High-strength, high-wear-resistance and high-toughness hot work die steel for extrusion die and preparation method thereof

Abstract

The invention relates to a preparation process of high-strength, high-wear-resistance and high-toughness hot work die steel for an extrusion die, which is characterized in that on the basis of common hot work die steel H13, component design is carried out by adopting a component design concept of high C, low Si, high Mo and low V, and special smelting, forging and heat treatment processes are added. The prepared product has excellent purity, structure uniformity and mechanical property, and a mold made of the material can better meet the requirements of modern industrial production for high-end molds. The process route comprises the steps of electric furnace smelting, ladle refining furnace refining, circulating vacuum refining furnace refining, electrode blank continuous casting, electrode blank annealing, electroslag remelting, forging, pretreatment after forging and solid solution and spheroidizing treatment. The invention further relates to the high-strength, high-wear-resistance and high-toughness hot work die steel for the extrusion die.

Description

Technical Field

[0001] The invention relates to the technical field of die steel preparation, in particular to a hot working die steel for an extrusion die with high strength, high wear resistance and high toughness and a preparation process thereof. Background Art

[0002] With the development of modern industry, molds are used more and more widely in products such as automobiles, electronics, instruments and meters, home appliances, aerospace, building materials, motors and communication equipment, among which the construction industry accounts for 35%, the automobile industry accounts for 25%, and the aerospace and other high-end manufacturing industries account for 20%. In 2022, the global aluminum alloy extrusion mold market size is about 4.5 billion US dollars, and it is expected to reach 6 billion US dollars by 2027. Among them, China is one of the world's largest producers and consumers of aluminum alloy extrusion molds. In 2022, the Chinese market size reached 1.8 billion US dollars, accounting for about 40% of the global market.

[0003] At present, H13 steel is usually used in China to make extrusion dies for aluminum alloy profiles, but the average service life of extrusion dies lags far behind the international advanced level. Therefore, improving the service life of dies is one of the key measures to reduce production costs and improve economic benefits. Aluminum alloy extrusion dies have high operating temperatures and withstand large impact forces, and are easily invalidated and scrapped due to wear or cracking. Summary of the invention

[0004] The purpose of the present invention is to provide a preparation process of hot working die steel for extrusion dies with high strength, high wear resistance and high toughness. The hot working die steel H13 is commonly used as the basis, and the composition design concept of high C, low Si, high Mo and low V is adopted for composition design. In addition, special smelting, forging and heat treatment processes are added to make the prepared product have excellent purity, organizational uniformity and mechanical properties. The molds made of this material can better meet the requirements of modern industrial production for high-end molds.

[0005] In order to achieve the purpose of the above invention, a preparation process of a hot working die steel for an extrusion die with high strength, high wear resistance and high toughness is provided, and the main steps are as follows:

[0006] S1. Electric furnace smelting:

[0007] According to the component content of hot working die steel, blast furnace molten iron, shearing charge and bulk surplus steel are prepared, CaO, Ca F2, aluminum block and dolomite are added, and the steel is melted and smelted in an electric furnace; after slagging, CaO, cleaning agent and aluminum block are added and the steel is tapped, and the tapping temperature is ≥1620℃;

[0008] Among them, the component contents of hot working die steel are, by mass percentage, C 0.38% to 0.43%, Mn 0.40% to 0.60%, Si 0.10% to 0.30%, S≤0.001%, P≤0.010%, Cr 4.90% to 5.20%, Mo 1.80% to 2.20%, V 0.40% to 0.60%, and the rest is Fe, and the residual gas content is, H≤1.5ppm, O≤13ppm, N≤90ppm; the residual harmful elements Cu≤0.05%, Ti, Sn, Pb are all ≤0.002%;

[0009] The carbon content is increased on the basis of H13: the hardness adaptability range and wear resistance of the mold are improved; the Si content is reduced, the dendrite segregation of the electrode blank and the electroslag ingot is reduced, the amount of liquid precipitation carbide produced is reduced, and the composition uniformity of the electroslag ingot is improved; the Mo content is increased, which plays a role in solid solution strengthening and inhibits the precipitation of Cr carbides (this carbide is easy to form network carbides and coarsening, resulting in a decrease in material properties); the V content is reduced, the amount of liquid precipitation carbides produced, and the dendrite segregation of the electrode blank and the electroslag ingot are reduced. Improve the toughness of the material.

[0010] S2, ladle refining furnace refining:

[0011] The ladle refining furnace is heated, and slag CaO, CaF2, C-Si powder are added to reduce and adjust the slag system;

[0012] S3, refining in circulating vacuum refining furnace:

[0013] The integrated circulating vacuum tank is equipped with a vacuum pump, and the vacuum degree is ≤15Pa. Under vacuum conditions, the circulation flow rate is ≥100t / min, and the processing time is ≥35 minutes. After ensuring that the residual gas H is ≤1.5ppm and N is ≤80ppm, take samples for analysis, and blow argon into the hanging bag after the components are qualified.

