C：0.20～0.32wt％、Si：≤0.5wt％、Mn：≤0.5wt％、Cr：1.5～2.8wt％、Mo：1.5～2.5wt％、W：0.5～1.2wt％、Ni：0.5～1.6wt％、V：0.15～0.7wt％，Nb：0.01～0.1wt％余量为铁，合金度为5～7％；
所述热作模具钢在700℃时的抗拉强度为560～700MPa，优选为600～700MPa，进一步优选为650～690MPa；
所述热作模具钢在700℃下保温3～5h后的室温硬度值为32至38HRC，本申请对保温时 间不做具体限定，例如可以是3～5h，具体地，可以是3h、4h或5h，优选为4h。
所述热作模具钢在室温下的延伸率为14％～16％；断面收缩率为48％～65％；室温冲击韧性为52～63J。
发明人研究发现，碳(C)作为热作模具钢中的重要元素，决定了淬火时形成马氏体的硬度和强度，且对回火二次硬化起关键作用，对热作模具钢的强度及韧性均有重要影响。不限于任何理论，低碳钢淬火组织通常为位错马氏体，不仅韧性高，且有一定塑性变形能力，可以避免和减轻淬火裂纹的形成；而中高碳钢形成的针状马氏体为爆发式形成，不仅应力很大，且孪晶型马氏体韧性低，不能发生塑性变形，而且易在淬火时产生显微裂纹。
基于上述研究发现，碳含量设计需保持中低碳水平，基体中碳含量在0.25wt％以下，淬火后可获得全板条马氏体组织，但考虑到实际制备中，Mo、W、V等强碳化物形成元素形成一次碳化物对碳的消耗等原因，故本申请的热作模具钢中碳含量控制为0.20～0.32wt％，从而在提升材料韧性及疲劳性能的同时，更符合实际生产需求，以利于热作模具钢的大规模生产。
发明人研究还发现，硅(Si)和锰(Mn)主要作用是在钢中同样脱氧，并具有一定的固溶强化作用和提高淬透性作用。Si的固溶强化效果较好，少量的Si即能获得良好的固溶强化效果，然而过量的Si会使材料的韧性快速降低；而Mn是奥氏体化形成元素，过多的Mn会导致材料淬火后组织残留残余奥氏体，过多的残余奥氏体不利于材料高温性能，故本申请中Si、Mn含量控制为：Si≤0.5wt％，Mn≤0.5wt％。
铬(Cr)主要作用是提高钢的强度、淬透性和抗氧化性，并且，Cr是一种碳化物形成元素，它能与碳形成多种碳化物，如Cr 7C 3，Cr 23C 6等，但这些碳化物与基体错配度较大，共格关系难以保持至高温，因此高温下易于长大粗化，过高的Cr含量不利于提高热作模具钢的高温强度，故本申请中Cr含量控制为1.5～2.8wt％。
钨(W)和钼(Mo)不仅能提高材料淬透性，更可在材料中形成大量高熔点W 2C、Mo 2C碳化物，还可溶入碳化物VC中形成合金碳化物，产生二次硬化效果，并能够抑制碳化物的聚集和长大，从而提高高温强度。但W、Mo含量过高则会导致高温下碳化物与基体错配度过大而丧失共格关系，还会促进M 6C等易于长大粗化碳化物的形成，导致高温强化效果消失。本申请中，通过调整Mo的含量为1.5～2.5wt％，W的含量为：0.5～1.2wt％，使Mo、W与V的含量相互配合，形成高温下可与基体保持共格关系的低错配度MC型合金碳化物，提高了热作模具钢的高温强度。
钒(V)为强碳化物形成元素，形成的碳化物颗粒细小分布弥散，且需要1200℃以上才能完全溶于奥氏体中，因此具有细化奥氏体晶粒的作用，并且所形成的MC型合金碳化物与基体具有良好的错配度，但过高的钒含量易于形成粗大的一次碳化物，导致钢的塑性、韧性将明显降低。发明人研究时意外发现，通过控制V的含量为0.15～0.7wt％，不仅能够利用W、Mo、V元素的共同作用，使MC型合金碳化物与基体的高温共格关系保持至700℃，从而显著提高热作模具钢的高温强度及热稳定性，还能提高热作模具钢的塑性和韧性。
镍(Ni)能够有效的增加钢的淬透性，并提高低温韧性，但加入过多不仅会带来成本增加，同时还会降低热作模具钢的临界点Ac1，对红硬性不利，故本申请将Ni的含量控制为Ni：0.5～1.6％wt。
铌(Nb)能够优先与C结合形成强碳化物，在高温奥氏体化时控制晶粒长大，起到细化晶粒之作用，但如果含量过高，在材料凝固时形成的一次碳化物过多且尺寸较大，不利于热作模具钢冲击韧性和疲劳性能的提高，因此本申请将Nb的含量控制为0.01～0.1wt％，以最大发挥细化晶粒的作用。
本申请的一种实施方案中，所述热作模具钢还含有以下化学成分中的至少一种：
