CN114703425B - Martensite and bainite dual-phase hot work die steel and preparation method thereof - Google Patents

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

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CN114703425B
CN114703425B CN202210357457.2A CN202210357457A CN114703425B CN 114703425 B CN114703425 B CN 114703425B CN 202210357457 A CN202210357457 A CN 202210357457A CN 114703425 B CN114703425 B CN 114703425B
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bainite
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王天生
孙晓文
王岳峰
冯熠婷
荣盛伟
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Yanshan University
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    • C21D2211/00—Microstructure comprising significant phases
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    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/008—Martensite

Abstract

The invention discloses martensite and bainite dual-phase hot work die steel which comprises the following chemical components in percentage by mass: 0.32 to 0.50 percent of C, 1.40 to 1.80 percent of Si, 0.30 to 0.50 percent of Mn, 2.80 to 3.50 percent of Cr, 1.20 to 2.00 percent of Mo, 0.80 to 1.00 percent of V, 1.00 to 2.00 percent of Ni, 0.04 to 0.08 percent of N, 0.9 to 1.5 percent of Co, 0.5 to 1 percent of Al, 0.01 percent of P, 0.005 percent of S, and the balance of Fe and inevitable impurities. The invention also discloses a preparation method of the hot work die steel. The invention has the beneficial effects that: 1. the unnotched impact energy of the three tempered samples is not less than 500J, the tensile strength is not less than 1850 MPa, and the hardness is not less than 50.0 HRC. 2. The preparation process flow is simple and easy to implement, is beneficial to industrial production, and has high preparation efficiency.

Description

Martensite and bainite dual-phase hot work die steel and preparation method thereof
Technical Field
The invention relates to the technical field of die steel, in particular to martensite and bainite dual-phase hot work die steel and a preparation method thereof, wherein the tensile strength of the martensite and bainite dual-phase hot work die steel after three times of tempering is not lower than 1850 MPa, the hardness is not lower than 50.0 HRC, the unnotched impact power is not lower than 500J, and the martensite and bainite dual-phase hot work die steel is particularly suitable for the fields of hot die casting, hot extrusion and the like.
Background
The die steel includes hot-work die steel, cold-work die steel, plastic die steel, special-performance die steel and the like. The hot work die steel has shorter service life due to the special condition of service conditions, so the requirement on the mechanical property of the hot work die steel is higher. The hot work die steel generally requires the prepared material to have high hardenability, wear resistance, obdurability, good tempering stability and the like.
However, compared with the imported hot-work die steel, the domestic traditional hot-work die steel has defects of banded segregation, intergranular carbides and the like in the smelting process, so that the problems of poor isotropic performance, short service time and the like are caused, and the service life of the die is influenced. Thus, some large, precise, complex, long-life die steels almost entirely require imported materials. Therefore, how to improve the production quality of the die steel in China, reduce the cost and meet the requirement of high-quality die steel in China as soon as possible becomes a main target and task of die steel research in China at the present stage.
At present, in order to solve the problems existing in the mold industry, many research and development units also perform a lot of research and development work on the improvement and development of hot-work mold steel, and the following descriptions are provided: patent document CN101240400B proposes a low-cost hot-work die steel, which contains the following components: 0.38 to 0.42%, si:0.9 to 1.1%, mn:0.3 to 0.5%, W:0.9 to 1.2%, cr:4.8 to 5.8 percent, mo:0.45 to 0.55%, V:0.25 to 0.45 percent, has the characteristics of good anti-tempering stability and low cost, and can replace H13 with higher alloy content.
The invention patent with the granted publication number of CN 101240399B 'a low-chromium low-cost hot work die steel' contains C:0.38 to 0.42%, si:0.9 to 1.1%, mn:0.3 to 0.5%, W:0.9 to 1.2%, cr:2.8 to 3.2%, mo:0.45 to 0.55%, V:0.25 to 0.45%, nb:0.08 to 0.15 percent, the steel has the advantages of low chromium and low cost, and the reasonable alloying ratio saves the cost by more than 20 percent compared with H13 steel, thereby having better economic benefit.
The patent document with the publication number of CN 110468345A proposes a high-wear-resistance hot-work die steel, which is subjected to alloying optimization design on H13 steel, and the JDCXN steel comprises the following components in percentage by mass: 0.36 to 0.4 percent of C, 0.6 to 0.7 percent of Mn, 1.9 to 2.0 percent of Cr, 0.6 to 0.7 percent of Si, 1.1 to 1.2 percent of V, 1.5 to 1.7 percent of W, 2.7 to 2.9 percent of Mo, less than or equal to 0.02 percent of P and S, and the balance of Fe and inevitable impurities. The JDCXN steel effectively improves the wear resistance of the steel by adding the W element, simultaneously accords with the alloying thought of 'low Si, cr and Mo', and effectively ensures the strength and hardness of the material.
The patent document with the granted publication number of CN 110484812A provides a high-performance hot stamping die steel and a manufacturing process thereof, wherein the high-performance hot stamping die steel comprises, by mass, 0.66-0.80% of C, 0.80-1.20% of Si, 0.20-0.50% of Mn, 5.00-6.50% of Cr, 1.50-2.00% of Mo, 0.40-0.80% of V, less than 0.015% of P and less than 0.015% of S, and the die steel has the advantages that: the hardenability, thermal stability, wear resistance and thermal fatigue performance of the hot work die steel are superior to those of H13 steel.
