CN116855824A - Die steel with uniformly distributed and spherical inclusions and preparation method thereof - Google Patents

Die steel with uniformly distributed and spherical inclusions and preparation method thereof Download PDF

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CN116855824A
CN116855824A CN202310480989.XA CN202310480989A CN116855824A CN 116855824 A CN116855824 A CN 116855824A CN 202310480989 A CN202310480989 A CN 202310480989A CN 116855824 A CN116855824 A CN 116855824A
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percent
inclusions
steel
die steel
die
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冯丹竹
黄健
范刘群
张宏亮
张建平
庞宗旭
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Angang Steel Co Ltd
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Angang Steel Co Ltd
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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
    • C21D1/25—Hardening, combined with annealing between 300 degrees Celsius and 600 degrees Celsius, i.e. heat refining ("Vergüten")
    • 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
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/26—Methods of annealing
    • C21D1/28—Normalising
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous alloys
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0226—Hot rolling
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C21D8/0263—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment following hot rolling
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C33/00—Making ferrous alloys
    • C22C33/04—Making ferrous alloys by melting
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/005—Ferrous alloys, e.g. steel alloys containing rare earths, i.e. Sc, Y, Lanthanides
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P10/00—Technologies related to metal processing
    • Y02P10/20—Recycling

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Abstract

The invention provides a die steel with evenly distributed inclusions with low deformation rate and a manufacturing method thereof, wherein the steel plate comprises the following components by weightThe weight percentage is as follows: c:0.45% -0.55%, si:0.20 to 0.30 percent of Mn:0.20 to 0.40 percent, P is less than or equal to 0.015 percent, S is less than or equal to 0.015 percent, cr:3.0 to 4.0 percent, mo:3.0 to 3.5 percent, V:0.70 to 0.80 percent of Ni:0.80 to 0.90 percent, sc:0.02% -0.03%, zn:0.03 to 0.05 percent, wherein Ni/V=1.125 to 1.145, sc+Zn=0.06 to 0.07 percent, and the balance being Fe and unavoidable impurities. The production method of the steel plate comprises smelting, continuous casting, slab heating, rolling, straightening, slow cooling, normalizing and annealing pretreatment and tempering. The number of inclusions per unit area in the microstructure of the die steel is (192-205) per mm 2 The average grain diameter is 1.75-1.85 mu m, the inclusions are distributed in a fine and uniform dispersion way, and the ratio of the maximum diameter to the minimum diameter is 1.69-1.78, and the inclusions are approximately spherical. The thickness of the die steel is 30-180 mm; the hardness of the steel plate is 46-48 HRC, and the thickness section hardness difference is less than or equal to 2HRC; the transverse impact toughness of the notch-free room temperature center part is 220-230J; the abrasion volume is (25-26) multiplied by 10 at 800 DEG C ‑3 mm 3 The method comprises the steps of carrying out a first treatment on the surface of the Has higher high-temperature heat conductivity, and the thermal conductivity at 800 ℃ is (35-36) W.m ‑1 ·K ‑1 。

Description

Die steel with uniformly distributed and spherical inclusions and preparation method thereof
Technical Field
The invention belongs to the technical field of metal material production, and particularly relates to die steel with uniformly distributed spherical inclusions and a preparation method thereof.
Background
The automotive industry faces problems of energy utilization, environmental protection, potential safety hazards, and the like. Due to the requirements of environmental protection and energy conservation, the automobile is light, and is an effective method for realizing energy conservation and emission reduction, and with the development of the automobile light, the ultra-high strength steel is gradually developed and applied. The improvement of the strength of the high-strength steel material and the reduction of the elongation lead to the great reduction of the formability of the high-strength steel, and the cold stamping technology cannot meet the processing technology requirements and the production requirements of the high-strength steel plate. Therefore, the die steel suitable for the hot stamping technology needs to be developed, and the die steel ensures that the heat conductivity is improved and the surface of the material has certain corrosion resistance on the premise of ensuring a series of basic mechanical properties such as strength, hardness and the like through reasonable alloy component proportion, so that the speed of a plate material of a part in the hot stamping forming pressure-maintaining quenching stage is improved, the part is improved in good microstructure strength, and the efficiency in actual production and the service life of a die can be improved.
