Nano-reinforced high-thermal-conductivity high-thermal-fatigue-resistance die steel and preparation method thereof

Abstract

The application provides a nano-reinforced high-thermal-conductivity high-thermal-fatigue-resistance die steel and a preparation method thereof. The preparation method comprises the following steps: mixing carbon powder, iron-titanium powder and iron powder to obtain a mixture 1, wrapping the mixture 1 with aluminum foil, and then performing thermal explosion reaction to obtain an alloy block A containing micron-level active inoculation phases; mixing B powder, iron-titanium powder and iron powder to obtain a mixture 2, wrapping the mixture 2 with aluminum foil, and then performing thermal explosion reaction to obtain an alloy block B containing micron-level active inoculation phases; mixing the alloy block A and the alloy block B, crushing, and then performing plasma reaction to obtain an iron-coated TiC+TiB2 nano ceramic particle alloy; mixing the iron-coated TiC+TiB2 nano ceramic particle alloy with molten die steel liquid, and then performing impurity removal, casting, forging, annealing, quenching and tempering to obtain the nano-reinforced high-thermal-conductivity high-thermal-fatigue-resistance die steel. The nano-reinforced high-thermal-conductivity high-thermal-fatigue-resistance die steel prepared by the application has a thermal conductivity of 55-58 W / m.K; and after 25-600 DEG C cold and hot fatigue cycles for 1800-3200 times, the main crack length of the nano-reinforced high-thermal-conductivity high-thermal-fatigue-resistance die is less than or equal to 396 mu m.

Description

Technical Field

[0001] This invention belongs to the field of mold steel manufacturing technology, specifically relating to a nano-reinforced mold steel with high thermal conductivity and high resistance to thermal fatigue, and its preparation method. Background Technology

[0002] In die casting, hot forging, and hot extrusion processes, mold failure modes are often complex and diverse, with thermal fatigue failure accounting for approximately 70%, making it the most prevalent failure mode. The essence of thermal fatigue stems from the restricted free expansion and contraction of materials during temperature changes, inducing thermal stress within the material. Under the influence of a cyclical alternating temperature field, periodically fluctuating hot and cold alternating stresses are generated within the mold material, leading to cumulative damage over time. Die casting molds, hot forging molds, and hot extrusion molds, due to the extreme conditions of rapid heating and cooling cycles, experience severe hot and cold alternating stresses in their cavities. When this stress exceeds the yield strength of the mold cavity, micro-cracks begin to initiate. With the continued action of hot and cold alternating thermal stress, these micro-cracks propagate and connect, eventually leading to thermal cracking. Therefore, thermal stress is the direct cause of thermal fatigue failure in molds. Currently, existing technologies focus on enhancing the strength of mold steel to improve its resistance to thermal stress, thereby improving the thermal fatigue resistance of the mold steel. For example, the high-end mold steel DIEVAR achieves high strength through optimized alloy composition design, thus exhibiting excellent resistance to thermal fatigue. However, the high variety and content of alloying elements in DIEVAR steel result in high raw material costs. More importantly, simply relying on strength enhancement to passively resist thermal stress has inherent limitations. When the mold cavity experiences a large temperature gradient due to rapid heating and cooling, even high-strength materials cannot completely suppress the initiation and propagation of microcracks. To address these limitations, it is necessary to explore new methods that differ from the traditional approach of relying solely on strength to improve thermal fatigue resistance while also reducing costs. Summary of the Invention

[0003] To address the aforementioned technical challenges, this invention provides a nano-reinforced high thermal conductivity and high thermal fatigue resistance die steel, the preparation method of which includes the following steps: (1) Carbon powder, iron-titanium powder and iron powder are mixed at a mass ratio of 2-5: 4-8: 18-38 for 21-28 hours at a speed of 111-142 r / min to obtain powder mixture 1; after wrapping powder mixture 1 with aluminum foil, thermal explosion reaction 1 is carried out to obtain self-fractured alloy block A containing micron-sized active inoculated phase; The mass ratio of the aluminum foil to the powder mixture 1 is 1:1320-1380; The thermal explosion reaction 1 is carried out under argon protection at a pressure of 0.015-0.045 MPa, a temperature of 1120-1180℃, and a reaction time of 70-120 s. The carbon powder has a particle size of 4-9µm. By mass percentage, the main components of the iron-titanium powder include: titanium: 28-35%, with the balance being iron. The particle size of the iron-titanium powder is 70-190µm, and the particle size of the iron powder is 25-55µm. (2) Mix B powder, iron-titanium powder and iron powder at a mass ratio of 1-4: 3-7: 20-42 at a rotation speed of 90-125 r / min for 30-42 h to obtain powder mixture 2; wrap powder mixture 2 with aluminum foil and carry out thermal explosion reaction 2 to obtain self-fractured alloy block B containing micron-sized active inoculated phase; The mass ratio of the aluminum foil to the powder mixture 2 is 1:1260-1440; The thermal explosion reaction 2 is carried out under argon protection at a pressure of 0.018-0.038 MPa, a temperature of 1140-1210℃, and a reaction time of 40-100 s. The particle size of the B powder is 37-72µm. By mass percentage, the main components of the iron-titanium powder include: titanium: 56-63%, with the balance being iron. The particle size of the iron-titanium powder is 55-135µm, and the particle size of the iron powder is 23-63µm. (3) The alloy block A containing micron-sized active inoculated phase obtained in step (1) and the alloy block B containing micron-sized active inoculated phase obtained in step (2) are mixed and crushed at a mass ratio of 12-16: 3-7, and then subjected to plasma reaction to obtain iron-coated TiC+TiB2 nano-ceramic particle alloy. The plasma reaction is carried out under argon protection, with a reaction pressure of 0.015-0.045 MPa, a reaction temperature of 4900-5300℃, a power supply operating frequency of 2.3-4.5 MHz, and an output power of 50-100 kW. (4) The mold steel is heated to 1525-1575℃ until it is completely melted to obtain molten steel. The iron-coated TiC+TiB2 nano-ceramic particle alloy obtained in step (3) is mixed with the molten steel at a mass ratio of 0.11%-0.13%:1. After impurity removal and casting, an ingot is obtained. The ingot is then forged, annealed, quenched and tempered to obtain nano-reinforced high thermal conductivity and high thermal fatigue resistance mold steel. The composition of the mold steel, by weight percentage, is as follows: C: 0.345-0.375 wt.%; Mo: 2.8-2.9 wt.%; Mn: 0.61-0.69 wt.%; V: 0.4-0.55 wt.%; unavoidable impurities are P: ≤0.009 wt.%; S: ≤0.008 wt.%; N: ≤0.0085 wt.%; H: ≤0.0009 wt.%; O: ≤0.002 wt.%; balance is Fe; The casting process is as follows: casting temperature 1550-1585℃, casting speed 95-175mm / min; The forging process is as follows: the forging temperature is 925-1115℃, and the total forging ratio is 7-11:1; the forging process adopts a three-upsetting and three-drawing process; the first upsetting and drawing is carried out along the axial direction of the ingot, with a reduction rate of 40-50%, and then upsetting to 35-39% of the original height; the second upsetting and drawing is carried out by rotating 90° clockwise around the axial direction of the ingot and drawing along the radial direction of the ingot, with a reduction rate of 42-52%, and then upsetting to 40-45% of the original height; the third upsetting and drawing is carried out by rotating 90° clockwise around the radial direction of the ingot and drawing along another axial direction, with a reduction rate of 45-55%, and then upsetting to 42-49% of the original height. The annealing process is as follows: under vacuum conditions, the temperature is held at 770-820℃ for 2 hours and then cooled in the furnace. The quenching process is as follows: oil quenching is performed after holding at 1000-1020℃ for 1 hour under vacuum conditions; The tempering process is as follows: under vacuum conditions, the temperature is held at 610-630℃ for 5 hours and then air-cooled. The aforementioned nano-reinforced high thermal conductivity and high thermal fatigue resistance die steel contains TiC+TiB2 nano-ceramic particles with an average particle size of 154-196 nm; the mass fraction of TiC+TiB2 nano-ceramic particles in the nano-reinforced high thermal conductivity and high thermal fatigue resistance die steel is 0.055-0.065 wt.%. The aforementioned nano-reinforced high thermal conductivity and high thermal fatigue resistance mold steel has a thermal conductivity of 55-58 W / m·K; after 1800-3200 cycles of thermal fatigue at 25-600℃, the main crack length of the nano-reinforced high thermal conductivity and high thermal fatigue resistance mold steel is ≤396µm.