Zr：0.01～0.03wt％、Co：0.10～0.50wt％、B：0.001～0.005wt％、Re：0.01～0.10wt％、Ti：0.02～0.06wt％、以及Y：0.01～0.1wt％。
发明人研究还发现，不限于任何理论，当热作模具钢中含有上述Zr、Co、B、Re、Ti以及Y中的至少一种时，能够进一步提高热作模具钢的高温稳定性、纯净度和晶粒度，这可能是由于：
锆(Zr)在炼钢过程中具有强有力的脱氧和脱氮元素作用，因此，加入少量Zr能在冶炼过程中使Zr与氧氮结合形成基体中细小弥散分布的氧化物与氮化物，有利于细化晶粒组织。并且，Zr元素还能与杂质元素S结合生成硫化物，避免钢材的热脆性。因此，为获得组织细小且更为纯净的钢，故本申请中将Zr含量控制为0.01～0.03％wt。
钴(Co)同Ni、Mn一样能够与铁形成连续固溶体，可以在回火过程中阻碍、延缓其它合金碳化物的析出和聚集，从而显著提高材料的热强性，但钴元素会降低马氏体钢淬透性，故不宜添加过量，因此本申请将钴的含量控制为0.10～0.50wt％。
硼(B)在一定含量范围内提高淬透性的能力非常强，但在钢中超过0.005wt％后对淬透性的提高不大，并且B在钢中起到强化晶界的作用，能够显著提高材料的高温强度，故本申请中将B含量控制为0.001～0.005wt％。
铼(Re)作为稀土元素，在钢中可以控制硫化物的形态，同时具有脱氧、脱硫、提高横向性能及低温韧性作用，并且在低硫钢中还有弥散硬化作用，因此，为使钢脱氧脱硫净化钢液，提高钢的强韧性，本申请中将Re含量控制为0.01～0.10wt％。
钛(Ti)能够优先与C结合形成强碳化物，在高温奥氏体化时控制晶粒长大，起到细化晶粒之作用，但如果含量过高，在材料凝固时形成的一次碳化物过多且尺寸较大，不利于热作模具钢冲击韧性和疲劳性能的提高，因此本申请将Ti的含量控制为0.02～0.06wt％，以发挥其细化晶粒的作用。
钢中微量的钇(Y)含量在高温下可在晶界偏聚，从而在高温下能够强化晶界，提高高温强度，因此本申请将Y的含量控制为0.01～0.1wt％。
而硫(S)、磷(P)作为杂质元素，均对材料韧性不利，这可能是由于S除形成硫化物夹杂使塑性降低外，在含硫气氛中还易形成(Fe+FeS)共晶，出现龟裂现象，因此应尽量降低其含量；P含量过高会导致低温韧性降低和冷脆转变温度上升，故其含量也应尽量降低，以避免或减轻对塑性的不利影响。不过，当S和P在钢中的含量越低，则除去这些元素的成本也将越高，为了使热作模具钢在保证优良性能的同时，还能够尽可能降低其生产成本以利于大规模生产，故本申请将S含量控制为小于0.02wt％，P含量控制为小于0.02wt％。
本申请的一种实施方案中，所述热作模具钢在700℃经拉伸后，其回火索氏体组织中保留有板条特征，板条内部分布着高密度纳米级MC型合金碳化物，表明本申请的热作模具钢中，纳米碳化物具有更高的热稳定性。
本申请的一种实施方案中，所述热作模具钢在700℃经拉伸后，所述热作模具钢中的碳化物为纳米级针状MC型合金碳化物，这种碳化物为多元合金碳化物，经原子探针分析后，所述纳米级针状MC型合金碳化物为：V 0.5～0.8Mo 0.5～0.6Cr 0.15～0.3W 0.06～0.14Nb 0.01～0.02C，不限于任何理论，这种碳化物能与基体保持更高温度的共格关系，从而实现热作模具钢在低合金度下的高温高强度。
本申请提供的一种热作模具钢，与现有的热作模具钢相比，由于其在700℃时的抗拉强度为560～700MPa，在700℃下保温3～5h后的室温硬度值为32至38HRC，因此能够将热作模具钢使用温度从现有的600℃提高到约700℃，提升幅度高达100℃，从而提升热作模具钢在更高温度下的应用稳定性，并且，本申请具有良好的室温塑韧性，从而提高了热作模具钢的应用范围。
本申请还提供了一种如上述任一实施方案所述热作模具钢的制备方法，包括以下步骤：
熔炼步骤：
按以下质量百分比配制原料：C：0.20～0.32wt％、Si：≤0.5wt％、Mn：≤0.5wt％、Cr：1.5～2.8wt％、Mo：1.5～2.5wt％、W：0.5～1.2wt％、Ni：0.5～1.6wt％、V：0.15～0.7wt％、Nb：0.01～0.1wt％，余量为铁，然后将所述原料经电弧熔炼、炉外精炼、真空脱气、锻造开坯为电极棒。