Many units in China do a lot of work in developing new die steel, improving product quality, optimizing production process, prolonging die life and the like. The patent with application number of CN202110261649.9 discloses a low-vanadium nitrogen-containing hot work die steel and a preparation method thereof, wherein the low-vanadium nitrogen-containing hot work die steel comprises the following components in percentage: c:0.3% -0.4%, si:0.2% -0.6%, mn:0.2% -0.5%, cr:4.5% -5.5%, mo:1.1% -1.7%, V:0.4% -0.6%, N:0.02% -0.07%, ce:0.005% -0.03%, mg:0.001% -0.006% and the balance of Fe. The adopted process is as follows: (1) Smelting molten steel according to the set components, adding nitrogen by adopting a gas phase nitriding method, and casting; (2) homogenizing at 1200-1250 ℃; (3) forging; (4) normalizing at 1000-1100 ℃; (5) spheroidizing annealing; (6) heat preservation at 1000-1050 ℃ and oil cooling to finish quenching; (7) heat preservation is carried out for 2-6 hours at 530-620 ℃ for two times and tempering is carried out. The V, si content is reduced, a proper amount of N is increased, trace rare earth and magnesium are cooperatively added, the cleanliness of steel is improved, the carbide distribution effect is improved, and the performance of die steel is improved. But it is difficult to ensure the uniformity of the cross-sectional hardness, corrosion resistance and abrasion resistance. The patent with application number 200610116358.6 discloses hot work die steel which comprises the following components in percentage by weight: cr:3.5% -4.0%, mo:2.0% -2.5%, V:1.0% -1.5%, W:1.0% -1.5%, mn:0.1% -0.5%, ni:0.1% -0.25%, C:0.3% -0.35%, si:0.1% -0.5%, S:0.005% -0.01%, P:0.01% -0.02%. The die steel has higher service hardness, the hardness is in the range of 48-54HRC, the room temperature impact toughness of the material is more than 300J, and the die steel has better thermal fatigue performance, but the corrosion resistance cannot be ensured. The patent with application number 201410194383.0, namely the ultra-high strength die steel with good corrosion resistance and toughness, comprises the following components in percentage by mass: 0.08% -0.32%, si: less than or equal to 0.8 percent, mn: less than or equal to 0.5 percent, cr:5% -10%, ni:6.0% -8.0%, co:1.3% -1.8%, W:0.9% -1.1%, V:0.2% -0.5%, nb:0.08% -0.15%, N: less than or equal to 0.002 percent, O: less than or equal to 0.0015 percent, mo:0.9% -1.4%, ti:0.05% -0.4%, S:0.011% -0.025%. The die steel can be widely applied to the automobile industry requiring high strength and high toughness through forging processing means. But the forging cost is high, the yield is low, and the impact performance of the plastic die steel is difficult to ensure. The patent with application number 202111273495.1 discloses a soft nitriding heat treatment method for die steel with high steel hardness and high impact energy, which comprises the following steps: step 1: and preprocessing the surface of the die steel to be nitrided by adopting an ultrasonic pressurizing shot blasting mode so as to form a nanocrystalline layer on the surface of the die steel. The beneficial effects are that: the nanocrystalline layer is arranged at the surface processing part of the die steel in advance before nitriding, rare earth is added in the nitriding process to promote the nitriding, so that the nitriding rate of the die steel can be accelerated from two aspects of the die steel and external conditions, the nitriding time of the die steel is effectively shortened, the integral efficiency of the soft nitriding process of the die steel is improved, the nitriding temperature is obviously reduced while the nitriding rate of the die steel is improved through the nanocrystalline layer, the process difficulty of the soft nitriding process of the die steel is effectively reduced, the influence of the traditional high-temperature nitriding on the performance of the die steel is avoided, and the hardness and the shock resistance of the surface of the soft nitriding die steel are greatly improved. While ensuring the hardness and toughness of the surface of the die steel, the hardness and toughness of the core are difficult to ensure, and the performances such as fatigue resistance and the like are difficult to prove. The patent with application number 202010836798.9 discloses a die steel with low cost and high thermal conductivity at high temperature and a preparation method thereof, wherein the die steel comprises the following components in percentage: c:0.28% -0.34%, cr:0.38% -0.45%, si:0.68% -0.74%, mn:0.40% -0.48%, mo:1.05 to 1.15 percent, V is less than or equal to 0.08 percent, and the balance is iron and unavoidable impurities. The heat conductivity is improved by adjusting the content of Cr, si, mn, mo, V, the content of Mo is lower, the high-temperature heat conductivity still exists, and the content of Si, cr and other elements is reduced, so that the heat conductivity can be deteriorated, but the important performances such as the hardenability, the heat stability, the strength and hardness, the wear resistance and the like of the material are difficult to ensure.
Disclosure of Invention
Aiming at the defects of the prior art, the invention aims to provide die steel with uniformly distributed and spherical inclusions and a preparation method thereof. The invention changes the types, forms, sizes and distributions of oxides, sulfides and carbides in molten steel through reasonable addition and interaction of alloy elements, and realizes sphericization, miniaturization and diffusion of inclusions in modified steel. Meanwhile, the high-efficiency and economic production process is adopted, the service life of the die is effectively prolonged, the die is suitable for the die market with the application range being continuously enlarged, and the application requirement is continuously improved, so that the international advanced die material level is achieved, and the application prospect is wide.
The invention aims at realizing the following steps:
the composite material comprises the following components in percentage by weight: c:0.45% -0.55%, si:0.20 to 0.30 percent of Mn:0.20 to 0.40 percent, P is less than or equal to 0.015 percent, S is less than or equal to 0.015 percent, cr:3.0 to 4.0 percent, mo:3.0 to 3.5 percent, V:0.70 to 0.80 percent of Ni:0.80 to 0.90 percent, sc:0.02% -0.03%, zn:0.03 to 0.05 percent, and the balance of Fe and unavoidable impurities.
Further, the Ni/V of the die steel is 1.125-1.145.
Further, the Sc+Zn content of the die steel is 0.06% -0.07%.
