Novel high-strength and high-toughness hot work die steel and preparation method thereof

Abstract

The invention discloses novel high-strength and high-toughness hot work die steel and a preparation method thereof, and belongs to the technical field of material preparation. The steel comprises the following chemical components in percentage by mass: 0.25%-0.45% of C, 0.35%-0.65% of Si, 0.34%-0.56% of Mn, 0.72%-0.96% of Ni, 2.35%-2.89% of Cr, 2.28%-2.56% of Mo, 0.95%-1.25% of Co, 0.86%-1.26% of V, 0.25%-0.48% of Nb, less than or equal to 0.015% of P, less than or equal to 0.01% of S and the balance of Fe and inevitable impurities. On the basis of the universal hot work die steel, Co is added to improve the high-temperature strength and thermal stability of the die steel, the Cr element is reduced, the tempering resistance of the die steel is improved, and the Mo, V and Nb elements are beneficial to precipitation of secondary carbides in the tempering process so as to improve the obdurability. In the preparation process, film-shaped retained austenite which is distributed in a dispersed mode and is high in mechanical stability is introduced into the structure of the die steel through the quenching partition technology, so that the die steel material has high strength and meanwhile has high toughness, and the die steel material can be used in the working environment with complex working conditions.

Description

Technical Field

[0001] The invention relates to a novel high-strength and high-toughness hot working die steel and a preparation method thereof, belonging to the technical field of material preparation. Background Art

[0002] Hot working die steel is an important branch of die steel. Its working conditions are more severe than those of other types of die. It not only has to withstand high pressure and impact loads, thermal wear of the metal on the die cavity, but also has to be repeatedly subjected to alternating hot and cold cycles.

[0003] Although the hot working die steel widely used at present meets the needs of industrial production to a certain extent, it still has certain defects in high temperature stability and toughness. In a high temperature environment, die steel is prone to softening and oxidation, resulting in deformation and failure of the die. Many molds have poor toughness and are prone to cracking when subjected to impact loads, which seriously affects the service life of the die steel. The balance between high strength and high toughness of hot working die steel has always been a technical problem. At the same time, with the rapid development of industry in recent decades, hot working die steel is required to develop in the direction of large-scale and complex structure, and only a few of the current mainstream die steels can meet this demand. Therefore, the development of a hot working die steel with both high temperature thermal stability and high strength and toughness is of great significance to improving the high temperature resistance of the mold, extending its service life, and improving processing efficiency.

[0004] In order to obtain the above-mentioned properties, Chinese invention patent CN 115747612 B discloses a method for preparing a complex phase H13 hot working die steel. This method uses martensite pretreatment + isothermal treatment to introduce residual austenite into H13 to improve the impact toughness of H13 steel. However, due to the limitation of H13 components, the improved impact toughness is still not excellent. Chinese invention patent CN111593257B discloses a hot working die steel with high toughness and high thermal stability and a preparation method thereof, which adopts electric furnace smelting, ladle refining furnace refining, vacuum refining furnace refining, electrode billet casting, protective atmosphere electric slag furnace remelting, forging, ultrafine treatment, spheroidizing annealing production and other processes. The final product obtained has the problem of low hardness under high impact toughness. At the same time, this method has high requirements for smelting equipment and large cost investment. Therefore, how to improve the impact toughness of die steel under the premise of ensuring strength and achieve unified regulation of organization and performance is a problem to be solved in the field of hot working die steel. Summary of the invention

[0005] In order to solve the problems existing in the existing hot working dies, one of the purposes of the present invention is to provide a high-strength and toughness hot working die steel, which includes the following elements in weight percentage: C: 0.25% to 0.45%, Si: 0.35% to 0.65%, Mn: 0.34% to 0.56%, Ni: 0.72% to 0.96%, Cr: 2.35% to 2.89%, Mo: 2.28% to 2.56%, Co: 0.95% to 1.25%, V: 0.86% to 1.26%, Nb: 0.25% to 0.48%, P≤0.015%, S≤0.01%, and the rest are Fe and unavoidable impurities, and the total weight percentage of all elements is 100%.

