Production process of high-strength and high-toughness hot work die steel

Abstract

The invention relates to the technical field of metal heat treatment, in particular to a production process of high-strength and high-toughness hot work die steel. According to the hot work die steel prepared through the method, the problems that die steel is insufficient in toughness and low in hardness are solved. Through the process steps of smelting and casting, hot forging, annealing, circulating hot forging and annealing, solid solution-quenching-partitioning treatment, tempering treatment, finishing and surface treatment, process parameters of all treatment stages are adjusted, and the steps of nitriding treatment and carburizing treatment are added in the surface treatment stage. The high-strength and high-toughness hot work die steel is high in toughness, high in hardness and good in thermal fatigue resistance.

Description

Technical Field

[0001] The invention relates to the technical field of metal heat treatment, in particular to a production process of high-strength and toughness hot working die steel. Background Art

[0002] High-strength and toughness hot working die steel is an alloy tool steel with high strength and excellent toughness, which is widely used in die-casting dies, hot forging dies and hot extrusion dies. It can not only maintain good mechanical properties for a long time at high temperature, but also maintain high hardness and good thermal stability. In addition, it has strong tensile, compressive and impact resistance, can withstand large loads and working stresses, and is not prone to cracking and other failure forms under harsh working conditions such as alternating hot and cold cycles. It can effectively resist wear and maintain accuracy and surface quality for a long time.

[0003] However, the market has increasingly higher requirements for hot working die steel, and the existing hot working die steel can no longer meet the high usage demand. In the automotive industry, when manufacturing molds such as car bodies, engine parts and suspension systems, high-strength and toughness hot working die steel is required to ensure the precision and durability of the mold. Although the hot working die steel that is widely used at present has met the needs of industrial production to a certain extent, it still has certain defects in terms of thermal fatigue resistance and toughness. In a high temperature environment, the die steel is prone to softening and oxidation, resulting in deformation and failure of the mold; the toughness of the mold is poor, and it is easy to crack when subjected to impact loads; in addition, there is also the low surface hardness of the hot working die steel, which seriously affects the service life of the die steel.

[0004] Therefore, a production process of high strength and toughness hot working die steel is proposed. Summary of the invention

[0005] The object of the present invention is to provide a production process for high-strength and toughness hot working die steel, by carrying out the process steps of melting and casting, hot forging, annealing, cyclic hot forging and annealing, solution-quenching-partitioning treatment, tempering treatment, finishing processing and surface treatment, adjusting the process parameters of each treatment stage, and adding the steps of nitriding treatment and carburizing treatment in the surface treatment stage, so that the high-strength and toughness hot working die steel has strong toughness, high hardness and good heat fatigue resistance.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] The present invention provides a production process for high-strength and high-toughness hot-working die steel, and the production process is as follows:

[0008] S1 Melting and Casting: Alloy Raw Material 1 is placed in a prefabricated calcium oxide crucible and melted into molten steel in a vacuum induction furnace at a melting temperature of 1600-1650°C; the molten steel is refined, and then alloy Raw Material 2 is added to obtain a slurry to be cast; the pouring temperature is 1450-1550°C, the casting flow rate is 1.6-2.4m / s, and a foam ceramic filter is added during the pouring process; then the steel ingot is obtained by cooling and heat preservation;

[0009] S2 hot forging: the steel ingot is homogenized, then cooled for heat treatment, and steel is obtained after two upsetting and two drawing;

[0010] S3 annealing: the steel is heated to 820-860°C at a heating rate of 5°C / min and kept at this temperature for 1.5 hours; then cooled to 640-660°C at a rate of 5-8°C / min, kept at this temperature for 1 hour, and then air-cooled to room temperature;

[0011] S4 cycle hot forging and annealing: secondary hot forging and re-annealing to obtain steel;

[0012] S5 solution-quenching-partitioning treatment: the steel is subjected to solution-quenching, quenching and partitioning to obtain a workpiece;

[0013] S6 tempering treatment: the workpiece is kept at 580-620℃ for the first time and then air-cooled to room temperature, and then kept at 550-570℃ for 1.5-2.5h for the second time, and air-cooled to obtain a high-strength and toughness hot working die steel precursor;

[0014] S7 finishing process: using ceramic bond cubic boron nitride grinding wheel to grind high-strength and toughness hot working die steel intermediate;

[0015] S8 surface treatment: The high-strength and toughness hot working die steel intermediate is subjected to nitriding treatment and then carburizing treatment to obtain high-strength and toughness hot working die steel.

[0016] Preferably, the refining in S1 is vacuum-exhausted to achieve a vacuum degree of 0.35 to 1.30 N / m 2 The specific steps of cooling and keeping warm are as follows: cool down to 1100°C at a rate of 8°C / min, keep warm for 60 minutes and then cool down to 400°C at a rate of 5°C / min, keep warm for 30 minutes and then cool down to 100°C at a rate of 3°C / min, keep warm for 20 minutes and then cool down to 50°C at a rate of 1°C / min, and finally air cool to room temperature to obtain a steel ingot.

[0017] Preferably, the element composition of alloy raw material one is as follows: Ni: 0.72%~0.96%, Mo: 2.28%~2.56%, Co: 0.95%~1.25%, Nb: 0.25%~0.48%, W: 1.15~2.89%, Ce: 0.05%~0.15%, La: 0.08%~0.20%, C: 0.05%~0.20% and Fe; the element composition of alloy raw material two is as follows: Si: 0.35%~0.65%, Mn: 0.34%~0.56%, Cr: 2.35%~2.89%, V: 0.86%~1.26%, P≤0.015%, S≤0.01%, Ti: 0.30%, C: 0.10%~0.25%.

[0018] Preferably, the homogenization treatment in S2 is a heating rate of 2.5 to 6°C / min, a holding temperature of 1260°C to 1320°C, and a holding time of 1 to 2h; the cooling and heat treatment is cooling to 1060°C to 1120°C at a cooling rate of 10°C / s, and hot forging for 1h; the conditions for two upsetting and two drawing are: the first upsetting ratio is 1.5 to 1.8, the drawing and forging ratio is 1.8 to 2.0, the second upsetting ratio is 2.2 to 2.4, the drawing and forging ratio is 2 to 2.2, and the total forging ratio is 10 to 12.

[0019] Preferably, the secondary hot forging and re-annealing in S4 are as follows: hot forging treatment is performed with a heating rate of 5°C / min, an initial forging temperature of 1150°C, and a holding time of 2.5h; then cooling to 1020°C-1050°C at a cooling rate of 10°C / s for secondary calcination, keeping warm for 40min and then air cooling to room temperature; re-annealing is performed, followed by heating to 870°C-920°C at a heating rate of 5°C / min and keeping warm for 2h; furnace cooling to 650°C and then air cooling to room temperature to obtain steel.

