CN114411043B - Preparation method of large hot forging hot work die steel - Google Patents
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- 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
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- 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
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- 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
- C21D1/32—Soft annealing, e.g. spheroidising
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- 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
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- 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
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- 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
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- 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
- C21D8/005—Modifying the physical properties by deformation combined with, or followed by, heat treatment of ferrous alloys
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- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
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- 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
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- 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
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- C—CHEMISTRY; METALLURGY
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- 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
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/54—Ferrous alloys, e.g. steel alloys containing chromium with nickel with boron
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Abstract
A preparation method of large-scale hot forging hot work die steel belongs to the technical field of hot work die steel. The method comprises the following steps: the method comprises the following steps: an electric furnace, an electric furnace and electroslag remelting or a vacuum induction furnace are adopted to smelt into steel ingots, and the steel ingots comprise the following chemical components in percentage by weight: 0.30-0.39% of C, 0.35-0.55% of Si, less than or equal to 0.002% of S, less than or equal to 0.02% of P, 0.50-0.7% of Mn, 1.40-1.70% of Mo, 2.60-3.40% of Cr, 0.10-0.30% of V, 0.80-1.20% of Ni, less than or equal to 0.2% of Al and Nb, less than or equal to 0.1% of B, and the balance of Fe and inevitable impurities; step two: pre-cogging a steel ingot; step three: pre-opening a blank and diffusing at high temperature; step four: forging a blank; step five: normalizing and spheroidizing annealing process. The beneficial effects are as follows: by improving the components and content of the steel and using a new forging method, the obtained large-scale hot forging hot working die steel has good obdurability, high tempering stability and good high-temperature strength, and can meet the use requirements of large-section hot forging hot working die steel.
Description
Technical Field
The invention belongs to the technical field of hot work die steel, and particularly relates to a preparation method of large hot forging hot work die steel.
Background
Hot forged hot work die steels are used for solid metal forming above the recrystallization temperature, and account for a considerable proportion of hot work die steels. At present, almost all heavy stressed members are produced by hot forging forming, and particularly in the manufacturing industries of various fasteners, standard parts, automobile engines, airplanes and the like, the heavy stress members have great dependence on the hot forging forming process. The new generation of main bearing components such as main beams and landing gears of airplanes and die forgings for high-end equipment such as engine blades and the like develop towards the trend of large-scale, integration, precision, near-net shape and low cost. The service temperature of the hot forging die reaches 700-1100 ℃ or even higher, and the die is large in size, complex in structure, large in size difference in a cavity, uneven in material deformation and complex in stress, so that the reliability and the service life of the die are extremely low. The stability of the die material is a key factor influencing the quality, batch stability, production efficiency and cost of die forgings, and is also the problem to be solved primarily in the development of the hot die forging advanced die forging technology.
Therefore, the preparation method of the large hot forging hot work die steel with good obdurability, high tempering stability and low cost is designed aiming at the requirements of the large hot forging hot work die steel with the thickness of more than or equal to 650mm and the length of more than or equal to 900mm, and is the pioneering machine of the invention.
Disclosure of Invention
The invention aims to provide a preparation method of large hot forging hot work die steel, which overcomes the defects of extremely low reliability and service life of the die in the prior art. The invention limits different components and contents of the large hot forging hot working die steel, obtains a new preparation method of the steel grade with the new components and contents, and can be used for manufacturing the large hot forging hot working die with the thickness of more than or equal to 650mm and the length of more than or equal to 900 mm. Realizes good obdurability, high tempering stability and low cost.
According to the invention, by improving the components and content of the steel and using a new forging method, the obtained large-scale hot forging hot die steel has good obdurability, high tempering stability and good high-temperature strength (including tensile strength and yield strength), and can meet the use requirements of large-section hot forging hot die steel.
The preparation method of the large hot forging hot work die steel provided by the invention comprises the following process steps and technical parameters of control:
the method comprises the following steps: an electric furnace, an electric furnace and electroslag remelting or a vacuum induction furnace are adopted to smelt into steel ingots, and the steel ingots comprise the following chemical components in percentage by weight: 0.30-0.39% of C, 0.35-0.55% of Si, less than or equal to 0.002% of S, less than or equal to 0.02% of P, 0.50-0.7% of Mn, 1.40-1.70% of Mo, 2.60-3.40% of Cr, 0.10-0.30% of V, 0.80-1.20% of Ni, less than or equal to 0.2% of Al + Nb, B: less than or equal to 0.1 percent, and the balance of Fe and inevitable impurities;
step two: pre-cogging of steel ingots: the steel ingot is preheated in two stages, the temperature is raised to 600-650 ℃ at the heating speed of less than or equal to 80 ℃/h and is preserved for 1h, then the temperature is raised to 800-850 ℃ at the heating speed of less than or equal to 80 ℃/h and is preserved for 1h, the temperature is raised to 1170-1190 ℃ at the heating speed of less than or equal to 80 ℃/h and is diffused for 4-6 h, the steel ingot is pulled out in a single direction after being taken out of a furnace pressure clamp handle, and the reduction is less than or equal to 8%; the heating rate is preferably 50-80 ℃/h, and the reduction is preferably 5-8%.
Step three: pre-opening blank high-temperature diffusion: returning the blank to the furnace, directly heating to 1205-1220 ℃, and preserving heat for 15-16 h to homogenize the components of the steel ingot;
step four: forging a blank: directly cooling to 1160-1170 ℃ after diffusion, preserving heat for 2.5-3 h, performing open forging at 1110-1140 ℃, performing multidirectional forging processing, wherein the total forging ratio is 6-8, the finish forging temperature is 950-960 ℃, and slowly cooling to room temperature;
step five: normalizing and spheroidizing annealing process: preheating a forging stock to 950-980 ℃ along with a furnace, homogenizing a forged tissue, keeping the temperature for 8h, immediately cooling the forging stock in a pool for 15-20 min, hanging out, placing in air for cooling, performing secondary pool water cooling when the surface of the forging stock returns to 650 ℃, performing tertiary pool water cooling when the water cooling time is 15-20 min, when the surface of the forging stock returns to 500 ℃, performing tertiary pool water cooling when the water cooling time in the pool is 10-15 min, hanging out the surface of the forging stock steel after the water cooling is finished, starting air cooling to room temperature, checking that the surface of the forging stock is dry and free of water vapor, and immediately putting into an annealing heat treatment furnace;
spheroidizing annealing process: the temperature of the furnace is 410-430 ℃, the blank is hot-loaded into the furnace, the blank is heated to 600-650 ℃ along with the furnace, preheated and insulated for 2h, the blank is heated to 820-840 ℃ along with the furnace, insulated for 10-12 h, cooled to 700-730 ℃ at a cooling rate of less than or equal to 15 ℃/h, insulated for 20-24 h, cooled to below 300 ℃ at a cooling rate of less than or equal to 15 ℃/h, and taken out of the furnace for air cooling. The cooling speed is preferably 10-15 ℃/h.
Preferably, the thickness of the steel ingot is more than or equal to 650mm, and the length of the steel ingot is more than or equal to 900 mm.
C: the carbon content in the steel determines the matrix hardness of the quenched steel, and in the case of hot work die steel, a part of the carbon in the steel enters the matrix of the steel to cause solid solution strengthening, and the other part of the carbon combines with carbide-forming elements in the alloying elements to form alloy carbides. For hot-work die steel, besides a small amount of residual alloy carbide, the alloy carbide is required to be dispersed and precipitated on a quenched martensite matrix during tempering to generate a secondary hardening phenomenon, so that the properties of the hot-work die steel are determined by uniformly distributed residual alloy carbide and tempered martensite structures. When the carbon content in the die steel is too high, the number of carbides is increased, so that the high-temperature strength, the hardness and the red hardness of the steel are improved, the wear resistance of the steel is improved, but the toughness and the plasticity are reduced, and the technological performance is deteriorated; when the carbon content is too low, sufficient formation of carbides in the steel is not ensured, and the contents of carbon and alloying elements in solid solution are reduced during quenching heating, resulting in a decrease in the strength, hardness, hot hardness, and wear resistance of the steel. A large number of researches show that when the carbon content is about 0.40%, the hot-work die steel has better toughness matching. In the invention, the carbon content is controlled to be 0.30-0.39%, and the high-temperature heat strength is improved by increasing or decreasing other elements.
Cr: chromium forms carbide, and the hardenability, corrosion resistance and wear resistance of the steel can be improved in the hot work die steel. Chromium is dissolved in austenite during quenching and heating and dissolved in martensite after quenching, so that the tempering softening resistance of the steel can be improved, and the chromium is separated out from a matrix during tempering and generally forms Cr 23 C 6 Based on the theory that alloy carbide has a tendency of coarsening along with the rise of tempering temperature and the prolonging of time, the tempering hardness is reduced, and the chromium content of the steel is preferably 2.60-3.40%.
V: vanadium can reduce the tendency of steel to be sensitive to overheating. A small amount of vanadium can refine steel grains, and when carbide is dispersed and precipitated through proper heat treatment, the vanadium can improve the high-temperature endurance strength and creep resistance of the steel, and the addition of 0.1-0.3% of vanadium into the low-alloy steel has an obvious effect. The vanadium content in the hot-work die steel is too high, so that the forming probability of primary carbide VC in the steel is increased, the toughness of the steel is obviously influenced by the large amount of the primary carbide, and the capability of the hot-work die steel for resisting large cracks is reduced.
Mo: molybdenum is a strong carbide forming element and is also a core strengthening element in the steel of the invention, and the molybdenum can improve the hardenability of the steel in the steel, and simultaneously form special carbide in the steel, thereby improving the secondary hardening capacity and the tempering stability of the steel. The molybdenum element has a large diffusion coefficient in steel, the structure is difficult to homogenize, a band-shaped structure is easy to form in the steel, and the isotropy is low, so that the molybdenum content is reduced.
Mn: manganese has the effect of solid solution strengthening in steel, so that the strength and the hardness of the die steel are improved, the hardenability of the steel is improved, the harmful effect of sulfur can be eliminated, and the Mn content is controlled to be 0.50-0.7%.
Si: silicon exists in ferrite or austenite in the form of a solid solution as an alloying element in steel, does not form carbides, increases the annealing, normalizing and quenching temperatures, and increases hardenability. Because the silicon has a promotion effect on segregation, the content of the silicon in the steel is controlled to be 0.35-0.55%.
Ni: the nickel is an austenite stabilizing element and plays an important role in improving the hardenability of the steel, the content of the chromium element is reduced in the design idea of the steel, the hardenability of the steel is influenced to a certain extent, and the nickel element is added in order to realize large section of a die made of the steel. The content range of nickel element in the steel is 0.80-1.20%, and the steel is based on the following research results:
(1) 1% of nickel is contained, and the critical point of the steel is reduced by about 40-50 ℃ relative to the H13 steel without nickel. The CCT curve is shifted to the right, so that the critical cooling speed of martensite transformation is reduced from 4170 ℃/h to 500 ℃/h, the hardenability is greatly improved (which is an important basis for enlarging the section of the die and keeping the core part at high strength), but the nickel content is continuously increased without generating great influence.
(2) The addition of about 1% of nickel in the steel can improve the high-temperature tempering hardness and the high-temperature strength, but the hardness and the high-temperature strength are not obviously increased by continuously increasing the nickel content.
Al: aluminum is a ferrite-forming element, a non-carbide-forming element, and does not participate in the formation of carbide, but promotes the transformation from austenite to martensite and promotes the formation of carbide, and therefore, can promote secondary hardeningAnd (4) effect. Aluminum increases the a3 temperature, narrowing the gamma-stable phase region. The aluminum has the functions of deoxidation and nitrogen determination during steel making, and the strength and hardness of the alloy are not changed by adding a small amount of aluminum, but the high-temperature oxidation resistance is enhanced; adding proper content of aluminium can form Ni in dispersion distribution in matrix 3 Al intermetallic compound can raise yield strength and high temperature strength. In practical application, the aluminum content is higher than 0.6%, which easily causes segregation of nonmetallic inclusions of liquated carbides, and reduces impact toughness.
Nb: the strong carbide former, which acts similarly to V, forms MC type carbide and may be used as a partial substitute for V. The MC type carbide in the steel is increased by utilizing Nb, so that the wear resistance of the steel is enhanced, the grain size is refined, and the impact toughness is improved. However, when the Nb content is too high, coarsening of primary grains is observed, and carbide particles are coarse. According to the consideration of other components and contents, the content of Al + Nb is less than or equal to 0.2 percent.
S: sulfur is easily combined with manganese in steel to form a nonmetallic inclusion MnS, the nonmetallic inclusion MnS is usually elongated into a strip shape along the processing direction in the hot working process, the transverse toughness of steel is greatly influenced, the steel isotropic performance is reduced, sulfur element is often considered as harmful element in hot work die steel, therefore, the sulfur element is reduced as much as possible under the condition of permission of metallurgical conditions, and the sulfur content in the steel is controlled to be below 0.002%. By reducing the sulphide content, the impact toughness in the transverse direction of the tool steel can be very close to the impact toughness in the longitudinal direction, the sulphide content is particularly easy to extend in the fibre direction, i.e. in the forging extension direction to as low a level as possible, and silicate inclusions and oxide inclusions are further minimized by providing the die steel with an extremely high degree of cleanliness associated with such non-metallic inclusions. That is, the isotropic tool steel according to the present invention consists essentially of essential elements, and the mass fraction of S is less than 0.002% or less, preferably 0.001% or less.
P: phosphorus forms micro-segregation when molten steel is solidified, and then is segregated at grain boundaries when heated at an austenitizing temperature, so that the brittleness of steel is remarkably increased. The content of phosphorus is controlled to be 0.02% or less, and the lower the content, the better.
B: boron is used to precipitate intermetallic compounds, effectively improving softening resistance by increasing temperature and high temperature strength. When added in excess, they can seriously affect the toughness of the tool steel. Therefore, their weight percentage should be 0.1% or less, preferably 0.01 to 0.05%.
Cobalt and rare earth elements are high-cost components, and the steel disclosed by the invention is not added with cobalt and rare earth elements, so that the cost can be reduced.
The implementation of the invention comprises the following technical effects:
the preparation method of the large-scale hot forging hot work die steel of the invention relates to the innovation of the components: (1) the content of C, Mo and V is reduced, the number of primary carbides in the material is reduced, and the material has higher toughness; (2) properly increasing the content of carbide forming element Mo to make up the high-temperature strength loss caused by the reduction of V content, improving the grain level in the quenching process, improving the secondary hardening effect, and separating out nano-grade Mo in the tempering process 2 C, improving the high-temperature strength of the material; (3) the high-temperature tempering stability of the material is improved by reducing the Cr content; (4) determining an optimal control range through the rule of influence of Al + Nb on hardenability and high-temperature strength; by adding small amount of Al, intermetallic compound Ni is formed with Ni in steel 3 Al strengthening phase, and a small amount of Al as a deoxidizing and nitrogen-fixing agent in steel making, so that the oxygen content in steel is reduced, crystal grains are refined, and the quenching temperature is increased.
Innovation on the preparation method: the method is characterized in that a steel ingot pre-cogging step is added, the traditional high-temperature diffusion process is directly carried out on the smelted steel ingot, the diffusion temperature is generally selected to be 1200-1250 ℃ for heat preservation according to different steel grades, the heat preservation time is calculated according to the size of the steel ingot, but for the blank with the thickness of more than or equal to 650mm, the size of the steel ingot usually reaches more than 900mm, in order to reduce the tissue segregation, the diffusion time needs to be more than or equal to 30h, at the moment, the crystal grains of the edge part of the steel ingot are coarsened and reach 1-2 grades, and if the subsequent forging ratio is insufficient, the final mechanical property of the steel is seriously influenced. Therefore, aiming at the steel grade of the invention, the invention provides a steel ingot pre-cogging process innovatively, ensures proper reduction through unidirectional drawing, can shorten the secondary dendrite spacing of the steel ingot, and dissolves a part of liquated carbides precipitated among the dendrites of the steel ingot, thereby shortening the diffusion time of the steel ingot to 15-16 h, saving the diffusion cost, and ensuring the mechanical property of a steel billet. As for the improvement of the normalizing and spheroidizing annealing steps, considering that the V content of the steel is only about 0.10-0.30%, the critical quenching temperature is about 980 ℃, the homogenization of the structure after forging can be realized by keeping the temperature for a long time in the temperature range, the structure can be refined by adopting a water-cooling rapid cooling method, and the cracking of the large-scale die molten steel in the cooling process is avoided by adopting a multi-stage water-cooling process. According to the CCT continuous cooling transformation curve of the steel, the austenitizing temperature is set to be 820-840 ℃, a small amount of undissolved carbide can be used as a carbide precipitation core in the cooling and isothermal processes, the carbide is uniformly dispersed and precipitated after annealing, and the tissue uniformity is improved.
Detailed Description
The present invention will be described in detail with reference to the following examples, which are intended to facilitate the understanding of the present invention and should not be construed as limiting in any way.
Example 1
The preparation method of the large hot forging and hot working die steel provided by the embodiment comprises the following steps:
the method comprises the following steps: an electric furnace, an electric furnace and electroslag remelting or a vacuum induction furnace are adopted to smelt into steel ingots, and the steel ingots comprise the following chemical components in percentage by weight: 0.38% of C, 0.44% of Si, S: 0.002%, P: 0.02%, Mn 0.62%, Mo 1.51%, Cr 3.02%, V0.15%, Ni 1.20%, Al + Nb less than or equal to 0.101% (wherein Al 0.05%, Nb 0.051%), B: less than or equal to 0.07 percent, and the balance of Fe and inevitable impurities;
step two: pre-cogging of steel ingots: the steel ingot is preheated in two stages, the temperature is increased to 600 ℃ at the heating speed of 80 ℃/h and is preserved for 1h, then the temperature is increased to 800 ℃ at the heating speed of 80 ℃/h and is preserved for 1h, the temperature is increased to 1170 ℃ at the heating speed of 80 ℃/h and is diffused for 4h, the steel ingot is pulled out of a furnace pressure clamp handle in a single direction, and the reduction is 8%;
step three: pre-opening blank high-temperature diffusion: returning the blank to the furnace, directly heating to 1205 ℃, and preserving the heat for 15h to homogenize the components of the steel ingot;
step four: forging a blank: directly cooling to 1160 ℃ after diffusion, preserving heat for 2.5h, performing start forging at 1110 ℃, performing multidirectional forging processing, wherein the total forging ratio is 6, the finish forging temperature is 950 ℃, and slowly cooling to room temperature;
step five: normalizing and spheroidizing annealing process: preheating a forging stock to 950 ℃ along with a furnace, homogenizing a forged tissue, keeping the temperature for 8 hours, immediately cooling the forging stock in a pool for 15 minutes, hanging out the forging stock, placing the forging stock in air for cooling, performing secondary pool water cooling when the surface of the forging stock returns to 650 ℃, cooling the forging stock in the pool for 15 minutes, performing tertiary pool water cooling when the surface of the forging stock returns to 500 ℃, cooling the forging stock in the pool for 10 minutes, hanging out the surface of the forging stock steel when the surface temperature is lower than 300 ℃, starting air cooling to room temperature, checking that the surface of the forging stock is dry and has no water vapor, and immediately putting the forging stock into an annealing heat treatment furnace;
spheroidizing annealing process: and (3) heating the blank to 410 ℃, putting the blank into a furnace, preheating and preserving heat for 2h along with the temperature rise of the furnace to 600 ℃, preserving heat for 10h along with the temperature rise of the furnace, cooling to 700 ℃ at a cooling rate of 15 ℃/h, preserving heat for 20h, cooling to below 300 ℃ at a cooling rate of 15 ℃/h, discharging and air cooling.
The traditional high-temperature diffusion process is directly carried out on a smelted steel ingot, the diffusion temperature is generally 1200-1250 ℃ for heat preservation according to different steel grades, the heat preservation duration is calculated according to the size of the steel ingot, but for a blank with the thickness of more than or equal to 650mm, the size of the steel ingot usually reaches more than 900mm, the diffusion time needs to be more than or equal to 30h for reducing the tissue segregation, at the moment, the crystal grains of the edge tissue of the steel ingot are coarsened to reach 1-2 levels, and if the subsequent forging ratio is insufficient, the final mechanical property of the steel is seriously influenced. Therefore, the embodiment provides a steel ingot pre-cogging process innovatively aiming at the steel grade of the invention, ensures proper rolling reduction through unidirectional drawing, does not crack, can shorten the secondary dendrite spacing of the steel ingot, and dissolves a part of liquated carbides precipitated among dendrites of the steel ingot, thereby shortening the diffusion time of the steel ingot to 15-16 h, saving the diffusion cost, and ensuring the mechanical property of a steel billet.
The V content of the steel is only about 0.10-0.30%, the critical quenching temperature is about 980 ℃, the homogenization of the structure after forging can be realized by keeping the temperature for a long time in the temperature range, the structure grain refining can be realized by adopting a water-cooling rapid cooling method, and the cracking of a large-scale die in the molten steel cooling process is avoided by adopting a multi-stage water-cooling process. According to the CCT continuous cooling transformation curve of the steel, the austenitizing temperature is set to be 820-840 ℃, a small amount of undissolved carbide can be used as a carbide precipitation core in the cooling and isothermal processes, the carbide is uniformly dispersed and precipitated after annealing, and the tissue uniformity is improved.
Example 2
The preparation method of the large hot forging and hot working die steel provided by the embodiment comprises the following steps:
the method comprises the following steps: an electric furnace, an electric furnace and electroslag remelting or a vacuum induction furnace are adopted to smelt into steel ingots, and the steel ingots comprise the following chemical components in percentage by weight: 0.35% of C, 0.51% of Si, S: 0.002%, P: 0.02%, Mn 0.52%, Mo 1.53%, Cr 3.05%, V0.1%, Ni 0.91%, Al not more than 0.06%, B: less than or equal to 0.08 percent, and the balance of Fe and inevitable impurities;
step two: pre-cogging steel ingots: the steel ingot is preheated in two stages, the temperature is increased to 630 ℃ at the heating speed of 70 ℃/h and is preserved for 1h, then the temperature is increased to 830 ℃ at the heating speed of 70 ℃/h and is preserved for 1h, the temperature is increased to 1180 ℃ at the heating speed of 70 ℃/h, the high-temperature diffusion is carried out for 5h, the steel ingot is taken out of a furnace pressure clamp handle and is pulled out in a single direction, and the reduction is 7%;
step three: pre-opening blank high-temperature diffusion: returning the blank to the furnace, directly heating to 1215 ℃, and preserving heat for 16h to homogenize the components of the steel ingot;
step four: forging a blank: directly cooling to 1165 ℃ after diffusion, preserving heat for 2.5-3 h, performing forging at 1130 ℃, and performing multidirectional forging processing, wherein the total forging ratio is 7, the final forging temperature is 960 ℃, and slowly cooling to room temperature;
step five: normalizing and spheroidizing annealing process: preheating a forging stock to 970 ℃ along with a furnace, homogenizing a forged tissue, keeping the temperature for 8 hours, immediately cooling the forging stock in a pool for 18 minutes, hanging out the forging stock, placing the forging stock in air for cooling, performing secondary pool water cooling when the surface of the forging stock returns to 650 ℃, cooling the forging stock in the pool for 18 minutes, performing tertiary pool water cooling when the surface of the forging stock returns to 500 ℃, cooling the forging stock in the pool for 13 minutes, hanging out the surface of the forging stock steel when the surface temperature is lower than 300 ℃, starting air cooling to room temperature, checking that the surface of the forging stock is dry and has no water vapor, and immediately putting the forging stock into an annealing heat treatment furnace;
spheroidizing annealing process: and (3) heating the blank to 420 ℃, putting the blank into the furnace, preheating and preserving heat for 2h when the temperature of the blank is raised to 630 ℃ along with the furnace, preserving heat for 11h when the temperature of the blank is raised to 830 ℃ along with the furnace, cooling to 720 ℃ at a cooling rate of 14 ℃/h, preserving heat for 22h, cooling to below 300 ℃ at a cooling rate of 14 ℃/h, discharging and air cooling.
Example 3
The preparation method of the large hot forging and hot working die steel provided by the embodiment comprises the following steps:
the method comprises the following steps: an electric furnace, an electric furnace and electroslag remelting or a vacuum induction furnace are adopted to smelt into steel ingots, and the steel ingots comprise the following chemical components in percentage by weight: 0.39% of C, 0.35% of Si, S: 0.002%, P: 0.02%, Mn 0.62%, Mo 1.62%, Cr 3.38%, V0.26%, Ni 1.12%, Al + Nb not more than 0.0.7% (wherein Al 0.04%, Nb 0.067%), B: 0.1 percent, and the balance of Fe and inevitable impurities;
step two: pre-cogging steel ingots: the steel ingot is preheated in two stages, the temperature is increased to 650 ℃ at the heating speed of 60 ℃/h and is preserved for 1h, then the temperature is increased to 850 ℃ at the heating speed of 60 ℃/h and is preserved for 1h, the temperature is increased to 1190 ℃ at the heating speed of 60 ℃/h and is high-temperature diffused for 6h, the steel ingot is taken out of a furnace pressure tong handle and is pulled out in a single direction, and the reduction is 6%;
step three: pre-opening blank high-temperature diffusion: returning the blank to the furnace, directly heating to 1220 ℃, and preserving heat for 16h to homogenize the components of the steel ingot;
step four: forging a blank: directly cooling to 1170 ℃ after diffusion, preserving heat for 3h, performing open forging at 1140 ℃, performing multi-directional forging processing, wherein the total forging ratio is 8, the finish forging temperature is 960 ℃, and slowly cooling to room temperature;
step five: normalizing and spheroidizing annealing process: preheating a forging stock to 980 ℃ along with a furnace, homogenizing a forged tissue, keeping the temperature for 8 hours, immediately cooling the forging stock in a pool for 20 minutes, hanging out, placing in air for cooling, performing secondary pool water cooling when the surface of the forging stock returns to 650 ℃, cooling the forging stock in the pool for 20 minutes, performing tertiary pool water cooling when the surface of the forging stock returns to 500 ℃, cooling the forging stock in the pool for 15 minutes, hanging out the surface of the forging stock steel when the surface temperature is lower than 300 ℃, starting air cooling to room temperature, checking that the surface of the forging stock is dry and has no water vapor, and immediately putting into an annealing heat treatment furnace;
spheroidizing annealing process: and (3) heating the blank to 430 ℃, putting the blank into a furnace, preheating and preserving heat for 2h when the temperature of the blank is raised to 650 ℃ along with the furnace, preserving heat for 12h when the temperature of the blank is raised to 840 ℃, cooling to 730 ℃ at a cooling rate of 13 ℃/h, preserving heat for 24h, cooling to below 300 ℃ at a cooling rate of 13 ℃/h, discharging from the furnace, and air cooling.
The large hot-forged hot-work die steels obtained in examples 1 to 3 were subjected to mechanical property tests, and the results were as follows:
TABLE 1U-notch impact toughness tables of die steels of examples 1 to 3 after tempering at different temperatures
TABLE 2 TABLE of tensile Strength of die steels of examples 1 to 3 after tempering at different temperatures
Table 3 table of yield strengths of die steels of examples 1 to 3 after tempering at different temperatures
Table 4 elongation of die steels of examples 1 to 3 after tempering at different temperatures
TABLE 5 surface shrinkage tables of die steels of examples 1 to 3 after tempering at different temperatures
From the mechanical properties of tables 1 to 5, the large hot-forging hot-working die steel obtained by the technical scheme defined by the invention has good obdurability, high tempering stability and good high-temperature strength (including tensile strength and yield strength), and can completely meet the use requirement of the large-section hot-forging hot-working die steel.
Finally, it should be noted that the above embodiments are only used for illustrating the technical solutions of the present invention, and not for limiting the protection scope of the present invention, although the present invention is described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that modifications or equivalent substitutions can be made on the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.