The patent document with the granted publication number of CN 106834931B provides a hot work die steel with thermal fatigue resistance and a preparation method thereof, wherein the components (mass percent) of the hot work die steel comprise 0.38-0.42% of C, 0.8-1.1% of Si, 0.2-0.5% of Mn, 2.8-3.3% of Cr, 1.2-1.5% of Mo, 1.2-1.5% of V, 0.0005-0.003% of Mg, 0.01-0.3% of Zr, 0.001-0.03% of Nb, 0.03% of impurity P, 0.03% of S and the balance of Fe. The invention reasonably combines the components, wherein Mg microalloys to block fatigue crack initiation, zr microalloying enables the alloy to generate a stable precipitated phase ZrN with fine dispersion distribution, and the invention has the advantages of pinning dislocation and improving the fatigue softening resistance of the alloy. Compared with general H13 steel, the hot work die steel has higher thermal stability, thermal fatigue resistance and high-temperature strength.
However, the hot work die steel is mostly prepared by a heat treatment method of quenching and secondary tempering, and the matrix structure of the hot work die steel is martensite. The nano bainite has higher toughness and thermal stability, so the nano bainite can show performance advantages when being used for hot-work die steel, and a Ma Bei dual-phase structure obtained by special heat treatment in the hot-work die steel can be one of the development directions for improving the tempering performance of the die steel. Therefore, it is necessary to develop a martensite and bainite dual-phase hot-work die steel by organically combining the research and application of new steel types with the research of a new heat treatment process, which can greatly improve the comprehensive quality and performance of the steel, give full play to the potential of materials, and is an effective way to improve the service life of the die.
Disclosure of Invention
In order to solve the problem that the prior art can not meet the use requirements of high toughness, strength and thermal stability on a die material, the invention provides martensite and bainite dual-phase hot-work die steel and a preparation method thereof, and the comprehensive mechanical property of the hot-work die steel is improved through component design and a heat treatment process.
In order to solve the technical problems, the invention adopts the technical scheme that: a martensite and bainite dual-phase hot work die steel is characterized by comprising the following chemical components in percentage by mass: 0.32 to 0.50 percent of C, 1.40 to 1.80 percent of Si, 0.30 to 0.50 percent of Mn, 2.80 to 3.50 percent of Cr, 1.20 to 2.00 percent of Mo, 0.80 to 1.00 percent of V, 1.00 to 2.00 percent of Ni, 0.04 to 0.08 percent of N, 0.9 to 1.5 percent of Co, 0.5 to 1 percent of Al, 0.01 percent of P, 0.005 percent of S, and the balance of Fe and inevitable impurities.
The proportion of the chemical components meets the following requirements: alpha is more than or equal to 2.57 and less than or equal to 5.14, beta is more than or equal to 247 and less than or equal to 300, and B is more than or equal to 85 F ≤105，
Wherein alpha = (Si +3Al + 1.5Co-Cr)/(C + Mn + N-0.1 (Ni + V + Mo)),
β=565-(31Mn+13Si+10Cr+18Ni+12Mo-8.6Co-15Al)-600(1-exp(-0.96C))，
B F is the thickness of the bainite lath in nanometers, B F =232+0.01785×D-0.5323×Y，
D=-(41-0.001×(T+275) 1.5 ) 2 ×Δg i ，
Δg i =∑(x i /8)×ln(Q i /(8.314×(T+275))，
In the formula, the content of the active carbon is shown in the specification,
Dis the driving energy of the total bainite phase transformation,
y is the strength of the supercooled austenite of the steel of the invention, Y = 6.5X (4.39 +21C +1.5Si +0.24Cr +0.85Mo +1.2V +0.7Co + 0.5Al),
t is the isothermal transformation temperature,
Δg i is the bainite transformation driving energy of each element, Q i And x i The diffusion activation energy and the mass fraction of each element are respectively, and i represents C, cr, ni, V, co, al and Mo elements.
In addition, the invention also provides a preparation method of the martensite and bainite dual-phase hot work die steel, which comprises the following steps: (1) smelting: feeding according to the design requirements of the composition components of steel, smelting in a vacuum induction furnace and casting into steel ingots, wherein the composition components of the steel comprise the following components in percentage by mass: 0.32 to 0.50 percent of C, 1.40 to 1.80 percent of Si, 0.30 to 0.50 percent of Mn, 2.80 to 3.50 percent of Cr, 1.20 to 2.00 percent of Mo, 0.80 to 1.00 percent of V, 1.00 to 2.00 percent of Ni, 0.04 to 0.08 percent of N, 0.9 to 1.5 percent of Co, 0.5 to 1 percent of Al, 0.01 percent of P, 0.005 percent of S, and the balance of Fe and inevitable impurities; (2) hot rolling: annealing and hot rolling the steel ingot, and air-cooling to room temperature after hot rolling to obtain a hot-rolled plate blank; (3) solution treatment and spheroidizing annealing: and (3) heating the hot rolled plate blank subjected to the heat treatment in the step (2) to 1050-1100 ℃, preserving heat for 20-30 min, and performing oil quenching. Heating the plate blank after solid solution to 830-870 ℃, preserving heat for 1-1.5 h, cooling to 740-770 ℃ along with a furnace, preserving heat for 2-2.5 h, finally cooling to 500 ℃ along with the furnace, and taking out of the furnace for air cooling; (4) isothermal quenching treatment: heating the plate blank subjected to the heat treatment in the step (3) to 990-1050 ℃, preserving heat for 20-30 min, then quickly putting the plate blank into a salt bath furnace at 240-274 ℃, quenching the plate blank at medium temperature for 2-4 h, and then air cooling the plate blank to room temperature; (5) tempering: and (4) heating the plate blank subjected to the heat treatment in the step (4) to 555 to 565 ℃, preserving the heat for 1 to 1.5 h, taking the plate blank out of the furnace, air-cooling the plate blank, and repeating the steps for three times.
