CN114086067A - Martensite hot-work die steel and preparation method thereof - Google Patents

Martensite hot-work die steel and preparation method thereof Download PDF

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CN114086067A
CN114086067A CN202111350778.1A CN202111350778A CN114086067A CN 114086067 A CN114086067 A CN 114086067A CN 202111350778 A CN202111350778 A CN 202111350778A CN 114086067 A CN114086067 A CN 114086067A
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die steel
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steel
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胡志强
李琪龙
师红旗
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Suqian College
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/18—Hardening; Quenching with or without subsequent tempering
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/26—Methods of annealing
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/005—Modifying the physical properties by deformation combined with, or followed by, heat treatment of ferrous alloys
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/005—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
    • C22C38/04—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
    • C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel with niobium or tantalum
    • C—CHEMISTRY; METALLURGY
    • 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

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Abstract

The invention discloses martensite hot work die steel and a preparation method thereof, and belongs to the technical field of material design and processing. The martensite hot-work die steel is based on the traditional hot-work die steel 5CrNiMoV, carbide forming elements Mo and V are adjusted according to thermodynamic calculation, a small amount of trace elements Nb and rare earth elements Ce are added, and the prepared hot-work die steel is more excellent in normal temperature performance and high temperature performance compared with the traditional hot-work die steel 5CrNiMoV through two-stage isothermal annealing treatment and quenching and tempering treatment, so that the service life of a hot-work die is remarkably prolonged, and the economic cost of industrial production is reduced. The high-temperature thermal stability of the hot work die steel of the invention is as follows: HRC reduction value of 600 ℃ heat stable hardness is 3.0-3.2, and HRC reduction value of 650 ℃ heat stable hardness is 6.2-7.8; high-temperature thermal fatigue: the length of the main crack is 65.10-85.12 μm, and the maximum width of the crack is 2.86-3.52 μm.

Description

Martensite hot-work die steel and preparation method thereof
Technical Field
The invention belongs to the technical field of material design and processing, and relates to martensite hot work die steel and a preparation method thereof.
Background
Hot die steel is a material for manufacturing a forming die for press working a material in a high temperature state. There are many types of hot work die steels, 5CrNiMoV and H13 being the two most widely used hot work die steels, with 5CrNiMoV being a typical low alloy hot work die steel. The 5CrNiMoV steel has low production cost, excellent hardenability and good wear resistance, and is widely used for various medium and large forging hammer dies, press forging hammer dies and the like.
However, because the content of the existing 5CrNiMoV steel alloy is too low, austenite grains are easy to coarsen in the heating process, and the high-temperature thermal stability and the high-temperature thermal fatigue performance are poor, when the service temperature exceeds 600 ℃, the hardness of the surface of the die is quickly reduced, a fatigue source is easy to generate on the surface, and the fatigue source is easy to expand to form a fatigue crack, so that the thermal stability or the fatigue failure is generated.
At present, the technology of die steel at home and abroad is mainly developed based on the existing hot die steel, a novel hot die steel is developed by adjusting alloy components, and forging and heat treatment processes are optimized, so that the comprehensive performance of the hot die steel is improved.
In order to improve the comprehensive performance of hot-work die steel and prolong the service life of a die, a common alloying idea is to greatly increase Mo, V and other noble alloy elements so as to improve the high-temperature service performance of the hot-work die. In addition, the addition of trace rare earth elements can not only refine crystal grains, but also obviously improve the impact toughness and the wear resistance of the die steel. However, the addition of high-content noble alloy elements inevitably brings problems of high cost, serious segregation and the like, and restricts the industrial popularization of the alloy.
For example: chinese patent CN113604730A discloses that H13 steel works at a temperature below 600 ℃, has good thermal stability and thermal fatigue resistance, and better toughness combination, but the strength and the thermal stability of the material are sharply reduced at a temperature above 600 ℃, and the original excellent performance is lost. The mode for solving the technical problem is realized by element adjustment and a complex preparation mode, wherein: the high-temperature molybdenum-molybdenum alloy has high content of molybdenum, so that the production cost is high, the process operation difficulty is high, and the high-temperature mechanical property and the thermal fatigue property are low.
Chinese patent CN113528971A discloses a preparation method of hot work die steel, which comprises the following steps: performing EBT electric furnace smelting, LF refining and VD refining on the alloy raw material to obtain alloy liquid; die casting the alloy liquid to obtain a casting; and carrying out electroslag remelting, primary annealing, forging and secondary annealing on the casting to obtain the hot work die steel. Wherein: the carbon content is low, the silicon-manganese-chromium content is high, the hardness and the impact energy at normal temperature are low, and the high-temperature performance of the hot-work die steel is not considered in the adopted method.
Chinese patent CN113403531A discloses high-heat-strength high-toughness hot work die steel, wherein the content of carbon, silicon, manganese, molybdenum and vanadium is low, the adopted preparation method comprises the steps of material smelting, diffusion annealing, forging, post-forging heat treatment, dehydrogenation annealing and tempering heat treatment, and obviously the high-temperature performance does not consider the reduction value of high-temperature hardness higher than 600 ℃ relative to normal-temperature hardness and the high-temperature thermal fatigue performance.
Therefore, the development of the novel hot-work die steel focuses on the service environment characteristics of the hot-work die, and obviously improves the high-temperature service performance of the hot-work die steel higher than 600 ℃ by optimizing the components and the content of the noble alloy and formulating reasonable forging and heat treatment processes on the premise of not obviously reducing other mechanical properties of the hot-work die steel and increasing the production cost, thereby improving the comprehensive mechanical property of the hot-work die steel.
Disclosure of Invention
The invention solves the technical problems that the hot work die steel in the prior art has low content of 5CrNiMoV alloy, austenite grains are easy to coarsen in the preparation process, and the high-temperature thermal stability and the high-temperature thermal fatigue performance are poor, and particularly after the service temperature exceeds 600 ℃, the surface hardness of the die is reduced at a high speed, fatigue sources are generated on the surface of the die in large quantity, and the fatigue cracks are easy to form by expansion, so that the thermal stability or the fatigue failure is caused.
In order to solve the technical problems, the invention provides the following technical scheme:
the martensitic hot work die steel is 5CrNiMoVNbCE and comprises the following chemical components in percentage by mass: 0.53 to 0.56 percent of C, 0.22 to 0.25 percent of Si, 0.68 to 0.72 percent of Mn, 0.95 to 1.00 percent of Cr, 0.10 to 0.14 percent of Cu, 1.50 to 1.58 percent of Ni, 1.78 to 1.83 percent of Mo, 0.79 to 0.85 percent of V, 0.01 to 0.04 percent of Nb, 0.08 to 0.12 percent of Ce, less than or equal to 0.012 percent of P, less than or equal to 0.003 percent of S, and the balance of Fe and inevitable impurities.
Preferably, the matrix structure of the martensite type hot-work die steel is martensite, and the strengthening phase is mainly carbide MC _ ETA with a low coarsening rate coefficient. By adopting aging treatment, alloy elements such as Cr, Mo and V are precipitated in the form of carbide, the strength, high-temperature hardness, wear resistance and the like of the material are improved by utilizing a second-phase dispersion strengthening mode, crystal grains can be obviously refined by adding rare earth element Ce, the impact toughness of the hot-work die steel is improved, and the wear resistance of the hot-work die steel is improved to a certain extent.
Preferably, the traditional hot-work die steel 5CrNiMoV has good wear resistance, hardenability, impact toughness and the like, in order to keep good mechanical and service properties, elements such as C, Mn, Si, Ni, Cu and the like in the 5 crnimmovnbce are kept unchanged, and other elements are selected for the following reasons:
cr: some Cr is dissolved in steel in solid solution and has favorable influence on the wear resistance, high temperature strength, hot hardness, impact toughness and hardenability of the steel, and other Cr is combined with C to generate various types of carbide, wherein M is M23C6The highest content plays a role in precipitation strengthening, and the martensite matrix is ensured to have higher hardness, however, once the service temperature of the hot-work die steel exceeds 600 ℃, the carbide M23C6The coarsening is easy to occur, thereby causing the reduction of the heat stable hardness and the reduction of the heat fatigue performance of the hot work die steel, and the failure of the die. In the invention, the Cr content is controlled to be 0.95-1.00%, and on the one hand, M can be reduced23C6Carbide content, on the other hand M23C6Rate of coarsening of carbideThe coefficient is lower.
Mo: mo dissolved in steel not only plays a role in solid solution strengthening, but also can improve the hardenability of the steel. In addition, Mo can be used as the most main alloy element of secondary hardening, and is easy to produce fine M2C or MC carbide which is generally fine and granular and is uniformly distributed, so that the tensile strength, high-temperature hardness, impact toughness and the like of the steel are improved, and the high-temperature thermal stability and thermal fatigue performance of the hot working die are obviously improved. Therefore, the Mo content is controlled to be 1.78-1.83% in the invention.
V: v can prevent austenite grains from coarsening and plays a role in fine grain strengthening; v can also be used as a secondary hardening alloy element, V carbide is in a small particle shape, the coarsening coefficient is very low, the thermal stability is very high, the comprehensive performance of the hot die steel can be improved, but the processing performance of the hot die steel is deteriorated due to the excessively high V content. Therefore, the V content is controlled to be 0.80-0.85% in the invention.
Nb: the micro Nb can improve the solid solubility of elements such as Mo and V, and in addition, the Nb and the V can be combined to form smaller MC carbide with lower coarsening coefficient, thereby improving the high-temperature strength, the hardness, the impact toughness and the like of the hot-work die steel. Therefore, the Nb content in the present invention is controlled to 0.01 to 0.04%.
Ce: the rare earth Ce element can obviously refine grains and improve the uniformity of components, tissues and properties, and in addition, the rare earth Ce can obviously improve the impact toughness and the high-temperature wear resistance of the hot-work die steel, and the content of Ce in the invention is controlled to be 0.08-0.12%.
Preferably, the normal temperature performance of the martensite hot work die steel is as follows: yield strength sigma0.21658-1685MPa, tensile strength sigmab1785-1790MPa, elongation of 12.08-12.50%, impact toughness of 22.9-24.5J, and surface hardness HRC of 47.5-49.2.
Preferably, the high temperature thermal stability of the martensitic hot work die steel: HRC reduction value of 600 ℃ heat stable hardness is 3.0-3.2, and HRC reduction value of 650 ℃ heat stable hardness is 6.2-7.8; high-temperature thermal fatigue: the length of the main crack is 65.10-85.12 μm, and the maximum width of the crack is 2.86-3.52 μm.
The preparation method of the martensite hot work die steel comprises the following steps:
s1, vacuum smelting: weighing raw materials according to chemical components of the martensite hot work die steel, and putting the raw materials into a vacuum furnace for vacuum smelting;
s2, casting: casting the melt obtained by vacuum smelting in the step S1 in a mould to obtain a steel ingot;
s3, heating and heat preservation: heating the steel ingot obtained in the step S2, and selecting heating and heat preservation time according to the size of the steel ingot;
s4, forging: forging the steel ingot heated in the step S3 with a forging ratio of more than 6;
s5, heat treatment process: and (4) carrying out isothermal annealing treatment and thermal refining treatment on the steel ingot forged in the step (S4) to finally obtain the martensite hot work die steel with excellent strength, hardness, impact toughness, high-temperature thermal stability and thermal fatigue property.
Preferably, the heating temperature in the step S3 is 1160-1220 ℃, and the heating time is more than 2 h.
Preferably, the forging start temperature in the step S4 is greater than 1160 ℃, and the forging finish temperature is greater than 900 ℃.
Preferably, the isothermal annealing process in step S5 is: selecting the sectional isothermal annealing according to the size of the steel ingot, wherein the temperature of the first-stage isothermal annealing is 850-870 ℃, and the time of the isothermal annealing is 3-5 h; the temperature of the isothermal annealing in the second stage is 720-760 ℃, the time of the isothermal annealing is 1-3h, and the total annealing time in the two stages is more than 3 h.
Preferably, the thermal refining in step S5 is: the quenching temperature is 940-1000 ℃; selecting heat preservation time according to the size of the steel ingot, wherein the heat preservation time is generally more than 2 hours; adopting water quenching, tempering immediately after quenching, wherein the tempering temperature is 560-.
Preferably, the weight of the steel ingot in the step S5 is 25.2-26.0kg, and the cross-sectional dimension of the forging is 450 × 450 and 550 × 550mm2。
The technical scheme provided by the embodiment of the invention at least has the following beneficial effects:
in the scheme, the invention aims at the technical problem that the carbide coarsening behavior of the hot work die steel easily occurs in the service process of the traditional martensite hot work die, so that the hot work die has reduced thermal stability and thermal fatigue cracks, and the die fails.
According to the invention, the content of Mo and V alloy elements is optimized on the basis of the traditional hot-work die steel 5CrNiMoV, a small amount of Nb microalloy elements and rare earth Ce elements are added, and the process regulation and control in the preparation method are combined to change the type, morphology and distribution of carbides, so that the normal-temperature mechanical property and the high-temperature service property of the hot-work die steel are finally improved.
The hot work die steel produced by the invention is 5CrNiMoVNbCE, the impact energy is 22.9-24.5J, the surface hardness is 47.5-49.2HRC, the tensile strength is 1785-1790MPa, and meanwhile, the hot work die steel has good elongation and shrinkage.
The service temperature of the hot-work die steel prepared by the invention is up to 680 ℃, and the high-temperature thermal stability and the thermal fatigue performance of the hot-work die steel are superior to those of domestic and foreign high-quality hot-work die steel.
The invention enables the prepared hot-work die steel to have more excellent normal temperature performance and high temperature performance compared with the traditional hot-work die steel 5CrNiMoV through two-stage isothermal annealing treatment and quenching and tempering treatment, so that the prepared hot-work die steel has excellent comprehensive mechanical performance and good high-temperature service performance, the service life of the hot-work die is obviously prolonged, the economic cost of industrial production is reduced, and the industrial production and popularization are facilitated.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the description of the embodiments will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without creative efforts.
FIG. 1 is a diagram showing equilibrium precipitated phases of a martensitic hot work die steel of example 1 of the present invention and hot work die steels of comparative examples 1 and 3; wherein: (a) the equilibrium precipitated phase diagram of the hot-work die steel of example 1, (b) the equilibrium precipitated phase diagram of the hot-work die steel of comparative example 1, and (c) the equilibrium precipitated phase diagram of the hot-work die steel of comparative example 3;
FIG. 2 is SEM images of a martensitic hot work die steel of example 1 of the present invention and hot work die steels of comparative examples 1 and 3; wherein: (a) SEM pictures of the hot die steel of example 1, (b) SEM pictures of the hot die steel of comparative example 1, and (c) SEM pictures of the hot die steel of comparative example 3;
FIG. 3 is a TEM image of a martensitic hot work die steel of example 1 of the present invention and hot work die steels of comparative examples 1 and 3; wherein: (a) a TEM image of the hot work die steel of example 1, (b) a TEM image of the hot work die steel of comparative example 1, and (c) a TEM image of the hot work die steel of comparative example 3;
FIG. 4 is a graph of the morphology of impact fractures of the martensitic hot work die steel of example 1 of the present invention and the hot work die steels of comparative examples 1 and 3; wherein: (a) the morphology graph of the hot-work die steel impact fracture of the example 1, (b) the morphology graph of the hot-work die steel impact fracture of the comparative example 1, and (c) the morphology graph of the hot-work die steel impact fracture of the comparative example 3;
FIG. 5 is a tensile fracture morphology of the martensitic hot work die steel of example 1 of the present invention and the hot work die steels of comparative examples 1 and 3; wherein: (a) the tensile fracture morphology of the hot-work die steel of example 1, (b) the tensile fracture morphology of the hot-work die steel of comparative example 1, and (c) the tensile fracture morphology of the hot-work die steel of comparative example 3.
Detailed Description
In order to make the technical problems, technical solutions and advantages of the present invention more apparent, the following detailed description is given with reference to the accompanying drawings and specific embodiments.
Example 1
As shown in (a) of fig. 1 to 5, a martensitic hot work die steel is 5 crnimovvnbce, and its chemical composition in mass percent is: 0.56% of C, 0.23% of Si, 0.69% of Mn, 0.98% of Cr, 0.11% of Cu, 1.52% of Ni, 1.82% of Mo, 0.81% of V, 0.022% of Nb, 0.10% of Ce, 0.010% of P, 0.002% of S, and the balance of Fe and inevitable impurities.
The preparation method of the martensite hot work die steel comprises the following steps:
s1, vacuum smelting: weighing raw materials according to chemical components of the martensite hot work die steel, and putting the raw materials into a vacuum furnace for vacuum smelting;
s2, casting: casting the melt obtained by vacuum smelting in the step S1 in a mould to obtain a steel ingot with the weight of 25.5 kg;
s3, heating and heat preservation: heating the steel ingot obtained in the step S2, and selecting heating and heat preservation time according to the size of the steel ingot; the heating temperature is 1200 ℃, and the heating time is more than 3 h;
s4, forging: forging the steel ingot heated in the step S3 at the initial forging temperature of 1185 ℃, the final forging temperature of more than 1000 ℃ and the cross-sectional dimension of the forged piece of 500 multiplied by 500mm to 8.52；
S5, heat treatment process: carrying out isothermal annealing treatment and thermal refining treatment on the steel ingot forged in the step S4 to finally obtain martensite hot work die steel with excellent strength, hardness, impact toughness, high-temperature thermal stability and thermal fatigue;
wherein, the isothermal annealing treatment in the step S5 is: selecting the sectional isothermal annealing according to the size of the steel ingot, wherein the temperature of the first-stage isothermal annealing is 850 ℃, and the time of the isothermal annealing is 3 hours; the temperature of isothermal annealing in the second stage is 720 ℃, the time of isothermal annealing is 1h, and the total annealing time in the two stages is more than 3 h;
wherein the thermal refining in step S5 is: the quenching temperature is 980 ℃; selecting heat preservation time according to the size of the steel ingot, wherein the heat preservation time is 2.1 h; water quenching is adopted, tempering is carried out immediately after quenching, the tempering temperature is 590 ℃, the heat preservation time is 2.1h, and the tempering times are 2 times.
The normal temperature performance of the martensite hot work die steel is as follows: yield strength sigma0.21670MPa, tensile strength sigmab1785MPa, elongation 12.50%, impact toughness 24.5J, and surface hardness HRC 48.5.
The high-temperature thermal stability of the martensite hot work die steel is as follows: the HRC reduction value of the heat stable hardness at 600 ℃ is 3.1, and the HRC reduction value of the heat stable hardness at 650 ℃ is 7.5; high-temperature thermal fatigue: the main crack length was 85.12 μm and the maximum crack width was 3.52. mu.m.
Example 2
The martensitic hot work die steel is 5CrNiMoVNbCE and comprises the following chemical components in percentage by mass: 0.53% of C, 0.25% of Si, 0.71% of Mn, 0.99% of Cr, 0.12% of Cu, 1.52% of Ni, 1.83% of Mo, 0.79% of V, 0.028% of Nb, 0.11% of Ce, 0.009% of P, 0.003% of S and the balance of Fe and inevitable impurities.
The preparation method of the martensite hot work die steel comprises the following steps:
s1, vacuum smelting: weighing raw materials according to chemical components of the martensite hot work die steel, and putting the raw materials into a vacuum furnace for vacuum smelting;
s2, casting: casting the melt obtained by vacuum smelting in the step S1 in a mould to obtain a steel ingot with the weight of 26.0 kg;
s3, heating and heat preservation: heating the steel ingot obtained in the step S2, and selecting heating and heat preservation time according to the size of the steel ingot; the heating temperature is 1200 ℃, and the heating time is 3 h;
s4, forging: forging the steel ingot heated in the step S3 at a forging ratio of 8.6, wherein the initial forging temperature is 1195 ℃, the final forging temperature is 960 ℃, and the section size of the forging is 500mm multiplied by 500mm2；
S5, heat treatment process: carrying out isothermal annealing treatment and thermal refining treatment on the steel ingot forged in the step S4 to finally obtain martensite hot work die steel with excellent strength, hardness, impact toughness, high-temperature thermal stability and thermal fatigue;
wherein, the isothermal annealing treatment in the step S5 is: selecting the sectional isothermal annealing according to the size of the steel ingot, wherein the temperature of the first-stage isothermal annealing is 870 ℃, and the time of the isothermal annealing is 5 hours; the temperature of the isothermal annealing in the second stage is 760 ℃, the time of the isothermal annealing is 1h, and the total annealing time in the two stages is more than 3 h;
wherein the thermal refining in step S5 is: the quenching temperature is 970 ℃; selecting heat preservation time according to the size of the steel ingot, wherein the heat preservation time is 2.2 hours; water quenching is adopted, tempering is carried out immediately after quenching, the tempering temperature is 620 ℃, the heat preservation time is 2.2 hours, and the tempering times are 3 times.
The normal temperature performance of the martensite hot work die steel is as follows: yield strength sigma0.21658MPa, tensile Strength σb1790MPa, elongation 12.10%, impact toughness 23.5J, surface hardness HRC 49.2.
The high-temperature thermal stability of the martensite hot work die steel is as follows: the HRC reduction value of the heat stable hardness at 600 ℃ is 3.2, and the HRC reduction value of the heat stable hardness at 650 ℃ is 7.8; high-temperature thermal fatigue: the main crack length was 65.10 μm and the maximum crack width was 2.86 μm.
Example 3
The martensitic hot work die steel is 5CrNiMoVNbCE and comprises the following chemical components in percentage by mass: 0.55% of C, 0.25% of Si, 0.70% of Mn, 0.96% of Cr, 0.11% of Cu, 1.53% of Ni, 1.80% of Mo, 0.82% of V, 0.025% of Nb, 0.09% of Ce, 0.008% of P, 0.001% of S, and the balance of Fe and inevitable impurities.
The preparation method of the martensite hot work die steel comprises the following steps:
s1, vacuum smelting: weighing raw materials according to chemical components of the martensite hot work die steel, and putting the raw materials into a vacuum furnace for vacuum smelting;
s2, casting: casting the melt obtained by vacuum smelting in the step S1 in a mould to obtain a steel ingot with the weight of 25.2 kg;
s3, heating and heat preservation: heating the steel ingot obtained in the step S2, and selecting heating and heat preservation time according to the size of the steel ingot; the heating temperature is 1180 ℃, and the heating time is 2.5 hours;
s4, forging: forging the steel ingot heated in the step S3 at the initial forging temperature of 1192 ℃, the final forging temperature of 980 ℃ and the cross-section size of the forged piece of 500 x 500mm according to the forging ratio of 8.52；
S5, heat treatment process: carrying out isothermal annealing treatment and thermal refining treatment on the steel ingot forged in the step S4 to finally obtain martensite hot work die steel with excellent strength, hardness, impact toughness, high-temperature thermal stability and thermal fatigue;
wherein, the isothermal annealing treatment in the step S5 is: selecting the sectional isothermal annealing according to the size of the steel ingot, wherein the temperature of the first-stage isothermal annealing is 860 ℃, and the time of the isothermal annealing is 4 hours; the temperature of the isothermal annealing in the second stage is 730 ℃, the time of the isothermal annealing is 1h, and the total annealing time in the two stages is more than 3 h;
wherein the thermal refining in step S5 is: the quenching temperature is 960 ℃; selecting heat preservation time according to the size of the steel ingot, wherein the heat preservation time is 2.5 hours; water quenching is adopted, tempering is carried out immediately after quenching, the tempering temperature is 580 ℃, the heat preservation time is 2.5 hours, and the tempering times are 2-3.
The normal temperature performance of the martensite hot work die steel is as follows: yield strength sigma0.21685MPa, tensile strength sigmab1789MPa, elongation 12.08%, impact toughness 22.9J, and surface hardness HRC 47.5.
The high-temperature thermal stability of the martensite hot work die steel is as follows: HRC reduction value of 600 ℃ heat stable hardness is 3.0, and HRC reduction value of 650 ℃ heat stable hardness is 6.2; high-temperature thermal fatigue: the main crack length was 68.21. mu.m, and the maximum crack width was 3.51. mu.m.
