A high-temperature resistant forging fixture steel and its preparation method

Abstract

This invention discloses a high-temperature resistant forging fixture steel and its preparation method, belonging to the technical field of special tooling steel. The steel, by mass percentage, consists of C 0.57%–0.65%, Mn 0.60%–0.90%, Si 0.20%–0.30%, S≤0.010%, P≤0.020%, Cr≤0.25%, Mo 0.10%–0.30%, Ni 0.40%–0.60%, Al 0.015%–0.035%, and the balance Fe. The preparation method includes electric furnace smelting, ladle refining, vacuum refining, ingot casting, ingot annealing, multi-directional forging, post-forging pretreatment, and final treatment steps. Through secondary white slag refining, multi-directional upsetting and drawing forging, and segmented controlled cooling normalizing + stress-relief tempering processes, a uniform sorbitic matrix with a grain size of 8.0–8.5 and a normalized microstructure of 2–3 is obtained. The steel of this invention possesses both high strength and excellent plasticity, with a yield strength of 406–415 MPa, tensile strength of 815–832 MPa, and elongation ≥15.5%. It exhibits excellent resistance to thermal fatigue, high-temperature creep, and cracking, making it suitable for core load-bearing components such as the clamping pins of hot forging hydraulic presses and the clamping jaws of loading and unloading machines.

Description

Technical Field

[0001] This invention relates to the field of special tooling steel and metallurgical forging heat treatment technology. Specifically, it relates to a high-temperature resistant cold and hot fatigue forging jig steel and its preparation method. Background Technology

[0002] Forging fixtures are critical consumable tooling in hot forging production lines. They directly contact forgings heated to 850℃~1250℃ and are subjected to alternating clamping stress, mechanical impact, and thermal cycles over long periods. Stress concentration is significant in the jaw teeth, and the material properties directly affect production line efficiency, forging machining accuracy, and tooling maintenance costs. To meet the demands of continuous production in the hot forging industry, the service conditions for fixtures are becoming increasingly stringent, requiring materials to possess excellent thermal fatigue resistance, high impact toughness, stable high-temperature strength, and low wear deformation.

[0003] Domestically, there are standardized hot work steel / impact tool steel grades (5CrNiMo, H13, 4Cr5MoSiV, etc.), but there are no dedicated tooling steels specifically for clamps and jaws used in forging hydraulic press production lines. Hot work die steels such as 45#, 42CrMo, 5CrMnMo, 5CrNiMo, and H13 are commonly used as substitutes. However, each of these materials has its own advantages and disadvantages, making it impossible to completely balance service life, toughness, wear resistance, and production costs. For example, H13 hot work die steel has good thermal stability and strong resistance to thermal fatigue, but its matrix toughness is insufficient. Forging fixtures subjected to high-frequency alternating impact loads for extended periods are prone to root cracking and tooth crack propagation failure during use, resulting in a high scrap rate. Secondly, there is 5CrNiMo, a traditional hot forging die steel. While the material has excellent impact toughness and good resistance to tooth chipping and fracture, its high-temperature working surface wear is insufficient. When clamping high-temperature forgings, the tooth surface wears rapidly, causing slippage and a rapid decrease in tooling clamping accuracy.

[0004] In summary, all existing forging fixture materials have performance shortcomings that cannot be simultaneously addressed. Summary of the Invention

[0005] The first objective of this invention is to provide a high-temperature resistant forging fixture steel. This steel is used in the clamping parts of clamping tooling for hot forging hydraulic presses, primarily for manufacturing core load-bearing components such as forging clamp pins and clamping jaws of material handling machines. It is widely used in the processing of forgings such as hot work die steel, plastic mold steel, and stepped shafts. The material is adaptable to the combined extreme working conditions of high-temperature heat radiation, high-frequency alternating clamping loads, and thermal cycling impacts, solving the problems of traditional fixture steels such as heat cracking, tooth breakage, high-temperature softening, and fatigue fracture. It meets the requirements of continuous hot forging production for tooling with high toughness, high temperature resistance, long service life, and low cost.