The technical scheme of the invention achieves the aim through the following principles and modes.
(1) On the basis of accurately understanding the control principle of the contents of C, N, si, mn, cr, ni, V, co, al and Mo multi-element alloying elements in the high-strength hot-working die steel, the chemical components (in percentage by weight) of the nano bainite hot-working die steel are reasonably designed and controlled.
C. N: the C element has stronger solid solution strengthening effect, and part of the C element is dissolved in the matrix in the hot die steel through a heat treatment process to improve the hardness and the strength of the matrix. The C and N elements can be combined with the alloy elements to form alloy carbide to enhance the wear resistance. The preferable content ranges of the C and N elements are 0.45 to 0.55 percent and 0.04 to 0.08 percent respectively.
Mn: mn has solid solution strengthening effect, and can improve the strength, hardness and hardenability of ferrite and austenite. Has stronger affinity with S element, avoids FeS from being formed at the crystal boundary, and eliminates the harmful effect of the S element. The preferable content range is 0.30 to 0.50%.
Si: si is an element that promotes ferrite formation and has a solid solution strengthening effect on ferrite. Meanwhile, si is an effective element for improving the tempering resistance, the diffusion speed of carbon in ferrite is reduced, carbides separated out during tempering are not easy to gather, and the tempering stability is improved. The preferable content range is 1.40 to 1.80%.
Mo: mo has solid solution strengthening effect, and Mo is dissolved in austenite to improve the hardenability of the steel. Meanwhile, mo element is combined with C element to precipitate Mo in martensite during tempering 2 C, the main alloy element causing the secondary hardening phenomenon. In addition, mo element can prevent tempering brittleness, improve the tempering stability of the steel, enable the hot die steel to be tempered at higher temperature and improve plasticity. The preferable content range is 1.20 to 2.00%.
V: in the hot work die steel, the V element has the function of refining the structure and the crystal grains of the steel, and forms VC with the C element during tempering to enhance the secondary hardening effect like the Mo element. Meanwhile, due to the thermal stability of VC, the tempering stability of steel can be improved. The preferable content range is 0.80 to 1.00%.
Cr: cr element can increase the hardenability of steel, improve the hardness and wear resistance of high-carbon steel without making the steel brittle, make the steel have good high-temperature oxidation resistance and oxidation medium corrosion resistance, and also increase the heat strength of the steel. However, the higher content of Cr can form high-chromium M with carbon in the quenching and tempering process 23 C 6 The high Cr carbide has poor thermal stability, so the invention adopts the component design of reducing the Cr content, inhibits the formation of the Cr carbide, promotes the C to be fully combined with the carbide stabilizing element V, mo, and forms MC and M with the advantages of fine size, dispersion distribution and good high-temperature stability 2 C type carbides, thereby improving the thermal strength and thermal fatigue resistance of the steel. The preferable content range is 2.80 to 3.50%.
Ni: the Ni element has the functions of solid solution strengthening and hardenability improvement, ferrite crystal grains are refined, the plasticity and toughness of the hot work die steel are improved, and the heat strength of the hot work die steel can be improved by combining with the Cr element and the Mo element. The preferable content range is 1.00 to 2.00%.
Co: co element can be dissolved in ferrite phase to strengthen the matrix. And Co can postpone the precipitation of alloy carbide in the tempering process and slow down the growth of the carbide, thereby ensuring the small size of the carbide in the steel, and being beneficial to improving the tempering stability and the service life of the hot-work die steel. The preferable content range is 0.9 to 1.5%.
Al: al element can be combined with N element to generate AlN in the smelting process, thereby reducing element segregation and refining the structure when molten iron is cooled. In addition, al and Co are matched to promote low-temperature bainite transformation, and the microstructure of the steel plate is obviously refined. The preferable content range is 0.5 to 1%.
(2) Besides the need of reasonably controlling the chemical component ranges of all elements, the following innovative technical requirements must be set, and the relative addition amount of a part of key elements must be accurately regulated and controlled so as to play the key regulation and control role of the elements on the comprehensive mechanical properties of the steel, such as strength, hardness, impact toughness and the like.
(a) Alpha is more than or equal to 2.57 and less than or equal to 5.14 by regulating and controlling a relational expression, C, N, si, mn, cr, ni, V, co, al and Mo alloy elements are required to carry out element content proportion control between 2.57 and 5.14 according to alpha = (Si +3Al + 1.5Co-Cr)/(C + Mn + N-0.1 (Ni + V + Mo)), so that the formation of a nano bainite tissue is promoted, and conditions are created for heterogeneous nucleation, tissue refinement and toughness improvement of a large amount of fine bainite ferrite. Too high alpha value easily causes coarsening of the tissue, and too low alpha value influences related tissue parameters, causes difficulty in preparation and is not beneficial to improvement of comprehensive mechanical properties.
(b) Beta is more than or equal to 247 and less than or equal to 300 through a regulation relation, the martensite and bainite dual-phase hot working die steel requires C, N, si, mn, cr, ni, V, co, al and Mo alloy elements, and the austenite → martensite initial transformation temperature beta of the steel is controlled between 247 ℃ and 300 ℃ according to beta =565- (31Mn +13Si +10Cr +18Ni +12Mo-8.6Co-15 Al) -600 (1-exp (-0.96C)), the low-temperature isothermal temperature below the transformation point of 7 ℃ to 26 ℃ is selected, the phase transformation temperature interval is controlled in a lower range to ensure the martensite transformation, and the pre-generation is facilitated. And the generation of a nano bainite structure is promoted by pre-generated martensite heterogeneous nucleation and a large phase change driving force brought by low-temperature isothermal, so that the small size of the nano bainite structure is ensured, and the mechanical property of the hot-work die steel is further improved.