[0006] The second object of the present invention is to provide a method for preparing high-strength and high-toughness hot working die steel, comprising the following steps:

[0007] (1) Melting and casting: According to the design requirements of steel components, the steel is melted and cast into ingots in a vacuum induction furnace.

[0008] (2) Hot forging: The steel ingot is homogenized, then cooled and hot forged. After hot forging, it is air-cooled to room temperature.

[0009] (3) Spheroidizing annealing: The steel obtained in step (2) is subjected to spheroidizing annealing. After the treatment is completed, it is cooled in the furnace to a certain temperature and then taken out and air-cooled to room temperature.

[0010] (4) Solution-quenching-partitioning treatment: The steel obtained in step (3) is solution treated, then isothermally quenched in a salt bath furnace, and then immediately taken out for heat preservation, and then quenched to room temperature, and the quenching medium is water.

[0011] (5) Tempering treatment: The workpiece obtained in step (4) is subjected to a first heat preservation treatment and then air-cooled to room temperature. The workpiece is then subjected to a second heat preservation treatment and then air-cooled to room temperature.

[0012] Preferably, the conditions for the homogenization treatment in step (2) are: a heating rate of 4 to 6°C / min, a holding temperature of 1230°C to 1280°C, and a holding time of 2h.

[0013] Preferably, the cooling condition in step (2) is: cooling to 1160°C to 1180°C at a cooling rate of 10°C / s.

[0014] Preferably, the hot forging conditions in step (2) are: the initial forging temperature is 1140°C to 1160°C, the forging ratio is 4 to 6, and the final forging temperature is not less than 980°C.

[0015] Preferably, the spheroidizing annealing conditions in step (3) are: heating to 830°C to 860°C at a heating rate of 4 to 6°C / min, keeping warm for 2 hours; and cooling to a certain temperature of 640 to 660°C in the furnace.

[0016] Preferably, the solution treatment conditions in step (4) are: instantaneous heating to 1040-1060° C. and keeping warm for 45 minutes.

[0017] Preferably, the isothermal quenching conditions in step (4) are: keeping at 320-340° C. for 5-10 min, and the isothermal quenching medium is: industrial quenching salt.

[0018] Preferably, in step (4), the insulation temperature is 380-400° C. and the insulation time is 30-50 min.

[0019] Preferably, in step (5), the first insulation temperature is 600-620° C., and the insulation time is 1.5-2.5 h; the second insulation temperature is 550-570° C., and the insulation time is 1.5-2.5 h.

[0020] The present invention appropriately increases the content of V and Nb elements, which can increase the amount of carbide precipitation in the mold steel during the tempering process, and improve the strength and hardness of the mold steel; introduces a quenching and partitioning heat treatment process on the basis of conventional heat treatment of general hot working die steel, and introduces a thin film of residual austenite with high mechanical stability into its structure, which can cause the mold steel to undergo phase transformation-induced plasticity effect (residual austenite undergoes phase transformation to martensite, improving strength, toughness and elongation) when subjected to large impact or strain, and significantly improve its plasticity and toughness; although the introduction of residual austenite in the structure will appropriately reduce the strength of the mold steel, the optimization of the chemical composition can produce a large number of dispersed precipitation phases and controlled refined grains by forging, that is, precipitation strengthening and fine grain strengthening can be used to make the mold steel in the present invention have a strength not lower than that of general hot working die steel, while having excellent impact toughness. The addition of Co element combined with heat treatment process can significantly hinder the movement of dislocations and provide nucleation sites for the precipitation of M2C type carbides, thereby improving the high temperature strength and hardness of hot working die steel. In addition, the addition of Co element can also improve the oxidation resistance and corrosion resistance of die steel, and has the effect of inhibiting crack propagation.