Claims (4)
1. The preparation method of the large-scale hot forging and hot working die steel is characterized by comprising the following steps of:
the method comprises the following steps: an electric furnace, an electric furnace and electroslag remelting or a vacuum induction furnace are adopted to smelt into steel ingots, and the steel ingots comprise the following chemical components in percentage by weight: 0.30 to 0.39 percent of C, 0.35 to 0.55 percent of Si, less than or equal to 0.002 percent of S, less than or equal to 0.02 percent of P, 0.50 to 0.7 percent of Mn, 1.40 to 1.70 percent of Mo, 2.60 to 3.40 percent of Cr, 0.10 to 0.30 percent of V, 0.80 to 1.20 percent of Ni, less than or equal to 0.2 percent of Al + Nb, B: less than or equal to 0.1 percent, and the balance of Fe and inevitable impurities;
step two: pre-cogging steel ingots: the steel ingot is preheated in two stages, the temperature is raised to 600-650 ℃ at the heating speed of less than or equal to 80 ℃/h and is preserved for 1h, then the temperature is raised to 800-850 ℃ at the heating speed of less than or equal to 80 ℃/h and is preserved for 1h, the temperature is raised to 1170-1190 ℃ at the heating speed of less than or equal to 80 ℃/h and is diffused for 4-6 h, the steel ingot is pulled out in a single direction after being taken out of a furnace pressure clamp handle, and the reduction is less than or equal to 8%;
step three: pre-opening blank high-temperature diffusion: returning the blank to the furnace, directly heating to 1205-1220 ℃, and preserving heat for 15-16 h to homogenize the components of the steel ingot;
step four: forging a blank: directly cooling to 1160-1170 ℃ after diffusion, preserving heat for 2.5-3 h, performing open forging at 1110-1140 ℃, performing multidirectional forging processing, wherein the total forging ratio is 6-8, the finish forging temperature is 950-960 ℃, and slowly cooling to room temperature;
step five: normalizing and spheroidizing annealing process: preheating a forging stock to 950-980 ℃ along with a furnace, homogenizing a forged tissue, keeping the temperature for 8h, immediately cooling the forging stock in a pool for 15-20 min, hanging out, placing in air for cooling, performing secondary pool water cooling when the surface of the forging stock returns to 650 ℃, performing tertiary pool water cooling when the water cooling time is 15-20 min, when the surface of the forging stock returns to 500 ℃, performing tertiary pool water cooling when the water cooling time in the pool is 10-15 min, hanging out the surface of the forging stock steel after the water cooling is finished, starting air cooling to room temperature, checking that the surface of the forging stock is dry and free of water vapor, and immediately putting into an annealing heat treatment furnace;
spheroidizing annealing process: the temperature of the furnace is 410-430 ℃, the blank is hot-loaded into the furnace, the blank is heated to 600-650 ℃ along with the furnace, preheated and insulated for 2h, the blank is heated to 820-840 ℃ along with the furnace, insulated for 10-12 h, cooled to 700-730 ℃ at a cooling rate of less than or equal to 15 ℃/h, insulated for 20-24 h, cooled to below 300 ℃ at a cooling rate of less than or equal to 15 ℃/h, and taken out of the furnace for air cooling.
2. The method for preparing large hot forging hot work die steel according to claim 1, characterized in that: the thickness of the steel ingot is larger than or equal to 650mm, and the length of the steel ingot is larger than or equal to 900 mm.
3. The method for preparing large hot forging hot work die steel according to claim 1, characterized in that: temperature rise rate in step two: firstly, heating to 600-650 ℃ at a heating speed of 50-80 ℃/h, preserving heat for 1h, then heating to 800-850 ℃ at a heating speed of 50-80 ℃/h, preserving heat for 1h, heating to 1170-1190 ℃ at a heating speed of 50-80 ℃/h, and diffusing at a high temperature for 4-6 h.
4. The method for preparing large hot forging hot work die steel according to claim 1, characterized in that: and the cooling speed of the spheroidizing annealing process in the fifth step is that the spheroidizing annealing process is cooled to 700-730 ℃ at the cooling speed of 10-15 ℃/h and is kept for 20-24 h, and the spheroidizing annealing process is cooled to below 300 ℃ at the cooling speed of 10-15 ℃/h and is discharged for air cooling.
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