[0006] To achieve the above-mentioned objectives, this invention provides a high-temperature resistant forging fixture steel, wherein the chemical composition of the steel, by weight percentage, comprises:

[0007] C 0.57%~0.65%; Mn 0.60%~0.90%; Si 0.20%~0.30%; S≤0.010%; P≤0.020%; Cr≤0.25%; Mo 0.10%~0.30%; Ni 0.40%~0.60%; Al 0.015%~0.035%; the balance is Fe and unavoidable impurities, and the residual gas content is: H≤1.5ppm, O≤13ppm, N≤90ppm; the residual harmful element content is: Cu≤0.20%, Ti≤0.002%, Sn≤0.002%, Pb≤0.002%.

[0008] Specifically, the austenitic grain size of the steel is 8.0 to 8.5, and the mechanical properties of the steel are: yield strength 406 to 415 MPa, tensile strength 815 to 832 MPa, and elongation after fracture ≥15.5%.

[0009] The second objective of this invention is to provide a method for preparing the above-mentioned high-temperature resistant forging fixture steel, comprising the following steps:

[0010] S1. Electric furnace smelting: Scrap steel and alloy materials are smelted in an electric furnace. The temperature of the molten steel is ≥1630℃. After oxidation and slag removal, alloy materials are added to make them completely melt. Lime and fluorite are added to form alkaline slag for dephosphorization and desulfurization treatment. Then, aluminum wire is added for deoxidation before tapping the steel.

[0011] S2. Ladle refining: The molten steel after electric furnace smelting is transferred to the ladle, and slag materials CaO, CaF2 and C-Si powder are added to reduce and create white slag. According to the deviation between the actual composition and the target composition, alloy materials are added for composition fine-tuning, desulfurization and deoxidation. After removing the white slag, it is reheated to ≥1630℃, and CaO, CaF2, C-Si powder and red bricks are added for secondary white slag creation. Al wire is fed until the Al content of the finished product is 0.015~0.035%, and Ca wire is fed at 0.5Kg / ton of steel.

[0012] S3. Vacuum refining furnace refining: Place the molten steel into the vacuum refining furnace, use a four-stage pump to evacuate to the final vacuum degree ≤67Pa, maintain the vacuum time twice for ≥20 minutes each time, so that the residual nitrogen is ≤80ppm. After degassing, take a sample for analysis. After the composition is qualified, blow argon gas into the ladle.

[0013] S4. Molded electric furnace ingot: Preheat the ingot mold to 40-60°C, fill it with argon gas for 3-6 minutes, and then cover and cast.

[0014] S5, steel ingot annealing;

[0015] S6, Forging;

[0016] S7. Pretreatment after forging;

[0017] S8, Final Processing.

[0018] Specifically, in step S4, the casting is protected by argon gas with asbestos cloth attached throughout the entire casting process. The argon gas flow rate is 20 m³ / h, the casting time is 6 minutes, and the casting is demolded 4 hours after casting.

[0019] Specifically, in step S5, the annealing of the steel ingot is carried out by annealing the demolded steel ingot at a temperature of 830 to 860°C, with a holding time of 1.5 min / mm, and then cooling it in the furnace to below 350°C before removing it from the furnace.

[0020] Specifically, in step S6, the forging operation is to heat the annealed steel ingot to 1220-1250°C, hold it at that temperature for 20-30 hours for diffusion homogenization, cool it in the furnace to 1200°C, hold it at that temperature for 3 hours, and then take it out of the furnace for forging.

[0021] Further, in step S6, after holding at the temperature for 3 hours, the billet is taken out of the furnace for forging. The first heat is used to complete the upsetting and drawing in both Z and X directions, and the second heat is used to complete the upsetting and drawing in both Y and Z directions. The billet is then returned to the furnace and reheated to 1200℃, held for ≥3 hours, and then drawn along the Z direction and rounded and drawn to the finished size. The final heat has a drawing ratio ≥3.