电极棒的制备过程为本领域技术人员所熟知的，本申请没有特别的限制，例如，电极棒可以通过以下过程制备：将上述各原料混合后，依次经电弧熔炼(EAF)、炉外精炼(LF)、真空脱气(VD)、锻造炉中锻造为电极棒。本申请对上述电弧熔炼、炉外精炼、真空脱气、锻造没有特别限制，只要能达到本申请的目的即可，例如，电弧熔炼出炉温度可以不低于1690℃，并控制钢液中气体含量和杂质元素含量为：[氮(N)]+[氢(H)]+[氧(O)]≤150ppm；所述炉外精炼的加热温度为1600～1700℃，精炼过程可以造高碱度还原性渣，并通过控制温度增强脱硫；所述真空脱气时间为15～20min，加热温度为1560～1675℃，绝对真空度在50～100Pa。
电渣重熔步骤：
将所述电极棒去除氧化皮，然后放入真空电渣重熔装置中进行二次精炼，并保持电渣重熔装置的水冷系统水温不高于70℃，对所述电极棒电渣重熔得到电渣钢锭。本申请对电渣重熔不做具体限定，只要能达到本申请目的即可，例如，熔化速度可以为7～12kg/min，结晶器冷却水水温保持在40～50℃，脱氧剂可以选用铝粒或硅钙粉中的至少一种，电渣重熔过程全程充惰性气体，例如氩气。
发明人研究发现，当电渣重熔装置的结晶器冷却水水温不高于70℃时，所制得的电渣钢锭组织更为均匀和细密，纯净度更高。
均质化退火步骤：
将所述电渣钢锭加热至1200～1250℃，保温15～23h；
锻造步骤：
将所述电渣钢锭降温至锻造加热温度1150～1200℃进行锻造，始锻温度为1130～1160℃，终锻温度≥850℃，得到钢锭。
本申请的锻造加热温度较现有模具钢的加热温度提高约50℃，以提高碳与合金元素的高温固溶度，使锻后组织、晶粒细小。
锻后退火步骤：
将所述钢锭在温度低于500℃时放入退火炉，以不大于100℃/h的加热速率加热到830～890℃后进行保温，保温时间为[120min+r(mm)×2min/mm]或[120min+d(mm)/2×2min/mm]，具体保温时间可以以材料尺寸确定，优选为6～8小时，然后再以20～40℃/h的速率随炉冷至500℃以下出退火炉空冷，得到退火后的钢锭。
其中，r为材料半径，d为材料厚度，当钢锭为圆柱体时可以采用上述r计算保温时间，当钢锭为立方体时可以采用上述d计算保温时间，具体计算方式以材料实际形状确定；并且将钢锭冷却至较低温度(如低于500℃)再退火可以避免因高温保温过长而导致的晶粒粗化。
细晶热处理步骤：
结合图1，图1为本申请热作模具钢的热处理工艺流程图，将退火后的钢锭加热至930～1150℃后进行第一次保温，保温时间为[(15～40)min+r(mm)×2min/mm]或[(15～40)min+d(mm)/2×2min/mm]，具体保温时间可以以材料尺寸确定，上述过程即为正火工序，然后在1～2min内水冷至400～500℃后，再空冷至250～280℃进行第二次保温，保温时间为5～10h；然后在660～700℃温度下保温5～10h；
其中，r为材料半径，d为材料厚度，当钢锭为圆柱体时可以采用上述r计算保温时间，当钢锭为立方体时可以采用上述d计算保温时间，具体计算方式以材料实际形状确定。
本申请中，采用正火后水冷至400～500℃后空冷至250～280℃保温5～10h，通过形成B/M(贝氏体/马氏体)复相组织细化晶粒，随后在660～700℃保温形成弥散二次碳化物，阻碍随后进行调质加热时奥氏体晶粒长大，发明人意外地发现，与现有热处理方法相比，材料的高温抗拉强度更高，这可能是由于本申请的细晶热处理方法在提高材料固溶度的同时还能细化晶粒。
调质处理步骤：
将保温后的钢锭加热到980～1100℃后保温，保温时间为[(15～40)min+r(mm)×2min/mm]或[(15～40)min+d(mm)/2×2min/mm]，然后冷却至50～150℃；再在580～660℃温度下回火保温，保温时间为6～16h，得到所述热作模具钢。
本申请的调质处理步骤中，加热温度较现有热作模具钢的淬火加热温度提高30～50℃，其目的是为了提高合金元素固溶度。另外，本申请对调质处理步骤的冷却方式没有特别限制，例如可以为空冷、水冷或油冷，
本申请的回火保温步骤中，在580～660℃回火，能够使热作模具钢形成纳米级低错配度MC型合金碳化物，使材料的热稳定性进一步提高。
本申请的一种实施方案中，所述原料还可以包含以下成分的至少一种：
Zr：0.01～0.03wt％、Co：0.10～0.50wt％、B：0.001～0.005wt％、Re：0.01～0.10wt％、Ti：0.02～0.06wt％、以及Y：0.01～0.1wt％。
本申请的一种实施方案中，锻造步骤具体可以包括：
利用精锻机成形锻造，其中，锻造加热温度为900～1050℃，始锻温度为850～950℃，终锻温度≥800℃；或者，利用液压锤或油压机成形锻造，其中，锻造加热温度为1150～1200℃，始锻温度为1130～1160℃，终锻温度≥850℃，从而得到形状、尺寸合适的锻件。
本申请对精锻机、液压锤或油压机的型号没有特别限制，只要能达到本申请的目的即可，例如，精锻机可以使用奥地利GFM公司生产的精锻机。
本申请提供的一种热作模具钢的热处理方法，通过控制各原料的添加比例以及合理的锻造和热处理工艺，能够使所制得的热作模具钢在700℃时的抗拉强度达到560～700MPa，在700℃下保温3～5h后的室温硬度值为32～38HRC，并且，本申请具有良好的室温塑韧性，从而提高了热作模具钢的应用范围。
以下，举出实施例及对比例来对本申请的实施方式进行更具体地说明。各种的试验及评价按照下述的方法进行。另外，只要无特别说明，“份”、“％”为重量基准。
实施例1
<熔炼>
按以下质量百分比配制原料：
C：0.19wt％、Si：0.20wt％、Mn：0.30wt％、Cr：2.22wt％、Mo：2.30wt％、W：0.50wt％、Ni：0.50wt％、V：0.22wt％、Nb：0.20wt％，余量为铁，将原料经电弧熔炼、精炼、真空脱气、锻造炉中锻造为电极棒。
<电渣重熔>
将电极棒去除氧化皮，然后放入真空电渣重熔装置中，并保持电渣重熔装置的水冷系统水温70℃，对电极棒电渣重熔得到电渣钢锭。
<均质化退火>
将电渣钢锭加热至1200℃，保温23h。
<锻造>
将电渣钢锭降温至锻造加热温度1150℃进行锻造，始锻温度为1130℃，终锻温度850℃，得到钢锭，钢锭半径为40mm，长度为100mm。
<锻后退火>
将钢锭在温度低于500℃时放入退火炉，以80℃/h的加热速率加热到830℃后进行保温，保温时间为200min，然后再以20℃/h的速率随炉冷至450℃出退火炉空冷，得到退火后的钢锭。
<细晶热处理>
将退火后的钢锭加热至930℃后进行第一次保温，保温时间为2h，在1min内水冷至400℃后，再空冷至250℃进行第二次保温，保温时间为10h；然后在660℃温度下保温10h。
<调质处理>
将保温后的钢锭加热到1000℃后保温2h，然后冷却至50℃；再在600℃温度下回火保温16h，得到热作模具钢。
实施例2
<熔炼>
按以下质量百分比配制原料：
C：0.23wt％、Si：0.20wt％、Mn：0.30wt％、Cr：2.48wt％、Mo：2.15wt％、W：0.50wt％、Ni：0.50wt％、V：0.28wt％、Nb：0.10wt％，余量为铁，将原料经电弧熔炼、精炼、真空脱气、锻造炉中锻造为电极棒。
<电渣重熔>
将电极棒去除氧化皮，然后放入真空电渣重熔装置中，并保持电渣重熔装置的水冷系 统水温65℃，对电极棒电渣重熔得到电渣钢锭。
<均质化退火>
将电渣钢锭加热至1230℃，保温20h。
<锻造>
将电渣钢锭降温至锻造加热温度1170℃进行锻造，始锻温度为1150℃，终锻温度860℃，得到钢锭，钢锭半径为40mm，长度为100mm。
<锻后退火>
将钢锭在温度低于500℃时放入退火炉，以90℃/h的加热速率加热到850℃后进行保温，保温时间为200min，然后再以30℃/h的速率随炉冷至480℃出退火炉空冷，得到退火后的钢锭。
<细晶热处理>
将退火后的钢锭加热至980℃后进行第一次保温，保温时间为2h，在1.5min内水冷至450℃后，再空冷至260℃进行第二次保温，保温时间为6h；然后在660℃温度下保温5h。
<调质处理>
将保温后的钢锭加热到1020℃后保温1.5h，然后冷却至100℃；再在620℃温度下回火保温10h，得到热作模具钢。
实施例3
<熔炼>
按以下质量百分比配制原料：
C：0.27wt％、Si：0.04wt％、Mn：0.07wt％、Cr：2.72wt％、Mo：1.90wt％、W：0.95wt％、Ni：1.22wt％、V：0.40wt％、Nb：0.10wt％、Y：0.02wt％，余量为铁，将原料经电弧熔炼、精炼、真空脱气、锻造炉中锻造为电极棒。
<电渣重熔>
将电极棒去除氧化皮，然后放入真空电渣重熔装置中，并保持电渣重熔装置的水冷系统水温68℃，对电极棒电渣重熔得到电渣钢锭。
<均质化退火>
将电渣钢锭加热至1250℃，保温15h。
<锻造>
将电渣钢锭降温至锻造加热温度1200℃进行锻造，始锻温度为1160℃，终锻温度 870℃，得到钢锭，钢锭半径为40mm，长度为100mm。
<锻后退火>
将钢锭在温度低于500℃时放入退火炉，以100℃/h的加热速率加热到900℃后进行保温，保温时间为200min，然后再以40℃/h的速率随炉冷至490℃出退火炉空冷，得到退火后的钢锭。
<细晶热处理>
将退火后的钢锭加热至1000℃后进行第一次保温，保温时间为2h，在2min内水冷至500℃后，再空冷至280℃进行第二次保温，保温时间为6h；然后在680℃温度下保温5h。
<调质处理>
将保温后的钢锭加热到1020℃后保温1.5h，然后冷却至150℃；再在635℃温度下回火保温6h，得到热作模具钢。
实施例4
<熔炼>
按以下质量百分比配制原料：
C：0.30wt％、Si：0.12wt％、Mn：0.02wt％、Cr：2.00wt％、Mo：1.65wt％、W：1.10wt％、Ni：1.42wt％、V：0.42wt％、Nb：0.02wt％、Zr：0.02wt％、Co：0.10wt％、B：0.003wt％、Re：0.012wt％、Ti：0.03wt％、Y：0.02wt％，余量为铁，将原料经电弧熔炼、精炼、真空脱气、锻造炉中锻造为电极棒。
<电渣重熔>
将电极棒去除氧化皮，然后放入真空电渣重熔装置中，并保持电渣重熔装置的水冷系统水温69℃，对电极棒电渣重熔得到电渣钢锭。
<均质化退火>
将电渣钢锭加热至1250℃，保温15h。
<锻造>
将电渣钢锭降温至锻造加热温度1200℃进行锻造，始锻温度为1160℃，终锻温度870℃，得到钢锭，钢锭半径为40mm，长度为100mm。
<锻后退火>
将钢锭在温度低于500℃时放入退火炉，以100℃/h的加热速率加热到900℃后进行保温，保温时间为200min，然后再以40℃/h的速率随炉冷至490℃出退火炉空冷，得到退火 后的钢锭。
<细晶热处理>
将退火后的钢锭加热至1100℃后进行第一次保温，保温时间为2h，在2min内水冷至500℃后，再空冷至270℃进行第二次保温，保温时间为6h；然后在700℃温度下保温5h。
<调质处理>
将保温后的钢锭加热到1050℃后保温1h，然后冷却至100℃；再在640℃温度下回火保温6h，得到热作模具钢。
实施例5
<熔炼>
按以下质量百分比配制原料：
C：0.32wt％、Si：0.30wt％、Mn：0.15wt％、Cr：2.75wt％、Mo：2.30wt％、W：0.65wt％、Ni：0.63wt％、V：0.70wt％、Nb：0.04wt％、Y：0.01wt％，余量为铁，将原料经电弧熔炼、精炼、真空脱气、锻造炉中锻造为电极棒。
<电渣重熔>
将电极棒去除氧化皮，然后放入真空电渣重熔装置中，并保持电渣重熔装置的水冷系统水温66℃，对电极棒电渣重熔得到电渣钢锭。
<均质化退火>
将电渣钢锭加热至1230℃，保温20h。
<锻造>
将电渣钢锭降温至锻造加热温度1180℃进行锻造，始锻温度为1140℃，终锻温度870℃，得到钢锭，钢锭半径为40mm，长度为100mm。
<锻后退火>
将钢锭在温度低于500℃时放入退火炉，以95℃/h的加热速率加热到850℃后进行保温，保温时间为200min，然后再以35℃/h的速率随炉冷至485℃出退火炉空冷，得到退火后的钢锭。
<细晶热处理>
将退火后的钢锭加热至1140℃后进行第一次保温，保温时间为2h，在1min内水冷至430℃后，再空冷至270℃进行第二次保温，保温时间为6h；然后在680℃温度下保温5h。
<调质处理>
将保温后的钢锭加热到1050℃后保温1h，然后冷却至70℃；先在580℃温度下保温4h回火，再在640℃温度下回火保温2h，得到热作模具钢。
实施例6
除原料中W为1.00wt％、Ni为1.22wt％、V为0.60wt％、Nb：0.02wt％且含有Zr：0.01wt％、Co：0.20wt％、B：0.001wt％、Re：0.05wt％、Ti：0.04wt％、Y：0.02wt％以外，其余与实施例5相同。
实施例7
除原料中Cr为1.50wt％、W为1.00wt％、Ni为1.22wt％、V为0.60wt％、Nb：0.02wt％，且含有Zr：0.03wt％、Co：0.40wt％、B：0.005wt％、Re：0.10wt％、Ti：0.06wt％、Y：0.10wt％以外，其余与实施例5相同。
对比例1
本对比例为H13热作模具钢，其规格为：半径40mm，长度100mm，其热处理工艺包括以下步骤：
淬火：将锻造成形后的钢锭加热至1050℃，保温1h，水冷；
回火：将淬火后的钢锭加热至590℃，先保温2h，然后加热至620℃，再保温2h。
对比例2
本对比例为3Cr2W8V热作模具钢，其规格为：半径40mm，长度100mm，其热处理工艺包括以下步骤：
淬火：将锻造成形后的钢锭加热至1130℃，保温1h，水冷；
回火：将淬火后的钢锭加热至610℃，先保温2h，然后加热至630℃，再保温2h。
<性能测试>
高温强度测试：
采用GB/T4338-2006《金属材料高温拉伸试验方法》，测试实施例1～7及对比例1、2的热作模具钢700℃的高温抗拉强度，测试结果如表2所示。
热稳定性测试：
测试实施例1和5及对比例1、2的热作模具钢在不同温度下保温4h后的室温洛氏硬度(HRC)，测试结果如表3所示。
室温性能测试：
测试实施例1和5及对比例1、2的热作模具钢的室温拉伸性能与冲击韧性(U形缺口)，测试结果包括延伸率(A)、断面收缩率(Z)及室温冲击韧性(A ku)，如表4所示。
断裂韧性测试：
采用GB/T 4161—2007《金属材料平面应变断裂韧度K IC实验方法》，选用实施例1和5及对比例1、2的紧凑拉伸试样，在疲劳实验平台上(型号MTS810)进行，测试结果如表5所示。
高温应变疲劳寿命测试：
采用GB/T15248-2002《金属材料轴向等幅低循环疲劳试验方法》，选用实施例5与对比例1，在MTS NEW810电子液压伺服疲劳试验机上进行疲劳寿命测试，结果如表6所示。
表1本申请各实施例与对比例热作模具钢的成分
Figure PCTCN2020091225-appb-000001
表2各实施例及对比例热作模具钢的高温强度测试结果
实施例 R m(MPa) R p0.2(MPa)
实施例1 560 345
实施例2 621 405
实施例3 634 410
实施例4 642 420
实施例5 678 450
实施例6 687 466
实施例7 694 483
对比例1 292 255
对比例2 415 364
表3实施例1、5及对比例1、2热稳定性测试结果(单位HRC)
钢号 600℃ 620℃ 660℃ 700℃
实施例1 45 43.5 39 32
实施例5 47 45.1 41.3 37.2
对比例1 47 40.2 31 24
对比例2 48 46 38.2 29.8
表4实施例1、5及对比例1、2室温性能测试结果
钢号 R m(Mpa) R p0.2(Mpa) A(％) Z(％) A ku(J)
实施例1 1310 1020 16 62 63
实施例5 1350 1050 14 48.3 52
对比例1 1389 1189 11.2 43.7 21.0
对比例2 1647 1449 10 30.8 13
表5实施例1、5及对比例1、2断裂韧性测试结果
钢号 硬度(HRC) K IC(MPa·m 0.5)
实施例1 41 144.2
实施例5 46 107.8
对比例1 44 83.2
对比例2 49 32.7
表6实施例5及对比例1高温应变疲劳寿命测试结果
Figure PCTCN2020091225-appb-000002
由表2可知，实施例1至5的700℃高温强度均高于对比1和对比例2的H13钢和3Cr2W8V钢，具体地，相比于对比例1，实施例1提高接近2倍，实施例2～5提高约2倍以上；相比于对比例2，实施例1和实施例2提高接近1.5倍，实施例3～5提高约1.5倍以上，表明本申请的热作模具钢具有优异的高温强度。
由表3可知，实施例1和5在600～700℃温度区间内保温4h后的室温硬度降低均小于对比例1的H13钢和对比例2的3Cr2W8V钢，表明本申请的热作模具钢具有很高的热稳定性。