[0020] Preferably, the solution-quenching-partitioning treatment in S5 is as follows: the steel is instantaneously heated to 1040-1060°C, kept warm for 45 minutes for solution treatment, and then kept warm at 920-980°C in a salt bath furnace for 5-10 minutes for isothermal quenching for 2.5 hours. The isothermal quenching medium is industrial quenching salt. After quenching, it is taken out immediately, kept warm at 960-1030°C for 30-50 minutes, and then quenched to room temperature. The quenching medium is water; then the temperature is raised to 250°C at a rate of 10°C / min, kept warm for 2 hours, and then air-cooled to room temperature to obtain the workpiece.

[0021] Preferably, the finishing process in S7 is as follows: the high-strength and toughness hot working die steel precursor is cut by plasma to remove the oxide layer and burrs, the extreme pressure emulsion is diluted to a concentration of 10% with deionized water, and then ground with a ceramic binder cubic boron nitride grinding wheel, the rotation speed is set to 80-150m / s, the feed speed is controlled at 0.05-0.1mm / min, and the single grinding depth is controlled at 0.02-0.05mm; the high-strength and toughness hot working die steel intermediate is obtained by milling by down milling.

[0022] Preferably, the preparation method of the ceramic bond cubic boron nitride grinding wheel is as follows: by mass percentage, 65% of cubic boron nitride abrasive, 24% of ceramic bond, 7% of functional additive and 4% of auxiliary material are mixed evenly and placed in a pressing mold for cold pressing, and then placed in a graphite boat with carbon paper on the surface, and then loaded into a vacuum sintering furnace for vacuum sintering; after the furnace door is sealed, the vacuum sintering furnace is evacuated by a vacuum pump to make the vacuum degree in the vacuum sintering furnace be 0.8×10 -2 Pa, when the vacuum sintering furnace is heated from room temperature to 200°C, the heating rate is 5°C / min; after being kept at 200°C for 2h, the furnace temperature is raised to 300°C at a heating rate of 4°C / min and kept for 1.5h, and then the furnace temperature is raised to 500°C at a heating rate of 4°C / min, and kept at 500°C for 1.5, and then the furnace temperature is raised to 850°C at a heating rate of 2°C / min and kept for 1h, and then the furnace temperature is lowered to 700°C at a cooling rate of 11°C / min, and then the heating is stopped, and a ceramic bond cubic boron nitride grinding wheel is obtained as the furnace is cooled; the ceramic bond is obtained by mixing silicon dioxide, titanium dioxide, aluminum oxide, boron oxide and lithium superoxide in a mass ratio of 1:1:1:1:1; the functional additive is obtained by mixing polyvinyl alcohol and nickel in a mass ratio of 9:1.

[0023] Preferably, the nitriding treatment is as follows: placing the high-strength and toughness hot-working die steel intermediate in a nitriding furnace, controlling the nitriding temperature to 500-550°C, the nitriding time to 20-26 hours, and then cooling with the furnace to remove the nitriding residue on the surface; the carburizing treatment is as follows: in a vacuum furnace, controlling the vacuum degree to 10 -5 Pa, methane is filled into the furnace, the furnace pressure is controlled at 28-45kPa, glow discharge is stimulated between the anode and the cathode and carburizing is carried out. The voltage at this time is 500V-800V. After processing for 1.2-2.5h, it is air-cooled to room temperature and tempered again to obtain high strength and toughness hot working die steel.

[0024] Preferably, the preparation method of the prefabricated calcium oxide crucible is as follows: 80% of composite calcium oxide, 18% of mullite fiber and 2% of composite sintering aid are mixed to obtain a mixture; the mixture is molded and demolded to obtain a crucible blank; the crucible blank is dried and then sintered in stages, pre-sintered at 300°C for 15 minutes; sintered at 1400°C for 4 hours; sintered at 1700°C for 5 hours to obtain a prefabricated calcium oxide crucible; the composite calcium oxide contains 25% 0.3mm calcium oxide fine powder, 30% 0.8mm calcium oxide sand, 25% 2.5mm calcium oxide sand and 15% 4.5mm calcium oxide sand; the composite sintering aid is obtained by mixing calcium oxide, zirconium oxide, silicon dioxide and boron trioxide in a weight ratio of 1:1:1:1.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] 1. By adjusting the component types and amounts of alloy raw materials 1 and 2, which are the raw materials for preparing high-strength and toughness hot working die steel, the inactive elements and active elements are added separately in sequence, and a segmented melting method is adopted to allow the elements to be fully melted without causing overheating effects on the elements; and partially adding some carbon elements to melt to play a role in deoxidation and promoting stirring, and adding rare earth elements, setting appropriate melting temperature, pouring temperature and pouring flow rate, so that the high-strength and toughness hot working die steel has good impact toughness and high Rockwell hardness.

[0027] 2. The prepared steel ingot is subjected to hot forging and annealing treatments, and high-temperature diffusion is performed before hot forging to improve the uniformity of atomic distribution; by adjusting the heating rate, holding temperature and cooling rate, and performing two upsetting and two drawing processes, repeated recovery recrystallization occurs, the grains are refined, and annealing treatment is performed. The annealing conditions are controlled, which can effectively eliminate the generated internal stress, promote the refinement of the internal grains of the steel, make the distribution of carbon in the steel more uniform, eliminate local segregation, and improve the toughness and hardness of the steel.

[0028] 3. By subjecting the annealed steel to cyclic hot forging and annealing treatment, the grains are further refined, and solid solution-quenching-partitioning and tempering treatment are performed again, so that the hot working die steel is heated to the soluble area, so that the various alloy elements in the steel are fully dissolved in the solid solution, and the structural defects in the steel are eliminated. Rapid cooling transforms the structure of the die steel into martensite or bainite, thereby improving the hardness of the die steel. In the cooling process after quenching, by controlling the cooling rate and temperature, the alloy elements such as carbon are reasonably distributed between martensite and austenite, further improving the strength of the steel; through tempering treatment, the residual stress generated during the quenching process is eliminated and the brittleness of the steel is reduced. By adjusting the temperature and time of the above processing steps, the toughness and hardness of the high-strength and toughness hot working die steel are further improved.

[0029] 4. The high-strength and toughness hot working die steel precursor obtained by tempering is further processed, and ceramic binder cubic boron nitride grinding wheel is used for grinding during the finishing process. During the grinding process, some particles of boron nitride and ceramic are embedded in the surface of the precursor, which improves the flatness of the surface of the high-strength and toughness hot working die steel on the one hand, and improves its own hardness on the other hand; by optimizing the finishing conditions; nitriding treatment can improve the toughness of the hot working die steel to a certain extent, and carburizing treatment can make the transition between the carburized layer and the core structure smooth, and cross-link with the pre-added carbon element, thereby improving the toughness and surface roughness of the high-strength and toughness hot working die steel, while improving the surface hardness, maintaining good toughness and heat fatigue resistance of the core. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a production process flow chart of the high-strength and toughness hot-working die steel of the present invention. DETAILED DESCRIPTION

[0031] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0032] See also Figure 1 The present invention provides a production process for high-strength and high-toughness hot-working die steel, and the technical solution is as follows:

[0033] Example 1

[0034] S1 Melting and Casting: Alloy raw material 1 (containing inactive elements Ni: 0.96%, Mo: 2.28%, Co: 1.05%, Nb: 0.36%, W: 2.10%, Ce: 0.10%, La: 0.15%, C: 0.20% and Fe) is placed in a prefabricated calcium oxide crucible and melted into molten steel in a vacuum induction furnace at a melting temperature of 1650°C; the molten steel is refined (to ensure the uniformity of the composition of the molten steel), and vacuum exhaust treatment is performed during the refining process to achieve a vacuum degree of 0.35-1.30N / m 2 , after complete deoxidation, add molten and deoxidized alloy raw material 2 (Si: 0.40%, Mn: 0.45%, Cr: 2.89%, V: 1.15%, P≤0.015%, S≤0.01%, Ti: 0.30%, C: 0.20%) to obtain a slurry to be cast; accurately control the pouring temperature to 1450°C, the casting flow rate to 2.0m / s, add a guide trough with a slag baffle or a foam ceramic filter, etc.; then reduce the temperature to 1100°C at a rate of 8°C / min, keep it warm for 60min, and then continue to reduce it to 400°C at a rate of 5°C / min, keep it warm for 30min, then reduce it to 100°C at a rate of 3°C / min, keep it warm for 20min and then reduce it to 50°C at a rate of 1°C / min, finally air cool it to room temperature to obtain a steel ingot; in terms of mass percentage, the total amount of inactive elements, active elements, C and Fe in alloy raw material 1 and alloy raw material 2 is 100%.

[0035] S2 hot forging: the steel ingot is homogenized, the heating rate is 2.5℃ / min, the holding temperature is 1300℃, and the holding time is 1.5h; then it is cooled to 1060℃ at a cooling rate of 10℃ / s, the first upsetting ratio is 1.8, the drawing ratio is 2.0, the second upsetting ratio is 2.3, the drawing ratio is 2.0, the total forging ratio is 11, and after hot forging for 1h, it is air-cooled to room temperature to obtain steel material;

[0036] S3 annealing: the hot forged steel is heated to 860°C at a heating rate of 8°C / min and kept at this temperature for 1.5h; then cooled to 640°C at a rate of 8°C / min, kept at this temperature for 1h, and then air-cooled to room temperature;

[0037] S4 cyclic hot forging and annealing: hot forging treatment is performed, the heating rate is 5℃ / min, the initial forging temperature is 1150℃, and the holding time is 2.5h; then it is cooled to 1020℃ at a cooling rate of 10℃ / s, kept at this temperature for 40min, and then air-cooled to room temperature; then annealing is performed again, the steel after the secondary hot forging is heated to 870℃ at a heating rate of 5℃ / min, and kept at this temperature for 2h; it is cooled to 650℃ with the furnace, and then taken out and air-cooled to room temperature to obtain steel;

[0038] S5 solution-quenching-partitioning treatment: the steel after secondary hot forging and secondary annealing is instantaneously heated to 1040°C, kept at this temperature for 45 minutes for solution treatment, and then kept at 950°C for 7 minutes in a salt bath furnace for isothermal quenching for 2.5 hours. The isothermal quenching medium is industrial quenching salt. After quenching, it is immediately taken out and kept at 960°C for 50 minutes, and then quenched to room temperature. The quenching medium is water; then the temperature is raised to 250°C at a rate of 10°C / min, kept at this temperature for 2 hours, and then air-cooled to room temperature to obtain the workpiece;

[0039] S6 tempering treatment: the workpiece is kept at 600°C for 1.5 hours and then air-cooled to room temperature, then kept at 570°C for 2.0 hours and then air-cooled to room temperature to obtain a high-strength and toughness hot working die steel precursor;

[0040] S7 finishing process: the high-strength and toughness hot working die steel precursor is cut by plasma to remove the oxide layer and burrs, the extreme pressure emulsion (purchased from Jiangsu Yingji Lubrication Technology Co., Ltd.) is diluted with deionized water to a concentration of 10%, and then ground with a ceramic bond cubic boron nitride grinding wheel, the speed is set to 120m / s, the feed speed is controlled at 0.07mm / min, and the single grinding depth is controlled at 0.05mm; the milling method of down milling is used to obtain a high-strength and toughness hot working die steel intermediate;

[0041] S8 surface treatment: Place the high-strength and toughness hot-working die steel intermediate in a nitriding furnace, control the nitriding temperature to 530°C, and the nitriding time to 24 hours. Then cool it with the furnace to remove the nitriding residue on the surface, and then transfer it to a vacuum furnace and control the vacuum degree to 10 -5 Pa, methane is filled in the furnace, the furnace pressure is controlled at 35kPa, glow discharge is stimulated between the anode and the cathode and carburizing is carried out. The voltage at this time is 600V. After processing for 2h, it is air-cooled to room temperature, tempered again, and kept warm at 560℃ for 2.5h to obtain high strength and toughness hot working die steel.

[0042] The above process flow is specifically shown in Figure 1 middle.

[0043] The preparation method of the prefabricated calcium oxide crucible is as follows: 80% of composite calcium oxide, 18% of mullite fiber and 2% of composite sintering aid are mixed to obtain a mixture; the mixture is subjected to cold isostatic pressing (wrapped in a rubber bag, carried out in an oil liquid medium, at a pressure of 300 MPa, maintained for 8 minutes, and operated at room temperature of 25°C), and a crucible blank is obtained after demolding; the crucible blank is dried, and then sintered in sections, pre-sintered at 300°C, and sintered for 15 minutes; The method comprises the following steps: low-temperature sintering is performed at 1400°C for 4 hours and high-temperature sintering is performed at 1700°C for 5 hours to obtain a prefabricated calcium oxide crucible; the composite calcium oxide contains 25% 0.3 mm calcium oxide fine powder, 30% 0.8 mm calcium oxide sand, 25% 2.5 mm calcium oxide sand and 15% 4.5 mm calcium oxide sand; the composite sintering aid is a mixture of calcium oxide, zirconium oxide, silicon dioxide and boron trioxide in a weight ratio of 1:1:1:1.

[0044] The preparation method of the ceramic bond cubic boron nitride grinding wheel is as follows: by mass percentage, 65% of cubic boron nitride abrasive (average particle size 50nm), 24% of ceramic bond, 7% of functional additive and 4% of auxiliary material are mixed evenly and placed in a pressing mold for cold pressing, and then placed in a graphite boat with carbon paper on the surface, and then loaded into a vacuum sintering furnace for vacuum sintering; after the furnace door is sealed, the vacuum sintering furnace is evacuated by a vacuum pump to make the vacuum degree in the vacuum sintering furnace be 0.8×10 -2 Pa, when the sintering furnace is heated from room temperature to 200℃, the heating rate is 5℃ / min; after being kept at 200℃ for 2h, the furnace temperature is raised to 300℃ at a heating rate of 4℃ / min and kept for 1.5h, then the furnace temperature is raised to 500℃ at a heating rate of 4℃ / min, kept at 500℃ for 1.5h, then the furnace temperature is raised to 850℃ at a heating rate of 2℃ / min and kept for 1h, then the furnace temperature is lowered to 700℃ at a cooling rate of 11℃ / min. , the heating program of the sintering furnace can be turned off, and the ceramic bond cubic boron nitride grinding wheel can be obtained as the furnace cools; the ceramic bond is obtained by mixing silicon dioxide (average particle size 200nm), titanium dioxide (average particle size 300nm), aluminum oxide (average particle size 350nm), boron oxide (average particle size 200nm) and lithium superoxide (average particle size 130nm) in a mass ratio of 1:1:1:1:1; the functional additive is a mixture of polyvinyl alcohol (35,000 low degree of polymerization) and nickel in a mass ratio of 9:1.

[0045] Example 2

[0046] Different from Example 1, the raw material dosage and preparation conditions of the smelting and casting process are changed, wherein the composition and dosage of the elements in the alloy raw material one are as follows: Ni: 0.72%, Mo: 2.40%, Co: 0.95%, Nb: 0.48%, W: 2.89%, Ce: 0.05%, La: 0.20%, C: 0.15% and Fe; the smelting temperature is 1650°C; the composition and dosage of the elements in the alloy raw material two are as follows: Si: 0.65%, Mn: 0.34%, Cr: 2.35%, V: 1.26%, P≤0.015%, S≤0.01%, Ti: 0.25%, C: 0.25%; the pouring temperature is 1550°C; and the casting flow rate is 2.4m / s.

[0047] Example 3

[0048] Different from Example 1, the raw material dosage and preparation conditions of the smelting and casting process are changed, wherein the composition and dosage of the elements in the alloy raw material one are as follows: Ni: 0.85%, Mo: 2.56%, Co: 1.25%, Nb: 0.25%, W: 1.15%, Ce: 0.15%, La: 0.08%, C: 0.25% and Fe; the smelting temperature is 1600°C; the composition and dosage of the elements in the alloy raw material two are as follows: Si: 0.35%, Mn: 0.56%, Cr: 2.67%, V: 0.86%, P≤0.015%, S≤0.01%, Ti: 0.35%, C: 0.20%; the pouring temperature is 1500°C; and the casting flow rate is 1.6 m / s.

[0049] Comparative Example 1

[0050] The difference from Example 1 is that all the C element is added into the first alloy raw material.

[0051] Comparative Example 2

[0052] Different from Example 1, no C element is added.

[0053] Comparative Example 3

[0054] Alloy raw material 1 and alloy raw material 2 are mixed and then smelted together, instead of using the method of separately smelting them in sequence as in Example 1.

[0055] Comparative Example 4

[0056] The difference from Example 1 is that the vacuum degree is 1.50 N / m 2 .

[0057] Comparative Example 5

[0058] Different from Example 1, the casting flow rate is 3.5 m / s.

[0059] Comparative Example 6

[0060] Different from Example 1, the casting flow rate is 1.0 m / s.

[0061] Comparative Example 7

[0062] Different from Example 1, the C content in the alloy raw material 1 is 3%, and the C content in the alloy raw material 2 is 4%.

[0063] Comparative Example 8

[0064] Different from Example 1, Nb, Ce and La are not added to the second alloy raw material.

[0065] Comparative Example 9

[0066] Different from Example 1, the order of adding alloy raw material 1 and alloy raw material 2 is replaced.

[0067] Experimental Example 1

[0068] The high-strength and toughness hot working die steels prepared in Examples 1-3 and Comparative Examples 1-9 were tested for impact toughness and surface hardness. The final test results are shown in Table 1.

[0069] Table 1 Impact toughness and surface hardness results of Examples 1-3 and Comparative Examples 1-6

[0070]

[0071] The high-strength and toughness hot-working die steel produced by the present invention has an impact toughness of 32.7-33.6 J / cm under the conditions of Examples 1-3. 2 , Rockwell hardness is HRC52; impact toughness under comparative examples 1-9 is 25.0-30.2J / cm 2, Rockwell hardness is HRC45-HRC49. Alloy raw material 1 is added, in which inactive elements Ni, Mo, Co, Nb, W, Ce and La and part of C element are added; then active elements Si, Mn, Cr, V, P, S and Ti and C element are added to alloy raw material 2. C element is added in batches, which, on the one hand, plays a role of deoxidation to prevent oxygen from interfering with the internal structure of steel, and on the other hand, promotes melting and stirring; however, if C is not added in batches, as shown in Comparative Example 1, the performance of high-strength and toughness hot working die steel decreases, and after C element dissolves in the iron matrix, it forms a solid solution, which plays a role of hindering dislocation movement in the lattice, thereby enhancing the strength of the steel. This is because when dislocations move in the crystal structure, carbon atoms will interact with the dislocations, increasing the difficulty of dislocation movement, thereby increasing the strength of the steel; and carbon can form carbides with other elements (such as chromium, molybdenum, vanadium, etc.) to prevent the movement of dislocations; in addition, it will promote the refinement of steel grains, and fine grains can hinder the slip of dislocations, thereby increasing the strength of the steel. Therefore, Example 2 does not contain the C element, and the toughness and hardness are significantly reduced; however, if the C content is too high, the performance of high-strength and toughness hot working die steel will be reduced, as shown in Example 7. In Examples 1-3, the inactive elements are first melted and then the active elements are added. The melting temperature of the active elements is lower than that of the inactive elements, so as to avoid overheating of the active elements at high temperatures, or decomposition and reaction that reduces the performance of the high-strength and toughness hot working die steel; in Comparative Example 9, alloy raw material 2 is added first, and the stability of the active elements is reduced, thereby reducing the overall performance of the material; in Comparative Example 3, alloy raw material 1 and alloy raw material 2 are mixed together, and elements such as Ce, Ti and Ni react with S to produce sulfides, thereby reducing the toughness of the die steel and increasing its brittleness; by adjusting the vacuum degree, oxygen and other gases are prevented from reacting with the elements. The vacuum degree of Comparative Example 4 is too high, which reduces the performance of the die steel; by adjusting the casting flow rate, within a suitable range, the slurry is mixed evenly and no partial condensation occurs, thereby causing uneven components of the hot working die steel. As shown in the results of Comparative Examples 5 and 6, too high or too low a casting flow rate will lead to reduced toughness and hardness. The addition of Nb can form stable carbides, prevent grain growth, and improve the thermal strength of steel. Its dispersed distribution on the grain boundary can form a fine and uniform grain structure. The addition of Ce and La can make the grains of the hot working die steel finer and more uniform, reduce defects at the grain boundaries, and thus improve the toughness and strength of the steel. Comparative Example 8 does not add the above elements, so the impact toughness and Rockwell hardness of the high-strength and toughness hot working die steel are significantly lower than those of Example 1.

[0072] Embodiment 4-7

[0073] Different from Example 2, the conditions of hot forging and annealing are changed, as shown in Table 2.

[0074] Table 2 Hot forging and annealing conditions

[0075]

[0076]

[0077] Comparative Example 10

[0078] Different from Example 2, the heating rate is 10°C / min and the holding temperature is 1350°C.

[0079] Comparative Example 11

[0080] Different from Example 2, no homogenization treatment is performed.

[0081] Comparative Examples 12 and 13

[0082] Different from Example 2, the cooling temperatures are 1200° C. and 900° C. respectively.

[0083] Comparative Example 14

[0084] The difference from Example 2 is that the first upsetting ratio is 2.2-2.4, the drawing ratio is 2.0-2.2, the second upsetting ratio is 1.5-1.8, and the drawing ratio is 1.8-2.0.

[0085] Comparative Example 15

[0086] Different from Example 2, the total forging ratio is 15.

[0087] Comparative Example 16

[0088] Different from Example 2, the total forging ratio is 5.

[0089] Comparative Example 17

[0090] Different from Example 2, the heating temperature is 960°C.

[0091] Comparative Example 18

[0092] The difference from Example 2 is that the cooling temperature is 500°C.

[0093] Experimental Example 2

[0094] The high-strength and toughness hot working die steels prepared in Examples 2, 4-7 and Comparative Examples 10-18 were tested for impact toughness and hardness. The final test results are shown in Table 3.

[0095] Table 3 Toughness and hardness test results of Examples 2, 4-7 and Comparative Examples 10-18

[0096]

[0097]

[0098] The high-strength and toughness hot-working die steel produced by the present invention has an impact toughness of 33.6-36.2 J / cm under the conditions of Examples 2 and 4-7. 2 , Rockwell hardness is HRC52-HRC53; Comparative Example 10-18 has an impact toughness of 26.0-29.4 J / cm 2, Rockwell hardness is HRC45-HRC49. In Examples 2, 4-7, by adjusting the heating rate, holding temperature, holding time, cooling rate, two upsetting and two drawing and total forging ratio during hot forging, and adjusting the heating temperature, cooling rate and cooling temperature of annealing, the obtained high-strength and toughness hot working die steel has high toughness and hardness. In the early stage of hot forging, homogenization treatment is carried out, and the steel ingot is heated to a suitable temperature at a suitable heating rate and kept warm for a period of time, so that the atoms obtain sufficient energy, promote the dissolution of carbides and the diffusion of alloy elements, thereby improving component segregation; when the heating temperature is within a reasonable range, the energy obtained by carbon atoms and alloy components is increased, and it is easy to migrate from high concentration areas to low concentration areas, so that the atoms are fully diffused and a material with uniform composition is obtained; the heating rate and temperature of Example 10 are too high, and Example 11 is not subjected to homogenization treatment, and the toughness and hardness of the high-strength and toughness hot working die steel are lower than those of Example 2. The temperature of hot forging needs to be controlled within a reasonable range. When the temperature of Example 12 is too high, the grains of the hot working die steel may be too coarse, resulting in a decrease in the toughness of the material; the coarse grains reduce the impact resistance of the material, especially at high temperatures, brittle fracture may occur easily; at the same time, too high forging temperature will cause excessive diffusion of carbon and alloy elements in the steel, making the steel too soft, resulting in a low Rockwell hardness; in addition, high temperature forging may also lead to the formation of an oxide layer of the steel, thereby affecting the uniformity of hardness. Example 13 The temperature is too low, and the deformation during the forging process is incomplete, resulting in more internal stress and defects inside the steel, which in turn leads to a decrease in the toughness of the material and is prone to brittle fracture during subsequent use; the steel cannot fully undergo plastic deformation, resulting in coarse grains and uneven structure, which makes the hardness uneven, and a higher hardness will appear that is not suitable for the working environment, especially at high temperature, causing wear and surface damage; in addition, some alloy elements in the steel cannot be completely dissolved or evenly distributed, resulting in uneven structure, fluctuations in the mechanical properties and hardness of the steel, and reducing the toughness and strength of the mold. By controlling the upsetting ratio and the drawing ratio within a reasonable range, the second upsetting ratio and the drawing ratio are higher than the first upsetting ratio and the drawing ratio. In the first stage, the upsetting ratio is small and the drawing ratio is moderate. This means that during the forging process, the metal deformation is relatively mild, the deformation amount is relatively small, and the grains of the material may not have been refined too much. This mild deformation helps to retain the toughness of the material; in the latter stage, the upsetting ratio and the drawing ratio increase, and the steel undergoes more severe deformation. The grains will be further refined in this process, thereby improving the toughness and hardness of the material.The upsetting ratio and drawing ratio of Comparative Example 14 are not conducive to grain refinement; the forging ratio of Comparative Example 15 is too large, and the deformation degree is too high, which may cause large deformation stress in the hot working die steel during the forging process, and may even cause cracks, defects or burns; it also causes excessive refinement of metal grains, which may increase the strength of the steel, but may also increase brittleness and reduce the toughness and impact resistance of the die; the forging ratio of Comparative Example 16 is too small, and the deformation degree is low, which may lead to insufficient plastic deformation of the steel, forming an uneven organizational structure, coarse grains, and reducing overall performance. Through annealing treatment, internal stress is eliminated, the refinement of grains inside the steel is promoted, and the distribution of carbon is more uniform, local segregation is eliminated, and the toughness and hardness of the steel are improved; in Comparative Examples 17 and 18, the heating temperature is too high and the cooling temperature is too low, which reduces the performance of high-strength and toughness hot working die steel.

[0099] Examples 8-12

[0100] Different from Example 6, the preparation processes of S4, S5 and S6 are changed, as shown in Table 4.

[0101] Table 4 Processing steps for S4, S5 and S6

[0102]

[0103] Comparative Example 19

[0104] Different from Example 6, the secondary hot calcination temperature is 1080°C.

[0105] Comparative Example 20

[0106] Different from Example 6, the secondary annealing temperature is 800°C.

[0107] Comparative Example 21

[0108] Different from Example 6, cyclic hot forging and annealing are not performed.

[0109] Comparative Example 22

[0110] The difference from Example 6 is that no solution-quenching-partitioning treatment is performed.

[0111] Comparative Example 23

[0112] Different from Example 6, no tempering treatment was performed.

[0113] Experimental Example 3

[0114] The high-strength and toughness hot working die steels prepared in Examples 6, 8-12 and Comparative Examples 19-23 were tested for impact toughness and hardness. The final test results are shown in Table 5.

[0115] Table 5 Toughness and strength test results of Examples 6, 8-12 and Comparative Examples 19-23

[0116] <![CDATA[Impact toughness (J / cm 2 )]]> Rockwell hardness Example 6 36.2 HRC53 Example 8 37.5 HRC55 Example 9 37.0 HRC55 Example 10 36.9 HRC54 Embodiment 11 37.8 HRC55 Example 12 37.3 HRC55 Comparative Example 19 30.8 HRC49 Comparative Example 20 28.7 HRC47 Comparative Example 21 25.0 HRC45 Comparative Example 22 24.2 HRC45 Comparative Example 23 26.8 HRC46

[0117] The high-strength and toughness hot working die steel prepared by the present invention has an impact toughness of 36.2-37.8 J / cm under the conditions of Examples 6 and 8-19. 2 , Rockwell hardness is HRC53-HRC55; the impact toughness under the conditions of comparative examples 19-23 is 24.2-30.8J / cm 2 , Rockwell hardness is HRC45-HRC49. In Examples 6, 8-19, by optimizing the temperature of cyclic hot forging and annealing, the instantaneous heating temperature, quenching temperature and time are optimized during the solution-quenching-partitioning treatment. Through cyclic hot forging and annealing treatment, hot forging can compact and weld the looseness, pores and other defects inside the steel ingot, thereby improving the density of the steel; breaking up the coarse grains and carbides in the cast structure to make them evenly distributed, refining the grains, improving the uniformity of the structure, and annealing again to further eliminate the internal stress. After alternating forging deformation grain refinement treatment and annealing phase transformation grain refinement treatment, through multiple austenitization and cooling processes, the phase transformation process is utilized to produce The stress and nucleation growth of new phases are used to refine the grains; after each forging deformation grain refinement treatment is completed, an annealing phase transformation grain refinement treatment is performed, the temperature of the last forging deformation grain refinement treatment is not higher than the temperature of the previous forging deformation grain refinement treatment, the temperature of the last annealing phase transformation grain refinement treatment is higher than the temperature of each previous annealing phase transformation grain refinement treatment, and the last annealing phase transformation grain refinement treatment obtains a spherical pearlite structure; and through the solution-quenching-partitioning treatment, the quenching temperature and time are adjusted; the tempering treatment is performed again to control the reaction temperature and time, so that the toughness and strength of the high-strength and toughness hot working die steel are further improved. The secondary hot forging temperature of Comparative Example 19 is higher than the temperature of the first hot forging, and the secondary annealing temperature of Comparative Example 20 is lower than the first annealing temperature, resulting in the lamellar pearlite structure not being completely transformed into the spherical pearlite structure, so compared with Example 6, the mechanical properties are reduced. In Comparative Examples 21-23, any of the steps of cyclic hot forging and annealing, solution-quenching-partitioning treatment and tempering treatment is not performed, so that the structural defects cannot be eliminated, the residual stress in the structure cannot be eliminated, the brittleness increases, and the impact toughness and Rockwell hardness of the high-strength and toughness hot working die steel are reduced.

[0118] Examples 13-17

[0119] Different from Example 11, the conditions of finishing and surface treatment are changed, as shown in Table 6.

[0120] Table 6 Conditions for finishing and surface treatment

[0121]

[0122] Comparative Example 24

[0123] Different from Example 11, no ceramic bonded cubic boron nitride grinding wheel is used for grinding.

[0124] Comparative Example 25

[0125] Different from Example 11, the rotation speed is set to 200 m / s, the feed speed is controlled at 0.02 mm / min, and the single grinding depth is controlled at 0.10 mm.

[0126] Comparative Example 26

[0127] Different from Example 11, no nitriding treatment was performed.

[0128] Comparative Example 27

[0129] Different from Example 11, no carburizing treatment was performed.

[0130] Comparative Example 28

[0131] The difference from Example 11 is that the carburizing treatment time is 5 hours.

[0132] Comparative Example 29

[0133] Different from Example 11, alloy raw materials 1 and 2 do not contain C element and no carburizing treatment is performed.

[0134] Comparative Example 30

[0135] Different from Example 11, a calcium oxide crucible is used in the smelting and casting process of S1 instead of a prefabricated calcium oxide crucible.

[0136] Experimental Example 4

[0137] The high-strength and toughness hot working die steels prepared in Examples 11, 13-17 and Comparative Examples 24-30 were tested for surface roughness, thermal fatigue resistance and toughness. The surface roughness is expressed as Ra value. The smaller the Ra value, the smoother the surface of the high-strength and toughness hot working die steel. The thermal fatigue resistance test method is as follows: thermal cycle treatment is performed from room temperature to 700°C. After 2000 cycles, the crack depth on the surface of the high-strength and toughness hot working die steel is tested. The final test results are shown in Table 7.

[0138] Table 7 Performance test results of Examples 11, 14-18 and Comparative Examples 24-30

[0139] <![CDATA[Impact toughness (J / cm 2 )]]> Surface roughness Ra(μm) Crack depth(mm) Embodiment 11 37.8 0.8 0.3 Embodiment 13 37.5 0.6 0.2 Embodiment 14 37.6 0.4 0.1 Embodiment 15 37.9 0.5 0.2 Example 16 37.8 0.6 0.1 Embodiment 17 37.4 0.4 0.4 Comparative Example 24 37.0 1.6 0.4 Comparative Example 25 36.8 2.1 0.8 Comparative Example 26 30.2 2.0 1.0 Comparative Example 27 31.0 1.4 0.7 Comparative Example 28 32.5 1.0 1.2 Comparative Example 29 26.5 3.0 1.5 Comparative Example 30 34.7 0.8 1.0

[0140] The high-strength and toughness hot working die steel prepared by the present invention has an impact toughness of 37.5-37.9 J / cm under the conditions of Examples 11, 13-17. 2 , Ra value is 0.4-0.8μm, crack depth is 0.1-0.4mm; under the conditions of comparative examples 24-30, impact toughness is 26.5-37.0J / cm 2, Ra value is 0.8-3.0μm, crack depth is 0.4-1.5mm. The high-strength and toughness hot-working die steel precursor is finished by using a ceramic bond cubic boron nitride grinding wheel. Using this grinding wheel for grinding can allow particles such as boron nitride, silicon dioxide, titanium dioxide, aluminum oxide, boron oxide and lithium superoxide to penetrate into the surface of the high-strength and toughness hot-working die steel during the grinding process, and optimize the grinding and cutting conditions; in addition, the conditions of nitriding and carburizing treatment are optimized, and nitrogen atoms penetrate into the surface of the steel to form nitrides. These nitrides can refine the grains, thereby improving the toughness of the steel; nitriding can also generate residual compressive stress on the surface, offset part of the tensile stress generated by external loads, reduce the formation of surface fatigue cracks, and reduce the formation of surface fatigue cracks. Improve toughness; carburizing treatment allows carbon atoms to penetrate into the surface of the mold steel, forming a high carbon layer on the surface, greatly improving the surface hardness; the high hardness surface layer formed by carburizing can effectively resist abrasive wear, adhesive wear and oxidative wear; the carburizing furnace pressure, voltage and processing time are reasonably adjusted to avoid the formation of coarse carbides or network carbides in the carburized layer, thereby increasing the brittleness of the carburized layer, reducing toughness, and when the mold is subjected to impact loads, the carburized layer is prone to cracks, and the cracks are easy to expand. The compressive stress state formed on the surface by carburizing treatment is conducive to improving the fatigue strength of the mold steel. Repeated thermal stress and mechanical stress will cause the generation and expansion of fatigue cracks. The compressive stress of the carburized layer can partially offset the tensile stress generated during work, hinder the initiation of fatigue cracks, and thus improve the fatigue life of the mold. The conditions for grinding using ordinary grinding wheels in Comparative Example 24 and finishing processing in Comparative Example 25 are not suitable. Compared with Example 11, the surface roughness increases and the heat fatigue resistance decreases. Comparative Example 26 did not undergo nitriding treatment, and the impact toughness was lower than that of Example 11, the surface roughness was improved, and the thermal fatigue resistance was reduced. Comparative Example 27 did not undergo carburizing treatment, and the mold performance was reduced. Comparative Example 28 The carburizing treatment time was too long, resulting in increased flexibility of the mold and reduced impact toughness. Comparative Example 29 Alloy Raw Materials 1 and 2 did not contain C element, and no carburizing treatment was performed. The overall performance of the mold was greatly reduced compared with Example 11. In Comparative Example 30, the calcium oxide crucible is used instead of the prefabricated calcium oxide crucible, and the comprehensive performance is reduced. The calcium oxide crucible has a short service life and is prone to cracking during use, which causes the alloy liquid to contact the external environment and introduce impurities. The prefabricated calcium oxide crucible has good thermal shock resistance, which can reduce smelting failures and alloy performance fluctuations caused by crucible rupture, and is conducive to the production of hot working die steel with stable quality and excellent performance. In addition, a sintering aid is added to the prefabricated calcium oxide crucible prepared therein, in which calcium oxide, zirconium oxide, silicon dioxide and boron trioxide are compounded with calcium oxide to form a stable crystalline phase structure. During the smelting and casting process, part of the zirconium, silicon and boron elements migrate into the alloy raw materials, ultimately improving the overall performance of the high-strength and toughness hot working die steel.

[0141] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A production process for high-strength and high-toughness hot-working die steel, characterized in that: The production process is as follows: S1 Melting and Casting: Alloy Raw Material 1 is placed in a prefabricated calcium oxide crucible, and melted into molten steel in a vacuum induction furnace at a melting temperature of 1600-1650°C; the molten steel is refined, and then alloy Raw Material 2 is added to obtain a slurry to be cast; the pouring temperature is 1450-1550°C, the casting flow rate is 1.6-2.4m / s, and a foam ceramic filter is added during the pouring process; then the steel ingot is obtained by cooling and heat preservation; S2 hot forging: the steel ingot is homogenized, then cooled for heat treatment, and steel material is obtained through two upsetting and two drawing processes; S3 annealing: the steel material is heated to 820°C-860°C at a heating rate of 5°C / min, and kept at this temperature for 1.5 hours; then cooled to 640-660°C at a rate of 5-8°C / min, kept at this temperature for 1 hour, and then air-cooled to room temperature; S4 cycle hot forging and annealing: secondary hot forging and re-annealing to obtain steel; S5 solution-quenching-partitioning treatment: the steel is subjected to solution-quenching, quenching and partitioning to obtain a workpiece; S6 tempering treatment: the workpiece is kept at 580-620°C for the first time and then air-cooled to room temperature, and then kept at 550-570°C for a second time for 1.5-2.5h, and air-cooled to obtain a high-strength and toughness hot working die steel precursor; S7 finishing process: using ceramic bond cubic boron nitride grinding wheel to grind high-strength and toughness hot working die steel intermediate; S8 Surface treatment: The high-strength and toughness hot working die steel intermediate is subjected to nitriding treatment and then carburizing treatment to obtain the high-strength and toughness hot working die steel.

2. The production process of a high-strength and toughness hot working die steel according to claim 1, characterized in that: The refining in S1 is vacuumed to a vacuum degree of 0.35 to 1.30 N / m 2 The specific steps of cooling and heat preservation are as follows: cooling to 1100°C at a rate of 8°C / min, cooling to 400°C at a rate of 5°C / min after heat preservation for 60 minutes, cooling to 100°C at a rate of 3°C / min after heat preservation for 30 minutes, cooling to 50°C at a rate of 1°C / min after heat preservation for 20 minutes, and finally air cooling to room temperature to obtain the steel ingot.

3. The production process of a high-strength and toughness hot working die steel according to claim 2, characterized in that: The element composition of the alloy raw material one is as follows: Ni: 0.72%-0.96%, Mo: 2.28%-2.56%, Co: 0.95%-1.25%, Nb: 0.25%-0.48%, W: 1.15-2.89%, Ce: 0.05%-0.15%, La: 0.08%-0.20%, C: 0.05%-0.20% and Fe; the element composition of the alloy raw material two is as follows: Si: 0.35%-0.65%, Mn: 0.34%-0.56%, Cr: 2.35%-2.89%, V: 0.86%-1.26%, P≤0.015%, S≤0.01%, Ti: 0.30%, C: 0.10%-0.25%.

4. The production process of a high-strength and toughness hot-working die steel according to claim 1, characterized in that: The homogenization treatment in S2 is a heating rate of 2.5-6°C / min, a holding temperature of 1260°C-1320°C, and a holding time of 1-2h; the cooling and heat treatment are cooling to 1060°C-1120°C at a cooling rate of 10°C / s, and hot forging for 1h; the conditions of the two upsetting and two drawing are: the first upsetting ratio is 1.5-1.8, the drawing-lengthening forging ratio is 1.8-2.0, the second upsetting ratio is 2.2-2.4, the drawing-lengthening forging ratio is 2-2.2, and the total forging ratio is 10-12.

5. The production process of high-strength and toughness hot-working die steel according to claim 1, characterized in that: The secondary hot forging and the re-annealing in S4 are as follows: hot forging treatment is performed with a heating rate of 5°C / min, an initial forging temperature of 1150°C, and a holding time of 2.5h; then cooling to 1020°C-1050°C at a cooling rate of 10°C / s for secondary hot forging, holding for 40min, and then air cooling to room temperature; re-annealing is performed, followed by heating to 870°C-920°C at a heating rate of 5°C / min, holding for 2h; furnace cooling to 650°C, and then air cooling to room temperature to obtain the steel.

6. The production process of a high-strength and toughness hot-working die steel according to claim 1, characterized in that: The solution-quenching-partitioning treatment in S5 is as follows: the steel is instantaneously heated to 1040-1060°C, kept warm for 45 minutes for solution treatment, and then kept warm at 920-980°C in a salt bath furnace for 5-10 minutes for isothermal quenching for 2.5 hours. The isothermal quenching medium is industrial quenching salt. The steel is taken out immediately after quenching, kept warm at 960-1030°C for 30-50 minutes, and then quenched to room temperature. The quenching medium is water; then the temperature is raised to 250°C at a rate of 10°C / min, kept warm for 2 hours, and then air-cooled to room temperature to obtain the workpiece.

7. The production process of high-strength and toughness hot-working die steel according to claim 1, characterized in that: The finishing process described in S7 is as follows: the high-strength and toughness hot working die steel precursor is cut by plasma to remove the oxide layer and burrs, the extreme pressure emulsion is diluted to a concentration of 10% with deionized water, and then ground with the ceramic binder cubic boron nitride grinding wheel, the rotation speed is set to 80-150m / s, the feed speed is controlled at 0.05-0.1mm / min, and the single grinding depth is controlled at 0.02-0.05mm; the high-strength and toughness hot working die steel intermediate is obtained by milling by down milling.

8. The production process of high-strength and toughness hot-working die steel according to claim 1, characterized in that: The preparation method of the ceramic bond cubic boron nitride grinding wheel is as follows: 65% of cubic boron nitride abrasive, 24% of ceramic bond, 7% of functional additive and 4% of auxiliary material are mixed evenly in mass percentage, put into a pressing mold for cold pressing, and then put into a graphite boat with carbon paper on the surface, and then put into a vacuum sintering furnace for vacuum sintering; after the furnace door is sealed, the vacuum sintering furnace is evacuated by a vacuum pump to make the vacuum degree in the vacuum sintering furnace be 0.8×10 -2 Pa, when the vacuum sintering furnace is heated from room temperature to 200°C, the heating rate is 5°C / min; after being kept at 200°C for 2h, the furnace temperature is raised to 300°C at a heating rate of 4°C / min and kept for 1.5h, and then the furnace temperature is raised to 500°C at a heating rate of 4°C / min, and kept at 500°C for 1.5, and then the furnace temperature is raised to 850°C at a heating rate of 2°C / min and kept for 1h, and then the furnace temperature is lowered to 700°C at a cooling rate of 11°C / min, and then the heating is stopped, and the ceramic bond cubic boron nitride grinding wheel is obtained with the furnace cooling; the ceramic bond is obtained by mixing silicon dioxide, titanium dioxide, aluminum oxide, boron oxide and lithium superoxide in a mass ratio of 1:1:1:1:1; the functional additive is obtained by mixing polyvinyl alcohol and nickel in a mass ratio of 9:

1.

9. The production process of high-strength and toughness hot-working die steel according to claim 1, characterized in that: The nitriding treatment is as follows: placing the high-strength and toughness hot-working die steel intermediate in a nitriding furnace, controlling the nitriding temperature to 500-550°C, the nitriding time to 20-26h, and then cooling with the furnace to remove the nitriding residue on the surface; the carburizing treatment is as follows: in a vacuum furnace, controlling the vacuum degree to 10 -5 Pa, methane is filled into the furnace, the furnace pressure is controlled at 28-45 kPa, glow discharge is stimulated between the anode and the cathode and carburizing is performed, the voltage at this time is 500V-800V, after processing for 1.2-2.5h, it is air-cooled to room temperature, and the tempering treatment is performed again to obtain the high-strength and toughness hot working die steel.

10. The production process of high-strength and high-toughness hot-working die steel according to claim 1, characterized in that: The preparation method of the prefabricated calcium oxide crucible is as follows: 80% of composite calcium oxide, 18% of mullite fiber and 2% of composite sintering aid are mixed to obtain a mixture; the mixture is molded and demolded to obtain a crucible blank; the crucible blank is dried and then sintered in stages, pre-sintering is performed at 300° C. for 15 minutes; sintering is performed at 1400° C. for 4 hours; sintering is performed at 1700° C. for 5 hours to obtain the prefabricated calcium oxide crucible; the composite calcium oxide contains 25% of 0.3 mm calcium oxide fine powder, 30% of 0.8 mm calcium oxide sand, 25% of 2.5 mm calcium oxide sand and 15% of 4.5 mm calcium oxide sand; the composite sintering aid is obtained by mixing calcium oxide, zirconium oxide, silicon dioxide and boron trioxide in a weight ratio of 1:1:1:1.

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