(c) B is more than or equal to 85 by regulating and controlling the relation F Less than or equal to 105, and the martensite and bainite dual-phase hot work die steel requires C, N, si, mn, cr, ni, V, co, al and Mo alloy elements according to the formula B F =232+0.01785×D-0.5323×Y"confirm that the thickness of the bainite ferrite lath of the steel of the invention is controlled between 85 to 105nm. Wherein the content of the first and second substances,D=-(41-0.001×(T+275) 1.5 ) 2 ×Δg i ，Δg i =∑(x i /8)×ln(Q i /(8.314 × (T + 275)), where,Das a total bainite transformation driving energy, Δg i Is the bainite transformation driving energy of each element, Q i And x i Respectively the diffusion activation energy and the mass fraction of each element, i refers to C, cr, ni, V, co, al and Mo elements, and T is the isothermal transformation temperature. Wherein Q is C =2.5×10 5 、Q Cr =4.055×10 5 、Q Ni =2.822×10 5 、Q V =2.411×10 5 、Q Mo =2.466×10 5 、Q Co =4.347×10 5 、Q Al =2.257×10 5 . Y =6.5 x (4.39 +21C +1.5Si +0.24Cr +0.85Mo +1.2V +0.7Co + 0.5Al), and Y is the strength of the supercooled austenite of the steel. The composition design and the isothermal process selection ensure that the phase change driving force is large and the strength of the super-cooled austenite is moderate, so that the thickness of the bainitic ferrite is small, and the mechanical property of the hot-work die steel is improved.
The invention has the beneficial effects that:
1. the martensite and bainite dual-phase hot work die steel mainly comprises pre-generated martensite and nano bainite. Wherein the content of the nano bainite accounts for 60% -73%, and the content of the pre-generated martensite accounts for 7% -24.9%.
2. The bainite ferrite lath of the martensite and bainite dual-phase hot work die steel is 85-105 nm, the three-time tempering structure still keeps the nanometer bainite morphology, the hardness of the nanometer bainite ferrite lath is not changed greatly compared with that before tempering, and the nanometer bainite ferrite lath has good tempering stability.
3. The unnotched impact energy of the three-time tempered sample of the martensite and bainite dual-phase hot work die steel is not less than 500J, the tensile strength is not less than 1850 MPa, and the hardness is not less than 50.0 HRC.
4. The martensite and bainite dual-phase hot-working die steel alloy system is reasonable in control, the preparation process flow is simple and feasible, industrial production is facilitated, and the preparation efficiency is high.
The present invention will be described in detail with reference to the accompanying drawings.
Drawings
FIG. 1 is a scanning and TEM image of the austempered structure of the dual-phase hot work die steel of martensite and bainite prepared in example 1;
FIG. 2 is a scanning and TEM image of the austempered structure of the dual-phase hot work die steel of martensite and bainite prepared in example 2;
FIG. 3 is a scanning and TEM image of the austempered structure of the dual-phase hot-work die steel for martensite and bainite prepared in example 3;
FIG. 4 is a scanning and TEM image of the austempered structure of the dual-phase hot-work die steel of martensite and bainite prepared in example 4;
FIG. 5 is a scanning electron micrograph of a triple-tempered structure of the martensite and bainite dual-phase hot work die steel prepared in example 5;
FIG. 6 is a SEM photograph of the triple-tempered structure of the dual-phase martensite and bainite hot-work die steel prepared in example 6;
FIG. 7 is a SEM photograph of the triple-tempered structure of the dual-phase hot-work die steel of martensite and bainite prepared in example 7;
FIG. 8 is a SEM photograph of the triple-tempered structure of the dual-phase martensite and bainite hot-work die steel prepared in example 8;
fig. 9 is a scanning electron micrograph of a triple-tempered structure of the H13 steel prepared in comparative example 1.
Detailed Description
The invention provides martensite and bainite dual-phase hot work die steel which comprises the following chemical components in percentage by mass: 0.32 to 0.50 percent of C, 1.20 to 1.80 percent of Si, 0.30 to 0.50 percent of Mn, 2.80 to 3.50 percent of Cr, 1.20 to 2.00 percent of Mo, 0.80 to 1.00 percent of V, 1.00 to 2.00 percent of Ni, 0.04 to 0.08 percent of N, 0.9 to 1.5 percent of Co, 0.5 to 1 percent of Al, 0.01 percent of P, 0.005 percent of S, and the balance of Fe and inevitable impurities.
In addition, the proportion of the chemical components meets the following requirements:
2.57≤α≤5.14，247≤β≤300，85≤B F ≤105。
wherein, alpha = (Si +3Al + 1.5Co-Cr)/(C + Mn + N-0.1 (Ni + V + Mo)),
β=565-(31Mn+13Si+10Cr+18Ni+12Mo-8.6Co-15Al)-600(1-exp(-0.96C))，B F is the thickness of the bainite lath in nanometers. B F =232+0.01785×D-0.5323×Y。
In the formula, the first step is that,
D=-(41-0.001×(T+275) 1.5 ) 2 ×Δg i ，
Δg i =∑(x i /8)×ln(Q i /(8.314×(T+275))，
Dis a total bainite phaseThe energy of the driving force is changed,
Δg i is the bainite transformation driving energy of each element,
Q i and x i Respectively the diffusion activation energy and the mass fraction of each element, i refers to C, cr, ni, V, co, al and Mo elements, Q C =2.5×10 5 、Q Cr =4.055×10 5 、Q Ni =2.822×10 5 、Q V =2.411×10 5 、Q Mo =2.466×10 5 、Q Co =4.347×10 5 、Q Al =2.257×10 5 And T is the isothermal transition temperature.
Y is the strength of the supercooled austenite of the steel of the invention, Y =6.5 x (4.39 +21C +1.5Si +0.24Cr +0.85Mo +1.2V +0.7Co + 0.5Al).
The invention also provides a preparation method of the martensite and bainite dual-phase hot work die steel, which comprises the following steps.
(1) And smelting: the steel is fed according to the design requirements of the composition components of the steel, melted in a vacuum induction furnace and cast into steel ingots.
The steel comprises the following components in percentage by mass: 0.32 to 0.50 percent of C, 1.20 to 1.80 percent of Si, 0.30 to 0.50 percent of Mn, 2.80 to 3.50 percent of Cr, 1.20 to 2.00 percent of Mo, 0.80 to 1.00 percent of V, 1.00 to 2.00 percent of Ni, 0.04 to 0.08 percent of N, 0.9 to 1.5 percent of Co, 0.5 to 1 percent of Al, and P<0.01%、S<0.005% and the balance of Fe and inevitable impurities; besides, the content of the alloy elements must satisfy the following weight percentages: alpha is more than or equal to 2.57 and less than or equal to 5.14, beta is more than or equal to 247 and less than or equal to 300, and B is more than or equal to 85 F ≤105。
(2) And hot rolling: and annealing and hot rolling the steel ingot, and air cooling to room temperature after hot rolling to obtain a hot rolled slab.
(3) Solution treatment and spheroidizing annealing: and (3) heating the hot rolled plate blank subjected to the heat treatment in the step (2) to 1050-1100 ℃, preserving heat for 20-30 min, and performing oil quenching. And then heating the plate blank subjected to solid solution to 830-870 ℃, preserving heat for 1-1.5 h, cooling to 740-770 ℃ in a furnace, preserving heat for 2-2.5 h, cooling to 500 ℃ in the furnace, and then taking out of the furnace for air cooling.
(4) And isothermal quenching treatment: heating the plate blank subjected to heat treatment in the step (3) to 990-1050 ℃, preserving heat for 20-30 min, then quickly putting the plate blank into a salt bath furnace at 240-274 ℃, quenching the plate blank at medium temperature for 2-4 h, and then cooling the plate blank to room temperature in air.
(5) And tempering treatment: and (5) heating the plate blank subjected to the heat treatment in the step (4) to 555 to 565 ℃, preserving heat for 1 to 1.5 hours, discharging from the furnace, air cooling, and repeating the steps for three times.
The present invention will be described in detail with reference to specific examples.
Example 1, see figure 1, in this example.
A. The weight percentages are as follows: 0.35 percent of C, 1.65 percent of Si, 0.31 percent of Mn, 2.80 percent of Cr, 1.55 percent of Mo, 0.85 percent of V, 1.72 percent of Ni, 0.04 percent of N, 1.26 percent of Co, 0.5 percent of Al, 0.0025 percent of P and 0.0035 percent of S, calculating the proportion of Fe for the rest, and casting the mixture into a round ingot with the diameter of phi 80mm after smelting and electroslag remelting in a vacuum high-frequency induction furnace.
B. Hot rolling: heating the steel ingot to 1150 ℃, preserving heat by 5 h, carrying out homogenizing annealing, and cooling along with the furnace. And then hot rolling and cogging the round ingot at 1150 ℃ into a steel plate with the thickness of 25 mm, and air cooling.
C. Solution treatment and spheroidizing annealing: and C, heating the hot rolled plate blank in the step B to 1050 ℃, preserving the heat for 20 min, and performing oil quenching. And then heating the solid-dissolved plate blank to 840 ℃, preserving heat for 1.5 h, cooling to 750 ℃ along with a furnace, preserving heat for 2 h, cooling to 500 ℃ along with the furnace, discharging from the furnace, and air cooling.
D. Isothermal quenching: and (3) putting the spheroidizing annealed plate into a temperature of 1000 ℃, preserving the heat for 30 min, then quickly putting the plate into a salt bath furnace at 274 ℃, carrying out medium-temperature quenching for 3h, and then carrying out air cooling to the room temperature.
The sheets obtained in this example were subjected to Scanning Electron Microscope (SEM) analysis, hardness, impact and tensile tests, and the results are shown in table 1 and fig. 1. As can be seen from fig. 1: the microstructure is nanometer bainite and pre-generated martensite, and the volume fractions of the nanometer bainite and the pre-generated martensite are 66% and 24.9%, respectively. This example produced martensitic and bainitic die steels with α =2.57 and β =300,b F =105, bainitic ferrite strip thickness 100 nm, wherein the structure hardness is 51.3 HRC, unnotched impact energy is not less than 500J, charpy U-notch impact energy (KU) 2 ) 44J and a tensile strength of 1820 MPa. See table 1 for data.
Example 2, see figure 2, in this example.
A. The weight percentages are as follows: 0.42 of C, 1.56 of Si, 0.42 of Mn, 3.20 of Cr, 1.72 of Mo, 0.89 of V, 1.53 of Ni, 0.06 of N, 0.98 of Co, 0.78 of Al, 0.0055 of P and 0.0041 of S, the balance of Fe, calculating the feeding proportion, and casting into a round ingot with the diameter of phi 80mm after remelting in a vacuum high-frequency induction furnace and electroslag smelting.
B. Hot rolling: heating the steel ingot to 1150 ℃, preserving heat by 5 h, carrying out homogenizing annealing, and cooling along with the furnace. And then hot rolling and cogging the round ingot at 1150 ℃ into a steel plate with the thickness of 25 mm, and air cooling.
C. Solution treatment and spheroidizing annealing: and C, heating the hot rolled plate blank in the step B to 1080 ℃, preserving the heat for 25 min, and performing oil quenching. And then heating the solid-dissolved plate blank to 850 ℃, preserving heat for 1.5 h, cooling to 740 ℃ along with a furnace, preserving heat for 2 h, cooling to 500 ℃ along with the furnace, discharging from the furnace, and air cooling.
D. Isothermal quenching: and (3) putting the spheroidizing annealed plate into a 1010 ℃ temperature condition, preserving the heat for 30 min, then quickly putting the plate into a 255 ℃ salt bath furnace for medium-temperature quenching for 3.5 h, and then air-cooling to room temperature.
The sheets obtained in this example were subjected to Scanning Electron Microscope (SEM) analysis, hardness, impact and tensile tests, and the results are shown in table 1 and fig. 2. As can be seen from fig. 2: the microstructure comprises nano bainite and pre-generated martensite, and the volume fractions of the nano bainite and the pre-generated martensite are 72% and 19.7%, respectively. This example produced martensitic and bainitic die steels with α =4.47, β =275 F =87, bainite ferrite lath thickness of 90 nm, wherein the structure hardness is 51.5 HRC, unnotched impact energy is not less than 500J, charpy U-shaped notch impact energy (KU) 2 ) 48J and tensile strength 1865 MPa. See table 1 for data.
Example 3, see figure 3, in this example.
A. The weight percentage is as follows: c0.45, si 1.78, mn 0.38, cr 3.30, mo 1.85, V0.95, ni 1.85, N0.05, co 0, al 0.92, P0.0065 and S0.0042, the balance of Fe, calculating the feeding proportion, smelting in a vacuum high-frequency induction furnace and remelting with electroslag, and then casting into a mm round ingot with the diameter of phi 80.
B. Hot rolling: heating the steel ingot to 1150 ℃, preserving heat by 5 h, carrying out homogenizing annealing, and cooling along with the furnace. And then hot rolling and cogging the round ingot at 1150 ℃ into a steel plate with the thickness of 25 mm, and air cooling.
C. Solution treatment and spheroidizing annealing: and C, heating the hot rolled plate blank in the step B to 1060 ℃, preserving the heat for 25 min, and performing oil quenching. And then heating the solid-dissolved plate blank to 860 ℃, preserving heat for 1.5 h, cooling to 760 ℃ along with a furnace, preserving heat for 2.5 h, cooling to 500 ℃ along with the furnace, discharging from the furnace, and air cooling.
D. Isothermal quenching: and putting the spheroidizing annealed plate into a salt bath furnace at 240 ℃ for moderate-temperature quenching of 4 h, and then cooling the plate to room temperature.
The sheets obtained in this example were subjected to Scanning Electron Microscope (SEM) analysis, hardness, impact and tensile tests, and the results are shown in table 1 and fig. 3. As can be seen in fig. 3: the microstructure is nanometer bainite and pre-generated martensite, and the volume fractions of the nanometer bainite and the pre-generated martensite are 83% and 7%, respectively. This example produced martensitic and bainitic die steels with α =2.99, β =247 F =85, the bainite ferrite strip thickness is 88 nm, wherein the structure hardness is 51.1 HRC, the unnotched impact energy is not less than 500J, and the Charpy U-shaped notch impact energy (KU) 2 ) 42J and a tensile strength of 1856 MPa. See table 1 for data.
Example 4, see figure 4, in this example.
A. The weight percentages are as follows: 0.39 percent of C, 1.44 percent of Si, 0.45 percent of Mn, 2.90 percent of Cr, 1.49 percent of Mo, 0.98 percent of V, 1.62 percent of Ni, 0.07 percent of N, 1.45 percent of Co, 0.62 percent of Al, 0.0075 percent of P and 0.0032 percent of S, and the balance of Fe, calculating the feeding proportion, pouring into a round ingot with the diameter of phi 80mm after a vacuum high-frequency induction furnace and electroslag remelting.
B. Hot rolling: heating the steel ingot to 1150 ℃, preserving heat by 5 h, carrying out homogenizing annealing, and cooling along with the furnace. And then hot rolling and cogging the round ingot at 1150 ℃ into a steel plate with the thickness of 25 mm, and air cooling.
C. Solution treatment and spheroidizing annealing: and C, heating the hot rolled plate blank in the step B to 1100 ℃, preserving the heat for 20 min, and performing oil quenching. And then heating the solid-dissolved plate blank to 870 ℃, preserving heat for 1.5 h, cooling to 770 ℃ along with a furnace, preserving heat for 2.5 h, cooling to 500 ℃ along with the furnace, discharging from the furnace, and air cooling.
D. Isothermal quenching: placing the spheroidizing annealed plate into a salt bath furnace at the temperature of 274 ℃ for heat preservation for 20 min, then quickly placing the plate into a salt bath furnace at the temperature of 1050 ℃ for moderate-temperature quenching for 3h, and then cooling the plate to room temperature in air.
The sheets obtained in this example were subjected to Scanning Electron Microscope (SEM) analysis, hardness, impact and tensile tests, and the results are shown in table 1 and fig. 4. As can be seen in fig. 4: the microstructure is nano bainite and pre-formed martensite, and the volume fractions of the nano bainite and the pre-formed martensite are 73% and 18.7%, respectively. This example produced martensitic and bainitic die steels, where α =5.14 and β =294,b F =94, the bainite ferrite strip thickness is 98 nm, wherein the structure hardness is 52.2 HRC, the unnotched impact energy is not less than 500J, and the Charpy U-shaped notch impact energy (KU) 2 ) 51J and tensile strength 1890 MPa. See table 1 for data.
Example 5 referring to FIG. 5, in this example, the austempered sheet material of example 1 above was placed in a box furnace at 560 ℃ and tempered at 1h, and was discharged from the furnace and air cooled to room temperature, and this was repeated three times.
The sheets obtained in this example were subjected to Scanning Electron Microscope (SEM) analysis, hardness, impact and tensile tests, and the results are shown in table 1 and fig. 5. As can be seen from fig. 5: in this example, tempered bainite, tempered martensite and globular undissolved carbide structures were prepared, the hardness of the structures was 51.5 HRC, the unnotched impact energy was not less than 500J, and the Charpy U-notch impact energy (KU) was obtained 2 ) 30J and a tensile strength of 1878 MPa. See table 1 for data.
Example 6 referring to FIG. 6, in this example, the austempered sheet material of example 2 was placed in a box furnace at 560 ℃ and tempered for 1 hour, taken out of the furnace and air-cooled to room temperature, and this was repeated three times.
The sheets obtained in this example were subjected to Scanning Electron Microscope (SEM) analysis, hardness, impact and tensile tests, and the results are shown in table 1 and fig. 6. As can be seen in fig. 6: in this example, tempered bainite, tempered martensite and spherical undissolved carbide structures were prepared, and the structure hardness thereof was 51.8HRC, unnotched impact energy not less than 500J, charpy U-shaped notched impact energy (KU) 2 ) It was 32J and had a tensile strength of 1920 MPa. See table 1 for data.
Example 7 referring to FIG. 7, in this example, the austempered sheet material of example 3 above was placed in a box furnace at 560 ℃ and tempered 1h, and was discharged from the furnace and air cooled to room temperature, and this was repeated three times.
The sheets obtained in this example were subjected to Scanning Electron Microscope (SEM) analysis, hardness, impact and tensile tests, and the results are shown in table 1 and fig. 7. As can be seen in fig. 7: in this example, tempered bainite, tempered martensite and spherical undissolved carbide structures were prepared, the hardness of the structure was 50.8 HRC, the unnotched impact energy was not less than 500J, and Charpy U-notch impact energy (KU) 2 ) 28J and tensile strength 1865 MPa. See table 1 for data.
Example 8 referring to fig. 8, in this example, the austempered sheet material of example 4 above was placed in a box furnace at 560 ℃, tempered at 1h, discharged from the furnace and air cooled to room temperature, and this was repeated three times.
The sheets obtained in this example were subjected to Scanning Electron Microscope (SEM) analysis, hardness, impact and tensile tests, and the results are shown in table 1 and fig. 8. As can be seen in fig. 8: in this example, tempered bainite, tempered martensite and spherical undissolved carbide structures were prepared, the hardness of the structure was 51.2 HRC, the unnotched impact energy was not less than 500J, and the Charpy U-notch impact energy (KU) was obtained 2 ) 34J and tensile strength 1912 MPa. See table 1 for data.
Comparative example 1, see fig. 9, in this comparative example H13 steel.
A. The weight percentages are as follows: c0.45, si 0.8, mn 0.37, cr 5.10, mo 1.2, V0.86, ni 0.17, P0.0065, S0.0042, the balance of Fe, calculating the feeding proportion, smelting in a vacuum high-frequency induction furnace and electroslag remelting, and then casting into round ingots with the diameter of phi 80 mm.
B. Hot rolling: heating the steel ingot to 1150 ℃, preserving heat by 5 h, carrying out homogenizing annealing, and cooling along with the furnace. And then hot rolling and cogging the round ingot at 1150 ℃ into a steel plate with the thickness of 25 mm, and air cooling.
C. Solution treatment and spheroidizing annealing: and C, heating the hot rolled plate blank in the step B to 1050 ℃, preserving heat for 25 min, and performing oil quenching. And then heating the solid-dissolved plate blank to 840 ℃, preserving heat for 1h, cooling to 760 ℃ along with a furnace, preserving heat for 2.5 h, cooling to 500 ℃ along with the furnace, discharging from the furnace, and air cooling.
D. Quenching and three times of tempering: and (3) placing the spheroidizing annealed plate at the temperature of 1030 ℃, preserving the heat for 20 min, and performing oil quenching. Then putting the mixture into a box furnace at 560 ℃, carrying out heat preservation tempering on the mixture to obtain 1h, discharging the mixture out of the furnace, carrying out air cooling on the mixture to room temperature, and repeating the steps for three times.
The sheets obtained in this example were subjected to Scanning Electron Microscope (SEM) analysis, hardness, impact and tensile tests, and the results are shown in table 1 and fig. 9. As can be seen in fig. 9: the structure is tempered martensite. This example prepared martensite and bainite die steels with a structure hardness of 48.5 HRC, unnotched impact power of 320J, charpy U-notch impact power (KU) 2 ) 18J and tensile strength 1720 MPa. See table 1 for data.
The results of the mechanical properties of the martensite and bainite dual-phase hot work die steels of examples 1 to 9 are shown in table 1 below:
Figure 12112DEST_PATH_IMAGE002
。
in conclusion, the martensite and bainite dual-phase hot work die steel obtained by the scheme of the invention has high preparation efficiency and excellent tempering performance. The comprehensive mechanical property of the martensite and bainite dual-phase hot work die steel after three times of tempering is superior to that of H13 steel.
Finally, it should be noted that: the above examples are only intended to illustrate the technical solution of the present invention and not to limit it; although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art will understand that: modifications to the specific embodiments of the invention or equivalent substitutions for parts of the technical features may be made; without departing from the spirit of the present invention, it is intended to cover all aspects of the invention as defined by the appended claims.

Claims (7)

1. A martensite and bainite dual-phase hot work die steel is characterized by comprising the following chemical components in percentage by mass: 0.32 to 0.50 percent of C, 1.40 to 1.80 percent of Si, 0.30 to 0.50 percent of Mn, 2.80 to 3.50 percent of Cr, 1.20 to 2.00 percent of Mo, 0.80 to 1.00 percent of V, 1.00 to 2.00 percent of Ni, 0.04 to 0.08 percent of N, 0.9 to 1.5 percent of Co, 0.5 to 1 percent of Al, 0.01 percent of P, 0.005 percent of S, and the balance of Fe and inevitable impurities;
the chemical component proportions of C, N, si, mn, cr, ni, V, co, al and Mo in the hot-work die steel are as follows: b is more than or equal to 85 F ≤105，
Wherein, B F Is the thickness of bainite ferrite lath, the unit is nanometer,
B F =232+0.01785×D-0.5323×Y，
D=-(41-0.001×(T+275) 1.5 ) 2 ×Δg i ，
Δg i =∑(x i /8)×ln(Q i /(8.314×(T+275))，
in the formula, the content of the active carbon is shown in the specification,
Dis the driving energy of the total bainite phase transformation,
y is the strength of the supercooled austenite of steel, Y = 6.5X (4.39 +21C +1.5Si +0.24Cr +0.85Mo +1.2V +0.7Co + 0.5Al),
t is the isothermal transformation temperature,
Δg i is the bainite transformation driving energy of each element, Q i And x i The diffusion activation energy and the mass fraction of each element are respectively, and i represents C, cr, ni, V, co, al and Mo elements.
2. The martensite and bainite dual-phase hot-work die steel according to claim 1, wherein the chemical composition ratio of C, N, si, mn, cr, ni, V, co, al and Mo in the hot-work die steel is as follows: alpha is more than or equal to 2.57 and less than or equal to 5.14,
wherein, alpha = (Si +3Al + 1.5Co-Cr)/(C + Mn + N-0.1 (Ni + V + Mo)).
3. The martensite and bainite dual-phase hot-work die steel according to claim 1, wherein the chemical composition ratio of C, N, si, mn, cr, ni, V, co, al and Mo in the hot-work die steel is as follows: beta is more than or equal to 247 and less than or equal to 300, wherein,
β=565-(31Mn+13Si+10Cr+18Ni+12Mo-8.6Co-15Al)-600(1-exp(-0.96C))。
4. a martensite and bainite dual phase hot work die steel according to any one of claims 1 to 3, wherein the structure of the hot work die steel consists of pre-formed martensite, nano bainite and undissolved carbides.
5. The martensite-bainite dual-phase hot work die steel according to claim 4, wherein the content of the nano bainite is 66% -83%, and the content of the pre-formed martensite is 7% -24.9%.
6. A martensite and bainite dual phase hot work die steel according to any one of claims 1 to 3, wherein the tensile strength of the hot work die steel is not lower than 1860 MPa, the hardness is not lower than 50.0 HRC, and the unnotched impact energy is not lower than 500J.
7. A method of producing a martensite and bainite dual phase hot work die steel, for producing a hot work die steel according to any one of claims 1 to 6, comprising the steps of:
(1) And smelting: feeding according to the design requirements of the components of the steel, smelting in a vacuum induction furnace and casting into steel ingots,
the steel comprises the following components in percentage by mass: 0.32 to 0.50 percent of C, 1.40 to 1.80 percent of Si, 0.30 to 0.50 percent of Mn, 2.80 to 3.50 percent of Cr, 1.20 to 2.00 percent of Mo, 0.80 to 1.00 percent of V, 1.00 to 2.00 percent of Ni, 0.04 to 0.08 percent of N, 0.9 to 1.5 percent of Co, 0.5 to 1 percent of Al, 0.01 percent of P, 0.005 percent of S, and the balance of Fe and inevitable impurities;
(2) And hot rolling: annealing and hot rolling the steel ingot, and air cooling to room temperature after hot rolling to obtain a hot rolled slab;
(3) Solution treatment and spheroidizing annealing: heating the hot rolled plate blank subjected to the heat treatment in the step (2) to 1050-1100 ℃, preserving heat for 20-30 min, and performing oil quenching; heating the plate blank subjected to solid solution to 830 to 870 ℃, preserving heat for 1 to 1.5 hours, cooling to 740 to 770 ℃ along with a furnace, preserving heat for 2 to 2.5 hours, finally cooling to 500 ℃ along with the furnace, and taking out of the furnace for air cooling;
(4) And isothermal quenching treatment: heating the plate blank subjected to the heat treatment in the step (3) to 990-1050 ℃, preserving heat for 20-30 min, then quickly putting the plate blank into a salt bath furnace at 240-274 ℃, quenching the plate blank at medium temperature for 2-4 h, and then air cooling the plate blank to room temperature;
(5) And tempering treatment: and (4) heating the plate blank subjected to the heat treatment in the step (4) to 555 to 565 ℃, preserving the heat for 1 to 1.5 h, taking the plate blank out of the furnace, air-cooling the plate blank, and repeating the steps for three times.
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