Further, the thickness of the die steel plate is 30-180 mm.
Further, the number of the die steel inclusions per unit area is (192-205) per mm 2 The average grain diameter is 1.75-1.85 mu m, the inclusions are distributed in a fine and uniform dispersion way, and the ratio of the maximum diameter to the minimum diameter is 1.69-1.78, and the inclusions are approximately spherical.
Further, the hardness of the die steel plate is 46-48 HRC, and the thickness section hardness difference is less than or equal to 2HRC; the transverse impact toughness of the notch-free room temperature core part is 220-230J.
Further, the wear volume of the die steel at 800 ℃ is (25-26) multiplied by 10 -3 mm 3 The method comprises the steps of carrying out a first treatment on the surface of the Has higher high-temperature heat conductivity, and the thermal conductivity at 800 ℃ is (35-36) W.m -1 ·K -1 。
The steel composition of the invention is designed for the following reasons:
c: in the die steel of the present invention, a part of carbon is solid-dissolved in the matrix to perform a solid-solution strengthening function, and a part of carbon interacts with the alloy element to precipitate as alloy carbide. The carbon content can directly influence the strength, the toughness, the high-temperature strength and the thermal stability of the steel, and particularly, in the tempering process, carbides decomposed by martensite and retained austenite are dispersed and distributed on an alpha phase, so that the comprehensive properties of the die steel, such as the strength, the toughness and the like, are improved. According to the invention, the carbon content is properly increased, so that more strong carbide forming elements and weak carbide forming elements such as Mn and the like can be distributed from the steel matrix to the carbide, thereby reducing the larger lattice distortion generated when the elements are dissolved in the steel matrix in a solid manner and reducing the adverse effect of the elements on the heat conductivity of the steel; on one hand, the strength and hardness of the steel are improved, the hardness reduction of a matrix caused by the reduction of Mn and Cr elements is made up, and the wear resistance of the steel is ensured; on one hand, the increase of the cold brittleness and aging sensitivity of the steel is avoided, and the welding performance and corrosion resistance of the steel are ensured. Thus, the present invention opts to add C:0.45 to 0.55 percent, so that the die steel has excellent comprehensive performance, more stable tissue structure and wear resistance.
Si: the Si in the invention can improve the hardenability and the matrix strength, is beneficial to secondary hardening, and can improve the dispersity of the precipitated alloy carbide of the die steel in the high-temperature tempering process, so that the die steel is more uniformly dispersed and distributed. Si limits the migration rate of carbon in the steel, and provides a preferential precipitation position of alloy elements during high-temperature tempering, so that the die steel precipitates tiny and dispersed carbide at a high Wen Shicai, and the thermal stability of the die steel is improved. In addition, it can diffuse into epsilon-carbide to increase epsilon stability in a solid solution manner, and delay cementite occurrence during tempering. The process can effectively shorten the temperature range of the first tempering brittleness, thereby adjusting the strength and toughness of the tempered martensite. The invention reduces the content of Si in a proper amount, on one hand, avoids the serious segregation condition, causes the steel to generate anisotropy, and has adverse effect on the structural uniformity of the steel; on the one hand, the difference between the outer electron structure of Si and Fe is larger, larger lattice distortion is generated when the Si is dissolved in steel, and the movement of interfering electrons and phonons is increased by enhancing the lattice distortion stress field, so that the heat resistance is increased, therefore, the Si content is required to be controlled to be 0.20-0.30%.
Mn: in the invention, mn plays a solid solution strengthening role, and although the solid solution strengthening effect is weaker than that of C, the effect on plasticity of steel is small, and the ductility of the steel is hardly reduced; secondly, the hardenability is improved, which is the most obvious element for improving the hardenability; thirdly, the secondary hardening temperature can be advanced, the dissolution of carbide is promoted, more carbide is dissolved into a matrix in the austenitizing heating process, and the carbide is formed by combining with other strong carbide elements, so that the secondary hardening peak value is improved. However, the Mn content is too high to have adverse effects on toughness and high temperature performance, element enrichment is easy to generate, segregation occurs to enable the components and the structure of a matrix material to be uneven, so that the difference of the whole plate performance of a final steel plate is large, in addition, the difference of an outer electronic structure of Mn and Fe is large, larger lattice distortion is generated when Mn is dissolved in steel, the movement of interfering electrons and phonons is increased by enhancing a lattice distortion stress field, and the heat resistance is increased.
P, S: s is distributed in steel in the form of MnS, and the MnS stretches along the rolling direction in the hot rolling process, so that the transverse mechanical property of the sulfur free-cutting steel is obviously reduced, the anisotropy of the steel is enhanced, and meanwhile, the sulfur free-cutting steel causes cavities in a matrix and becomes a channel for oxidation to develop to depth, and the thermal stability of the die steel is reduced. Although P can properly increase ferrite hardness and improve the surface finish and cutting performance of parts, the P is easier to segregate at austenite grain boundaries to weaken interatomic bonding force on the grain boundaries of a matrix material, so that the tempering brittleness of the material is high, the segregation of phosphorus element at the grain boundaries can cause inheritance of brittle fracture, and excessive S, P can influence the homogeneity and purity of steel. Considering the steelmaking cost and the influence of the steelmaking cost on steel comprehensively, the invention selects and adds less than or equal to 0.015 percent of P and less than or equal to 0.015 percent of S.