[0021] Beneficial Effects of the Invention

[0022] (1) The present invention adopts Nb-V composite alloying technology combined with matching forging and heat treatment processes, optimizes the chemical composition on the basis of general hot working die steel, and forges the steel billet after high-temperature homogenization in the single-phase austenite region. The forging ratio is greater than 4, and a large amount of deformation causes it to undergo repeated recovery recrystallization, refines the grains in the structure and eliminates casting defects. Large deformation can also cause deformation-induced precipitation of NbC and VC. In the subsequent heat treatment process, these carbides can also provide heterogeneous nucleation points for other types of carbides, thereby promoting the dispersion strengthening effect of carbides.

[0023] (2) The present invention innovatively introduces a quenching and partitioning process into the conventional heat treatment process of hot working die steel, thereby significantly improving the impact toughness of the die steel.

[0024] (3) The hot working die steel provided by the present invention has high thermal stability and excellent impact toughness. Its tensile strength reaches 1760-1850MPa, its yield strength reaches 1580-1650MPa, its elongation reaches 18%-26%, and its impact toughness reaches 32-38J / cm 2 , and is also suitable for larger size mold manufacturing. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a process flow chart of the present invention.

[0026] Figure 2 This is the SEM image of Example 1.

[0027] Figure 3 This is the TEM image of Example 1. DETAILED DESCRIPTION

[0028] The technical solution of the present invention is further described below in conjunction with the accompanying drawings and through specific implementation methods. However, the following embodiments are only simple examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention shall be subject to the claims.

[0029] Example 1

[0030] A new type of high-strength and high-toughness hot working die steel and its preparation method

[0031] The hot working die steel prepared in this embodiment includes the following elements in percentage by mass: C: 0.33%, Si: 0.45%, Mn: 0.46%, Ni: 0.81%, Cr: 2.52%, Mo: 2.43%, Co: 1.16%, V: 1.06%, Nb: 0.32%, P: 0.08%, S: 0.006%, and the rest are Fe and unavoidable impurities.

[0032] The specific preparation method comprises the following steps:

[0033] (1) Melting and casting: According to the design requirements of steel components, the steel is melted and cast into ingots in a vacuum induction furnace.

[0034] (2) Hot forging: The steel ingot obtained in step (1) was heated to 1250°C at a heating rate of 5°C / min and homogenized for 2 h, then cooled to 1170°C at a cooling rate of 10°C / s and hot forged. The initial forging temperature was 1150°C, the forging ratio was 5, the final forging temperature was 1000°C, and after hot forging was completed, it was air-cooled to room temperature.

[0035] (3) Spheroidizing annealing: The workpiece obtained in step (2) was heated to 845°C in a furnace at a heating rate of 5°C / min and kept at that temperature for 2 h for spheroidizing annealing. After the holding was completed, it was cooled to 650°C in the furnace and then taken out and air-cooled to room temperature.

[0036] (4) Solution-quenching-partitioning treatment: The workpiece obtained in step (3) was instantaneously heated to 1050°C for solution treatment, kept at this temperature for 45 min, and immediately quenched in a salt bath furnace at a temperature of 330°C. After being kept at this temperature for 8 min, it was immediately taken out and moved into another furnace at a temperature of 390°C and kept at this temperature for 40 min, and then water quenched to room temperature.

[0037] (5) Tempering treatment: The workpiece obtained in step (4) is placed in a furnace at a temperature of 610°C and kept at this temperature for 2 hours, then taken out and air-cooled to room temperature. The workpiece is then placed in a furnace at a temperature of 560°C and kept at this temperature for 2 hours, then taken out and air-cooled to room temperature.

[0038] Example 2

[0039] A new type of high-strength and high-toughness hot working die steel and its preparation method

[0040] The hot working die steel prepared in this embodiment includes the following elements in percentage by mass: C: 0.26%, Si: 0.37%, Mn: 0.36%, Ni: 0.75%, Cr: 2.38%, Mo: 2.30%, Co: 0.98%, V: 0.89%, Nb: 0.27%, P: 0.07%, S: 0.008%, and the rest are Fe and unavoidable impurities.