[0014] S4, continuous casting electrode billet:

[0015] The superheat of the first furnace is 20-35℃, and the continuous casting furnace is 18-30℃; the continuous casting speed is 0.13-0.20m / min, and three-stage electromagnetic stirring is adopted;

[0016] S5. Electrode blank annealing:

[0017] Annealing the electrode blank after continuous casting in step S4;

[0018] S6, electroslag remelting:

[0019] The electrode blank obtained in step S5 is surface-polished and smelted using a binary slag system of calcium fluoride and alumina to obtain an electroslag ingot;

[0020] S7, Forging:

[0021] The electroslag ingot obtained in step S6 is heated to 1280-1300° C., kept at this temperature for 50-70 hours for diffusion homogenization, and then furnace cooled to 1220-1240° C. for multi-directional upsetting, drawing, and rounding in three directions of X, Y and Z to the finished product size;

[0022] According to the empirical formula for high temperature homogenization of hot working die steel (t = 0.467λ2 / D, where λ is half the distance between dendrite axes; D is the diffusion coefficient at a certain temperature; t is the diffusion time), high diffusion temperature and long-term insulation are the most effective methods to eliminate dendrite segregation in hot working die steel electroslag ingots.

[0023] S8, pretreatment after forging:

[0024] The forging blank obtained in step S7 is subjected to post-forging extreme cooling control to inhibit the precipitation of grain boundary carbides;

[0025] S9, solution + spheroidizing treatment:

[0026] The workpiece obtained in step S8 is placed in a heating furnace and heated to 980-1020°C. After heat preservation, it is cooled by water cooling + air cooling + quenching liquid cooling, and the temperature of the large surface of the billet is ≤250°C. After cooling, the workpiece is placed in an annealing furnace, heated to 830-860°C, kept warm for 15-30h, furnace cooled to 730-750°C, kept warm for 25-50h for spheroidizing annealing, and then furnace cooled to below 350°C, taken out of the furnace and air cooled to room temperature.

[0027] Specifically, in step S1, the proportion of molten iron in the blast furnace is ≥ 60%.

[0028] Specifically, in step S3, the soft blowing time of argon gas is 18 to 39 minutes, and the bag temperature is 1550 to 1568°C.

[0029] Specifically, in step S5, the electrode blank after continuous casting in step S4 is annealed at an annealing temperature of 850°C and a holding time of 1.5 min / mm, and the blank is cooled to 340°C before being taken out of the furnace.

[0030] Specifically, in step S6, the starting melting rate value of the steady-state stage of electroslag smelting is 9-10 kg / min, and the terminal melting rate value is 6.5-7.5 kg / min, and an electroslag ingot is obtained, and then the furnace is shut down for cooling for 100-150 minutes before being sent to the forging process.

[0031] Preferably, in step S8, the forging blank obtained in step S7 is subjected to post-forging extreme cooling control: water cooling + quenching liquid double liquid cooling to the blank large surface temperature ≤ 250°C, then loaded into a heat treatment furnace, heated to 960-990°C, kept warm for 15-20h, furnace cooled to 730-750°C, kept warm for 25-40h for complete annealing + isothermal annealing treatment.

[0032] Furthermore, in step S8, water cooling is performed at a temperature above 600°C and quenching liquid cooling is performed at a temperature between 600°C and 250°C.

[0033] Rapid cooling is required from the solution temperature to 600°C to avoid the formation of network carbides and pearlite; a moderate cooling rate is required from 600°C to the martensitic phase transformation temperature: the undercooling before the phase transformation is reduced, martensite and lower bainite are obtained, and the content of residual austenite is reduced, preparing for the subsequent heat treatment to adjust the grain size and structure.

[0034] The second object of the present invention is to provide a high-strength, high-wear-resistant and high-toughness hot-working die steel for extrusion dies, wherein the components are C 0.38% to 0.43%, Mn 0.40% to 0.60%, Si 0.10% to 0.30%, S≤0.001%, P≤0.010%, Cr 4.90% to 5.20%, Mo 1.80% to 2.20%, V 0.40% to 0.60%, and the remainder is Fe, and the residual gas content is H≤1.5ppm, O≤13ppm, N≤90ppm; the residual harmful elements Cu≤0.05%, and Ti, Sn, and Pb are all ≤0.002%.

[0035] The preparation process of a high-strength, high-wear-resistant and high-toughness hot-working die steel for an extrusion die of the present invention has the following advantages compared with the prior art:

[0036] (1) The increase in carbon content increases the total content of carbides in the steel. The total amount of carbides precipitated during the mold tempering process increases, which can increase the wear resistance of the mold steel;

[0037] (2) The reduction of silicon content can reduce the segregation of carbon and alloy elements in the steel during the solidification process from molten steel to ingot, and improve the uniformity of the ingot composition;

[0038] (3) The addition of molybdenum plays a role in solid solution strengthening and inhibits the precipitation of Cr-based carbides (these carbides tend to form network carbides and coarsen, resulting in a decrease in material properties).

[0039] (4) The reduction of V reduces the production of liquid carbides, reduces the dendrite segregation of electrode blanks and electroslag ingots, and improves the toughness of the material.

[0040] (5) Long-term high-temperature homogenization treatment reduces dendrite segregation. Under the same subsequent heat treatment process conditions, the phase change uniformity of the material is increased, which improves the uniformity of the material's isotropic structure and performance.

[0041] (6) After heat treatment, the band segregation of the mold material is greatly reduced, and the transverse V-shaped impact energy is greatly improved compared with H13, which greatly reduces the risk of cracking during the use of the mold. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 This is a photo of the banded structure of the hot working die steel obtained in Example 1;

[0043] Figure 2 This is a photo of the ball destructured structure of the hot working die steel obtained in Example 1;

[0044] Figure 3 This is a photo of the banded structure of the hot working die steel obtained in Example 2;

[0045] Figure 4 This is a photo of the ball destructured structure of the hot working die steel obtained in Example 2;

[0046] Figure 5 This is a photo of the banded structure of the hot working die steel obtained in Example 3;

[0047] Figure 6 This is a photo of the ball destructured structure of the hot working die steel obtained in Example 3;

[0048] Figure 7 This is a photo of the banded structure of the hot working die steel obtained in Example 4;

[0049] Figure 8 This is a photo of the ball destructured structure of the hot working die steel obtained in Example 4;

[0050] Fig. 9 This is a photo of the banded structure of the hot working die steel obtained in Example 5;

[0051] Fig.10 This is a photo of the ball destructured structure of the hot working die steel obtained in Example 5. DETAILED DESCRIPTION

[0052] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments.

[0053] Example 1

[0054] A high-strength, high-wear-resistant, high-toughness hot-working die steel for extrusion dies, which is basically composed of the elements shown in Table 1 according to mass fraction:

[0055] Table 1

[0056]

[0057] The preparation method thereof mainly comprises the following steps:

[0058] S1. Electric furnace smelting:

[0059] According to the component content of hot working die steel, blast furnace molten iron (ratio ≥ 60%), shear charge and bulk surplus steel are prepared, CaO, CaF2, aluminum block and dolomite are added, and the steel is melted and smelted in an electric furnace; the molten steel temperature is 1640°C for oxidation and slagging, and alloy material, lime and fluorite are added after slagging to adjust the chemical composition and dephosphorize. The tapping temperature is 1630°C, and aluminum wire is added during the tapping process. The aluminum wire is added at 1.0 kg / t for deoxidation.

[0060] S2, ladle refining furnace refining:

[0061] After smelting in the electric furnace, the molten steel is transferred into the ladle, hoisted to the refining furnace seat, and slag materials CaO, CaF2, and C-Si powder are added to reduce and make white slag. According to the actual composition, alloy materials are added to complete the composition fine-tuning, desulfurization, and deoxidation operations; after the operation is completed, the white slag is removed, and then reheated and new slag is added for secondary white slag making to further remove inclusions in the steel; in the process of secondary white slag making, aluminum wire and calcium wire are added for composite deoxidation; the amount of aluminum wire and calcium wire is added according to 1.0kg / t.

[0062] S3, refining in circulating vacuum refining furnace:

[0063] The integrated circulating vacuum tank is equipped with a vacuum pump and has a vacuum degree of 12Pa. Under vacuum conditions, the circulation flow rate is 120t / min and the processing time is 37 minutes. It is ensured that the residual gas H≤1.0ppm and N≤80ppm. After the vacuum degassing is completed, sampling and analysis are performed. After the composition is qualified, argon is blown into the hanging bag. The soft blowing time of argon is 25min and the hanging bag temperature is 1560℃.

[0064] S4, continuous casting electrode billet:

[0065] The superheat of the first furnace is 30℃, and that of the continuous casting furnace is 25℃; the continuous casting speed is 0.16m / min, and three-stage electromagnetic stirring is adopted.

[0066] S5. Electrode blank annealing:

[0067] The electrode blank after continuous casting in step S4 is annealed at a temperature of 850° C. and a holding time of 1.5 min / mm. The blank is cooled to 340° C. and then taken out of the furnace.

[0068] S6, electroslag remelting:

[0069] The electrode blank obtained in step S5 is surface polished and smelted using a binary slag system of calcium fluoride and alumina. The starting melting rate value in the steady-state stage of electroslag smelting is 9.5 kg / min and the end melting rate value is 7.0 kg / min. An electroslag ingot is obtained, and then the furnace is shut down for cooling for 140 minutes before being sent to a forging process.

[0070] S7, Forging:

[0071] The electroslag ingot obtained in step S6 is heated to 1290° C., kept at this temperature for 60 hours for diffusion homogenization, then furnace cooled to 1220° C., and then subjected to multi-directional upsetting, drawing, and rounding in three directions of X, Y, and Z to a finished product size;

[0072] S8, post-forging pretreatment

[0073] The forging blank obtained in step S7 is subjected to extreme cooling control after forging to inhibit the precipitation of carbides at the grain boundaries: water cooling + quenching liquid double liquid cooling to the blank large surface temperature of 240°C; then loaded into a heat treatment furnace, heated to 970°C, kept warm for 20 hours, furnace cooled to 740°C, kept warm for 35 hours for complete annealing + isothermal annealing treatment.

[0074] S9, solution + spheroidizing treatment:

[0075] The workpiece obtained in step S8 is placed in a heating furnace and heated to 1000°C. After keeping warm, it is cooled by water cooling + air cooling + quenching liquid cooling, and the temperature of the large surface of the billet is 220°C. After cooling, the workpiece is placed in an annealing furnace, heated to 860°C, kept warm for 25 hours, furnace cooled to 740°C, kept warm for 40 hours for spheroidizing annealing, and then furnace cooled to 300°C and air cooled to room temperature.

[0076] Example 2

[0077] A high-strength, high-wear-resistant, high-toughness hot-working die steel for extrusion dies, which is basically composed of the elements shown in Table 1 according to mass fraction:

[0078] Table 2

[0079]

[0080] The preparation method thereof mainly comprises the following steps:

[0081] S1. Electric furnace smelting:

[0082] According to the component content of hot working die steel, blast furnace molten iron (ratio ≥ 60%), shear charge and bulk surplus steel are prepared, CaO, CaF2, aluminum block and dolomite are added, and the steel is melted and smelted in an electric furnace; the molten steel temperature is 1640°C for oxidation and slagging, and alloy material, lime and fluorite are added after slagging to adjust the chemical composition and dephosphorize. The tapping temperature is 1630°C, and aluminum wire is added during the tapping process. The aluminum wire is added at 1.0 kg / t for deoxidation.

[0083] S2, ladle refining furnace refining:

[0084] After smelting in the electric furnace, the molten steel is transferred into the ladle, hoisted to the refining furnace seat, and slag materials CaO, CaF2, and C-Si powder are added to reduce and make white slag. According to the actual composition, alloy materials are added to complete the composition fine-tuning, desulfurization, and deoxidation operations; after the operation is completed, the white slag is removed, and then reheated and new slag is added for secondary white slag making to further remove inclusions in the steel; in the process of secondary white slag making, aluminum wire and calcium wire are added for composite deoxidation; the amount of aluminum wire and calcium wire is added according to 1.0kg / t.

[0085] S3, refining in circulating vacuum refining furnace:

[0086] The integrated circulating vacuum tank is equipped with a vacuum pump and has a vacuum degree of 12Pa. Under vacuum conditions, the circulation flow rate is 120t / min and the processing time is 37 minutes. After the vacuum degassing is completed, the residual gas H is ≤1.0ppm and N is ≤80ppm. Samples are taken for analysis. After the components are qualified, argon is blown into the hanging bag. The soft blowing time of argon is 25min and the hanging bag temperature is 1560℃.

[0087] S4, continuous casting electrode billet:

[0088] The superheat of the first furnace is 30℃, and that of the continuous casting furnace is 25℃; the continuous casting speed is 0.16m / min, and three-stage electromagnetic stirring is adopted.

[0089] S5. Electrode blank annealing:

[0090] The electrode blank after continuous casting in step S4 is annealed at a temperature of 850°C and a holding time of 1.5 min / mm, and the furnace is cooled to 340°C before being taken out of the furnace;

[0091] S6, electroslag remelting:

[0092] The electrode blank obtained in step S5 is surface polished and smelted using a binary slag system of calcium fluoride and alumina. The starting melting rate value in the steady-state stage of electroslag smelting is 9.5 kg / min and the end melting rate value is 7.0 kg / min. An electroslag ingot is obtained, and then the furnace is shut down for cooling for 140 minutes before being sent to a forging process.

[0093] S7, Forging:

[0094] The electroslag ingot obtained in step S6 is heated to 1290° C., kept at this temperature for 60 hours for diffusion homogenization, then furnace cooled to 1220° C., and then subjected to multi-directional upsetting, drawing, and rounding in three directions of X, Y, and Z to a finished product size;

[0095] S8, post-forging pretreatment

[0096] The forging blank obtained in step S7 is subjected to extreme cooling control after forging to inhibit the precipitation of carbides at the grain boundaries: water cooling + quenching liquid double liquid cooling to the blank large surface temperature of 200°C; then loaded into a heat treatment furnace, heated to 970°C, kept warm for 20 hours, furnace cooled to 740°C, kept warm for 35 hours for complete annealing + isothermal annealing treatment.

[0097] S9, solution + spheroidizing treatment:

[0098] The workpiece obtained in step S8 is placed in a heating furnace and heated to 1000°C. After keeping warm, it is cooled by water cooling + air cooling + quenching liquid cooling, and the temperature of the large surface of the billet is 210°C. After cooling, the workpiece is placed in an annealing furnace, heated to 860°C, kept warm for 25 hours, furnace cooled to 740°C, kept warm for 40 hours for spheroidizing annealing, and then furnace cooled to 300°C and air cooled to room temperature.

[0099] Example 3

[0100] A high-strength, high-wear-resistant, high-toughness hot-working die steel for extrusion dies, which is basically composed of the elements shown in Table 3 according to mass fraction:

[0101] Table 3

[0102]

[0103] The preparation method thereof mainly comprises the following steps:

[0104] S1. Electric furnace smelting:

[0105] According to the component content of hot working die steel, blast furnace molten iron (ratio ≥ 60%), shear charge and bulk surplus steel are prepared, CaO, CaF2, aluminum block and dolomite are added, and the steel is melted and smelted in an electric furnace; the molten steel temperature is 1640°C for oxidation and slagging, and alloy material, lime and fluorite are added after slagging to adjust the chemical composition and dephosphorize. The tapping temperature is 1630°C, and aluminum wire is added during the tapping process. The aluminum wire is added at 1.0 kg / t for deoxidation.

[0106] S2, ladle refining furnace refining:

[0107] After smelting in the electric furnace, the molten steel is transferred into the ladle, hoisted to the refining furnace seat, and slag materials CaO, CaF2, and C-Si powder are added to reduce and make white slag. According to the actual composition, alloy materials are added to complete the composition fine-tuning, desulfurization, and deoxidation operations; after the operation is completed, the white slag is removed, and then reheated and new slag is added for secondary white slag making to further remove inclusions in the steel; in the process of secondary white slag making, aluminum wire and calcium wire are added for composite deoxidation; the amount of aluminum wire and calcium wire is added according to 1.0kg / t.

[0108] S3, refining in circulating vacuum refining furnace:

[0109] The integrated circulating vacuum tank is equipped with a vacuum pump and has a vacuum degree of 12Pa. Under vacuum conditions, the circulation flow rate is 120t / min and the processing time is 37 minutes. After the vacuum degassing is completed, the residual gas H is ≤1.0ppm and N is ≤80ppm. Samples are taken for analysis. After the components are qualified, argon is blown into the hanging bag. The soft blowing time of argon is 25min and the hanging bag temperature is 1560℃.

[0110] S4, continuous casting electrode billet:

[0111] The superheat of the first furnace is 30℃, and that of the continuous casting furnace is 25℃; the continuous casting speed is 0.16m / min, and three-stage electromagnetic stirring is adopted.

[0112] S5. Electrode blank annealing:

[0113] The electrode blank after continuous casting in step S4 is annealed at a temperature of 850°C and a holding time of 1.5 min / mm, and the furnace is cooled to 340°C before being taken out of the furnace;

[0114] S6, electroslag remelting:

[0115] The electrode blank obtained in step S5 is surface polished and smelted using a binary slag system of calcium fluoride and alumina. The starting melting rate value in the steady-state stage of electroslag smelting is 9.5 kg / min and the end melting rate value is 7.0 kg / min. An electroslag ingot is obtained, and then the furnace is shut down for cooling for 140 minutes before being sent to a forging process.

[0116] S7, Forging:

[0117] The electroslag ingot obtained in step S6 is heated to 1290° C., kept at this temperature for 60 hours for diffusion homogenization, then furnace cooled to 1220° C., and then subjected to multi-directional upsetting, drawing, and rounding in three directions of X, Y, and Z to a finished product size;

[0118] S8, post-forging pretreatment

[0119] The forging blank obtained in step S7 is subjected to extreme cooling control after forging to inhibit the precipitation of carbides at the grain boundaries: water cooling + quenching liquid double liquid cooling to the blank large surface temperature of 215°C; then loaded into a heat treatment furnace, heated to 970°C, kept warm for 20 hours, furnace cooled to 740°C, kept warm for 35 hours for complete annealing + isothermal annealing treatment.

[0120] S9, solution + spheroidizing treatment:

[0121] The workpiece obtained in step S8 is placed in a heating furnace and heated to 1000°C. After keeping warm, it is cooled by water cooling + air cooling + quenching liquid cooling, and the temperature of the large surface of the billet is 210°C. After cooling, the workpiece is placed in an annealing furnace, heated to 860°C, kept warm for 25 hours, furnace cooled to 740°C, kept warm for 40 hours for spheroidizing annealing, and then furnace cooled to 300°C and air cooled to room temperature.

[0122] Example 4

[0123] A high-strength, high-wear-resistant, high-toughness hot-working die steel for extrusion dies, which is basically composed of the elements shown in Table 4 according to mass fraction:

[0124] Table 4

[0125]

[0126] The preparation method thereof mainly comprises the following steps:

[0127] S1. Electric furnace smelting:

[0128] According to the component content of hot working die steel, blast furnace molten iron (ratio ≥ 60%), shear charge and bulk surplus steel are prepared, CaO, CaF2, aluminum block and dolomite are added, and the steel is melted and smelted in an electric furnace; the molten steel temperature is 1640°C for oxidation and slagging, and alloy material, lime and fluorite are added after slagging to adjust the chemical composition and dephosphorize. The tapping temperature is 1630°C, and aluminum wire is added during the tapping process. The aluminum wire is added at 1.0 kg / t for deoxidation.

[0129] S2, ladle refining furnace refining:

[0130] After smelting in the electric furnace, the molten steel is transferred into the ladle, hoisted to the refining furnace seat, and slag materials CaO, CaF2, and C-Si powder are added to reduce and make white slag. According to the actual composition, alloy materials are added to complete the composition fine-tuning, desulfurization, and deoxidation operations; after the operation is completed, the white slag is removed, and then reheated and new slag is added for secondary white slag making to further remove inclusions in the steel; in the process of secondary white slag making, aluminum wire and calcium wire are added for composite deoxidation; the amount of aluminum wire and calcium wire is added according to 1.0kg / t.

[0131] S3, refining in circulating vacuum refining furnace:

[0132] The integrated circulating vacuum tank is equipped with a vacuum pump and has a vacuum degree of 12Pa. Under vacuum conditions, the circulation flow rate is 120t / min and the processing time is 37 minutes. After the vacuum degassing is completed, the residual gas H is ≤1.0ppm and N is ≤80ppm. Samples are taken for analysis. After the components are qualified, argon is blown into the hanging bag. The soft blowing time of argon is 25min and the hanging bag temperature is 1560℃.

[0133] S4, continuous casting electrode billet:

[0134] The superheat of the first furnace is 30℃, and that of the continuous casting furnace is 25℃; the continuous casting speed is 0.16m / min, and three-stage electromagnetic stirring is adopted.

[0135] S5. Electrode blank annealing:

[0136] The electrode blank after continuous casting in step S4 is annealed at a temperature of 850°C and a holding time of 1.5 min / mm, and the furnace is cooled to 340°C before being taken out of the furnace;

[0137] S6, electroslag remelting:

[0138] The electrode blank obtained in step S5 is surface polished and smelted using a binary slag system of calcium fluoride and alumina. The starting melting rate value in the steady-state stage of electroslag smelting is 9.5 kg / min and the end melting rate value is 7.0 kg / min. An electroslag ingot is obtained, and then the furnace is shut down for cooling for 140 minutes before being sent to a forging process.

[0139] S7, Forging:

[0140] The electroslag ingot obtained in step S6 is heated to 1290° C., kept at this temperature for 60 hours for diffusion homogenization, then furnace cooled to 1220° C., and then subjected to multi-directional upsetting, drawing, and rounding in three directions of X, Y, and Z to a finished product size;

[0141] S8, post-forging pretreatment

[0142] The forging blank obtained in step S7 is subjected to extreme cooling control after forging to inhibit the precipitation of carbides at the grain boundaries: water cooling + quenching liquid double liquid cooling to the blank large surface temperature of 230°C; then loaded into a heat treatment furnace, heated to 970°C, kept warm for 20 hours, furnace cooled to 740°C, kept warm for 35 hours for complete annealing + isothermal annealing treatment.

[0143] S9, solution + spheroidizing treatment:

[0144] The workpiece obtained in step S8 is placed in a heating furnace and heated to 1000°C. After keeping warm, it is cooled by water cooling + air cooling + quenching liquid cooling, and the temperature of the large surface of the billet is 210°C. After cooling, the workpiece is placed in an annealing furnace, heated to 860°C, kept warm for 25 hours, furnace cooled to 740°C, kept warm for 40 hours for spheroidizing annealing, and then furnace cooled to 300°C and air cooled to room temperature.

[0145] Example 5

[0146] A high-strength, high-wear-resistant, high-toughness hot-working die steel for extrusion dies, which is basically composed of the elements shown in Table 5 according to mass fraction:

[0147] Table 5

[0148]

[0149] The preparation method thereof mainly comprises the following steps:

[0150] S1. Electric furnace smelting:

[0151] According to the component content of hot working die steel, blast furnace molten iron (ratio ≥ 60%), shear charge and bulk surplus steel are prepared, CaO, CaF2, aluminum block and dolomite are added, and the steel is melted and smelted in an electric furnace; the molten steel temperature is 1640°C for oxidation and slagging, and alloy material, lime and fluorite are added after slagging to adjust the chemical composition and dephosphorize. The tapping temperature is 1630°C, and aluminum wire is added during the tapping process. The aluminum wire is added at 1.0 kg / t for deoxidation.

[0152] S2, ladle refining furnace refining:

[0153] After smelting in the electric furnace, the molten steel is transferred into the ladle, hoisted to the refining furnace seat, and slag materials CaO, CaF2, and C-Si powder are added to reduce and make white slag. According to the actual composition, alloy materials are added to complete the composition fine-tuning, desulfurization, and deoxidation operations; after the operation is completed, the white slag is removed, and then reheated and new slag is added for secondary white slag making to further remove inclusions in the steel; in the process of secondary white slag making, aluminum wire and calcium wire are added for composite deoxidation; the amount of aluminum wire and calcium wire is added according to 1.0kg / t.