Cr: the quenching degree of the steel can be improved, the secondary strengthening effect is achieved, alloying is promoted, pearlite and bainite transformation is delayed, the hardness and wear resistance of the steel are improved without embrittling the steel, and the manufacture and production of a die with a large cross section area can be ensured. Cr element is easy to combine with carbon element, and can form various carbides, and the carbides are distributed in a steel matrix, so that the Cr element plays an important role in improving the hardness, wear resistance and heat stability of the die steel. If the Cr content is too high, other alloy elements in the carbide are replaced by Cr during high-temperature tempering or long-time tempering, so that coarse and softer high-chromium carbide is formed, and the heat resistance of the die steel is reduced; in addition, if the Cr content is higher, the dissolution amount in the matrix is more, so that the steel matrix generates larger degree of lattice distortion to reduce the heat conductivity of the steel, therefore, the invention adds a proper amount of Cr, on one hand, the permeability of the steel can be obviously enhanced after the Cr is dissolved in the matrix, the manufacture and the production of a large-sectional area die are ensured, on the other hand, the heat intensity and the heat stability of the die steel are ensured, and on the other hand, the heat conductivity of the steel is ensured. In addition, the invention can form very dense Cr on the surface by adding a proper amount of Cr 2 O 3 Oxide film, improves the pitting corrosion resistance of steel. Under the combined action of alloy elements such as Zn, the diffusion rate of Cr in the steel can be increased, and the segregation formed by gathering the Cr in the core part of the steel plate is reduced, so that the Cr content is 3.0-4.0%.
Mo: in the present invention, mo has the first effect of being dissolved in the matrix to strengthen the strength and hardness of the die steel in a solid solution strengthening manner. Mo dissolved in the matrix is biased around the dislocation to reduce the degree of distortion of the collective crystal lattice, and forms kohlrabi gas clusters or suzuki gas clusters to pin the dislocation, which hinders the start of the dislocation, improves the yield strength of the die steel, even presents a yield platform, and during tempering, the dislocation in the alpha phase is difficult to aggregate and merge or cancel due to the pinning effect of the gas clusters, so that the temperature of the subgrain is delayed, the reversion, even recrystallization of the alpha phase is obviously hindered, and the tempering stability of the material is increased; secondly, separating MC and M out during subsequent tempering 2 The C carbide has small size and dispersed distribution, and contributes to the secondary hardening effect greatly. But is excessive inMo of (2) results in Mo 2 Conversion of C to M 6 C, separating out along the prior austenite grain boundary and martensite lath boundary, and large granular M 6 C embrittles the material, reduces its toughness, and furthermore these M' s 6 C is easily re-dissolved into the matrix during solution treatment, which results in a large increase in Mo element in the form of a solid solution, while Mo and Fe atoms are greatly different in size, so that the solid solution Mo generates a large polar potential, and electron scattering is increased, thereby reducing thermal conductivity. However, too small a content results in insignificant secondary hardening effects by Mo. Therefore, the content of Mo added in the invention is 3.0-3.5%.
V: the V element has the functions of solid solution in the matrix and solid solution strengthening, and the V element is combined with the C element in the material to form alloy carbide in the material, so that VC with higher melting point can be formed in the invention and is difficult to melt in the heat treatment process, therefore, the grain boundary can be pinned in the austenitizing process of the material, austenite grains are organized to grow up, the size of the matrix grains can be effectively reduced, and the effect of fine grain strengthening is achieved. The carbide is uniformly dispersed in the material, has the characteristics of high melting point, high hardness, strong stability and difficult growth, can effectively strengthen the wear resistance of the material, can be separated out from a matrix in the high-temperature tempering process, promotes secondary hardening of the material, improves the high-temperature stability of the material, further reduces the overheat sensitivity of the material, and can improve the tempering softening resistance of the material. However, the excessive V element can reduce the plasticity and toughness of the material, so that V is added: 0.70 to 0.80 percent.
Ni: the appropriate amount of Ni can improve the strength and toughness of the steel and the hardenability. Can improve the passivation tendency of the Fe-Cr alloy and can improve the corrosion resistance of steel in a reducing medium, namely, the steel has the rust resistance and the oxidation resistance at high temperature, and in the invention, a spinel oxide film NiO-Cr with good protection can be formed by coaction with Cr in a certain temperature range 2 O 3 Composite oxide film, etc., to effectively improve the corrosion resistance of the die steel,In addition, in the tempering process of the die steel, ni element is enriched around carbide, so that the continuous diffusion of carbon atoms in ferrite around the carbide is prevented, the activation energy of coarsening of the carbide is improved, the carbide is prevented from growing, the hardness reduction of the steel is reduced, the high-temperature abrasion resistance of the steel is improved, the stress concentration is reduced, and cracks are not easy to generate on the surface of the die. However, the Ni content is too high, so that the cost is increased, and the lattice constant of the matrix is reduced when Ni is dissolved in the matrix, so that lattice distortion is caused, the diffusion speed of carbon in the matrix is reduced, the phase transformation kinetics is hindered, and the dissolution process of undissolved carbide into austenite is delayed. Thus in the present invention Ni:0.80 to 0.90 percent.
The invention controls Ni/V=1.125-1.145, and the V carbide has good capability of keeping dimensional stability in the tempering process, and the fine V-containing carbide can more effectively block dislocation movement and improve the high-temperature thermal stability of the die steel. The Ni/V ratio and the carbon content in the steel promote the precipitation of MC-type carbide containing V in the steel, and the fine MC-type carbide has stable size and better pinning effect on dislocation. A large amount of nano-scale carbide can be separated out in the tempering process, the pinning effect on dislocation is obvious, and the tempering softening resistance is improved. The invention can promote MC precipitation and delay M due to setting the Ni/V ratio 23 C 6 And the precipitation and transformation of the fine carbide are effectively prevented, and the thermal stability of the material is improved. The Ni/V ratio set by the invention can improve the high-temperature wear performance, carbide is not easy to gather and grow up even under the service condition of 700-800 ℃, the carbide tends to be in a fine and dispersed distribution state, and adverse effect of V element on the toughness of the die steel plastic can be made up.
Sc: the addition of a proper amount of Sc element has the following effects: firstly, rare earth inclusions are formed in the molten steel solidification process and can be used as a non-uniform nucleation core in the liquid phase metal solidification process, so that the grain size is promoted to be reduced, and the solidification structure is improved; secondly, the catalyst is used as a deoxidizing desulfurizing agent to react with harmful impurity elements in molten steel to generate compounds, so that the segregation of the compounds in grain boundaries is reduced, and the purpose of purifying the molten steel is achieved; thirdly, changing the types, shapes, sizes and distribution of oxides, sulfides and carbides in molten steel, modifying the inclusions in the steel, realizing sphericization, miniaturization and dispersion of the inclusions, reducing the average deformation rate of the inclusions, enhancing the pitting resistance of the steel, reducing the potential difference between a steel substrate and the inclusions to a certain extent, and reducing the corrosion rate due to the fact that pitting is an electrochemical catalytic process; fourthly, the micro solid solution can be carried out in the steel to realize micro alloying, and the micro alloying is realized by changing the size of austenite crystal grains and the precipitation behavior of precipitated phases in austenite and ferrite, so that the performances of wear resistance, corrosion resistance, fatigue resistance and the like are improved; and fifthly, homogenizing the structure is favorable for improving the pitting corrosion resistance of the die steel, a certain potential difference exists between the non-uniform structures, the potential difference easily causes the formation of corrosion micro-batteries, so that the corrosion resistance of the steel is reduced, the potential difference between the homogenized structures is small, the corrosion micro-batteries are difficult to form, sc belongs to a surface active element and is easy to adsorb on a growing crystal nucleus, austenite grains can be restrained from growing, the grains are further thinned, and the corrosion resistance of the material is improved. In summary, the invention selects Sc to be added: 0.02 to 0.03 percent.
Zn: the addition of proper amount of Zn element has three functions, namely, the adhesion between the base metal and the oxide film is increased, the base metal is pinned, the base metal still has higher strength and stability at high temperature, the diffusivity of Cr and Ni in the steel is increased, and the Cr formation on the surface of the steel is facilitated 2 O 3 And NiO.Cr 2 O 3 The composite oxide film improves the oxidation resistance and pitting corrosion resistance of the material; secondly, the form of the eutectic carbide in the die steel casting structure can be improved, so that the net-shaped eutectic carbide breaks the net and is uniformly dispersed and distributed in a spherical shape; and thirdly, the enrichment and segregation of P, mn and other easily segregated elements in the matrix material are relieved, a large amount of deformation energy stored in the material is released, the effect of P, mn and other elements on the grain boundary is weakened, the distribution is more uniform, the impact toughness and the uniformity of the tissue performance of the material are improved, and the service life of the die is prolonged. Thus, in the present invention Zn:0.03 to 0.05 percent％。
Because the wettability of molten steel to the nuclear particles of the rare earth inclusions is poor, the formed rare earth inclusions are easy to collide with each other and grow up under the vortex motion of the molten steel, most of large-size inclusions can float up to the surface of the molten steel or be adsorbed on the inner wall, and most of small-size inclusions are not floated up or are not captured by surface scum after floating up to the surface of the molten steel, so that the collision growth and floating trend of the inclusions are controlled to be in a reasonable range, and the sizes of the inclusions remained in the molten steel are more suitable at the moment. The rare earth inclusions are more similar to spherical inclusions, the number of inclusions with large deformation rate is reduced, and the number of inclusions with small deformation rate is increased. The smaller the number, the smaller the size and the smaller the deformation rate of the inclusions relative to the number, the size and the deformation of the inclusions, the lower the pitting induction sensitivity of the inclusions, and the pitting resistance of the die steel matrix is enhanced by adopting a combined action control means of Sc and Zn.
The second technical scheme of the invention is to provide a manufacturing method of die steel with uniformly distributed spherical inclusions, which comprises the process production of smelting, continuous casting, slab heating, rolling, straightening, slow cooling, normalizing and annealing pretreatment and tempering.
The continuous casting slab is heated to 1240-1280 ℃, and the soaking section is insulated for 4-5 hours, so that the die steel has higher alloy content, generally needs higher slab heating temperature, and longer insulation time ensures that alloy elements are fully dissolved in a matrix, improves the non-uniformity of slab components, reduces component segregation, further reduces subsequent tissue segregation, and ensures that large-size eutectic carbide is dissolved.
The initial rolling temperature is controlled to 1070-1100 ℃, and the reduction rate of the first three passes is 18-21% when the steel plate is rolled. The deformation penetration depth can be improved by adopting the large reduction rate, so that coarse columnar crystals can be crushed to form fine and uniform grains, and the defects of the central structure are welded to obtain the steel plate with the thickness of 30-180 mm. The steel plate off-line temperature is 300-400 ℃. And immediately stacking by adopting a lower-paving upper-cover mode after offline, wherein the slow cooling time is 36-48 h.
And carrying out normalizing and annealing pretreatment. Heating the steel plate to 1040-1060 ℃, preserving heat for 3-4 h, discharging and air cooling to room temperature, then heating the steel plate to 870-890 ℃, preserving heat for 2-3 h, furnace cooling to 300-350 ℃, discharging and air cooling to room temperature. The strength and toughness of the die steel can be obviously improved in a subsequent tempering temperature zone by adopting the pretreatment of the normalizing and annealing process; meanwhile, undissolved carbide and banded carbide distributed along grain boundary can be eliminated, the alloying degree in austenite is increased, crystal grains are refined, the distribution is uniform, the dislocation slip resistance is increased by the structure, the carbide dispersity after tempering is increased, and the fatigue strength, the wear resistance and the corrosion resistance are obviously improved.
Then quenching and tempering heat treatment is carried out, quenching heat treatment is carried out firstly, the steel plate is heated to 1050-1070 ℃, heat preservation is carried out for 2-3 h, the steel plate is discharged from the furnace and is cooled to room temperature, tempering heat treatment is carried out, the steel plate is heated to 600-620 ℃, heat preservation time is carried out for 2-3 h, and air cooling is carried out to room temperature. The die steel has higher carbon and alloy content, stronger carbide generating capacity, lower conventional heat treatment temperature and incapability of eliminating banded carbide, and the adoption of the normalizing and annealing pretreatment and quenching process can promote the carbide at the grain boundary to be completely diffused into austenite grains at high temperature, so that the banded carbide is eliminated, the components of the structure are more uniform, the grains are fine, the carbide is uniformly dispersed and distributed, the dislocation sliding resistance is increased by the structure, and the heat stability and the wear resistance of the die steel are obviously improved. The tempering process has the effects that firstly, residual stress is eliminated, the whole structure is homogenized, and the toughness of the material is improved; secondly, alloy elements are separated out from the solid solution, so that lattice distortion is reduced, the influence of the alloy elements on the heat conductivity of steel is reduced, more carbon elements dissolved in a matrix are consumed, the influence of the carbon elements on the lattice distortion of iron is reduced, and the heat conductivity of the material is improved; thirdly, the structure is uniform tempered martensite, a large number of tiny precipitated phases are dispersed and distributed on the matrix, the precipitated phases have higher thermal stability, the high-temperature strength of the material is improved, meanwhile, the toughness is better, in addition, the precipitated phases are hard phases, and the room temperature and high-temperature wear resistance of the material can be effectively improved.
The invention has the beneficial effects that:
the invention adopts the design idea of low Si and high Mn and Mo, ni and V are added according to proportion, sc and Zn are combined, and no noble metal element such as W, co is added, so that the die steel has tiny, uniform and dispersed and spherical inclusions, and simultaneously has high thermal conductivity, excellent wear resistance, pitting corrosion resistance and the like through process design. The method is produced by adopting the processes of smelting, continuous casting, slab heating, rolling, straightening, slow cooling, normalizing and annealing pretreatment and tempering.
1. The number of inclusions per unit area (192-205)/mm in the microstructure of the die steel 2 The average grain diameter is 1.75-1.85 mu m, the inclusions are fine and uniformly dispersed, and the ratio of the maximum diameter to the minimum diameter is
1.69 to 1.78, is similar to a sphere, and has high heat conductivity, excellent wear resistance, pitting corrosion resistance and other excellent comprehensive performances due to uniform distribution of inclusions, small size and nearly spherical morphology.
2. The die steel has higher hardness, toughness matching and performance uniformity, the room-temperature hardness of the final-state steel plate is 46-48 HRC, and the thickness section hardness difference is less than or equal to 2HRC; the transverse impact toughness of the notch-free room temperature core part of the final-state steel plate is 220-230J.
3. The die steel has good high-temperature abrasion resistance, and the abrasion volume at 800 ℃ is (25-26) multiplied by 10 - 3 mm 3 The method comprises the steps of carrying out a first treatment on the surface of the Has higher high-temperature heat conductivity, and the thermal conductivity at 800 ℃ is (35-36) W.m -1 ·K -1 。
4. Has good pitting resistance, pitting potential of (-0.30 to-0.31) V and pitting current of (3.014 to 3.025) multiplied by 10 under the conditions of 3.5 percent NaCl solution, pH value of 7 to 8, solution temperature of 55+/-1 ℃ and no degassing -4 /A·cm -2 。
Detailed Description
The invention is further illustrated by the following examples.
According to the component proportion of the technical scheme, the embodiment of the invention carries out alloying smelting, continuous casting, slab heating, rolling, straightening, slow cooling, normalizing and annealing pretreatment and tempering.
Slab heating
Heating the continuous casting slab to 1240-1280 ℃, and preserving heat for 4-5 h in a soaking section;
rolling
The initial rolling temperature is controlled to 1070-1100 ℃, and the reduction rate of the first three passes is 18-21% when the steel plate is rolled;
normalizing and annealing pretreatment
Heating the steel plate to 1040-1060 ℃, preserving heat for 3-4 h, discharging and air cooling to room temperature, then heating the steel plate to 870-890 ℃, preserving heat for 2-3 h, furnace cooling to 300-350 ℃, discharging and air cooling to room temperature;
tempering
Firstly, quenching heat treatment is carried out, the steel plate is heated to 1050-1070 ℃, the temperature is kept for 2-3 h, the steel plate is discharged from the furnace and is cooled to room temperature, then tempering heat treatment is carried out, the steel plate is heated to 600-620 ℃, the temperature is kept for 2-3 h, and the steel plate is air cooled to room temperature.
Further, the die steel plate is stacked slowly by adopting a lower-paving upper-cover mode immediately after being taken off line at the temperature of 300-400 ℃, and the slow cooling time is 36-48 h.
The following examples are only some of the best embodiments of the present invention and do not limit the scope and technical means of the foregoing invention. Wherein table 1 is the composition of each example, table 2 is the heating, rolling and cooling process of the example slab, table 3 is the heat treatment process of the example, table 4 is the rockwell hardness property of the final steel sheet of the example, table 5 is the transverse impact toughness of the room temperature core of each example, table 6 is the number of inclusions, average particle size and diameter ratio in the rolled state of each example, table 7 is the high temperature wear property of the example, table 8 is the high temperature heat conductivity of the example, and table 9 is the electrochemical corrosion property of the example in 3.5% nacl solution.
TABLE 1 chemical composition (wt%) of the examples of the present invention
Table 2 example slab heating, rolling and cooling processes
Table 3 heat treatment process of examples
TABLE 4 Rockwell hardness Property of Final Steel sheet
TABLE 5 Room temperature core transverse impact toughness for each example
Note that: the impact specimen was 10X 7X 55mm (no notch)
TABLE 6 number of inclusions in rolled state, average particle diameter and diameter ratio in each example
Note that: at 300X 250 μm 2 The core samples of the steel plates of the examples were randomly photographed under the visual field, and the area, the number and the size of inclusions in 30 visual fields were statistically analyzed.
Table 7 example high temperature wear performance
Examples Wear volume at 800 ℃ 10 -3 mm 3
1 25.6
2 25.7
3 25.2
4 25.0
5 25.9
6 25.1
7 25.8
8 26.0
9 25.3
10 25.4
Note that: the core test blocks of each example were cut out to a size of phi 20mm by 8mm. For 45 steel as a grinding material, the testing temperature is 800 ℃, the rotating speed of the grinding wheel is 250r/min, the load is 450N, the testing time is 6h, and the weight loss of the test block is recorded.
TABLE 8 high temperature thermal conductivity/W.m of examples -1 ·K -1
Examples 100℃ 200℃ 300℃ 400℃ 500℃ 600℃ 700℃ 800℃
1 46.5 45.6 44.7 43.5 42.2 42.3 38.8 35.2
2 46.8 45.7 44.6 43.7 42.4 42.5 39.0 35.8
3 46.3 45.4 44.3 43.1 42.3 42.1 39.2 35.5
4 46.9 46.0 44.1 43.2 42.1 42.2 39.3 35.9
5 47.0 45.9 45.0 43.9 42.8 42.9 38.6 35.4
6 46.4 45.3 44.2 43.3 42.0 42.2 38.7 35.0
7 46.2 45.2 44.4 43.6 42.7 42.8 38.5 35.7
8 46.7 45.5 44.5 43.4 42.5 42.6 39.4 36.0
9 46.0 45.8 44.9 44.0 42.9 43.0 39.5 35.3
10 46.6 45.0 44.0 43.8 43.0 42.7 38.9 35.6
TABLE 9 electrochemical corrosion performance of the examples in 3.5% NaCl solution
Examples Pitting potential/V Pitting current/(. Times.10) -4 /A·cm -2 )
1 -0.304 3.016
2 -0.307 3.018
3 -0.300 3.020
4 -0.302 3.022
5 -0.308 3.024
6 -0.309 3.014
7 -0.310 3.019
8 -0.305 3.023
9 -0.306 3.025
10 -0.303 3.021
Note that: examples the core of the steel plate was cut in the rolling direction to 10X 2mm specimens, the 10X 10mm working surface was polished to 2000 mesh, the control potential was started at-1500 mV, scanned positively in the negative direction at a rate of 1mV/s, and terminated when the voltage reached 0V.