[0041] The specific preparation method comprises the following steps:

[0042] (1) Melting and casting: According to the design requirements of steel components, the steel is melted and cast into ingots in a vacuum induction furnace.

[0043] (2) Hot forging: The steel ingot obtained in step (1) is heated to 1230°C at a heating rate of 4°C / min and homogenized for 2 h, then cooled to 1160°C at a cooling rate of 10°C / s and hot forged. The initial forging temperature is 1140°C, the forging ratio is 4, the final forging temperature is 984°C, and after hot forging is completed, the steel ingot is air-cooled to room temperature;

[0044] (3) Spheroidizing annealing: The workpiece obtained in step (2) is heated to 830°C at a heating rate of 4°C / min in a furnace, and kept at this temperature for 2 hours for spheroidizing annealing. After the heat preservation is completed, the workpiece is cooled to 640°C in the furnace, and then taken out and air-cooled to room temperature;

[0045] (4) Solution-quenching-partitioning treatment: The workpiece obtained in step (3) was instantaneously heated to 1040°C for solution treatment, kept at this temperature for 45 min, and then immediately quenched in a salt bath furnace at a temperature of 320°C. After being kept at this temperature for 5 min, it was immediately taken out and moved into another furnace at a temperature of 380°C and kept at this temperature for 30 min, and then water quenched to room temperature.

[0046] (5) Tempering treatment: The workpiece obtained in step (4) is placed in a furnace at a temperature of 600°C and kept at this temperature for 1.5 hours, and then air-cooled to room temperature. The workpiece is then placed in a furnace at a temperature of 550°C and kept at this temperature for 1.5 hours, and then air-cooled to room temperature.

[0047] Example 3

[0048] A new type of high-strength and high-toughness hot working die steel and its preparation method

[0049] The hot working die steel prepared in this embodiment includes the following elements in percentage by mass: C: 0.42%, Si: 0.62%, Mn: 0.56%, Ni: 0.93%, Cr: 2.82%, Mo: 2.53%, Co: 1.25%, V: 1.21%, Nb: 0.43%, 0.06%, S: 0.005%, and the rest are Fe and unavoidable impurities.

[0050] The specific preparation method comprises the following steps:

[0051] (1) Melting and casting: According to the design requirements of steel components, the steel is melted and cast into steel ingots in a vacuum induction furnace;

[0052] (2) Hot forging: The steel ingot obtained in step (1) is heated to 1280°C at a heating rate of 6°C / min and homogenized for 2 h, then cooled to 1180°C at a cooling rate of 10°C / s and hot forged. The initial forging temperature is 1160°C, the forging ratio is 6, the final forging temperature is 993°C, and after hot forging is completed, the steel ingot is air-cooled to room temperature;

[0053] (3) Spheroidizing annealing: The workpiece obtained in step (2) is heated to 860°C at a heating rate of 6°C / min in a furnace, and kept at this temperature for 2 hours for spheroidizing annealing. After the heat preservation is completed, the workpiece is cooled to 660°C in the furnace, and then taken out and air-cooled to room temperature;

[0054] (4) Solution-quenching-partitioning treatment: The workpiece obtained in step (3) was instantaneously heated to 1060°C for solution treatment, kept at this temperature for 45 min, and immediately quenched in a salt bath furnace at a temperature of 340°C. After being kept at this temperature for 10 min, it was immediately taken out and moved into another furnace at a temperature of 400°C and kept at this temperature for 50 min, and then water quenched to room temperature.

[0055] (5) Tempering treatment: The workpiece obtained in step (4) is placed in a furnace at a temperature of 620°C and kept at this temperature for 2.5 hours, and then air-cooled to room temperature. The workpiece is then placed in a furnace at a temperature of 570°C and kept at this temperature for 2.5 hours, and then air-cooled to room temperature.