[0154] S3, refining in circulating vacuum refining furnace:

[0155] The integrated circulating vacuum tank is equipped with a vacuum pump and has a vacuum degree of 12Pa. Under vacuum conditions, the circulation flow rate is 120t / min and the processing time is 37 minutes. After the vacuum degassing is completed, the residual gas H is ≤1.0ppm and N is ≤80ppm. Samples are taken for analysis. After the components are qualified, argon is blown into the hanging bag. The soft blowing time of argon is 25min and the hanging bag temperature is 1560℃.

[0156] S4, continuous casting electrode billet:

[0157] The superheat of the first furnace is 30℃, and that of the continuous casting furnace is 25℃; the continuous casting speed is 0.16m / min, and three-stage electromagnetic stirring is adopted.

[0158] S5. Electrode blank annealing:

[0159] The electrode blank after continuous casting in step S4 is annealed at a temperature of 850°C and a holding time of 1.5 min / mm, and the furnace is cooled to 340°C before being taken out of the furnace;

[0160] S6, electroslag remelting:

[0161] The electrode blank obtained in step S5 is surface polished and smelted using a binary slag system of calcium fluoride and alumina. The starting melting rate value in the steady-state stage of electroslag smelting is 9.5 kg / min and the end melting rate value is 7.0 kg / min. An electroslag ingot is obtained, and then the furnace is shut down for cooling for 140 minutes before being sent to a forging process.

[0162] S7, Forging:

[0163] The electroslag ingot obtained in step S6 is heated to 1290° C., kept at this temperature for 60 hours for diffusion homogenization, then furnace cooled to 1220° C., and then subjected to multi-directional upsetting, drawing, and rounding in three directions of X, Y, and Z to a finished product size;

[0164] S8, post-forging pretreatment

[0165] The forging blank obtained in step S7 is subjected to extreme cooling control after forging to inhibit the precipitation of carbides at the grain boundaries: water cooling + quenching liquid double liquid cooling to the blank large surface temperature of 220°C; then loaded into a heat treatment furnace, heated to 970°C, kept warm for 20 hours, furnace cooled to 740°C, kept warm for 35 hours for complete annealing + isothermal annealing treatment.

[0166] S9, solution + spheroidizing treatment:

[0167] The workpiece obtained in step S8 is placed in a heating furnace and heated to 1000°C. After keeping warm, it is cooled by water cooling + air cooling + quenching liquid cooling, and the temperature of the large surface of the billet is 200°C. After cooling, the workpiece is placed in an annealing furnace, heated to 860°C, kept warm for 25 hours, furnace cooled to 740°C, kept warm for 40 hours for spheroidizing annealing, and then furnace cooled to 300°C and air cooled to room temperature.

[0168] In order to verify the comprehensive performance of the hot working die steel provided by the preparation method of the present invention, the inventors took samples of the hot working die steel billets obtained in Examples 1 to 5 to test inclusions, banded structure, spherical degenerate structure, Charpy V-notch impact toughness, and austenite grain size. The test data are shown in Tables 6 and 7.

[0169] Table 6

[0170] Case Number A thin A thick B thin B thick C Thin C thick D Thin D thick Ds Example 1 0 0 0.5 0 0 0 0.5 0.5 0 Example 2 0 0 0.5 0.5 0 0 1 0.5 0 Example 3 0 0 0.5 0 0 0 1 0.5 0 Example 4 0 0 0.5 0 0 0 1 0.5 0 Example 5 0 0 0.5 0 0 0 1 0.5 0

[0171] Table 7

[0172]

[0173] It can be seen that 1, as Figure 1-5 As shown in the figure, the mold material has a uniform microstructure in the spheroidized annealed state, and fine spherical secondary carbides are evenly distributed on the ferrite matrix. According to the NADCA#207-2022 standard, it is rated at AS2-AS5. At the same time, the implementation of the high-temperature homogenization process greatly reduces the band segregation of the mold material, and according to the NADCA#207-2022 standard, it is rated at SB1-SB2.

[0174] The increase in the carbon content of the mold material increases the content of tempered carbides per unit area of ​​the mold steel, which can greatly improve the strength and wear resistance of the mold material.

[0175] The composition design of high C, low Si, high Mo, and low V, while matching the long-term ultra-high temperature homogenization process and the implementation of reasonable ultra-fine process, improves the composition uniformity of the mold material. During the mold quenching and tempering process, the phase change uniformity of each region is improved. On the basis of high strength and wear resistance, the transverse Charpy V-notch impact performance of the mold material is improved. The average transverse Charpy V-notch impact performance of the core of the mold material is ≥25J.