Example 4
The martensitic hot work die steel is 5CrNiMoVNbCE and comprises the following chemical components in percentage by mass: 0.54% of C, 0.24% of Si, 0.68% of Mn, 0.97% of Cr, 0.13% of Cu, 1.55% of Ni, 1.79% of Mo, 0.85% of V, 0.013% of Nb, 0.08% of Ce, 0.011% of P, 0.0025% of S, and the balance of Fe and inevitable impurities.
The preparation method of the martensite hot work die steel comprises the following steps:
s1, vacuum smelting: weighing raw materials according to chemical components of the martensite hot work die steel, and putting the raw materials into a vacuum furnace for vacuum smelting;
s2, casting: casting the melt obtained by vacuum smelting in the step S1 in a mould to obtain a steel ingot with the weight of 25.4 kg;
s3, heating and heat preservation: heating the steel ingot obtained in the step S2, and selecting heating and heat preservation time according to the size of the steel ingot; heating at 1190 deg.C for 3 h;
s4, forging: forging the steel ingot heated in step S3 at a forging ratio of 8.7 and a forging start temperature1191 ℃, the finish forging temperature of 970 ℃, and the section size of the forged piece is 450 multiplied by 450mm2；
S5, heat treatment process: carrying out isothermal annealing treatment and thermal refining treatment on the steel ingot forged in the step S4 to finally obtain martensite hot work die steel with excellent strength, hardness, impact toughness, high-temperature thermal stability and thermal fatigue;
wherein, the isothermal annealing treatment in the step S5 is: selecting the sectional isothermal annealing according to the size of the steel ingot, wherein the temperature of the first-stage isothermal annealing is 855 ℃, and the time of the isothermal annealing is 3 hours; the temperature of the isothermal annealing in the second stage is 740 ℃, the time of the isothermal annealing is 2h, and the total annealing time in the two stages is more than 3 h;
wherein the thermal refining in step S5 is: the quenching temperature is 970 ℃; selecting heat preservation time according to the size of the steel ingot, wherein the heat preservation time is 2.4 hours; water quenching is adopted, tempering is carried out immediately after quenching, the tempering temperature is 600 ℃, the heat preservation time is 2.4 hours, and the tempering times are 3 times.
The normal temperature performance of the martensite hot work die steel is as follows: yield strength sigma0.21662MPa, tensile strength sigmab1787MPa, elongation 12.32%, impact toughness 23.3J, and surface hardness HRC 48.0.
The high-temperature thermal stability of the martensite hot work die steel is as follows: the HRC reduction value of the heat stable hardness at 600 ℃ is 3.1, and the HRC reduction value of the heat stable hardness at 650 ℃ is 6.8; high-temperature thermal fatigue: the main crack length was 75.13 μm and the maximum crack width was 2.93. mu.m.
Example 5
The martensitic hot work die steel is 5CrNiMoVNbCE and comprises the following chemical components in percentage by mass: 0.56% of C, 0.22% of Si, 0.72% of Mn, 0.95% of Cr, 0.14% of Cu, 1.50% of Ni, 1.78% of Mo, 0.85% of V, 0.03% of Nb, 0.12% of Ce, 0.010% of P, 0.002% of S, and the balance of Fe and inevitable impurities.
The preparation method of the martensite hot work die steel comprises the following steps:
s1, vacuum smelting: weighing raw materials according to chemical components of the martensite hot work die steel, and putting the raw materials into a vacuum furnace for vacuum smelting;
s2, casting: casting the melt obtained by vacuum smelting in the step S1 in a mould to obtain a steel ingot with the weight of 25.7 kg;
s3, heating and heat preservation: heating the steel ingot obtained in the step S2, and selecting heating and heat preservation time according to the size of the steel ingot; the heating temperature is 1220 ℃, and the heating time is 2.3 h;
s4, forging: forging the steel ingot heated in the step S3 at the initial forging temperature of 1180 ℃, the final forging temperature of 940 ℃ and the section size of the forged piece of 550 multiplied by 550mm compared with 8.52；
S5, heat treatment process: carrying out isothermal annealing treatment and thermal refining treatment on the steel ingot forged in the step S4 to finally obtain martensite hot work die steel with excellent strength, hardness, impact toughness, high-temperature thermal stability and thermal fatigue;
wherein, the isothermal annealing treatment in the step S5 is: selecting sectional isothermal annealing according to the size of a steel ingot, wherein the temperature of the first-stage isothermal annealing is 865 ℃, and the time of the isothermal annealing is 3 hours; the temperature of isothermal annealing in the second stage is 7450 ℃, the time of isothermal annealing is 1.5h, and the total annealing time in the two stages is more than 3 h;
wherein the thermal refining in step S5 is: the quenching temperature is 980 ℃; selecting heat preservation time according to the size of the steel ingot, wherein the heat preservation time is 2.8 hours; water quenching is adopted, tempering is carried out immediately after quenching, the tempering temperature is 610 ℃, the heat preservation time is 2.2 hours, and the tempering times are 2 times.
The normal temperature performance of the martensite hot work die steel is as follows: yield strength sigma0.21681MPa, tensile strength sigmab1786MPa, elongation 12.22%, impact toughness 23.5J, and surface hardness HRC 48.1.
The high-temperature thermal stability of the martensite hot work die steel is as follows: HRC reduction value of 600 ℃ heat stable hardness is 3.0, and HRC reduction value of 650 ℃ heat stable hardness is 6.7; high-temperature thermal fatigue: the main crack length was 70.22 μm and the maximum crack width was 3.25. mu.m.
Example 6
The martensitic hot work die steel is 5CrNiMoVNbCE and comprises the following chemical components in percentage by mass: 0.53 percent of C, 0.23 percent of Si, 0.69 percent of Mn, 0.97 percent of Cr, 0.13 percent of Cu, 1.51 percent of Ni, 1.80 percent of Mo, 0.79 percent of V, 0.01 percent of Nb, 0.08 percent of Ce, less than or equal to 0.012 percent of P, less than or equal to 0.003 percent of S, and the balance of Fe and inevitable impurities.
The preparation method of the martensite hot work die steel comprises the following steps:
s1, vacuum smelting: weighing raw materials according to chemical components of the martensite hot work die steel, and putting the raw materials into a vacuum furnace for vacuum smelting;
s2, casting: casting the melt obtained by vacuum smelting in the step S1 in a mould to obtain a steel ingot with the weight of 25.5 kg;
s3, heating and heat preservation: heating the steel ingot obtained in the step S2, and selecting heating and heat preservation time according to the size of the steel ingot; the heating temperature is 1160 ℃, and the heating time is 3 h;
s4, forging: forging the steel ingot heated in the step S3 at a forging ratio of more than 6, wherein the initial forging temperature is 1187 ℃, the final forging temperature is 960 ℃, and the section size of the forging is 520 multiplied by 520mm2；
S5, heat treatment process: carrying out isothermal annealing treatment and thermal refining treatment on the steel ingot forged in the step S4 to finally obtain martensite hot work die steel with excellent strength, hardness, impact toughness, high-temperature thermal stability and thermal fatigue;
wherein, the isothermal annealing treatment in the step S5 is: selecting the sectional isothermal annealing according to the size of the steel ingot, wherein the temperature of the first-stage isothermal annealing is 850 ℃, and the time of the isothermal annealing is 3 hours; the temperature of the isothermal annealing in the second stage is 730 ℃, the time of the isothermal annealing is 2.3h, and the total annealing time in the two stages is more than 3 h;
wherein the thermal refining in step S5 is: the quenching temperature is 950 ℃; selecting heat preservation time according to the size of the steel ingot, wherein the heat preservation time is 2.7 hours; water quenching is adopted, tempering is carried out immediately after quenching, the tempering temperature is 590 ℃, the heat preservation time is 2.7h, and the tempering times are 2 times.
The normal temperature performance of the martensite hot work die steel is as follows: yield strength sigma0.21665MPa, tensile strength sigmabElongation at 1786MPaThe ratio was 12.33%, the impact toughness was 23.8J, and the surface hardness HRC was 47.9.
The high-temperature thermal stability of the martensite hot work die steel is as follows: the HRC reduction value of the heat stable hardness at 600 ℃ is 3.1, and the HRC reduction value of the heat stable hardness at 650 ℃ is 6.7; high-temperature thermal fatigue: the main crack length was 67.56 μm and the maximum crack width was 3.36. mu.m.
Comparative example 1
As shown in (b) of fig. 1 to 5, the hot-work die steel is 5 crnimovavnb, and the chemical composition thereof by mass percent is as follows: 0.55% of C, 0.24% of Si, 0.70% of Mn, 0.97% of Cr, 0.12% of Cu, 1.55% of Ni, 1.80% of Mo, 0.80% of V, 0.020% of Nb, 0.010% of P, 0.002% of S and the balance of Fe and inevitable impurities.
The preparation method of the hot work die steel comprises the following steps:
s1, vacuum smelting: weighing raw materials according to chemical components of the martensite hot work die steel, and putting the raw materials into a vacuum furnace for vacuum smelting;
s2, casting: casting the melt obtained by vacuum smelting in the step S1 in a mould to obtain a steel ingot with the weight of 25.6 kg;
s3, heating and heat preservation: heating the steel ingot obtained in the step S2, and selecting heating and heat preservation time according to the size of the steel ingot; the heating temperature is 1200 ℃, and the heating time is 3 h;
s4, forging: forging the steel ingot heated in the step S3 at the initial forging temperature of 1185 ℃, the final forging temperature of 920 ℃ and the cross-sectional dimension of the forged piece of 500 multiplied by 500mm in comparison with 8.62；
S5, heat treatment process: carrying out isothermal annealing treatment and thermal refining treatment on the steel ingot forged in the step S4 to finally obtain martensite hot work die steel with excellent strength, hardness, impact toughness, high-temperature thermal stability and thermal fatigue;
wherein, the isothermal annealing treatment in the step S5 is: the temperature of isothermal annealing is 850 ℃, and the time of isothermal annealing is 3 h;
wherein the thermal refining in step S5 is: the quenching temperature is 960 ℃; selecting heat preservation time according to the size of the steel ingot, wherein the heat preservation time is 2 hours; water quenching is adopted, tempering is carried out immediately after quenching, the tempering temperature is 590 ℃, the heat preservation time is 2 hours, and the tempering times are 2 times.
The normal temperature performance of the hot work die steel is as follows: yield strength sigma0.21646MPa, tensile strength sigmab1761MPa, elongation 11.40%, impact toughness 20.5J, and surface hardness HRC 48.3.
The high-temperature thermal stability of the martensite hot work die steel is as follows: the HRC reduction value of the heat stable hardness at 600 ℃ is 4.3, and the HRC reduction value of the heat stable hardness at 650 ℃ is 9.6; high-temperature thermal fatigue: the main crack length was 104.06 μm and the maximum crack width was 4.86 μm.
Comparative example 2
The martensitic hot work die steel is 5CrNiMoVNb, and the chemical components of the martensitic hot work die steel in percentage by mass are as follows: 0.54% of C, 0.22% of Si, 0.72% of Mn, 0.94% of Cr, 0.10% of Cu, 1.50% of Ni, 1.81% of Mo, 0.79% of V, 0.019% of Nb, 0.008% of P, 0.001% of S and the balance of Fe and inevitable impurities.
The preparation method of the martensite hot work die steel comprises the following steps:
s1, vacuum smelting: weighing raw materials according to chemical components of the martensite hot work die steel, and putting the raw materials into a vacuum furnace for vacuum smelting;
s2, casting: casting the melt obtained by vacuum smelting in the step S1 in a mould to obtain a steel ingot with the weight of 25.2 kg;
s3, heating and heat preservation: heating the steel ingot obtained in the step S2, and selecting heating and heat preservation time according to the size of the steel ingot; the heating temperature is 1200 ℃, and the heating time is 3 h;
s4, forging: forging the steel ingot heated in the step S3 at the initial forging temperature of 1190 ℃ and the final forging temperature of 950 ℃ according to the forging ratio of 8.4, wherein the section size of the forged piece is 500mm multiplied by 500mm2；
S5, heat treatment process: carrying out isothermal annealing treatment and thermal refining treatment on the steel ingot forged in the step S4 to finally obtain martensite hot work die steel with excellent strength, hardness, impact toughness, high-temperature thermal stability and thermal fatigue;
wherein, the isothermal annealing treatment in the step S5 is: the temperature of isothermal annealing is 850 ℃, and the time of isothermal annealing is 3 h;
wherein the thermal refining in step S5 is: the quenching temperature is 960 ℃; selecting heat preservation time according to the size of the steel ingot, wherein the heat preservation time is 2 hours; water quenching is adopted, tempering is carried out immediately after quenching, the tempering temperature is 580 ℃, the heat preservation time is 2 hours, and the tempering times are 2 times.
The normal temperature performance of the martensite hot work die steel is as follows: yield strength sigma0.21610MPa, tensile strength σb1750MPa, elongation of 11.50%, impact toughness of 19.2J and surface hardness HRC of 46.5.
The high-temperature thermal stability of the martensite hot work die steel is as follows: HRC reduction value of 600 ℃ heat stable hardness is 4.0, and HRC reduction value of 650 ℃ heat stable hardness is 9.5; high-temperature thermal fatigue: the main crack length was 103.05 μm and the maximum crack width was 4.88. mu.m.
Comparative example 3
As shown in (c) of fig. 1 to 5, the martensitic hot-work die steel is 5CrNiMoV, and the chemical composition thereof by mass percent is as follows: 0.54% of C, 0.25% of Si, 0.72% of Mn, 0.96% of Cr, 0.12% of Cu, 1.58% of Ni, 0.36% of Mo, 0.074% of V, 0.012% of P, 0.003% of S and the balance of Fe and inevitable impurities.
The preparation method of the martensite hot work die steel comprises the following steps:
s1, vacuum smelting: weighing raw materials according to chemical components of the martensite hot work die steel, and putting the raw materials into a vacuum furnace for vacuum smelting;
s2, casting: casting the melt obtained by vacuum smelting in the step S1 in a mould to obtain a steel ingot with the weight of 25.8 kg;
s3, heating and heat preservation: heating the steel ingot obtained in the step S2, and selecting heating and heat preservation time according to the size of the steel ingot; the heating temperature is 1200 ℃, and the heating time is 3 h;
s4, forging: forging the steel ingot heated in the step S3 at a forging ratio of more than 8.0, wherein the initial forging temperature is 1180 ℃, the final forging temperature is 910 ℃, and the section size of the forging is 500 multiplied by 500mm2；
S5, heat treatment process: carrying out isothermal annealing treatment and thermal refining treatment on the steel ingot forged in the step S4 to finally obtain martensite hot work die steel with excellent strength, hardness, impact toughness, high-temperature thermal stability and thermal fatigue;
wherein, the isothermal annealing treatment in the step S5 is: the temperature of isothermal annealing is 850 ℃, and the time of isothermal annealing is 3 h;
wherein the thermal refining in step S5 is: the quenching temperature is 870 ℃; selecting heat preservation time according to the size of the steel ingot, wherein the heat preservation time is 2 hours; oil quenching is adopted, tempering is carried out immediately after quenching, the tempering temperature is 550 ℃, the heat preservation time is 2 hours, and the tempering times are 2 times.
The normal temperature performance of the martensite hot work die steel is as follows: yield strength sigma0.21195MPa, tensile strength sigmab1360MPa, elongation 10.13%, impact toughness 15.5J, and surface hardness HRC 36.2.
The high-temperature thermal stability of the martensite hot work die steel is as follows: the HRC reduction value of the heat stable hardness at 600 ℃ is 6.5, and the HRC reduction value of the heat stable hardness at 650 ℃ is 17.5; high-temperature thermal fatigue: the main crack length was 184.47 μm and the maximum crack width was 8.73. mu.m.
Comparative example 4
The martensite hot work die steel is 5CrNiMoV and comprises the following chemical components in percentage by mass: 0.53% of C, 0.25% of Si, 0.70% of Mn, 0.98% of Cr, 0.10% of Cu, 1.55% of Ni, 0.37% of Mo, 0.070% of V, 0.010% of P, 0.002% of S and the balance of Fe and inevitable impurities.
The preparation method of the martensite hot work die steel comprises the following steps:
s1, vacuum smelting: weighing raw materials according to chemical components of the martensite hot work die steel, and putting the raw materials into a vacuum furnace for vacuum smelting;
s2, casting: casting the melt obtained by vacuum smelting in the step S1 in a mould to obtain a steel ingot with the weight of 25.1 kg;
s3, heating and heat preservation: heating the steel ingot obtained in the step S2, and selecting heating and heat preservation time according to the size of the steel ingot; the heating temperature is 1200 ℃, and the heating time is 3 h;
s4, forging: forging the steel ingot heated in the step S3 at a forging ratio of 8.6, wherein the initial forging temperature is 1175 ℃, the final forging temperature is 860 ℃, and the section size of the forged piece is 500 x 500mm2；
S5, heat treatment process: carrying out isothermal annealing treatment and thermal refining treatment on the steel ingot forged in the step S4 to finally obtain martensite hot work die steel with excellent strength, hardness, impact toughness, high-temperature thermal stability and thermal fatigue;
wherein, the isothermal annealing treatment in the step S5 is: the temperature of isothermal annealing is 850 ℃, and the time of isothermal annealing is 3 h;
wherein the thermal refining in step S5 is: the quenching temperature is 870 ℃; selecting heat preservation time according to the size of the steel ingot, wherein the heat preservation time is 2 hours; oil quenching is adopted, tempering is carried out immediately after quenching, the tempering temperature is 550 ℃, the heat preservation time is 2 hours, and the tempering times are 2 times.
The normal temperature performance of the martensite hot work die steel is as follows: yield strength sigma0.21200MPa, tensile strength sigmab1370MPa, elongation 11.10%, impact toughness 15.2J, and surface hardness HRC 37.0.
The high-temperature thermal stability of the martensite hot work die steel is as follows: the HRC reduction value of the heat stable hardness at 600 ℃ is 7.1, and the HRC reduction value of the heat stable hardness at 650 ℃ is 16.8; high-temperature thermal fatigue: the main crack length was 187.88 μm and the maximum crack width was 8.95. mu.m.
In summary, as shown in fig. 1 to 5, in example 1, compared with comparative examples 1 and 3, it can be seen that the strengthening phase of the hot work die steel 5CrNiMoVNbCe prepared by the present invention is mainly the carbide MC _ ETA with a low coarsening rate coefficient, and the strengthening phase of the carbide is mostly fine granular carbide as seen from the microstructure.