[0056] Comparative Example 1

[0057] Comparative Example 1 of the present invention has the same chemical composition as that of Example 1 except that it does not contain the Co element, and includes the following elements in mass percentage: C: 0.33%, Si: 0.45%, Mn: 0.46%, Ni: 0.81%, Cr: 2.52%, Mo: 2.43%, V: 1.06%, Nb: 0.32%, and the rest are Fe and unavoidable impurities.

[0058] The preparation method is exactly the same as that in Example 1.

[0059] Comparative Example 2

[0060] Comparative Example 2 of the present invention is a conventional hot working die steel on the market, and its chemical composition by mass percentage is: C: 0.41%, Si: 0.92%, Mn: 0.35%, Cr: 5.12%, Mo: 1.32%, V: 1.06%, and the rest is Fe and unavoidable impurities.

[0061] The preparation method is exactly the same as that in Example 1.

[0062] Comparative Example 3

[0063] Comparative Example 3 of the present invention has the same chemical composition as Example 1, and the preparation method comprises the following steps:

[0064] (1) Melting and casting: According to the design requirements of steel components, the steel is melted and cast into steel ingots in a vacuum induction furnace;

[0065] (2) Hot forging: The steel ingot obtained in step (1) is heated to 1250°C at a heating rate of 5°C / min and homogenized for 2 h, then cooled to 1170°C at a cooling rate of 10°C / s and hot forged. The initial forging temperature is 1150°C, the forging ratio is 5, the final forging temperature is 1000°C, and after hot forging is completed, the steel ingot is air-cooled to room temperature;

[0066] (3) Spheroidizing annealing: The workpiece obtained in step (2) was heated to 845°C in a furnace at a heating rate of 5°C / min and kept at that temperature for 2 h for spheroidizing annealing. After the holding was completed, it was cooled to 650°C in the furnace and then taken out and air-cooled to room temperature.

[0067] (4) Solution-quenching treatment: The workpiece obtained in step (3) is instantaneously heated to 1050°C for solution treatment, kept at this temperature for 45 minutes, and then immediately quenched to room temperature. The quenching medium is industrial quenching oil.

[0068] (5) Tempering treatment: The workpiece obtained in step (4) is placed in a furnace at a temperature of 610°C and kept at this temperature for 2 hours, and then air-cooled to room temperature. The workpiece is then placed in a furnace at a temperature of 560°C and kept at this temperature for 2 hours, and then air-cooled to room temperature.

[0069] Comparative Example 4

[0070] Comparative Example 4 of the present invention has the same chemical composition as Example 1, and the preparation method comprises the following steps:

[0071] (1) Melting and casting: According to the design requirements of steel components, the steel is melted and cast into ingots in a vacuum induction furnace.

[0072] (2) Hot forging: The steel ingot obtained in step (1) was heated to 1250°C at a heating rate of 5°C / min and homogenized for 2 h, then cooled to 1170°C at a cooling rate of 10°C / s and hot forged. The initial forging temperature was 1150°C, the forging ratio was 5, the final forging temperature was 1000°C, and after hot forging was completed, it was air-cooled to room temperature.

[0073] (3) Spheroidizing annealing: The workpiece obtained in step (2) was heated to 845°C in a furnace at a heating rate of 5°C / min and kept at that temperature for 2 h for spheroidizing annealing. After the holding was completed, it was cooled to 650°C in the furnace and then taken out and air-cooled to room temperature.

[0074] (4) Solution-isothermal quenching treatment: The workpiece obtained in step (3) was instantaneously heated to 1050°C for solution treatment, kept at this temperature for 45 min, and immediately quenched in a salt bath furnace at a temperature of 390°C. After isothermal treatment for 48 min, the workpiece was water quenched to room temperature.

[0075] (5) Tempering treatment: The workpiece obtained in step (4) is placed in a furnace at a temperature of 610°C and kept at this temperature for 2 hours, and then air-cooled to room temperature. The workpiece is then placed in a furnace at a temperature of 560°C and kept at this temperature for 2 hours, and then air-cooled to room temperature.

[0076] The new high-strength and high-toughness hot working die steel structures obtained in the present inventions 1 to 3 are all alternately distributed with fine martensite laths and film-like retained austenite with high mechanical stability, and a large number of small-sized carbides are dispersed in the structure. This makes the die steel have high strength and surface hardness while having excellent impact toughness. The new high-strength and high-toughness hot working die steel prepared in Example 1 is used as an example for detailed description:

[0077] Figure 2 This is the SEM image of Example 1. It can be seen from the figure that its structure includes martensite and some film-like retained austenite, and there are many dispersed carbides distributed in its structure. The size of the primary carbide is about 300nm, and the size of the secondary carbide is smaller, both of which are in the nanometer order. The dispersion strengthening provided by the dispersed distribution of carbides and the fine grain strengthening provided by the fine martensite laths ensure that the mold steel has high strength and hardness.

[0078] Figure 3 The TEM image of Example 1 shows more intuitively that the microstructure of the mold steel is an alternating distribution of martensite laths and film-like retained austenite with high mechanical stability. This special structure is obtained by introducing a quenching-partitioning process during its preparation. The phase transformation-induced plasticity effect of the film-like retained austenite when subjected to large impact loads or stresses ensures that the mold steel has excellent impact toughness.

[0079] The mechanical properties of the mold steels prepared in Examples 1 to 3 and Comparative Examples 1 to 4 were tested according to the following method and the results are listed in Table 1. Strength: The dog-bone-shaped samples with a processing diameter of 5 mm and a gauge length of 35 mm were processed on Shimadzu AGS100 at 10 -3 s -1 Tensile test was carried out at a strain rate of 10000 ℃ and 10000 ℃ respectively; Impact toughness: carried out on a SUNS PTM2302-B testing machine, with a Charpy V-notch specimen of 10×10×55mm in size; Hardness: a HRS-150 Rockwell hardness tester was used to measure the hardness values ​​at five points on each sample to be tested, and the average value was taken as the final result; Thermal stability hardness: the samples were kept at 600℃ and 650℃ for 24h, respectively, and then their hardness was tested.

[0080] As can be seen from Table 1, the hot working die steel provided by the present invention has high toughness and excellent impact toughness, and also has excellent high thermal stability. Compared with Example 1, the chemical composition of Comparative Example 1 does not contain the Co element, and the strength and thermal stability of Comparative Example 1 are far inferior to those of Example 1. It can be seen that the addition of the Co element is of great significance to improving the thermal stability of hot working die steel. Comparative Example 2 is a hot working die steel commonly used on the market. After adopting the same preparation process as Example 1, its mechanical properties are generally good, indicating that if you want to obtain the mechanical properties shown by the present invention, you must use a special chemical composition combined with a matching preparation method to achieve it. The chemical composition of Comparative Examples 3 and 4 is the same as that of Example 1, and its preparation process is conventional solution-quenching treatment and conventional isothermal quenching treatment, respectively. It can be seen from the mechanical property results that the die steel obtained by conventional solution-quenching treatment has low impact toughness. Although the die steel obtained by conventional isothermal quenching treatment has high impact toughness, its strength and hardness are low. It can be seen that the quenching-partitioning process can retain high strength and hardness as much as possible while making it have excellent impact toughness.

[0081] Table 1 Mechanical properties of hot working die steels prepared in Examples 1 to 3 and Comparative Examples 1 to 4

[0082]

[0083] In summary, the present invention aims to obtain a high-strength and toughness hot working die steel, adopts a special composition design and combines a matching preparation method, introduces the quenching-partitioning process into the preparation of the die steel, so that the prepared hot working die steel has high strength and toughness while having excellent high temperature thermal stability. The tensile strength of the die steel provided by the present invention can reach 1760-1850MPa, the yield strength can reach 1580-1650MPa, the elongation can reach 18%-26%, and the impact toughness can reach 32-38J / cm 2 .

[0084] The above is only an embodiment of the present invention, and the common knowledge such as the known specific technical solutions and / or characteristics in the solution is not described in detail here. It should be pointed out that for those skilled in the art, without departing from the technical solution of the present invention, several modifications and improvements can be made, which should also be regarded as the protection scope of the present invention, and these will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the specification can be used to interpret the content of the claims.

Claims

1. A new type of high-strength and high-toughness hot working die steel, characterized in that: The invention comprises the following elements in weight percentage: C: 0.25% to 0.45%, Si: 0.35% to 0.65%, Mn: 0.34% to 0.56%, Ni: 0.72% to 0.96%, Cr: 2.35% to 2.89%, Mo: 2.28% to 2.56%, Co: 0.95% to 1.25%, V: 0.86% to 1.26%, Nb: 0.25% to 0.48%, P≤0.015%, S≤0.01%, and the rest are Fe and unavoidable impurities. The total weight percentage of all elements is 100%.

2. The method for preparing the novel high-strength and high-toughness hot working die steel according to claim 1, characterized in that: The following steps are involved: (1) Melting and casting: According to the design requirements of steel components, the steel is melted and cast into steel ingots in a vacuum induction furnace; (2) Hot forging: The steel ingot is homogenized, then cooled and hot forged. After hot forging, it is air-cooled to room temperature. (3) Spheroidizing annealing: The steel obtained in step (2) is subjected to spheroidizing annealing. After the treatment is completed, the steel is cooled to a certain temperature in the furnace and then taken out and air-cooled to room temperature. (4) Solution-quenching-partitioning treatment: The steel obtained in step (3) is solution treated, then isothermally quenched in a salt bath furnace, immediately taken out for heat preservation, and then quenched to room temperature, with water as the quenching medium; (5) Tempering treatment: The workpiece obtained in step (4) is subjected to a first heat preservation treatment and then air-cooled to room temperature. The workpiece is then subjected to a second heat preservation treatment and then air-cooled to room temperature.

3. The method for preparing the new high-strength and high-toughness hot working die steel according to claim 2, characterized in that: The conditions for the homogenization treatment in step (2) are: a heating rate of 4 to 6°C / min, a holding temperature of 1230°C to 1280°C, and a holding time of 2h.

4. The method for preparing the novel high-strength and high-toughness hot working die steel according to claim 2 is characterized in that: The cooling condition in step (2) is: cooling to 1160°C to 1180°C at a cooling rate of 10°C / s.

5. The method for preparing the novel high-strength and high-toughness hot working die steel according to claim 2 is characterized in that: The hot forging conditions in step (2) are: the initial forging temperature is 1140°C to 1160°C, the forging ratio is 4 to 6, and the final forging temperature is not less than 980°C.

6. The method for preparing the novel high-strength and high-toughness hot working die steel according to claim 2 is characterized in that: The spheroidizing annealing conditions in step (3) are: heating to 830°C to 860°C at a heating rate of 4 to 6°C / min, keeping warm for 2 hours; and cooling to a certain temperature of 640 to 660°C in the furnace.

7. The method for preparing the novel high-strength and high-toughness hot working die steel according to claim 2 is characterized in that: The solution treatment conditions in step (4) are: instantaneous heating to 1040-1060° C. and keeping warm for 45 minutes.

8. The method for preparing the novel high-strength and high-toughness hot working die steel according to claim 2 is characterized in that: The isothermal quenching conditions in step (4) are: 320-340° C. for 5-10 min, and the isothermal quenching medium is: industrial quenching salt.

9. The method for preparing the novel high-strength and high-toughness hot working die steel according to claim 2, characterized in that: In step (4), the holding temperature is 380-400° C. and the holding time is 30-50 min.

10. The method for preparing the novel high-strength and high-toughness hot working die steel according to claim 2, characterized in that: In step (5), the first insulation temperature is 600-620° C., and the insulation time is 1.5-2.5 h; the second insulation temperature is 550-570° C., and the insulation time is 1.5-2.5 h.

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