[0004] Further, the mass ratio of aluminum foil to powder mixture 1 in step (1) is 1:1322-1374; the thermal explosion reaction 1 is: under argon protection, pressure 0.016-0.044MPa, temperature 1122-1178℃, reaction time 73-114s; the particle size of the carbon powder is 4.2-8.7µm, and the main components of the iron-titanium powder by mass percentage include: titanium: 29-34%, the balance being iron, the particle size of the iron-titanium powder is 72.1-182.5µm, and the particle size of the Fe powder is 25.3-53.1µm.

[0005] Further, the mass ratio of aluminum foil to powder mixture 2 in step (2) is 1:1261-1432; the thermal explosion reaction 2 is carried out under argon protection, with a pressure of 0.019-0.031 MPa, a temperature of 1144-1207℃, and a reaction time of 42-98 s; the particle size of B powder is 39.6-69.2 µm, and the main components of the iron-titanium powder by mass percentage include: titanium: 57-62%, with the balance being iron, the particle size of the iron-titanium powder is 59.2-123.4 µm, and the particle size of the Fe powder is 27.3-60.2 µm.

[0006] Further, the plasma reaction described in step (3) is as follows: under argon protection, the reaction pressure is 0.018-0.042MPa, the reaction temperature is 4920-5260℃, the power supply operating frequency is 2.4-4.4MHz, and the output power is 52-95kW.

[0007] Further, the composition of the mold steel in step (4) by mass percentage is as follows: C: 0.347-0.372 wt.%; Mo: 2.81-2.88 wt.%; Mn: 0.615-0.688 wt.%; V: 0.44-0.54 wt.%; unavoidable impurities are P: ≤0.0085 wt.%; S: ≤0.0077 wt.%; N: ≤0.0082 wt.%; H: ≤0.0008 wt.%; O: ≤0.0017 wt.%; the balance is Fe.

[0008] Further, the casting in step (4) is as follows: casting temperature 1552-1582℃, casting speed 97-174mm / min.

[0009] Further, the forging in step (4) is as follows: the forging temperature is 929-1111℃, and the total forging ratio is 8-10:1; the forging process adopts a three-upsetting and three-drawing process; the first upsetting and drawing is carried out along the ingot axis with a reduction rate of 41-49%, and then upsetting to 36-38% of the original height; the second upsetting and drawing is carried out by rotating 90° clockwise around the ingot axis and drawing along the ingot radially with a reduction rate of 44-51%, and then upsetting to 41-44% of the original height; the third upsetting and drawing is carried out by rotating 90° clockwise around the ingot radially and drawing along another axis with a reduction rate of 46-54%, and then upsetting to 43-48% of the original height.

[0010] Further, the annealing in step (4) is: under vacuum conditions, the temperature is held at 775-815℃ for 2 hours and then cooled in the furnace; the quenching is: under vacuum conditions, the temperature is held at 1008-1018℃ for 1 hour and then oil quenched; the tempering is: under vacuum conditions, the temperature is held at 612-628℃ for 5 hours and then air cooled.

[0011] Furthermore, the nano-reinforced high thermal conductivity and high thermal fatigue resistance mold steel described in step (4) contains TiC+TiB2 nano-ceramic particles with an average particle size of 155-192 nm; the mass fraction of TiC+TiB2 nano-ceramic particles in the nano-reinforced high thermal conductivity and high thermal fatigue resistance mold steel is 0.056-0.064 wt.%.

[0012] Furthermore, the thermal conductivity of the nano-reinforced high thermal conductivity and high thermal fatigue resistance mold steel obtained in step (4) is 55.4-57.8 W / m·K; after 2000-3000 cycles of hot and cold fatigue at 25-600℃, the main crack length of the nano-reinforced high thermal conductivity and high thermal fatigue resistance mold steel is 0-100µm.

[0013] Compared with the prior art, the present invention has the following advantages: The existing high-end mold steel DIEVAR contains 0.1-0.58 wt.% Si and 4.8-5.5 wt.% Cr. Si and Cr are two alloying elements that significantly deteriorate the thermal conductivity of mold steel. Therefore, compared with existing technologies, this invention significantly improves the thermal conductivity of mold steel while reducing raw material costs by not adding Si and Cr. The thermal conductivity of the nano-reinforced high thermal conductivity and high thermal fatigue resistance mold steel obtained by this invention is 55-58 W / m·K, which is twice that of mold steel obtained by existing technologies (the thermal conductivity of existing mold steel is 23-28 W / m·K). Higher thermal conductivity indicates better thermal conductivity of the material. After 1800-3200 cycles of thermal fatigue at 25-600℃, the nano-reinforced high thermal conductivity mold steel obtained by this invention... The main crack length of the reinforced, high thermal conductivity, and high thermal fatigue resistance die steel is ≤396µm; the shorter the main crack length, the stronger the thermal fatigue resistance of the material. High thermal conductivity gives the material a faster heat conduction speed, which effectively alleviates the thermal stress concentration inside the material through rapid heat conduction, delays the initiation of hot cracks, and thus improves the thermal fatigue resistance of the material. At the same time, nano-ceramic particles increase the strength of the material, further improving the thermal fatigue resistance of the material by enhancing its ability to resist stress concentration. The core innovation of this invention is that it breaks through the traditional technical means of improving the thermal fatigue resistance of die steel by simply increasing strength. For the first time, it achieves a significant improvement in the thermal fatigue resistance of die steel by synergistic regulation of high thermal conductivity matrix and nano-ceramic particles, ratio, process and process parameters, while reducing raw material costs.