[0022] Specifically, in step S7, the post-forging pretreatment operation is to air-cool the forged billet to a surface temperature of 680-720°C, and then air-cool it to room temperature.

[0023] Specifically, in step S8, the specific steps in the final treatment are as follows: the forging billet is placed in a resistance heating furnace and heated to 840-880°C, held for 8-12 hours, cooled by air and mist to a surface temperature of 680-720°C, and then air-cooled to below 250°C; then it is placed in a resistance annealing furnace and heated to 600-650°C, held for 20-30 hours, cooled in the furnace to below 300°C, and then air-cooled to room temperature.

[0024] Furthermore, in step S8, inert nitrogen gas is used for protection and the mixture is circulated and stirred throughout the process.

[0025] The present invention provides a high-temperature resistant forging fixture steel and its preparation method, which have the following advantages over the prior art:

[0026] (1) Based on the national standard 60# medium carbon steel, it is proposed to adopt Ni and Mo micro-alloying, and match it with electric furnace smelting, LF / VD refining, multi-directional forging grain refinement, normal tempering and other heat treatment processes to simultaneously balance the material's toughness, high temperature strength, wear resistance and thermal fatigue resistance. It can effectively solve common failure problems such as fixture cracking, wear, hot cracking and fatigue fracture, greatly extend the service life of tooling, reduce the frequency of equipment downtime for parts replacement, effectively reduce the tooling consumables and production and maintenance costs of forging enterprises, and meet the actual use needs of large-scale continuous hot forging production;

[0027] (2) The final heat treatment process is segmented controlled cooling normalizing + stress-relief tempering. The finished product has a uniform and stable sorbitic matrix structure with fine pearlite evenly dispersed, containing only a small amount of discontinuous intergranular ferrite, without continuous network ferrite or Widmanstätten structure. According to GB / T 13320-2007 standard, the rating is stably controlled at level 2 to 3, with uniform structure and slight compositional segregation. The yield strength is 406 to 415 MPa, the tensile strength is 815 to 832 MPa, and the elongation after fracture is ≥15.5%, achieving a good match between high strength and excellent plasticity.

[0028] (3) After refining and smelting, the grades of non-metallic inclusions of types A, B, and C are all controlled within 0.5, with no large-sized DS-type spherical inclusions, which greatly reduces crack initiation sources. The austenite grains are refined to grade 8.0 to 8.5, and the fine grain strengthening effect is significant;

[0029] (4) The structure of the tempered product is dense, continuous, and without obvious component segregation, and has excellent and stable thermal conductivity. Under long-term contact with high-temperature steel materials above 1200℃, the heat on the surface of the workpiece can be quickly and evenly conducted to the center, and the temperature gradient of the working surface is gentle, which effectively avoids the surface softening caused by local heat accumulation;

[0030] (5) Mo significantly increases the resistance to atomic diffusion at grain boundaries, effectively suppressing grain boundary slip and dislocation movement at high temperatures; fine grains of grade 8.0 to 8.5 further enhance the stability of the high-temperature structure, resulting in small creep on the tooling working surface and outstanding ability to maintain dimensions at high temperatures.

[0031] (6) After sufficient stress relief tempering, the overall residual stress is extremely low; Ni element enhances high-temperature plasticity reserves, and Mo element prevents the precipitation and aggregation of brittle carbides at grain boundaries. Combined with the advantage of fine grains dispersing thermal stress, it effectively delays the initiation and propagation of thermal fatigue cracks, and greatly improves the service life and service stability of high-temperature fixtures.