Therefore, the comprehensive normal-temperature mechanical property of the hot work die steel 5CrNiMoVNbCE prepared by the invention is superior to that of the comparative examples 1-4; the hot work die steel 5CrNiMoVNbCE has smaller reduction amplitude of the thermal stability hardness, short length and narrow width of a thermal fatigue main crack, and shows more excellent high-temperature thermal stability and high-temperature thermal fatigue performance.
The high-temperature service performance of the hot-work die steel 5CrNiMoVNbCE prepared by the invention is superior to that of comparative examples 1-4 and exceeds that of most domestic and foreign high-quality hot-work die steel.
In the scheme, the invention aims at the technical problem that the carbide coarsening behavior of the hot work die steel easily occurs in the service process of the traditional martensite hot work die, so that the hot work die has reduced thermal stability and thermal fatigue cracks, and the die fails.
According to the invention, the content of Mo and V alloy elements is optimized on the basis of the traditional hot-work die steel 5CrNiMoV, a small amount of Nb microalloy elements and rare earth Ce elements are added, and the process regulation and control in the preparation method are combined to change the type, morphology and distribution of carbides, so that the normal-temperature mechanical property and the high-temperature service property of the hot-work die steel are finally improved.
The hot work die steel produced by the invention is 5CrNiMoVNbCE, the impact energy is 22.9-24.5J, the surface hardness is 47.5-49.2HRC, the tensile strength is 1785-1790MPa, and meanwhile, the hot work die steel has good elongation and shrinkage.
The service temperature of the hot-work die steel prepared by the invention is up to 680 ℃, and the high-temperature thermal stability and the thermal fatigue performance of the hot-work die steel are superior to those of domestic and foreign high-quality hot-work die steel.
The invention enables the prepared hot-work die steel to have more excellent normal temperature performance and high temperature performance compared with the traditional hot-work die steel 5CrNiMoV through two-stage isothermal annealing treatment and quenching and tempering treatment, so that the prepared hot-work die steel has excellent comprehensive mechanical performance and good high-temperature service performance, the service life of the hot-work die is obviously prolonged, the economic cost of industrial production is reduced, and the industrial production and popularization are facilitated.
While the foregoing is directed to the preferred embodiment of the present invention, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the appended claims.

Claims (10)

1. The martensitic hot work die steel is characterized by being 5CrNiMoVNbCE and comprising the following chemical components in percentage by mass: 0.53 to 0.56 percent of C, 0.22 to 0.25 percent of Si, 0.68 to 0.72 percent of Mn, 0.95 to 1.00 percent of Cr, 0.10 to 0.14 percent of Cu, 1.50 to 1.58 percent of Ni, 1.78 to 1.83 percent of Mo, 0.79 to 0.85 percent of V, 0.01 to 0.04 percent of Nb, 0.08 to 0.12 percent of Ce, less than or equal to 0.012 percent of P, less than or equal to 0.003 percent of S, and the balance of Fe and inevitable impurities.
2. The martensitic hot work die steel as claimed in claim 1, wherein the martensitic hot work die steel has a matrix structure of martensite, and the strengthening phase is mainly carbide MC _ ETA having a low coarsening rate coefficient.
3. The martensitic hot-work die steel as claimed in claim 1, wherein the martensitic hot-work die steel has room temperature properties of: yield strength sigma0.21658-1685MPa, tensile strength sigmab1785-1790MPa, elongation of 12.08-12.50%, impact toughness of 22.9-24.5J, and surface hardness HRC of 47.5-49.2.
4. The martensitic hot-work die steel according to claim 1, characterized in that the high temperature thermal stability of the martensitic hot-work die steel: HRC reduction value of 600 ℃ heat stable hardness is 3.0-3.2, and HRC reduction value of 650 ℃ heat stable hardness is 6.2-7.8; high-temperature thermal fatigue: the length of the main crack is 65.10-85.12 μm, and the maximum width of the crack is 2.86-3.52 μm.
5. A method of producing a martensitic hot work die steel according to any one of claims 1 to 4, characterized in that the method of producing comprises the steps of:
s1, vacuum smelting: weighing raw materials according to chemical components of the martensite hot work die steel, and putting the raw materials into a vacuum furnace for vacuum smelting;
s2, casting: casting the melt obtained by vacuum smelting in the step S1 in a mould to obtain a steel ingot;
s3, heating and heat preservation: heating the steel ingot obtained in the step S2, and selecting heating and heat preservation time according to the size of the steel ingot;
s4, forging: forging the steel ingot heated in the step S3 with a forging ratio of more than 6;
s5, heat treatment process: and (4) carrying out isothermal annealing treatment and thermal refining treatment on the steel ingot forged in the step (S4) to finally obtain the martensite hot work die steel with excellent strength, hardness, impact toughness, high-temperature thermal stability and thermal fatigue property.
6. The method for preparing the martensitic hot-work die steel as claimed in claim 5, wherein the heating temperature in the step S3 is 1160-1220 ℃, and the heating time is more than 2 h.
7. The method of claim 5, wherein the forging temperature of step S4 is 1160 ℃ or higher, and the forging temperature is 900 ℃ or higher.
8. The method for preparing a martensitic hot-work die steel as claimed in claim 5, wherein the isothermal annealing treatment in the step S5 is: selecting the sectional isothermal annealing according to the size of the steel ingot, wherein the temperature of the first-stage isothermal annealing is 850-870 ℃, and the time of the isothermal annealing is 3-5 h; the temperature of the isothermal annealing in the second stage is 720-760 ℃, the time of the isothermal annealing is 1-3h, and the total annealing time in the two stages is more than 3 h.
9. The method for producing a martensitic hot work die steel as claimed in claim 5, wherein the thermal refining in the step S5 is: the quenching temperature is 940-1000 ℃; selecting heat preservation time according to the size of the steel ingot, wherein the heat preservation time is generally more than 2 hours; adopting water quenching, tempering immediately after quenching, wherein the tempering temperature is 560-.
10. The method for preparing a martensitic hot work die steel as claimed in claim 5, wherein the steel ingot weight in the step S5 is 25.2-26.0kg, and the cross-sectional dimension of the forging is 450X 450 and 550X 550mm2。
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