[0014] In summary, this invention significantly improves the thermal conductivity of mold steel by reducing raw material costs without adding Si and Cr elements, which degrade the thermal conductivity of mold steel. It proposes a new approach to enhance the thermal fatigue resistance of mold steel by improving its thermal conductivity: shifting from passively resisting thermal stress with high strength to actively suppressing thermal stress at its source by improving thermal conductivity to reduce the amplitude of thermal stress induced by rapid cooling and heating. Furthermore, by combining the suppression and resistance of thermal stress, this invention develops mold steels that possess both high thermal conductivity and high strength, representing a new direction for improving the thermal fatigue resistance of mold steel. Attached Figure Description

[0015] Figure 1 The image shows the thermal fatigue crack propagation of the nano-reinforced high thermal conductivity and high thermal fatigue resistance mold steel 1 obtained in Example 1 of the present invention after 2000 cycles of hot and cold fatigue at 25-600℃.

[0016] Figure 2 The image shows the thermal fatigue crack propagation of the nano-reinforced high thermal conductivity and high thermal fatigue resistance mold steel 1 obtained in Example 1 of the present invention after 3000 cycles of hot and cold fatigue at 25-600℃.

[0017] Figure 3 The image shows the thermal fatigue crack propagation of the nano-reinforced high thermal conductivity and high thermal fatigue resistance mold steel 2 obtained in Example 2 of the present invention after 2000 cycles of hot and cold fatigue at 25-600℃.

[0018] Figure 4 The image shows the thermal fatigue crack propagation of the nano-reinforced high thermal conductivity and high thermal fatigue resistance mold steel 2 obtained in Example 2 of the present invention after 3000 cycles of hot and cold fatigue at 25-600℃.

[0019] Figure 5 The image shows the thermal fatigue crack propagation of the nano-reinforced high thermal conductivity and high thermal fatigue resistance mold steel 3 obtained in Example 3 of the present invention after 2000 cycles of hot and cold fatigue at 25-600℃.

[0020] Figure 6 The image shows the thermal fatigue crack propagation of the nano-reinforced high thermal conductivity and high thermal fatigue resistance mold steel 3 obtained in Example 3 of the present invention after 3000 cycles of hot and cold fatigue at 25-600℃.

[0021] Figure 7 The diagram shows the thermal fatigue crack propagation of DIEVAR, a high-end mold steel obtained for comparison, after 2000 cycles of thermal fatigue at 25-600℃.

[0022] Figure 8 The diagram shows the thermal fatigue crack propagation of DIEVAR, a high-end mold steel obtained for comparison, after 2800 cycles of thermal fatigue at 25-600℃. Detailed Implementation

[0023] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Example 1

[0024] The preparation method of nano-reinforced high thermal conductivity and high thermal fatigue resistance die steel 1 includes the following steps: (1) Carbon powder, iron-titanium powder and iron powder are mixed at a mass ratio of 3:5:23 for 23 hours to obtain powder mixture 1; powder mixture 1 is wrapped with aluminum foil and subjected to thermal explosion reaction 1 to obtain self-breaking alloy block A containing micron-sized active inoculated phase; The mass ratio of the aluminum foil to the powder mixture 1 is 1:1335; The thermal explosion reaction 1 is carried out under argon protection at a pressure of 0.022 MPa, a temperature of 1145°C, and a reaction time of 87 s. The carbon powder has a particle size of 5.6µm. By mass percentage, the main components of the iron-titanium powder include: titanium: 29%, with the balance being iron. The particle size of the iron-titanium powder is 88µm, and the particle size of the iron powder is 39µm. (2) Mix B powder, iron-titanium powder and iron powder at a mass ratio of 2:6:31 for 34 hours to obtain powder mixture 2; wrap powder mixture 2 with aluminum foil and carry out thermal explosion reaction 2 to obtain self-breaking alloy block B containing micron-sized active inoculated phase; The mass ratio of the aluminum foil to the powder mixture 2 is 1:1290; The thermal explosion reaction 2 is carried out under argon protection at a pressure of 0.024 MPa, a temperature of 1165°C, and a reaction time of 75 s. The particle size of the B powder is 57µm. By mass percentage, the main components of the iron-titanium powder include: titanium: 58%, with the balance being iron. The particle size of the iron-titanium powder is 111µm, and the particle size of the iron powder is 48µm. (3) The alloy block A containing micron-sized active inoculum obtained in step (1) and the alloy block B containing micron-sized active inoculum obtained in step (2) are mixed and crushed at a mass ratio of 14:5 and then subjected to plasma reaction to obtain iron-coated TiC+TiB2 nano-ceramic particle alloy. The plasma reaction is carried out under argon protection, with a reaction pressure of 0.029 MPa, a reaction temperature of 5220℃, a power supply operating frequency of 3.3 MHz, and an output power of 73 kW. (4) The mold steel is heated to 1536℃ until it is completely melted to obtain molten steel. The iron-coated TiC+TiB2 nano-ceramic particle alloy obtained in step (3) is mixed with the molten steel at a mass ratio of 0.116%:1. After impurity removal and casting, an ingot is obtained. The ingot is then forged, annealed, quenched and tempered to obtain nano-reinforced high thermal conductivity and high thermal fatigue resistance mold steel. The composition of the mold steel, by weight percentage, is as follows: C: 0.359 wt.%; Mo: 2.825 wt.%; Mn: 0.65 wt.%; V: 0.45 wt.%; unavoidable impurities are P: 0.003 wt.%; S: 0.007 wt.%; N: 0.0075 wt.%; H: 0.0006 wt.%; O: 0.0018 wt.%; balance is Fe; The casting process is as follows: casting temperature 1566℃, casting speed 158mm / min; The forging process is as follows: the forging temperature is 1110℃, and the total forging ratio is 8:1; the forging process adopts a three-upsetting and three-drawing process; the first upsetting and drawing is carried out along the axial direction of the ingot, with a reduction rate of 42%, and then upsetting to 38% of the original height; the second upsetting and drawing is carried out by rotating 90° clockwise around the axial direction of the ingot and drawing along the radial direction of the ingot, with a reduction rate of 45%, and then upsetting to 42% of the original height; the third upsetting and drawing is carried out by rotating 90° clockwise around the radial direction of the ingot and drawing along another axial direction, with a reduction rate of 47%, and then upsetting to 45% of the original height. The annealing process is as follows: under vacuum conditions, the temperature is held at 780°C for 2 hours and then cooled in the furnace. The quenching process is as follows: oil quenching is performed after holding at 1010℃ for 1 hour under vacuum conditions. The tempering process is as follows: under vacuum conditions, the temperature is held at 620℃ for 5 hours and then air-cooled. The aforementioned nano-reinforced high thermal conductivity and high thermal fatigue resistance die steel contains TiC+TiB2 nano-ceramic particles with an average particle size of 173 nm; the mass fraction of TiC+TiB2 nano-ceramic particles in the nano-reinforced high thermal conductivity and high thermal fatigue resistance die steel is 0.058 wt.%. In this embodiment, the nano-reinforced high thermal conductivity and high thermal fatigue resistance mold steel 1 does not contain Si and Cr elements that reduce the thermal conductivity of mold steel (comparative high-end mold steel DIEVAR contains Si: 0.33wt.% and Cr: 5.12wt.%). The contents of other alloying elements are similar to those in the comparative example. While effectively reducing raw material costs, the thermal conductivity of the nano-reinforced high thermal conductivity and high thermal fatigue resistance mold steel 1 reaches 56.2 W / m·K, which is significantly higher than the 26.8 W / m·K of the comparative high-end mold steel DIEVAR. The surface thermal fatigue crack propagation of the nano-reinforced high thermal conductivity and high thermal fatigue resistance mold steel 1 after 2000 cycles of cold and hot fatigue at 20-600℃ is as follows. Figure 1 As shown, no surface cracks were generated, and no microcracks or network cracks were observed. Only localized areas of slight oxidation and corrosion were present. In contrast, the comparative sample showed obvious cracks under the same cyclic temperature and number of cycles. The surface thermal fatigue crack propagation of nano-reinforced high thermal conductivity and high thermal fatigue resistance mold steel 1 after 3000 cycles of cold and hot fatigue at 20-600℃ is shown in the figure. Figure 2 As shown, the main crack length is 353µm. Compared with the comparative example, under the same cycling temperature and 200 more cycles of thermal fatigue, the main crack length is shortened by 37%, and the crack trace is significantly shallower. The shorter the main crack, the better the thermal fatigue resistance of the material. The shorter main crack length indicates that the nano-reinforced high thermal conductivity and high thermal fatigue resistance mold steel has excellent thermal fatigue resistance. Example 2

[0025] The preparation method of nano-reinforced high thermal conductivity and high thermal fatigue resistance mold steel 2 includes the following steps: (1) Carbon powder, iron-titanium powder and iron powder were mixed at a mass ratio of 3.5:6:25 for 24 hours to obtain powder mixture 1; powder mixture 1 was wrapped with aluminum foil and subjected to thermal explosion reaction 1 to obtain self-breaking alloy block A containing micron-sized active inoculated phase; The mass ratio of the aluminum foil to the powder mixture 1 is 1:1376; The thermal explosion reaction 1 is carried out under argon protection at a pressure of 0.032 MPa, a temperature of 1130°C, and a reaction time of 95 s. The carbon powder has a particle size of 6.8µm. By mass percentage, the main components of the iron-titanium powder include: titanium: 32%, with the balance being iron. The particle size of the iron-titanium powder is 118µm, and the particle size of the iron powder is 44µm. (2) Mix B powder, iron-titanium powder and iron powder at a mass ratio of 2.5:4:33 for 32 hours to obtain powder mixture 2; wrap powder mixture 2 with aluminum foil and carry out thermal explosion reaction 2 to obtain self-breaking alloy block B containing micron-sized active inoculated phase; The mass ratio of the aluminum foil to the powder mixture 2 is 1:1330; The thermal explosion reaction 2 is carried out under argon protection at a pressure of 0.027 MPa, a temperature of 1180°C, and a reaction time of 85 s. The particle size of the B powder is 66µm. By mass percentage, the main components of the iron-titanium powder include: titanium: 60%, with the balance being iron. The particle size of the iron-titanium powder is 122µm, and the particle size of the iron powder is 52µm. (3) The alloy block A containing micron-sized active inoculated phase obtained in step (1) and the alloy block B containing micron-sized active inoculated phase obtained in step (2) are mixed and crushed at a mass ratio of 13:4, and then subjected to plasma reaction to obtain iron-coated TiC+TiB2 nano-ceramic particle alloy. The plasma reaction is carried out under argon protection, with a reaction pressure of 0.03 MPa, a reaction temperature of 5110℃, a power supply operating frequency of 3.6 MHz, and an output power of 82 kW. (4) The mold steel is heated to 1542℃ until it is completely melted to obtain molten steel. The iron-coated TiC+TiB2 nano-ceramic particle alloy obtained in step (3) is mixed with the molten steel at a mass ratio of 0.126%:1. After impurity removal and casting, an ingot is obtained. The ingot is then forged, annealed, quenched and tempered to obtain nano-reinforced high thermal conductivity and high thermal fatigue resistance mold steel. The composition of the mold steel, by weight percentage, is as follows: C: 0.363 wt.%; Mo: 2.84 wt.%; Mn: 0.67 wt.%; V: 0.48 wt.%; unavoidable impurities are P: 0.007 wt.%; S: 0.006 wt.%; N: 0.006 wt.%; H: 0.0007 wt.%; O: 0.0015 wt.%; balance is Fe; The casting process is as follows: casting temperature 1575℃, casting speed 146mm / min; The forging process is as follows: the forging temperature is 1105℃, and the total forging ratio is 9:1; the forging process adopts a three-upsetting and three-drawing process; the first upsetting and drawing is carried out along the axial direction of the ingot, with a reduction rate of 43%, and then upsetting to 36% of the original height; the second upsetting and drawing is carried out by rotating 90° clockwise around the axial direction of the ingot and drawing along the radial direction of the ingot, with a reduction rate of 44%, and then upsetting to 44% of the original height; the third upsetting and drawing is carried out by rotating 90° clockwise around the radial direction of the ingot and drawing along another axial direction, with a reduction rate of 50%, and then upsetting to 43% of the original height. The annealing process is as follows: under vacuum conditions, the temperature is held at 785°C for 2 hours and then cooled in the furnace. The quenching process is as follows: oil quenching is performed after holding at 1012℃ for 1 hour under vacuum conditions; The tempering process is as follows: under vacuum conditions, the temperature is held at 618°C for 5 hours and then air-cooled. The nano-reinforced high thermal conductivity and high thermal fatigue resistance die steel contains TiC+TiB2 nano-ceramic particles with an average particle size of 161 nm; the mass fraction of TiC+TiB2 nano-ceramic particles in the nano-reinforced high thermal conductivity and high thermal fatigue resistance die steel is 0.063 wt.%. In this embodiment, the nano-reinforced high thermal conductivity and high thermal fatigue resistance mold steel 2 does not contain Si and Cr elements that reduce the thermal conductivity of mold steel (compared to the high-end mold steel DIEVAR containing Si: 0.33wt.% and Cr: 5.12wt.%). The content of other alloying elements is similar to that of the comparative example. While effectively reducing raw material costs, the thermal conductivity of the nano-reinforced high thermal conductivity and high thermal fatigue resistance mold steel 2 reaches 56.7W / m·K, which is 111% higher than that of the high-end mold steel DIEVAR (26.8W / m·K). The surface thermal fatigue crack propagation of the nano-reinforced high thermal conductivity and high thermal fatigue resistance mold steel 2 after 2000 cycles of cold and hot fatigue at 20-600℃ is as follows. Figure 3 As shown, no crack morphology was observed on the surface, with oxidation corrosion only observed at the tip of the pre-set notch; in contrast, at the same cyclic temperature and number of cycles, the surface of the comparative DIEVAR showed obvious cracks; the surface thermal fatigue crack propagation of nano-reinforced high thermal conductivity and high thermal fatigue resistance mold steel 2 after 3000 cycles of cold and hot fatigue at 20-600℃ is shown in the figure. Figure 4 As shown, the main crack length is 374µm. Compared with the comparative example, under the same cycling temperature and 200 more cycles of thermal fatigue, the main crack length is shortened by 34%, and the crack trace is significantly shallower than that of the comparative example. The shorter the main crack, the better the thermal fatigue resistance of the material. The shorter main crack length indicates that the nano-reinforced high thermal conductivity and high thermal fatigue resistance mold steel has excellent thermal fatigue resistance. Example 3

[0026] The preparation method of nano-reinforced high thermal conductivity and high thermal fatigue resistance mold steel 3 includes the following steps: (1) Carbon powder, iron-titanium powder and iron powder were mixed at a mass ratio of 4:7:32 for 27 hours at a rotation speed of 134 r / min to obtain powder mixture 1; powder mixture 1 was wrapped with aluminum foil and subjected to thermal explosion reaction 1 to obtain self-fractured alloy block A containing micron-sized active inoculated phase; The mass ratio of the aluminum foil to the powder mixture 1 is 1:1343; The thermal explosion reaction 1 is carried out under argon protection at a pressure of 0.042 MPa, a temperature of 1155 °C, and a reaction time of 105 s. The carbon powder has a particle size of 7.2µm. By mass percentage, the main components of the iron-titanium powder include: titanium: 34%, with the balance being iron. The particle size of the iron-titanium powder is 165µm, and the particle size of the iron powder is 52µm. (2) Powder B, iron-titanium powder and iron powder were mixed at a mass ratio of 2.2:5:36 for 41 hours at a speed of 117 r / min to obtain powder mixture 2; powder mixture 2 was wrapped with aluminum foil and subjected to thermal explosion reaction 2 to obtain self-fractured alloy block B containing micron-sized active inoculated phase; The mass ratio of the aluminum foil to the powder mixture 2 is 1:1425; The thermal explosion reaction 2 is carried out under argon protection at a pressure of 0.034 MPa, a temperature of 1205°C, and a reaction time of 76 s. The particle size of the B powder is 68µm. By mass percentage, the main components of the iron-titanium powder include: titanium: 62%, with the balance being iron. The particle size of the iron-titanium powder is 129µm, and the particle size of the iron powder is 50µm. (3) The alloy block A containing micron-sized active inoculum phase obtained in step (1) and the alloy block B containing micron-sized active inoculum phase obtained in step (2) are mixed and crushed at a mass ratio of 15:5.2 and then subjected to plasma reaction to obtain iron-coated TiC+TiB2 nano-ceramic particle alloy. The plasma reaction is carried out under argon protection, with a reaction pressure of 0.039 MPa, a reaction temperature of 5260℃, a power supply operating frequency of 4.3 MHz, and an output power of 68 kW. (4) The mold steel is heated to 1560℃ until it is completely melted to obtain molten steel. The iron-coated TiC+TiB2 nano-ceramic particle alloy obtained in step (3) is mixed with the molten steel at a mass ratio of 0.12%:1. After impurity removal and casting, an ingot is obtained. The ingot is then forged, annealed, quenched and tempered to obtain nano-reinforced high thermal conductivity and high thermal fatigue resistance mold steel. The composition of the mold steel, by weight percentage, is as follows: C: 0.373 wt.%; Mo: 2.85 wt.%; Mn: 0.66 wt.%; V: 0.51 wt.%; unavoidable impurities are P: 0.006 wt.%; S: 0.005 wt.%; N: 0.007 wt.%; H: 0.0008 wt.%; O: 0.0019 wt.%; balance is Fe; The casting process is as follows: casting temperature 1580℃, casting speed 168mm / min; The forging process is as follows: the forging temperature is 1075℃, and the total forging ratio is 10:1; the forging process adopts a three-upsetting and three-drawing process; the first upsetting and drawing is carried out along the axial direction of the ingot, with a reduction rate of 44%, and then upsetting to 37% of the original height; the second upsetting and drawing is carried out by rotating 90° clockwise around the axial direction of the ingot and drawing along the radial direction of the ingot, with a reduction rate of 46%, and then upsetting to 43% of the original height; the third upsetting and drawing is carried out by rotating 90° clockwise around the radial direction of the ingot and drawing along another axial direction, with a reduction rate of 52%, and then upsetting to 48% of the original height. The annealing process is as follows: under vacuum conditions, the temperature is held at 790°C for 2 hours and then cooled in the furnace. The quenching process is as follows: oil quenching is performed after holding at 1018℃ for 1 hour under vacuum conditions; The tempering process is as follows: under vacuum conditions, the temperature is held at 622℃ for 5 hours and then air-cooled. The nano-reinforced high thermal conductivity and high thermal fatigue resistance die steel contains TiC+TiB2 nano-ceramic particles with an average particle size of 178 nm; the mass fraction of TiC+TiB2 nano-ceramic particles in the nano-reinforced high thermal conductivity and high thermal fatigue resistance die steel is 0.06 wt.%. In this embodiment, the nano-reinforced high thermal conductivity and high thermal fatigue resistance mold steel 3 does not contain Si and Cr elements that reduce the thermal conductivity of mold steel (comparative high-end mold steel DIEVAR contains Si: 0.33wt.% and Cr: 5.12wt.%). The content of other alloying elements is similar to that of the comparative example. While effectively reducing raw material costs, the thermal conductivity of the nano-reinforced high thermal conductivity and high thermal fatigue resistance mold steel 3 reaches 57.5W / m·K, which is significantly higher than the 26.8W / m·K of the comparative high-end mold steel DIEVAR. The surface thermal fatigue crack propagation of the nano-reinforced high thermal conductivity and high thermal fatigue resistance mold steel 3 after 2000 cycles of hot and cold fatigue at 20-600℃ is as follows. Figure 5 As shown, no cracks were observed on the surface; in contrast, significantly longer cracks were observed on the surface of the comparative DIEVAR. The surface thermal fatigue crack propagation of nano-reinforced high thermal conductivity and high thermal fatigue resistance mold steel 3 after 3000 cycles of thermal fatigue at 20-600℃ is shown in the figure. Figure 6 As shown, the main crack length is 278µm. Compared with the comparative example, under the same cycling temperature and 200 more cycles of thermal fatigue, the main crack length is shortened by 51%, and the crack trace is not obvious. The shorter the main crack, the better the thermal fatigue resistance of the material. The shorter main crack length indicates that the nano-reinforced high thermal conductivity and high thermal fatigue resistance mold steel has excellent thermal fatigue resistance. Comparative Example

[0027] DIEVAR steel is prepared by the following steps: (1) DIEVAR steel is heated to 1560℃ until it is completely melted to obtain molten steel. After removing impurities and casting, an ingot is obtained. The ingot is then forged, annealed, quenched and tempered to obtain DIEVAR steel. The composition of the DIEVAR steel, by weight percentage, is as follows: C: 0.371 wt.%; Mo: 2.85 wt.%; Mn: 0.67 wt.%; V: 0.58 wt.%; Si: 0.33 wt.%; Cr: 5.12 wt.%; unavoidable impurities are P: 0.006 wt.%; S: 0.005 wt.%; N: 0.007 wt.%; H: 0.0008 wt.%; O: 0.0019 wt.%; balance is Fe; The casting process is as follows: casting temperature 1580℃, casting speed 168mm / min; The forging process is as follows: the forging temperature is 1075℃, and the total forging ratio is 10:1; the forging process adopts a three-upsetting and three-drawing process; the first upsetting and drawing is carried out along the axial direction of the ingot, with a reduction rate of 44%, and then upsetting to 37% of the original height; the second upsetting and drawing is carried out by rotating 90° clockwise around the axial direction of the ingot and drawing along the radial direction of the ingot, with a reduction rate of 46%, and then upsetting to 43% of the original height; the third upsetting and drawing is carried out by rotating 90° clockwise around the radial direction of the ingot and drawing along another axial direction, with a reduction rate of 52%, and then upsetting to 48% of the original height. The annealing process is as follows: under vacuum conditions, the temperature is held at 790°C for 2 hours and then cooled in the furnace. The quenching process is as follows: oil quenching is performed after holding at 1018℃ for 1 hour under vacuum conditions; The tempering process is as follows: under vacuum conditions, the temperature is held at 622℃ for 5 hours and then air-cooled. The surface thermal fatigue crack propagation of the DIEVAR steel prepared in this comparative example after 2000 cycles of thermal fatigue at 20-600℃ is as follows: Figure 7 As shown, the main crack length is 310µm, while no cracks were observed in the nano-reinforced high thermal conductivity and high thermal fatigue resistance mold steel prepared in the examples; the surface thermal fatigue crack propagation of DIEVAR steel after 2800 cycles of thermal fatigue at 20-600℃ is as follows. Figure 8 As shown, the main crack length is 565µm, and there is a distinct network-like oxidation erosion zone.

[0028] The present invention and the comparative examples belong to the same series of hot work die steels and are therefore comparable; compared with the comparative examples, embodiments 1-3 of the present invention have the following advantages: Compared to the comparative example, the nano-reinforced high thermal conductivity and high thermal fatigue resistance mold steel 1 obtained in Example 1 of this invention does not contain Si and Cr elements in its alloy composition, while the DIEVAR steel in the comparative example contains 0.33 wt.% Si and 5.12 wt.% Cr, and the content of other alloying elements is similar to that of the comparative example. Therefore, this invention reduces raw material costs. Compared with the prior art that adds elements such as Si and Cr, the nano-reinforced high thermal conductivity and high thermal fatigue resistance mold steel 1 obtained in Example 1 of this invention achieves a thermal conductivity of 56.2 W / m·K without adding Si and Cr, which is 109% higher than the thermal conductivity of the DIEVAR steel prepared in the comparative example. Higher thermal conductivity indicates better thermal conductivity of the material. Therefore, the nano-reinforced high thermal conductivity and high thermal fatigue resistance mold steel 1 obtained in Example 1 of this invention has excellent thermal conductivity. The performance is significantly better than that of DIEVAR steel. Furthermore, the nano-reinforced high thermal conductivity and high thermal fatigue resistance mold steel 1 obtained in Example 1 of this invention showed no surface cracks after 2000 cycles of thermal fatigue at 20-600℃, while the DIEVAR steel prepared in the comparative example showed a main surface crack length of 310µm after 2000 cycles of thermal fatigue at 20-600℃, and exhibited a network of oxidation and corrosion zones. The nano-reinforced high thermal conductivity and high thermal fatigue resistance mold steel 1 obtained in Example 1 of this invention, after 3000 cycles of thermal fatigue at 20-600℃, showed a 37% reduction in the main surface crack length compared to the comparative example at the same cycle temperature and with 200 more cycles. This shorter main crack length indicates that the nano-reinforced high thermal conductivity and high thermal fatigue resistance mold steel 1 obtained in Example 1 of this invention has superior thermal fatigue resistance.

[0029] Compared to the comparative example, the nano-reinforced high thermal conductivity and high thermal fatigue resistance mold steel 2 obtained in Example 2 of this invention does not contain Si and Cr elements in its alloy composition, while the DIEVAR steel in the comparative example contains 0.33 wt.% Si and 5.12 wt.% Cr, and the content of other alloying elements is similar to that of the comparative example, thus reducing raw material costs. Compared with the prior art that adds elements such as Si and Cr, the nano-reinforced high thermal conductivity and high thermal fatigue resistance mold steel 2 obtained in Example 2 of this invention achieves a thermal conductivity of 56.7 W / m·K without adding Si and Cr, which is 111% higher than the thermal conductivity of the DIEVAR steel prepared in the comparative example. Higher thermal conductivity means better thermal conductivity of the material. Therefore, the thermal conductivity of the nano-reinforced high thermal conductivity and high thermal fatigue resistance mold steel 2 obtained in Example 2 of this invention is much higher than that of DIEVAR steel. AR steel; furthermore, the nano-reinforced high thermal conductivity and high thermal fatigue resistance mold steel 2 obtained in Example 2 of this invention showed no surface cracks after 2000 cycles of thermal fatigue at 20-600℃, while the surface main crack length of the DIEVAR steel prepared in the comparative example was 310µm after 2000 cycles of thermal fatigue at 20-600℃; the surface main crack length of the nano-reinforced high thermal conductivity and high thermal fatigue resistance mold steel 2 obtained in Example 2 of this invention was still 34% shorter than that of the comparative example after 3000 cycles of thermal fatigue at 20-600℃ under more stringent cyclic conditions (same cyclic temperature, 200 more cycles than the comparative example), and the crack traces were significantly shallower and the crack width was narrower. The results show that the nano-reinforced high thermal conductivity and high thermal fatigue resistance mold steel 2 obtained in Example 2 of this invention has significantly superior thermal fatigue resistance.

[0030] Compared to the comparative example, the nano-reinforced high thermal conductivity and high thermal fatigue resistance mold steel 3 obtained in Example 3 of this invention does not contain Si and Cr elements in its alloy composition, while the DIEVAR steel in the comparative example contains 0.33 wt.% Si and 5.12 wt.% Cr, and the content of other alloying elements is similar to that of the comparative example, thus reducing raw material costs. Compared with the prior art that adds elements such as Si and Cr, the nano-reinforced high thermal conductivity and high thermal fatigue resistance mold steel 3 obtained in Example 3 of this invention achieves a thermal conductivity of 57.5 W / m·K without adding Si and Cr, which is 114% higher than the thermal conductivity of the DIEVAR steel prepared in the comparative example. The higher the thermal conductivity, the better the thermal conductivity of the material. Therefore, the thermal conductivity of the nano-reinforced high thermal conductivity and high thermal fatigue resistance mold steel 3 obtained in Example 3 of this invention is much higher than that of DIEVAR steel. AR steel; furthermore, the nano-reinforced high thermal conductivity and high thermal fatigue resistance mold steel 3 obtained in Example 3 of the present invention showed no surface cracks after 2000 cycles of thermal fatigue at 20-600℃, while the surface main crack length of the DIEVAR steel prepared in the comparative example was 310µm after 2000 cycles of thermal fatigue at 20-600℃; the surface main crack length of the nano-reinforced high thermal conductivity and high thermal fatigue resistance mold steel 3 obtained in Example 3 of the present invention was shortened by 51% after 3000 cycles of thermal fatigue at 20-600℃, at the same cycle temperature and with 200 more cycles than the comparative example, and there was only one main crack, without obvious signs of network crack propagation. The results show that the nano-reinforced high thermal conductivity and high thermal fatigue resistance mold steel 3 obtained in Example 3 of the present invention has superior thermal fatigue resistance.

[0031] Table 1. Comparison of thermal conductivity and thermal fatigue resistance of mold steels in various embodiments and comparative examples.

[0032] In summary, compared with existing technologies, the thermal conductivity of the nano-reinforced high thermal conductivity and high thermal fatigue resistance mold steel obtained by this invention is significantly improved to 55-58 W / m·K; after thousands of thermal fatigue cycles at 25-600℃, the main crack length of the nano-reinforced high thermal conductivity and high thermal fatigue resistance mold steel obtained by this invention is significantly shorter than that of existing technologies, and the crack depth is shallower, the width is narrower, and the distribution is sparser, exhibiting significantly better thermal fatigue resistance; the existing high-end mold steel DIEVAR with excellent thermal fatigue resistance contains Si element content between 0.1-0.58 wt.% and Cr element content between 4.8-5.5 wt.%; compared with existing technologies, this invention does not add Si and Cr elements, which greatly improves the thermal conductivity of the mold steel while reducing raw material costs; high thermal conductivity is beneficial for the material to withstand rapid cooling and heating. Under thermal conditions, rapid heat conduction reduces the instantaneous temperature gradient on the cavity surface, thereby suppressing the generation and accumulation of thermal stress from the source and delaying the initiation and propagation of hot cracks. Furthermore, this invention simultaneously enhances the strength of the mold steel, strengthening its resistance to thermal stress and further hindering the initiation and propagation of hot cracks, thus improving the thermal fatigue resistance of the mold steel. Compared with existing technologies, the core innovation of this invention lies in breaking through the traditional method of solely relying on increasing strength to improve the thermal fatigue resistance of mold steel. This invention combines the suppression and resistance of thermal stress, achieving a breakthrough improvement in the thermal fatigue resistance of mold steel through the synergistic regulation of a high thermal conductivity matrix and nano-ceramic particles, proportions, processes, and process parameters. This overcomes the technical bottleneck of existing technologies that improve fatigue resistance by increasing strength. Moreover, the proportions and process parameters differ in each embodiment of this invention, resulting in different performance in each embodiment. This demonstrates that the optimal effect obtained by this invention is not determined by a specific component, proportion, process, or process parameter, but rather by the interaction of components, proportions, processes, and the synergistic regulation of process parameters. Furthermore, only within the scope of the claims of this invention can a significantly improved technical effect be achieved.

Claims

1. A nano-reinforced high thermal conductivity and high thermal fatigue resistance die steel, characterized in that, Its preparation method includes the following steps: (1) Carbon powder, iron-titanium powder and iron powder are mixed at a mass ratio of 2-5: 4-8: 18-38 for 21-28 hours at a speed of 111-142 r / min to obtain powder mixture 1; after wrapping powder mixture 1 with aluminum foil, thermal explosion reaction 1 is carried out to obtain self-fractured alloy block A containing micron-sized active inoculated phase; The mass ratio of the aluminum foil to the powder mixture 1 is 1:1320-1380; The thermal explosion reaction 1 is carried out under argon protection at a pressure of 0.015-0.045 MPa, a temperature of 1120-1180℃, and a reaction time of 70-120 s. The carbon powder has a particle size of 4-9µm. By mass percentage, the main components of the iron-titanium powder include: titanium: 28-35%, with the balance being iron. The particle size of the iron-titanium powder is 70-190µm, and the particle size of the iron powder is 25-55µm. (2) Mix B powder, iron-titanium powder and iron powder at a mass ratio of 1-4: 3-7: 20-42 at a rotation speed of 90-125 r / min for 30-42 h to obtain powder mixture 2; wrap powder mixture 2 with aluminum foil and carry out thermal explosion reaction 2 to obtain self-fractured alloy block B containing micron-sized active inoculated phase; The mass ratio of the aluminum foil to the powder mixture 2 is 1:1260-1440; The thermal explosion reaction 2 is carried out under argon protection at a pressure of 0.018-0.038 MPa, a temperature of 1140-1210℃, and a reaction time of 40-100 s. The particle size of the B powder is 37-72µm. By mass percentage, the main components of the iron-titanium powder include: titanium: 56-63%, with the balance being iron. The particle size of the iron-titanium powder is 55-135µm, and the particle size of the iron powder is 23-63µm. (3) The alloy block A containing micron-sized active inoculated phase obtained in step (1) and the alloy block B containing micron-sized active inoculated phase obtained in step (2) are mixed and crushed at a mass ratio of 12-16: 3-7, and then subjected to plasma reaction to obtain iron-coated TiC+TiB2 nano-ceramic particle alloy. The plasma reaction is carried out under argon protection, with a reaction pressure of 0.015-0.045 MPa, a reaction temperature of 4900-5300℃, a power supply operating frequency of 2.3-4.5 MHz, and an output power of 50-100 kW. (4) The mold steel is heated to 1525-1575℃ until it is completely melted to obtain molten steel. The iron-coated TiC+TiB2 nano-ceramic particle alloy obtained in step (3) is mixed with the molten steel at a mass ratio of 0.11%-0.13%:

1. After impurity removal and casting, an ingot is obtained. The ingot is then forged, annealed, quenched and tempered to obtain nano-reinforced high thermal conductivity and high thermal fatigue resistance mold steel. The composition of the mold steel, by weight percentage, is as follows: C: 0.345-0.375 wt.%; Mo: 2.8-2.9 wt.%; Mn: 0.61-0.69 wt.%; V: 0.4-0.55 wt.%; unavoidable impurities are P: ≤0.009 wt.%; S: ≤0.008 wt.%; N: ≤0.0085 wt.%; H: ≤0.0009 wt.%; O: ≤0.002 wt.%; balance is Fe; The casting process is as follows: casting temperature 1550-1585℃, casting speed 95-175mm / min; The forging process is as follows: the forging temperature is 925-1115℃, and the total forging ratio is 7-11:1; the forging process adopts a three-upsetting and three-drawing process; the first upsetting and drawing is carried out along the axial direction of the ingot, with a reduction rate of 40-50%, and then upsetting to 35-39% of the original height; the second upsetting and drawing is carried out by rotating 90° clockwise around the axial direction of the ingot and drawing along the radial direction of the ingot, with a reduction rate of 42-52%, and then upsetting to 40-45% of the original height; the third upsetting and drawing is carried out by rotating 90° clockwise around the radial direction of the ingot and drawing along another axial direction, with a reduction rate of 45-55%, and then upsetting to 42-49% of the original height. The annealing process is as follows: under vacuum conditions, the temperature is held at 770-820℃ for 2 hours and then cooled in the furnace. The quenching process is as follows: oil quenching is performed after holding at 1000-1020℃ for 1 hour under vacuum conditions; The tempering process is as follows: under vacuum conditions, the temperature is held at 610-630℃ for 5 hours and then air-cooled. The aforementioned nano-reinforced high thermal conductivity and high thermal fatigue resistance die steel contains TiC+TiB2 nano-ceramic particles with an average particle size of 154-196 nm; the mass fraction of TiC+TiB2 nano-ceramic particles in the nano-reinforced high thermal conductivity and high thermal fatigue resistance die steel is 0.055-0.065 wt.%. The aforementioned nano-reinforced high thermal conductivity and high thermal fatigue resistance mold steel has a thermal conductivity of 55-58 W / m·K; after 1800-3200 cycles of thermal fatigue at 25-600℃, the main crack length of the nano-reinforced high thermal conductivity and high thermal fatigue resistance mold steel is ≤396µm.

2. The nano-reinforced high thermal conductivity and high thermal fatigue resistance die steel according to claim 1, characterized in that, The mass ratio of aluminum foil to powder mixture 1 in step (1) is 1:1322-1374; the thermal explosion reaction 1 is carried out under argon protection, with a pressure of 0.016-0.044 MPa, a temperature of 1122-1178℃, and a reaction time of 73-114 s; the particle size of the carbon powder is 4.2-8.7 µm, and the main components of the iron-titanium powder by mass percentage are: titanium: 29-34%, with the balance being iron, the particle size of the iron-titanium powder is 72.1-182.5 µm, and the particle size of the Fe powder is 25.3-53.1 µm.

3. The nano-reinforced high thermal conductivity and high thermal fatigue resistance die steel according to claim 1, characterized in that, The mass ratio of aluminum foil to powder mixture 2 in step (2) is 1:1261-1432; the thermal explosion reaction 2 is: under argon protection, pressure 0.019-0.031MPa, temperature 1144-1207℃, reaction time 42-98s; The particle size of the B powder is 39.6-69.2µm. By mass percentage, the main components of the iron-titanium powder include: titanium: 57-62%, with the balance being iron. The particle size of the iron-titanium powder is 59.2-123.4µm, and the particle size of the Fe powder is 27.3-60.2µm.

4. The nano-reinforced high thermal conductivity and high thermal fatigue resistance die steel according to claim 1, characterized in that, The plasma reaction described in step (3) is as follows: under argon protection, the reaction pressure is 0.018-0.042MPa, the reaction temperature is 4920-5260℃, the power supply operating frequency is 2.4-4.4MHz, and the output power is 52-95kW.

5. The nano-reinforced high thermal conductivity and high thermal fatigue resistance die steel according to claim 1, characterized in that, The composition of the mold steel described in step (4) by mass percentage is as follows: C: 0.347-0.372 wt.%; Mo: 2.81-2.88 wt.%; Mn: 0.615-0.688 wt.%; V: 0.44-0.54 wt.%; unavoidable impurities are P: ≤0.0085 wt.%. S: ≤0.0077wt.%; N: ≤0.0082 wt.%; H: ≤0.0008 wt.%; O: ≤0.0017 wt.%; balance Fe.

6. The nano-reinforced high thermal conductivity and high thermal fatigue resistance die steel according to claim 1, characterized in that, The casting in step (4) is as follows: casting temperature 1552-1582℃, casting speed 97-174mm / min.

7. The nano-reinforced high thermal conductivity and high thermal fatigue resistance die steel according to claim 1, characterized in that, The forging process described in step (4) is as follows: the forging temperature is 929-1111℃, and the total forging ratio is 8-10:1; the forging process adopts a three-upsetting and three-drawing process; the first upsetting and drawing is carried out along the axial direction of the ingot, with a reduction rate of 41-49%, and then upsetting to 36-38% of the original height; the second upsetting and drawing is carried out by rotating 90° clockwise around the axial direction of the ingot and drawing along the radial direction of the ingot, with a reduction rate of 44-51%, and then upsetting to 41-44% of the original height; the third upsetting and drawing is carried out by rotating 90° clockwise around the radial direction of the ingot and drawing along another axial direction, with a reduction rate of 46-54%, and then upsetting to 43-48% of the original height.

8. The nano-reinforced high thermal conductivity and high thermal fatigue resistance die steel according to claim 1, characterized in that, The annealing in step (4) is: under vacuum conditions, heat at 775-815℃ for 2 hours and then cooled in the furnace; the quenching is: under vacuum conditions, heat at 1008-1018℃ for 1 hour and then oil quenching; the tempering is: under vacuum conditions, heat at 612-628℃ for 5 hours and then air cooling.

9. The nano-reinforced high thermal conductivity and high thermal fatigue resistance die steel according to claim 1, characterized in that, The nano-reinforced high thermal conductivity and high thermal fatigue resistance mold steel described in step (4) contains TiC+TiB2 nano-ceramic particles with an average particle size of 155-192nm; the mass fraction of TiC+TiB2 nano-ceramic particles in the nano-reinforced high thermal conductivity and high thermal fatigue resistance mold steel is 0.056-0.064wt.%.

10. The nano-reinforced high thermal conductivity and high thermal fatigue resistance die steel according to claim 1, characterized in that, The thermal conductivity of the nano-reinforced high thermal conductivity and high thermal fatigue resistance mold steel obtained in step (4) is 55.4-57.8 W / m·K; after 2000-3000 cycles of hot and cold fatigue at 25-600℃, the main crack length of the nano-reinforced high thermal conductivity and high thermal fatigue resistance mold steel is 0-100µm.

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