由表4可知，实施例1和5的延伸率(A)、断面收缩率(Z)及室温冲击韧性(A ku)均高于对比例1的H13钢和对比例2的3Cr2W8V钢，表明本申请的热作模具钢具有良好的室温塑韧性。
由表5可知，实施例1和5在41HRC和46HRC下，其断裂韧性K IC为107.8～144.2MPa·m 0.5，提高到对比例1的H13钢的1.3倍以上，对比例2的3Cr2W8V钢的约3倍以上，表明本申请的热作模具钢具有良好的室温抗疲劳性能。
由表6可知，实施例5各直径试样在应变幅0.2％～0.6％下的疲劳寿命均高于对比例1相同直径试样的H13钢，表明本申请的热作模具钢抗高温低周疲劳性能优于H13钢。
图2为本申请实施例5制得的热作模具钢及对比例1的H13钢抗拉强度随温度变化的示意图，图2中，H13钢在温度超过600℃后抗拉强度迅速衰减，700℃抗拉强度仅有292MPa，而本申请的热作模具钢随温度升高，其抗拉强度下降缓慢，650℃以上温度的抗拉强度高于H13钢，即使在700℃抗拉强度达到约700MPa，提高到H13钢的约2倍以上。
图3a为本申请实施例5的热作模具钢在室温(25℃)时的电镜照片；图3b为本申请实施例5的热作模具钢经700℃拉伸后的电镜照片；图3c为图3b的局部放大图。
图4a为对比例1的H13钢在室温时的电镜照片；图4b为对比例1的H13钢经700℃拉伸后的电镜照片；图4c为图4b的局部放大图。
通过图3a和图4a对比，本申请与对比例1的热作模具钢在室温下钢组织为保留板条特征的回火索氏体组织；通过图3b和图4b对比，以及通过图3c和图4c对比，在700℃拉伸后，本申请的热作模具钢仍保留板条特征，板条内部分布着高密度纳米级MC型合金碳化物，而对比例1的H13钢则完全丧失板条特征，碳化物发生粗化球化，这表明本申请的热作模具钢中纳米碳化物具有更高的热稳定性，700℃下仍不长大，因此本申请的热作模具钢具有优良的热稳定性。
图5a为本申请实施例5的热作模具钢经700℃拉伸后的碳化物显微形貌图，具体为TEM明场像，如图5a所示，该碳化物为纳米级针状MC型合金碳化物。
图5b为本申请实施例5的热作模具钢经700℃拉伸后的选区电子衍射花样图，如图5b所示，α基体的(200)面与MC碳化物的(200)平行，同时α基体的[001]方向与MC碳化物的[011]方向相平行，表明经700℃后，MC碳化物仍与α基体保持良好的B-N位向关系。
图5c为本申请实施例5的热作模具钢经700℃拉伸后的MC型合金碳化物的高分辨图像，如图5c所示，碳化物/基体界面仍保持高度共格，表明本申请的热作模具钢具有良好的高温稳定性。
图6为本申请实施例5的热作模具钢的碳化物成分分析图，原子探针分析结果显示，其中虚线框中表示的是成分分析来自于该区域的碳化物，该碳化物为多元合金碳化物(V 0.5～0.8Mo 0.5～0.6Cr 0.15～0.3W 0.06～0.14Nb 0.01～0.02C)，该特殊碳化物能与基体保持更高温度的共格关系，从而实现低合金度下的高温高强度。
综上，不限于任何理论，发明人认为，本申请通过各组分相互配合以及创新的热处理工艺，能够使热作模具钢的碳化物与基体保持高温共格关系，实现碳化物/基体界面错配度的调控，使碳化物与基体的共格关系稳定性可保持至700℃，从而提高热作模具钢的高温抗拉强度。
以上所述仅为本申请的较佳实施例，并非用于限定本申请的保护范围。凡在本申请的精神和原则之内所作的任何修改、等同替换、改进等，均包含在本申请的保护范围内。

Claims (11)

  1. 一种热作模具钢，其化学成分质量百分比为：
    C：0.20～0.32wt％、Si：≤0.5wt％、Mn：≤0.5wt％、Cr：1.5～2.8wt％、Mo：1.5～2.5wt％、W：0.5～1.2wt％、Ni：0.5～1.6wt％、V：0.15～0.7wt％、Nb：0.01～0.1wt％，余量为铁，合金度为5～7％；
    所述热作模具钢在700℃时的抗拉强度为560～700MPa；
    所述热作模具钢在700℃下保温3～5h后的室温硬度值为32至38HRC；
    所述热作模具钢在室温下的延伸率为14％～16％，断面收缩率为48％～65％，室温冲击韧性为52～63J。
  2. 根据权利要求1所述的热作模具钢，所述热作模具钢还含有以下化学成分中的至少一种：