Claims

1. A process for preparing hot working die steel for extrusion die with high strength, high wear resistance and high toughness, characterized in that: The main steps are as follows: S1. Electric furnace smelting: According to the component content of hot working die steel, blast furnace molten iron, shearing charge and bulk surplus steel are prepared, CaO, CaF2, aluminum block and dolomite are added, and the steel is melted and smelted in an electric furnace; after slagging, CaO, cleaning agent and aluminum block are added before tapping, and the tapping temperature is ≥1620℃; Among them, the component contents of hot working die steel are, by mass percentage, C 0.38% to 0.43%, Mn 0.40% to 0.60%, Si 0.10% to 0.30%, S≤0.001%, P≤0.010%, Cr 4.90% to 5.20%, Mo 1.80% to 2.20%, V 0.40% to 0.60%, and the rest is Fe, and the residual gas content is, H≤1.5ppm, O≤13ppm, N≤90ppm; the residual harmful elements Cu≤0.05%, 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, refining in circulating vacuum refining furnace: The integrated circulating vacuum tank is equipped with a vacuum pump, and the vacuum degree is ≤15Pa. Under vacuum conditions, the circulation flow rate is ≥100t / min, and the processing time is ≥35 minutes. After ensuring that the residual gas H is ≤1.5ppm and N is ≤80ppm, take samples for analysis, and blow argon into the hanging bag after the components are qualified. S4, continuous casting electrode billet: The superheat of the first furnace is 20-35℃, and the continuous casting furnace is 18-30℃; the continuous casting speed is 0.13-0.20m / min, and three-stage electromagnetic stirring is adopted; S5. Electrode blank annealing: Annealing the electrode blank after continuous casting in step S4; S6, electroslag remelting: The electrode blank obtained in step S5 is surface-polished and smelted using a binary slag system of calcium fluoride and alumina to obtain an electroslag ingot; S7, Forging: The electroslag ingot obtained in step S6 is heated to 1280-1300° C., kept at this temperature for 50-70 hours for diffusion homogenization, and then furnace cooled to 1220-1240° C. for multi-directional upsetting, drawing, and rounding in three directions of X, Y and Z to the finished product size; S8. Pretreatment after forging: The forging blank obtained in step S7 is subjected to post-forging extreme cooling control to inhibit the precipitation of grain boundary carbides; S9, solution + spheroidizing treatment: The workpiece obtained in step S8 is placed in a heating furnace and heated to 980-1020°C. After heat preservation, it is cooled by water cooling + air cooling + quenching liquid cooling, and the temperature of the large surface of the billet is ≤250°C. After cooling, the workpiece is placed in an annealing furnace, heated to 830-860°C, kept warm for 15-30h, furnace cooled to 730-750°C, kept warm for 25-50h for spheroidizing annealing, and then furnace cooled to below 350°C, taken out of the furnace and air cooled to room temperature.

2. The process for preparing a hot working die steel for an extrusion die with high strength, high wear resistance and high toughness according to claim 1, characterized in that: In step S1, the proportion of blast furnace molten iron is ≥ 60%.

3. The process for preparing a hot working die steel for an extrusion die with high strength, high wear resistance and high toughness according to claim 1, characterized in that: In step S3, the soft blowing time of argon is 18 to 39 minutes, and the bag temperature is 1550 to 1568°C.

4. The process for preparing a hot working die steel for an extrusion die with high strength, high wear resistance and high toughness according to claim 1, characterized in that: In step S5, the electrode blank after continuous casting in step S4 is annealed at a temperature of 850°C and a holding time of 1.5 min / mm. The blank is cooled to 340°C and then taken out of the furnace.

5. The process for preparing a hot working die steel for an extrusion die with high strength, high wear resistance and high toughness according to claim 1, characterized in that: In step S6, the starting melting rate value of the steady-state stage of electroslag smelting is 9-10 kg / min, and the terminal melting rate value is 6.5-7.5 kg / min, and an electroslag ingot is obtained. The furnace is then shut down for cooling for 100-150 minutes before being sent to the forging process.

6. The process for preparing a hot working die steel for an extrusion die with high strength, high wear resistance and high toughness according to claim 1, characterized in that: In step S8, the forging blank obtained in step S7 is subjected to post-forging extreme cooling control: water cooling + quenching liquid double liquid cooling until the temperature of the large surface of the blank is ≤250°C, then loaded into a heat treatment furnace, heated to 960-990°C, kept warm for 15-20h, furnace cooled to 730-750°C, kept warm for 25-40h for complete annealing + isothermal annealing treatment.

7. The process for preparing a hot working die steel for an extrusion die with high strength, high wear resistance and high toughness according to claim 1, characterized in that: In step S8, water cooling is performed at 600°C or above, and quenching liquid cooling is performed at 600-250°C.

8. A hot working die steel for extrusion dies with high strength, high wear resistance and high toughness according to any one of claims 1 to 7, characterized in that: Its component content is C 0.38%~0.43%, Mn 0.40%~0.60%, Si 0.10%~0.30%, S≤0.001%, P≤0.010%, Cr 4.90%~5.20%, Mo 1.80%~2.20%, V 0.40%~0.60%, and the rest is Fe, and the residual gas content is H≤1.5ppm, O≤13ppm, N≤90ppm; the residual harmful elements Cu≤0.05%, Ti, Sn, and Pb are all ≤0.002%.

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