From the above, the die steel has tiny and uniformly dispersed spherical inclusions, so that the die steel has good pitting corrosion resistance, excellent high-temperature wear resistance and high thermal conductivityMeanwhile, the toughness matching is considered, the efficient and economical production process is adopted, the service life of the die is effectively prolonged, and the die is suitable for the die market with the continuously expanded application range. The number of inclusions per unit area in the microstructure of the die steel is (192-205) per mm 2 The average grain diameter is 1.75-1.85 mu m, the inclusions are distributed in a fine and uniform dispersion way, and the ratio of the maximum diameter to the minimum diameter is 1.69-1.78, and the inclusions are approximately spherical. The hardness of the steel plate is 46-48 HRC, and the thickness section hardness difference is less than or equal to 2HRC; the transverse impact toughness of the notch-free room temperature center part is 220-230J; the abrasion volume is (25-26) multiplied by 10 at 800 DEG C -3 mm 3 The method comprises the steps of carrying out a first treatment on the surface of the Has higher high-temperature heat conductivity, and the thermal conductivity at 800 ℃ is (35-36) W.m -1 ·K -1 。
The present invention has been properly and fully described in the foregoing embodiments by way of example only, and not by way of limitation, and various changes and modifications may be made by one skilled in the art without departing from the spirit and scope of the invention, any modification, equivalent substitution, improvement, etc. should be included in the scope of the invention, and the scope of the invention is defined by the claims.

Claims (9)

1. A die steel having uniformly distributed and spheroidized inclusions, comprising the following components in weight percent: c:0.45% -0.55%, si:0.20 to 0.30 percent of Mn:0.20 to 0.40 percent, P is less than or equal to 0.015 percent, S is less than or equal to 0.015 percent, cr:3.0 to 4.0 percent, mo:3.0 to 3.5 percent, V:0.70 to 0.80 percent of Ni:0.80 to 0.90 percent, sc:0.02% -0.03%, zn:0.03 to 0.05 percent, and the balance of Fe and unavoidable impurities.
2. The die steel with uniformly distributed and spheroidized inclusions of claim 1, wherein the die steel Ni/V is 1.125-1.145.
3. A die steel with uniformly distributed and spheroidized inclusions as claimed in claim 1, wherein the die steel sc+zn is 0.06% -0.07%.
4. The die steel with uniformly distributed and spheroidized inclusions as claimed in claim 1, wherein the thickness of the die steel sheet is 30 to 180mm.
5. The die steel with uniformly distributed and spherical inclusions as claimed in claim 1, wherein the number of inclusions per unit area in the die steel microstructure is (192-205) per mm 2 The average grain diameter is 1.75-1.85 mu m, the inclusions are distributed in a fine and uniform dispersion way, and the ratio of the maximum diameter to the minimum diameter is 1.69-1.78, and the inclusions are approximately spherical.
6. The die steel with uniformly distributed and spherical inclusions according to claim 1, wherein the hardness of the die steel plate is 46-48 HRC, and the thickness section hardness difference is less than or equal to 2HRC; the transverse impact toughness of the notch-free room temperature core part is 220-230J.
7. The die steel with uniformly distributed and spheroidized inclusions as claimed in claim 1, wherein the die steel has a wear volume of (25 to 26) ×10 at 800 ℃ -3 mm 3 The method comprises the steps of carrying out a first treatment on the surface of the Has higher high-temperature heat conductivity, and the thermal conductivity at 800 ℃ is (35-36) W.m -1 ·K -1 。
8. A method for producing a die steel having uniformly distributed and spheroidized inclusions according to any one of claims 1 to 7, comprising smelting, continuous casting, slab heating, rolling, straightening, slow cooling, normalizing + annealing pretreatment, tempering,
slab heating
Heating the continuous casting slab to 1240-1280 ℃, and preserving heat for 4-5 h in a soaking section;
rolling
The initial rolling temperature is controlled to 1070-1100 ℃, and the reduction rate of the first three passes is 18-21% when the steel plate is rolled;
normalizing and annealing pretreatment
Heating the steel plate to 1040-1060 ℃, preserving heat for 3-4 h, discharging and air cooling to room temperature, then heating the steel plate to 870-890 ℃, preserving heat for 2-3 h, furnace cooling to 300-350 ℃, discharging and air cooling to room temperature;
tempering
Firstly, quenching heat treatment is carried out, the steel plate is heated to 1050-1070 ℃, the temperature is kept for 2-3 h, the steel plate is discharged from the furnace and is cooled to room temperature, then tempering heat treatment is carried out, the steel plate is heated to 600-620 ℃, the temperature is kept for 2-3 h, and the steel plate is air cooled to room temperature.
9. The method for manufacturing a die steel having uniformly distributed and spherical inclusions according to claim 8, wherein the die steel sheet is stacked in a "lower-laid upper-cover" manner immediately after being taken off line at a temperature of 300 to 400 ℃ for a slow cooling time of 36 to 48 hours.
CN202310480989.XA 2023-04-28 2023-04-28 Die steel with uniformly distributed and spherical inclusions and preparation method thereof Pending CN116855824A (en)

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