    Zr：0.01～0.03wt％、Co：0.10～0.50wt％、B：0.001～0.005wt％、Re：0.01～0.10wt％、Ti：0.02～0.06wt％、以及Y：0.01～0.1wt％。
  3. 根据权利要求1或2所述的热作模具钢，所述热作模具钢中，S含量小于0.02wt％，P含量小于0.02wt％。
  4. 根据权利要求1或2所述的热作模具钢，所述热作模具钢在700℃经拉伸后，其回火索氏体组织仍保留有板条特征。
  5. 根据权利要求1或2所述的热作模具钢，所述热作模具钢在700℃经拉伸后，所述热作模具钢中的碳化物为纳米级针状MC型合金碳化物。
  6. 根据权利要求5所述的热作模具钢，所述纳米级针状MC型合金碳化物为：V 0.5～0.8Mo 0.5～0.6Cr 0.15～0.3W 0.06～0.14Nb 0.01～0.02C。
  7. 根据权利要求1或2所述的热作模具钢，所述热作模具钢在700℃时的抗拉强度为600～700MPa。
  8. 一种如权利要求1～7任一项所述的热作模具钢的制备方法，包括以下步骤：
    熔炼步骤：按以下质量百分比配制原料：
    C：0.20～0.32wt％、Si：≤0.5wt％、Mn：≤0.5wt％、Cr：1.5～2.8wt％、Mo：1.5～2.5wt％、 W：0.5～1.2wt％、Ni：0.5～1.6wt％、V：0.15～0.7wt％、Nb：0.01～0.1wt％，余量为铁，
    将所述原料经电弧熔炼、炉外精炼、真空脱气、锻造炉中锻造为电极棒；
    电渣重熔步骤：将所述电极棒去除氧化皮，然后放入真空电渣重熔装置中进行二次精炼，并保持电渣重熔装置的水冷系统水温不高于70℃，对所述电极棒电渣重熔得到电渣钢锭，其中，熔化速度为7～12kg/min，结晶器冷却水水温保持在40～50℃；
    均质化退火步骤：将所述电渣钢锭加热至1200～1250℃，保温15～23h；
    锻造步骤：将所述电渣钢锭降温至锻造加热温度1150～1200℃进行锻造，始锻温度为1130～1160℃，终锻温度≥850℃，得到钢锭；
    锻后退火步骤：将所述钢锭在温度低于500℃时放入退火炉，以不大于100℃/h的加热速率加热到830～890℃后进行保温，保温时间为[120min+r(mm)×2min/mm]或[120min+d(mm)/2×2min/mm]，然后再以20～40℃/h的速率随炉冷至500℃以下出退火炉空冷，得到退火后的钢锭；
    细晶热处理步骤：将退火后的钢锭加热至930～1150℃后进行第一次保温，保温时间为[(15～40)min+r(mm)×2min/mm]或[(15～40)min+d(mm)/2×2min/mm]，在1～2min内水冷至400～500℃后，再空冷至250～280℃进行第二次保温，保温时间为5～10h；然后在660～700℃温度下保温5～10h；
    调质处理步骤：将保温后的钢锭加热到980～1100℃后保温，保温时间为[(15～40)min+r(mm)×2min/mm]或[(15～40)min+d(mm)/2×2min/mm]，然后冷却至50～150℃，再在580～660℃温度下回火保温，保温时间6～16h，得到所述热作模具钢；
    其中，r为材料半径，d为材料厚度。
  9. 根据权利要求8所述的热作模具钢的制备方法，所述原料还包含以下成分的至少一种：Zr：0.01～0.03wt％、Co：0.10～0.50wt％、B：0.001～0.005wt％、Re：0.01～0.10wt％、Ti：0.02～0.06wt％、以及Y：0.01～0.1wt％。
  10. 根据权利要求8所述的热作模具钢的制备方法，锻造步骤具体包括：
    利用精锻机成形锻造，其中，锻造加热温度为900～1050℃，始锻温度为850～950℃，终锻温度≥800℃；
    或者，利用液压锤或油压机成形锻造，其中，锻造加热温度为1150～1200℃，始锻温度为1130～1160℃，终锻温度≥850℃。
  11. 根据权利要求8所述的热作模具钢的制备方法，锻后退火的保温时间为6～8h。
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