[0032] (7) The matrix structure in the tempered state is moderately soft and hard with excellent uniformity. It is not easy to produce built-up edge, tool marks and processing deformation during the processing. It can be used directly as a finished product without additional tempering treatment. Attached Figure Description

[0033] Figure 1 Metallographic photograph showing the grain size of a high-temperature forging fixture steel prepared in Example 1;

[0034] Figure 2 A photograph of the microstructure of a high-temperature forging fixture steel prepared in Example 1;

[0035] Figure 3 Metallographic photograph showing the grain size of a high-temperature forging fixture steel prepared in Example 2;

[0036] Figure 4 This is a microstructure photograph of a high-temperature forging fixture steel prepared in Example 2;

[0037] Figure 5 Metallographic photograph showing the grain size of a high-temperature forging fixture steel prepared in Example 3;

[0038] Figure 6 This is a microstructure photograph of a high-temperature forging fixture steel prepared in Example 3. Detailed Implementation

[0039] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0040] Example 1

[0041] A high-temperature resistant forging fixture steel, by mass fraction, is basically composed of the elements shown in Table 1:

[0042] Table 1

[0043]

[0044] Its preparation method includes the following steps;

[0045] S1, Electric furnace smelting:

[0046] Based on the chemical composition of the steel grade to be smelted, scrap steel and alloy materials are prepared in advance. Scrap steel is smelted in an electric furnace at a temperature of 1670℃. Oxidation slag removal is performed. After slag removal, alloy materials are added and completely melted. Then, lime and fluorite are added to form alkaline slag. The molten steel in the electric furnace is dephosphorized and desulfurized. When the temperature of the molten steel reaches 1670℃, aluminum wire is added for deoxidation, and then the steel is tapped.

[0047] S2, Ladle refining furnace refining:

[0048] After smelting in the electric arc furnace, the molten steel is transferred to a ladle, hoisted onto the refining furnace base, and reduced with slag materials CaO, CaF2, and C-Si powder to create primary white slag. Based on the deviation between the actual composition and the target composition of the molten steel in the refining furnace base, corresponding alloy materials are added to complete the composition fine-tuning, desulfurization, and deoxidation operations. After the operation, the white slag is removed, and then the steel is reheated to a temperature of 1670℃. CaO, CaF2, C-Si powder, and red bricks are added to create secondary white slag. Al wire is fed (the finished product is controlled at 0.015-0.035%), and Ca wire is also fed at 0.5 kg / ton of steel.

[0049] S3. Vacuum refining furnace refining: The vacuum refining furnace has a four-stage inlet pump, with a final vacuum of 38 Pa. The vacuum time is maintained for more than 20 minutes in both stages, and the target value of residual gas nitrogen is ≤80 ppm. After degassing, samples are taken for analysis. After the composition is qualified, argon gas is blown into the hoisting bag.

[0050] S4, Ingot casting in electric furnace:

[0051] Preheat the ingot mold to 40–60°C, then fill the mold with argon gas for 5 minutes per mold. Afterward, remove the argon gas pipe, cover the mold with a lid, and proceed with casting. Throughout the casting process, the casting is protected with argon gas using an asbestos-lined cloth, and the argon gas flow rate is 20 m³ / h. 3 / h, casting time 6min, demolding after 4h;

[0052] S5. Ingot annealing:

[0053] The electrode blank after demolding in step S4 is annealed at a temperature of 850℃ and a holding time of 1.5 min / mm, and then furnace cooled to 340℃ before being removed from the furnace.

[0054] S6, Forging:

[0055] The electroslag ingot obtained in step S5 is heated to 1230℃ and held for 25 hours for diffusion homogenization. Then, it is furnace cooled to 1200℃ and held for 3 hours before being taken out of the furnace for forging. The first forging completes the Z and X-axis upset drawing, and the second forging completes the Y and Z-axis upset drawing. It is then returned to the furnace and reheated to 1200℃, held for ≥3 hours, and then drawn along the Z-axis to the finished size. The theoretical drawing ratio for the final forging is 3.

[0056] S7. