High-purity, high-toughness and high-isotropy hot work die steel and preparation method thereof

Abstract

The invention relates to a preparation method of high-purity, high-toughness and high-isotropy hot work die steel, which optimizes alloy components and strictly controls the production process. The specific process route is as follows: electric furnace smelting, ladle refining furnace refining, vacuum refining furnace refining, electrode blank casting, protective atmosphere electroslag furnace remelting, forging, ultrafine treatment and spheroidizing annealing production processes are simultaneously adopted. The invention further relates to the high-purity, high-toughness and high-isotropy hot work die steel prepared through the preparation method. The product is uniform in annealed microstructure structure, good in spheroidized structure, fine and uniform in grain distribution and uniform in quenched and tempered structure, fine precipitated phases of Mo and Cr carbides play a role in dispersion strengthening in the using process, the performance of the material is improved, and the material has high purity, high toughness, high isotropy and the like. The product can be widely used for manufacturing a hot extrusion die, a core rod, a hammer die of a die forging hammer, a die of a forging press and a die for a precision forging machine, and particularly can be used as a high-end die-casting die made of aluminum, copper and alloys thereof.

Description

Technical Field

[0001] The present invention relates to a die steel and a preparation method thereof, in particular to a hot work die steel with high purity, high toughness and high isotropy and a preparation method thereof. Background Art

[0002] With the development of China's industry, the demand for die steel has increased rapidly. Among many products in the machinery industry, dies are listed as key industries supported for development, which has greatly promoted the development of the die industry. Hot work dies generally work under harsh working conditions such as high temperature and thermal shock, so hot work die steel is required to have excellent comprehensive properties.

[0003] The dies made of H13 steel often fail due to the occurrence of turtle cracks during use, which greatly reduces the service life of the dies and increases the production cost. The main reason is that the low impact toughness and low isotropy cause the turtle cracks to preferentially appear on the surface of the weak grain boundary regions, and at the same time, the low toughness leads to poor crack arrest performance, resulting in rapid crack propagation and finally causing the die to crack and fail.

[0004] Therefore, it is desired to provide a preparation method of hot work die steel in order to solve the above technical problems. Summary of the Invention

[0005] The first object of the present invention is to provide a preparation method of a hot work die steel with high purity, high toughness and high isotropy. Based on H13 steel, the chemical composition is finely adjusted and the process production process is optimized, so that the prepared product has better tissue properties and mechanical properties and better meets the requirements of modern production for high-end dies.

[0006] A preparation method of a hot work die steel with high purity, high toughness and high isotropy, the main steps are as follows:

[0007] S1. Electric furnace smelting:

[0008] The component content of the hot work die steel is, by mass percentage, C 0.37% - 0.42%, Mn 0.30% - 0.50%, Si 0.80% - 1.00%, S ≤ 0.002%, P ≤ 0.010%, Cr 4.90% - 5.10%, Mo 1.30% - 1.50%, Ni 0.20% - 0.30%, V 0.80% - 1.10%, the rest is Fe, and the residual gas content is, H ≤ 1.5 ppm, O ≤ 13 ppm, N ≤ 90 ppm, the residual harmful element Ca ≤ 0.0005%, Ti, Sn, Pb are all ≤ 0.002%;

[0009] S2. Ladle furnace refining:

[0010] The ladle refining furnace is heated, and slag CaO, CaF2, C-Si powder are added to reduce and adjust the slag system;

[0011] S3, vacuum refining furnace refining;

[0012] S4, continuous casting rectangular billet:

[0013] Superheat of the first furnace is 20~35℃, and that of the continuous casting furnace is 18~30℃;

[0014] The continuous casting speed is 0.13-0.20 m / min, and three-stage electromagnetic stirring is adopted;

[0015] S5. Annealing of continuous casting rectangular billet:

[0016] Annealing the continuously cast rectangular billet after continuous casting in step S4;

[0017] S6, electroslag remelting:

[0018] The electrode blank obtained in step S5 is first subjected to a surface shot blasting treatment using a shot blasting machine to remove the surface iron oxide scale;

[0019] The ternary slag system of calcium fluoride, aluminum oxide and magnesium oxide is used for smelting;

[0020] S7, primary heating and forging:

[0021] The electroslag ingot obtained in step S6 is heated in an ultra-high temperature chamber type heating furnace to perform ultra-high temperature diffusion;

[0022] Then the blank is forged by upsetting and drawing, and then drawn in three directions, X, Y and Z, to an intermediate blank. The main deformation rate of the last single pass of the fire is ≥50%.

[0023] S8, heat treatment after primary forging;

[0024] S9, secondary heating and forging:

[0025] The intermediate billet obtained in step S8 is heated in a chamber heating furnace to achieve uniform temperature;

[0026] Then, the product is upset, stretched, and forged in three directions, X, Y, and Z, and the main deformation rate of the last single pass of the forging process is ≥50%.

[0027] S10, residual heat quenching and spheroidizing treatment:

[0028] The finished product obtained in step S9 is directly put into water for forced cooling, and the final cooling large surface return temperature is ≤100°C;

[0029] Then put it into the heat treatment furnace and heat it to 850-880℃, keep it warm for 15-20h, and then cool it to 720-750℃, keep it warm for 30-40h for spheroidizing annealing;

[0030] After the spheroidizing treatment, when the furnace temperature drops to ≤350°C, the molten metal is discharged from the furnace and air-cooled to room temperature.

[0031] Specifically, in step S1, the burdening of blast furnace hot metal, sheared furnace charge and ladle residue steel is carried out according to the component content of hot work die steel, where the proportion of blast furnace hot metal is ≥70%;

[0032] CaO, CaF2, aluminum blocks and dolomite are added and melted and smelted in an electric furnace;

[0033] After slag skimming, CaO, cleaning agent and aluminum blocks are added and then the steel is tapped. The tapping temperature is ≥1620°C.

[0034] Specifically, in step S3, refining is carried out using a vacuum circulation refining furnace. The molten steel treated in step S2 is poured into an integrated circulation vacuum tank and cooperated with a vacuum pump, and the vacuum degree is ≤15 Pa;

[0035] Under vacuum conditions, the circulation flow rate is ≥100 t / min, and the treatment time is ≥35 minutes to ensure that the residual gas H ≤ 1.5 ppm and N ≤ 70 ppm;

[0036] After vacuum degassing, sampling and analysis are carried out. After the composition is qualified, argon is blown into the ladle until the ladle is lifted. The soft argon blowing time is 18 - 39 min, and the ladle temperature is 1550 - 1568°C.

[0037] Specifically, in step S5, the annealing temperature is 860 - 880°C, the holding time is 1 - 1.5 min / mm, and the furnace is cooled to below 350°C before discharging.

[0038] Specifically, in step S6, the starting melting rate value in the steady state stage of electroslag smelting is 7.5 - 8.5 kg / min, and the ending melting rate value is 5.5 - 6.5 kg / min to obtain an electroslag ingot. Then, after the electric furnace is powered off and air-cooled for 80 - 100 min, it is sent to the forging process.

[0039] Specifically, in step S7, the specific parameters of the first heating are that the heating temperature is ≥1280°C and the holding time is 40 - 50 h for diffusion homogenization.

[0040] Specifically, in step S8, the intermediate billet obtained in step S7 is directly subjected to forced cooling by being immersed in water for the first time, and the final cooling large surface re-warming temperature is ≤350°C;

[0041] Then it is heated in the furnace to 700 - 730°C for high-temperature tempering, and after the tempering is completed, it is cooled in the furnace to ≤350°C and then discharged and air-cooled.

[0042] Specifically, in step S9, the specific parameters of the second heating are that the heating temperature is ≥1240°C and the holding time is 10 - 15 h.

[0043] The second object of the present invention is to provide a hot work die steel with high purity, high toughness and high isotropy prepared by the above-mentioned preparation method. The chemical component content of the hot work die steel, by mass percentage, is C 0.37% - 0.42%, Mn 0.30% - 0.50%, Si 0.80% - 1.00%, S ≤ 0.002%, P ≤ 0.010%, Cr 4.90% - 5.10%, Mo 1.30% - 1.50%, Ni 0.20% - 0.30%, V 0.80% - 1.10%, the rest is Fe, and the residual gas content is H ≤ 1.5 ppm, O ≤ 13 ppm, N ≤ 90 ppm, the residual harmful element Ca ≤ 0.0005%, and Ti, Sn, Pb are all ≤ 0.002%.

[0044] A hot work die steel with high purity, high toughness and high isotropy and its preparation method according to the present invention have the following advantages compared with the prior art:

[0045] (1) By combining blast furnace molten iron + selected alloys for electric furnace smelting, the contents of P, S and residual elements in the molten steel are controlled at a low level, especially Ca ≤ 0.0005%; the purpose of reducing the total amount of inclusions in the molten steel is achieved;

[0046] (2) LF + vacuum circulating refining furnace are used together to complete the refining and degassing processes. The inclusions in the molten steel are fully combined with the steel slag and adsorbed and removed by the steel slag; the reduction of nitrogen content and Ti content can reduce the total amount of titanium nitride inclusions generated in the molten steel. Finally, the comprehensive control of inclusions is achieved, and the purpose of improving toughness is realized.

[0047] (3) The electrode billet is optimized from the traditional continuous casting round billet to a rectangular square billet, increasing the specific surface area. The solidification speed of the molten steel in the continuous casting process increases, and at the same time, electromagnetic stirring can reduce composition segregation and inclusion aggregation.

[0048] (4) The electro-slag slag system is optimized from the traditional calcium fluoride, alumina binary slag to a calcium fluoride, alumina, magnesia ternary slag system. Magnesium oxide will form a magnesium oxide film covering the surface of the slag pool during smelting, cutting off contact with the outside air, reducing the diffusion of external oxygen into the slag pool and then into the molten steel, and increasing the total amount of oxides in the molten steel.

[0049] (5) Ultra-high temperature and long-time high-temperature diffusion are used to eliminate the liquid-phase carbide in the electroslag ingot. At the same time, by combining short-range diffusion and long-range diffusion, the carbon and alloy elements in the electroslag ingot are homogenized. The purpose of homogenizing the composition of the electroslag ingot is achieved;

[0050] (6) First, multi-directional forging is carried out using a hydraulic press. Through the action of hydrostatic pressure, the dendritic crystals in the electroslag ingot are fully broken, and mechanical mixing realizes the homogenization of alloy elements. At the same time, it cooperates with recrystallization after forging to complete the refinement of austenite grains;

[0051] (7) For the second time, electro-hydraulic hammer multi-directional forging is first used to fully break the austenite grains in the forging billet through the impact force. At the same time, it cooperates with post-forging heat treatment quenching to complete the solidification of the refined austenite grains and inhibit the precipitation of network carbide, and combines with the spheroidizing annealing process to complete the refinement of austenite grains;

[0052] (8) The fine austenite grains obtained through secondary forging can curve the conventional solution treatment process, and the total production cycle can be shortened.

[0053] (9) By controlling the raw materials and optimizing the process of the whole production process, on the premise of fine-tuning the composition, the impact toughness and isotropic properties of H13MOD flat steel are greatly improved. Description of the Drawings

[0054] Figure 1 Microstructure diagram of the die steel obtained in Example 1;

[0055] Figure 2 Austenite grain size diagram of the die steel obtained in Example 1;

[0056] Figure 3 Microstructure diagram of the die steel obtained in Example 2;

[0057] Figure 4 Austenite grain size diagram of the die steel obtained in Example 2;

[0058] Figure 5 Microstructure diagram of the die steel obtained in Example 3;

[0059] Figure 6 Austenite grain size diagram of the die steel obtained in Example 3;

[0060] Figure 7 Microstructure diagram of the die steel obtained in Example 4;

[0061] Figure 8 Austenite grain size diagram of the die steel obtained in Example 4;

[0062] Figure 9 Microstructure diagram of the die steel obtained in Example 5;

[0063] Figure 10 Austenite grain size diagram of the die steel obtained in Example 5. Detailed Description of the Invention

[0064] Example 1

[0065] A hot work die steel, by mass fraction, is basically composed of the elements shown in Table 1:

[0066] Table 1

[0067]

[0068] A preparation method of a hot - working die steel with high purity, high toughness and high isotropy is as follows:

[0069] S1. Electric furnace smelting:

[0070] According to the component content of the hot - working die steel, charge the blast furnace hot metal (proportion 80%), sheared furnace charge and the large - package remaining steel, add CaO, CaF2, aluminum blocks, and dolomite, and melt and smelt in the electric furnace; after slag skimming, add CaO, deoxidizer, and aluminum blocks and then tap the steel, with the tapping temperature of 1630 °C;

[0071] Among them, the component content of the hot - working die steel is, by mass percentage, C 0.37% - 0.42%, Mn 0.30% - 0.50%, Si 0.80% - 1.00%, S≤0.002%, P≤0.010%, Cr 4.90% - 5.10%, Mo 1.30% - 1.50%, Ni 0.20% - 0.30%, V 0.80% - 1.10%, and the rest is Fe, and the residual gas content is, H≤1.5 ppm, O≤13 ppm, N≤90 ppm; the residual harmful element Ca≤0.0005%, and Ti, Sn, Pb are all ≤0.002%.

[0072] S2. Ladle refining furnace refining:

[0073] Seat the ladle in the ladle refining furnace for heating, and add slag materials CaO, CaF2, C - Si powder to reduce and adjust the slag system;

[0074] S3. Vacuum circulation refining furnace refining:

[0075] An integrated circulating vacuum tank, combined with an advanced vacuum pump, with a vacuum degree ≤15 Pa; under vacuum conditions, the circulation flow rate ≥100 t / min, the treatment time ≥35 minutes, ensuring that the residual gas H≤1.5 ppm, N≤70 ppm. After vacuum degassing, take samples for analysis. After the composition is qualified, blow argon until lifting the ladle, and the soft blowing argon time is 18 - 39 min, and the ladle temperature is 1550 - 1568 °C;

[0076] S4. Continuous casting of rectangular billets:

[0077] The superheat degree is 20 - 35 °C for the first furnace and 18 - 30 °C for the continuous casting furnace; the continuous casting casting speed is 0.16 m / min, and three - stage electromagnetic stirring is adopted.

[0078] S5. Annealing of continuous - cast rectangular billets:

[0079] Anneal the continuously cast rectangular billet after step S4. The annealing temperature is 880 °C, the holding time is 1.3 min / mm, and it is cooled in the furnace to below 350 °C before taking out of the furnace;

[0080] S6. Electroslag remelting:

[0081] Use the electrode billet obtained in step S5. First, perform surface shot peening treatment with a shot peening machine to remove the surface scale. Then, use a ternary slag system of calcium fluoride, alumina, and magnesia for smelting. Ultra-low melting rate control: The starting melting rate value in the steady state stage of electroslag smelting is 7.5 - 8.5 kg / min, and the ending melting rate value is 5.5 - 6.5 kg / min to obtain an electroslag ingot. Then, after power-off and furnace cooling for 80 - 100 min, send it to the forging process;

[0082] S7. First heating and forging:

[0083] Heat the electroslag ingot obtained in step S6 using an ultra-high temperature (the ultimate heating temperature is 1300 °C) chamber furnace to ensure the effective implementation of the ultra-high temperature diffusion process: The heating temperature is 1290 °C, and keep it for 50 h for diffusion homogenization. Then, perform upsetting and drawing out forging to break the billet, and perform multi-directional drawing in the X, Y, and Z directions to obtain an intermediate billet. Finally, the main deformation rate in a single pass of the last heat is ≥50%;

[0084] S8. First post-forging heat treatment: Quench with residual heat + high tempering

[0085] Directly perform forced cooling in water for the intermediate billet obtained in step S7. The temperature of the large surface returning to room temperature after final cooling is 300 °C. Then, heat it in the furnace to 710 °C for high temperature tempering. After the tempering is completed, cool it in the furnace to 350 °C and then take it out of the furnace for air cooling.

[0086] S9. Second heating and forging

[0087] Heat the intermediate billet obtained in step S8 using a chamber furnace: The heating temperature is 1250 °C, keep it for 15 h for temperature equalization, then perform upsetting and drawing out in the X, Y, and Z directions to forge it into a finished product in one heat. Finally, the main deformation rate in a single pass of the last heat is ≥50%;

[0088] S10. Quench with residual heat + spheroidizing treatment

[0089] Directly put the finished product obtained in step S9 into water for forced cooling. The temperature of the large surface returning to room temperature after final cooling is 80 °C. Then, put it into a heat treatment furnace and heat it to 860 °C, keep it for 15 h. After the holding is completed, cool it in the furnace to 730 °C and keep it for 30 h for spheroidizing annealing. After the spheroidizing treatment is completed and the furnace temperature reaches 350 °C, take it out of the furnace and air cool it to room temperature.

[0090] Example 2

[0091] A hot work die steel, by mass fraction, is basically composed of the elements in Table 2:

[0092] Table 2

[0093]

[0094] S1. Electric furnace smelting:

[0095] Charge the blast furnace hot metal (mixing ratio 80%), sheared furnace charge and ladle remaining steel according to the component content of the hot work die steel, add CaO, CaF2, aluminum blocks and dolomite, and melt and smelt in the electric furnace; after slag skimming, add CaO, cleaning agent and aluminum blocks and then tap the steel, with the tapping temperature of 1630°C;

[0096] Among them, the component content of the hot work die steel is, by mass percentage, C 0.37% - 0.42%, Mn 0.30% - 0.50%, Si 0.80% - 1.00%, S ≤ 0.002%, P ≤ 0.010%, Cr 4.90% - 5.10%, Mo 1.30% - 1.50%, Ni 0.20% - 0.30%, V 0.80% - 1.10%, and the rest is Fe, and the residual gas content is, H ≤ 1.5 ppm, O ≤ 13 ppm, N ≤ 90 ppm; the residual harmful elements Ca ≤ 0.0005%, and Ti, Sn, Pb are all ≤ 0.002%.

[0097] S2. Ladle furnace refining:

[0098] Seat the ladle in the ladle furnace for heating, and add slag materials CaO, CaF2, C - Si powder to reduce and adjust the slag system;

[0099] S3. Vacuum circulation refining furnace refining:

[0100] Integrated circulating vacuum tank, combined with an advanced vacuum pump, with a vacuum degree ≤ 15 Pa; under vacuum conditions, the circulation flow rate ≥ 100 t / min, the treatment time ≥ 35 minutes, ensuring that the residual gas H ≤ 1.5 ppm, N ≤ 70 ppm. After vacuum degassing, take samples for analysis. After the composition is qualified, blow argon until the ladle is lifted, and the soft blowing argon time is 18 - 39 min, and the ladle temperature is 1550 - 1568°C;

[0101] S4. Continuous casting of rectangular billets:

[0102] The superheat degree is 20 - 35°C for the first furnace and 18 - 30°C for the continuous casting furnace; the continuous casting drawing speed is 0.16 m / min, and three-stage electromagnetic stirring is adopted.

[0103] S5. Annealing of continuous casting rectangular billets:

[0104] Anneal the continuous casting rectangular billets after continuous casting in step S4, with the annealing temperature of 880°C, the holding time of 1.3 min / mm, and furnace cooling to below 350°C before discharging from the furnace;

[0105] S6. Electro-slag remelting:

[0106] Using the electrode blank obtained in step S5, first perform surface shot peening treatment with a shot peening machine to remove the surface scale and then smelt using a ternary slag system of calcium fluoride, alumina, and magnesia. Ultra-low melting speed control: The starting melting speed value at the steady state stage of electro-slag smelting is 7.5 - 8.5 kg / min, and the ending melting speed value is 5.5 - 6.5 kg / min to obtain an electro-slag ingot, and then after power-off furnace cooling for 80 - 100 min, send it to the forging process;

[0107] S7. First heating and forging:

[0108] Heat the electro-slag ingot obtained in step S6 using an ultra-high temperature (ultimate heating temperature 1300 °C) chamber furnace to ensure the effective implementation of the ultra-high temperature diffusion process: The heating temperature is 1290 °C, hold for 50 h for diffusion homogenization, and then perform upsetting and drawing forging to open the blank, and perform multi-directional drawing in the X, Y, and Z directions to an intermediate blank, and finally the main deformation rate of a single pass in one heat is ≥ 50%;

[0109] S8. First post-forging heat treatment: Remaining heat quenching + high tempering

[0110] Directly perform forced cooling by immersing in water for the intermediate blank obtained in step S7, and the return temperature of the large surface after final cooling is 310 °C. Then heat it in the furnace to 710 °C for high temperature tempering, and after the tempering is completed, cool it in the furnace to 350 °C and then take it out of the furnace and air-cool.

[0111] S9. Second heating and forging

[0112] Heat the intermediate blank obtained in step S8 using a chamber furnace: The heating temperature is 1250 °C, hold for 15 h for temperature equalization, and then perform upsetting and drawing in the X, Y, and Z directions to forge it to the finished product in one heat, and finally the main deformation rate of a single pass in one heat is ≥ 50%;

[0113] S10. Remaining heat quenching + spheroidizing treatment

[0114] Directly immerse the finished product obtained in step S9 in water for forced cooling, and the return temperature of the large surface after final cooling is 86 °C. Then put it into a heat treatment furnace and heat it to 860 °C, hold for 15 h, and after the holding is completed, cool it in the furnace to 730 °C and hold for 30 h for spheroidizing annealing. After the spheroidizing treatment, when the furnace temperature reaches 350 °C, take it out of the furnace and air-cool to room temperature.

[0115] Example 3

[0116] A hot work die steel, by mass fraction, is basically composed of the elements in Table 3 as follows:

[0117] Table 3

[0118]

[0119] S1. Electric furnace smelting:

[0120] Batch the blast furnace hot metal (mixing ratio 80%), sheared furnace charge and ladle residue steel according to the component content of the hot work die steel, add CaO, CaF2, aluminum blocks, and dolomite, and melt and smelt in an electric furnace; after slag skimming, add CaO, cleaning agent, and aluminum blocks and then tap the steel, with the tapping temperature of 1630°C;

[0121] Among them, the component content of the hot work die steel is, by mass percentage, C 0.37% - 0.42%, Mn 0.30% - 0.50%, Si 0.80% - 1.00%, S ≤ 0.002%, P ≤ 0.010%, Cr 4.90% - 5.10%, Mo 1.30% - 1.50%, Ni 0.20% - 0.30%, V 0.80% - 1.10%, the rest is Fe, and the residual gas content is, H ≤ 1.5 ppm, O ≤ 13 ppm, N ≤ 90 ppm; the residual harmful elements Ca ≤ 0.0005%, Ti, Sn, Pb are all ≤ 0.002%.

[0122] S2. Ladle furnace refining:

[0123] Seat the ladle in the ladle furnace for heating, and add slag materials CaO, CaF2, C - Si powder to reduce and adjust the slag system;

[0124] S3. Vacuum circulation refining furnace refining:

[0125] Integrated circulation vacuum tank, combined with an advanced vacuum pump, with a vacuum degree ≤ 15 Pa; under vacuum conditions, the circulation flow rate ≥ 100 t / min, the treatment time ≥ 35 minutes, ensuring that the residual gas H ≤ 1.5 ppm, N ≤ 70 ppm. After vacuum degassing, take samples for analysis. After the composition is qualified, blow argon until the ladle is lifted, and the soft blowing argon time is 18 - 39 min, and the ladle temperature is 1550 - 1568°C;

[0126] S4. Continuous casting of rectangular billets:

[0127] The superheat degree is 20 - 35°C for the first furnace and 18 - 30°C for the continuous casting furnace; the continuous casting casting speed is 0.16 m / min, and three - stage electromagnetic stirring is adopted.

[0128] S5. Annealing of continuous - cast rectangular billets:

[0129] Anneal the continuous - cast rectangular billets after continuous casting in step S4, with the annealing temperature of 880°C, the holding time of 1.3 min / mm, and cool in the furnace to below 350°C and then take out of the furnace;

[0130] S6. Electroslag remelting:

[0131] The electrode blank obtained in step S5 is first subjected to surface shot peening treatment using a shot peening machine to remove the surface scale, and then smelted using a ternary slag system of calcium fluoride, alumina, and magnesia. Ultra-low melting rate control: The starting melting rate value in the steady state stage of electroslag smelting is 7.5 - 8.5 kg / min, and the ending melting rate value is 5.5 - 6.5 kg / min to obtain an electroslag ingot, and then after power-off furnace cooling for 80 - 100 min, it is sent to the forging process;

[0132] S7. Primary heating and forging:

[0133] The electroslag ingot obtained in step S6 is heated using an ultra-high temperature (limit heating temperature 1300 °C) chamber furnace to ensure the effective implementation of the ultra-high temperature diffusion process: The heating temperature is 1290 °C, and it is held for 50 h for diffusion homogenization, and then it is upset and drawn to forge and billet, and multi-directional drawing in the X, Y, and Z directions is carried out to an intermediate billet, and finally the main deformation rate in a single pass of the last heat is ≥50%.

[0134] S8. Primary post-forging heat treatment: Remaining heat quenching + high tempering

[0135] The intermediate billet obtained in step S7 is directly subjected to forced cooling by immersion in water once, and the temperature of the large surface returning after final cooling is 280 °C. Then it is heated in the furnace to 710 °C for high temperature tempering, and after the tempering is completed, it is cooled in the furnace to 350 °C and then taken out of the furnace and air-cooled.

[0136] S9. Secondary heating and forging

[0137] The intermediate billet obtained in step S8 is heated using a chamber furnace: The heating temperature is 1250 °C, and it is held for 15 h for temperature equalization, and then upset and drawn in the X, Y, and Z directions to forge to the finished product in one heat, and finally the main deformation rate in a single pass of the last heat is ≥50%.

[0138] S10. Remaining heat quenching + spheroidizing treatment

[0139] The finished product obtained in step S9 is directly immersed in water for forced cooling, and the temperature of the large surface returning after final cooling is 95 °C. Then it is put into a heat treatment furnace and heated to 860 °C, held for 15 h, and after the holding is completed, it is cooled in the furnace to 730 °C and held for 30 h for spheroidizing annealing. After the spheroidizing treatment, when the furnace temperature reaches 350 °C, it is taken out of the furnace and air-cooled to room temperature.

[0140] Example 4

[0141] A hot work die steel, by mass fraction, is basically composed of the elements in Table 4 as follows:

[0142] Table 4

[0143]

[0144] S1. Electric furnace smelting:

[0145] Batch the blast furnace hot metal (proportion 80%), sheared furnace charge and large ladle remaining steel according to the component content of the hot work die steel, add CaO, CaF2, aluminum ingots, and dolomite, and melt and smelt in an electric furnace; after slag skimming, add CaO, cleaning agent, and aluminum ingots and then tap the steel, with the tapping temperature of 1630 °C;

[0146] Among them, the component content of the hot work die steel is, by mass percentage, C 0.37% - 0.42%, Mn 0.30% - 0.50%, Si 0.80% - 1.00%, S ≤ 0.002%, P ≤ 0.010%, Cr 4.90% - 5.10%, Mo 1.30% - 1.50%, Ni 0.20% - 0.30%, V 0.80% - 1.10%, and the rest is Fe, and the residual gas content is, H ≤ 1.5 ppm, O ≤ 13 ppm, N ≤ 90 ppm; the residual harmful element Ca ≤ 0.0005%, and Ti, Sn, Pb are all ≤ 0.002%.

[0147] S2. Refining in the ladle furnace:

[0148] Heat the ladle in the ladle furnace, and add slag materials CaO, CaF2, C - Si powder to reduce and adjust the slag system;

[0149] S3. Refining in the vacuum circulation refining furnace:

[0150] Integrated circulating vacuum tank, combined with an advanced vacuum pump, with a vacuum degree ≤ 15 Pa; under vacuum conditions, the circulation flow rate ≥ 100 t / min, the treatment time ≥ 35 minutes, ensuring that the residual gas H ≤ 1.5 ppm, N ≤ 70 ppm. After vacuum degassing, take samples for analysis. After the composition is qualified, blow argon until the ladle is lifted, and the soft blowing time of argon is 18 - 39 min, and the ladle temperature is 1550 - 1568 °C;

[0151] S4. Continuous casting of rectangular billets:

[0152] The superheat degree is 20 - 35 °C for the first furnace and 18 - 30 °C for the continuous casting furnace; the continuous casting speed is 0.16 m / min, and three - stage electromagnetic stirring is adopted.

[0153] S5. Annealing of continuous - cast rectangular billets:

[0154] Anneal the continuous - cast rectangular billets after continuous casting in step S4, with an annealing temperature of 880 °C, a holding time of 1.3 min / mm, and furnace - cool to below 350 °C before discharging;

[0155] S6. Electroslag remelting:

[0156] Using the electrode blank obtained in step S5, first perform surface shot peening treatment with a shot peening machine to remove the surface scale, and then smelt it using a ternary slag system of calcium fluoride, alumina, and magnesia. Ultra-low melting rate control: The starting melting rate value in the steady state stage of electroslag smelting is 7.5 - 8.5 kg / min, and the ending melting rate value is 5.5 - 6.5 kg / min to obtain an electroslag ingot. Then, after powering off the furnace and cooling for 80 - 100 min, send it to the forging process;

[0157] S7. Primary heating and forging:

[0158] Heat the electroslag ingot obtained in step S6 using a chamber heating furnace with an ultra-high temperature (ultimate heating temperature 1300 °C) to ensure the effective implementation of the ultra-high temperature diffusion process: The heating temperature is 1290 °C, hold for 50 h for diffusion homogenization, and then perform upsetting and drawing forging to open the billet, and perform multi-directional drawing in the X, Y, and Z directions to the intermediate billet. Finally, the main deformation rate of a single pass in one heat is ≥50%.

[0159] S8. Primary post-forging heat treatment: Remainder quenching + high tempering

[0160] Directly perform forced cooling by immersing the intermediate billet obtained in step S7 into water once, and the back temperature of the large surface after final cooling is 320 °C. Then, heat it in the furnace to 710 °C for high temperature tempering. After the tempering is completed, cool it in the furnace to 350 °C and then take it out of the furnace and air cool it.

[0161] S9. Secondary heating and forging

[0162] Heat the intermediate billet obtained in step S8 using a chamber heating furnace: The heating temperature is 1250 °C, hold for 15 h for temperature equalization, and then perform upsetting and drawing in the X, Y, and Z directions to forge it to the finished product in one heat. Finally, the main deformation rate of a single pass in one heat is ≥50%.

[0163] S10. Remainder quenching + spheroidizing treatment

[0164] Directly immerse the finished product obtained in step S9 into water for forced cooling, and the back temperature of the large surface after final cooling is 90 °C. Then, heat it in a heat treatment furnace to 860 °C, hold for 15 h. After the holding is completed, cool it in the furnace to 730 °C and hold for 30 h for spheroidizing annealing. After the spheroidizing treatment is completed and the furnace temperature reaches 350 °C, take it out of the furnace and air cool it to room temperature.

[0165] Example 5

[0166] A hot work die steel, by mass fraction, is basically composed of the elements in Table 5 as follows:

[0167] Table 5

[0168]

[0169] S1. Electric furnace smelting:

[0170] Batch the blast furnace hot metal (proportion 80%), sheared furnace charge and ladle remaining steel according to the component content of the hot work die steel, add CaO, CaF2, aluminum blocks, and dolomite, and melt and smelt in an electric furnace; after slag skimming, add CaO, slag cleaning agent, and aluminum blocks and then tap the steel, with the tapping temperature of 1630°C;

[0171] Among them, the component content of the hot work die steel is, by mass percentage, C 0.37% - 0.42%, Mn 0.30% - 0.50%, Si 0.80% - 1.00%, S ≤ 0.002%, P ≤ 0.010%, Cr 4.90% - 5.10%, Mo 1.30% - 1.50%, Ni 0.20% - 0.30%, V 0.80% - 1.10%, and the rest is Fe, and the residual gas content is, H ≤ 1.5 ppm, O ≤ 13 ppm, N ≤ 90 ppm; the residual harmful element Ca ≤ 0.0005%, and Ti, Sn, Pb are all ≤ 0.002%.

[0172] S2. Ladle furnace refining:

[0173] Seat the ladle furnace for heating, and add slag materials CaO, CaF2, C - Si powder to reduce and adjust the slag system;

[0174] S3. Vacuum circulation refining furnace refining:

[0175] Integrated circulating vacuum tank, combined with an advanced vacuum pump, with a vacuum degree ≤ 15 Pa; under vacuum conditions, the circulation flow rate ≥ 100 t / min, the treatment time ≥ 35 minutes, ensure that the residual gas H ≤ 1.5 ppm, N ≤ 70 ppm. After vacuum degassing, take samples for analysis. After the composition is qualified, blow argon until lifting the ladle, and the soft blowing argon time is 18 - 39 min, and the lifting ladle temperature is 1550 - 1568°C;

[0176] S4. Continuous casting of rectangular billets:

[0177] The superheat degree for the first furnace is 20 - 35°C, and for the continuous casting furnace is 18 - 30°C; the continuous casting speed is 0.16 m / min, and three-stage electromagnetic stirring is adopted.

[0178] S5. Annealing of continuous-cast rectangular billets:

[0179] Anneal the continuous-cast rectangular billets after continuous casting in step S4, with an annealing temperature of 880°C, a holding time of 1.3 min / mm, and furnace cooling to below 350°C before discharging;

[0180] S6. Electroslag remelting:

[0181] For the electrode blank obtained in step S5, first perform surface shot peening treatment using a shot peening machine to remove the surface scale, and then smelt it using a ternary slag system of calcium fluoride, aluminum oxide, and magnesium oxide. Ultra-low melting rate control: The starting melting rate value at the steady state stage of electroslag smelting is 7.5 - 8.5 kg / min, and the ending melting rate value is 5.5 - 6.5 kg / min to obtain an electroslag ingot. Then, after powering off the furnace and cooling for 80 - 100 min, send it to the forging process;

[0182] S7. Primary heating and forging:

[0183] Heat the electroslag ingot obtained in step S6 using a chamber furnace with an ultra-high temperature (the maximum heating temperature is 1300 °C) to ensure the effective implementation of the ultra-high temperature diffusion process: The heating temperature is 1290 °C, and keep it warm for 50 h for diffusion homogenization. Then, perform upsetting and drawing forging to open the blank, and perform multi-directional drawing in the X, Y, and Z directions to obtain an intermediate blank. Finally, the main deformation rate in a single pass in one heat is ≥ 50%.

[0184] S8. Primary post-forging heat treatment: Remaining heat quenching + high tempering

[0185] Directly perform forced cooling by immersing the intermediate blank obtained in step S7 into water once. The return temperature of the large surface after final cooling is 275 °C. Then, heat it in the furnace to 710 °C for high temperature tempering. After the tempering is completed, cool it in the furnace to 350 °C and then take it out of the furnace and air cool it.

[0186] S9. Secondary heating and forging

[0187] Heat the intermediate blank obtained in step S8 using a chamber furnace: The heating temperature is 1250 °C, and keep it warm for 15 h for temperature equalization. Then, perform upsetting and drawing in the X, Y, and Z directions to forge it into a finished product in one heat. Finally, the main deformation rate in a single pass in one heat is ≥ 50%.

[0188] S10. Remaining heat quenching + spheroidizing treatment

[0189] Directly immerse the finished product obtained in step S9 into water for forced cooling. The return temperature of the large surface after final cooling is 87 °C. Then, put it into a heat treatment furnace and heat it to 860 °C, keep it warm for 15 h. After the heat preservation is completed, cool it in the furnace to 730 °C and keep it warm for 30 h for spheroidizing annealing. After the spheroidizing treatment is completed and the furnace temperature reaches 350 °C, take it out of the furnace and air cool it to room temperature.

[0190] To verify the mechanical properties of the plastic mold steel provided by the preparation method of the present invention, the inventors respectively took samples of the mold steel obtained in Examples 1 to 5 for mechanical property tests (the test results are shown in Tables 6 and 7) and metallographic structure and SEM analysis (as Figures 1 to 10 )

[0191] Table 6

[0192]

[0193] Table 7

[0194]

[0195] It can be seen that 1, as Figures 1 to 10 shown, the microstructure of the spheroidized annealing state of the die material is uniform, and the fine spherical secondary carbides are evenly distributed on the ferrite matrix. Graded according to the NADCA#207~2011 standard, the grade ≤ AS5. This spheroidized structure is conducive to full dissolution during the austenitization process, reducing the quantity and size of undissolved carbides. After dispersion precipitation during the tempering process, the purpose of improving the impact toughness is achieved;

[0196] 2, most alloying elements of the die material during the quenching process;

[0197] dissolve into the matrix, and disperse and precipitate from the matrix during the tempering process, mainly carbides of Mo and Cr. It is these fine precipitates that play a dispersion strengthening role during use, improving the properties of the material. The single-notch transverse impact energy at the core of the die material ≥ 360 J, and the average notch-free transverse impact performance ≥ 380 J;

[0198] 3, from the microstructural photos taken in Examples 1~10, it can be concluded that there is no liquid segregation carbide.

[0199] In order to verify the die steel prepared by using the preparation method provided by the present invention, the die steels in Examples 1~5 were placed at different temperatures, and their thermal expansion coefficients and heat transfer rates were measured respectively. The results are shown in Table 7;

[0200] Table 7

[0201]

[0202] It can be seen that the die steel prepared by this preparation method has high heat resistance and high thermal stability.

Claims

1. A preparation method of a high-purity, high-toughness, high-isotropy hot working die steel, characterized in that, The main steps are as follows: S1. Electric furnace smelting: The component contents of hot working die steel are, by mass percentage, C 0.37% to 0.42%, Mn 0.30% to 0.50%, Si0.80% to 1.00%, S≤0.002%, P≤0.010%, Cr 4.90% to 5.10%, Mo 1.30% to 1.50%, Ni0.20% to 0.30%, V 0.80% to 1.10%, and the rest is Fe, and the residual gas content is H≤1.5ppm, O≤13ppm, N≤90ppm, the residual harmful element Ca≤0.0005%, Ti, Sn, Pb are all ≤0.002%; S2, ladle refining furnace refining: The ladle refining furnace is heated, and slag CaO, CaF2, C-Si powder are added to reduce and adjust the slag system; S3, vacuum refining furnace refining; S4, continuous casting rectangular billet: Superheat of the first furnace is 20~35℃, and that of the continuous casting furnace is 18~30℃; The continuous casting speed is 0.13-0.20 m / min, and three-stage electromagnetic stirring is adopted; S5. Annealing of continuous casting rectangular billet: Annealing the continuously cast rectangular billet after continuous casting in step S4; S6, electroslag remelting: The electrode blank obtained in step S5 is first subjected to surface shot blasting treatment using a shot blasting machine to remove surface iron oxide scale; The ternary slag system of calcium fluoride, aluminum oxide and magnesium oxide is used for smelting; S7, primary heating and forging: The electroslag ingot obtained in step S6 is heated in an ultra-high temperature chamber type heating furnace to perform ultra-high temperature diffusion; Then the blank is forged by upsetting and drawing, and then drawn in three directions, X, Y and Z, to an intermediate blank. The main deformation rate of the last single pass of the fire is ≥50%. S8, heat treatment after primary forging; S9, secondary heating and forging: The intermediate billet obtained in step S8 is heated in a chamber heating furnace to achieve uniform temperature; Then, the product is upset, stretched, and forged in three directions, X, Y, and Z, and the main deformation rate of the last single pass of the forging process is ≥50%. S10, residual heat quenching and spheroidizing treatment: The finished product obtained in step S9 is directly put into water for forced cooling, and the final cooling large surface return temperature is ≤100°C; Then put it into the heat treatment furnace and heat it to 850-880℃, keep it warm for 15-20h, and then cool it to 720-750℃ and keep it warm for 30-40h for spheroidizing annealing. After the spheroidization treatment is completed, the furnace temperature reaches ≤350℃ and then it is air-cooled to room temperature.

2. The preparation method of a high-purity, high-toughness, high-isotropy hot work die steel according to claim 1, characterized in that, In step S1, blast furnace iron, shearing charge and bulk steel are proportioned according to the component content of hot working die steel, wherein the proportion of blast furnace iron is ≥70%; Add CaO, CaF2, aluminum block and dolomite, and melt and smelt in an electric furnace; After slagging, CaO, cleaning agent and aluminum block are added before tapping, and the tapping temperature is ≥1620℃.

3. The preparation method of a high-purity, high-toughness, high-isotropy hot work die steel according to claim 1, characterized in that In step S3, a vacuum circulating refining furnace is used for refining, and the molten steel treated in step S2 is poured into an integrated circulating vacuum tank, and a vacuum pump is used to achieve a vacuum degree of ≤15Pa; Under vacuum conditions, the circulation flow rate is ≥100t / min, the processing time is ≥35 minutes, and the residual gas H is ≤1.5ppm, N ≤70ppm; After vacuum degassing, samples are taken for analysis. After the composition is qualified, argon is blown into the ladle. The soft argon blowing time is 18 - 39 min, and the ladle temperature is 1550 - 1568 °C.

4. The preparation method of a high-purity, high-toughness, high-isotropy hot work die steel according to claim 1, characterized in that, In step S5, the annealing temperature is 860 - 880 °C, the holding time is 1 - 1.5 min / mm, and it is furnace-cooled to below 350 °C before discharging from the furnace.

5. The preparation method of a high-purity, high-toughness, high-isotropy hot work die steel according to claim 1, characterized in that, In step S6, the starting melting rate value in the steady state stage of electroslag remelting is 7.5 - 8.5 kg / min, and the ending melting rate value is 5.5 - 6.5 kg / min to obtain an electroslag ingot. Then, after the electric furnace is powered off and furnace-cooled for 80 - 100 min, it is sent to the forging process.

6. The preparation method of a high-purity, high-toughness, high-isotropy hot work die steel according to claim 1, characterized in that, In step S7, the specific parameters of the first heating are that the heating temperature is ≥1280 °C, and it is held for 40 - 50 h for diffusion homogenization.

7. The preparation method of a high-purity, high-toughness, high-isotropy hot work die steel according to claim 1, characterized in that, In step S8, the intermediate billet obtained in step S7 is directly subjected to forced cooling by being put into water once, and the temperature of the large surface after final cooling and temperature return is ≤350 °C; Then it is heated in the furnace to 700 - 730 °C for high-temperature tempering. After the tempering is completed, it is furnace-cooled to ≤350 °C and then discharged from the furnace for air cooling.

8. The preparation method of a high-purity, high-toughness, high-isotropy hot work die steel according to claim 1, characterized in that, In step S9, the specific parameters of the second heating are that the heating temperature is ≥1240 °C, and it is held for 10 - 15 h.

9. A high-purity, high-toughness, high-isotropy hot-work die steel prepared by the preparation method according to any one of claims 1 to 8, characterized in that, The chemical component content of the hot work die steel, by mass percentage, is C 0.37% - 0.42%, Mn 0.30% - 0.50%, Si 0.80% - 1.00%, S ≤ 0.002%, P ≤ 0.010%, Cr 4.90% - 5.10%, Mo 1.30% - 1.50%, Ni 0.20% - 0.30%, V 0.80% - 1.10%, and the rest is Fe. And the residual gas content is H ≤ 1.5 ppm, O ≤ 13 ppm, N ≤ 90 ppm, the residual harmful element Ca ≤ 0.0005%, and Ti, Sn, Pb are all ≤ 0.002%.

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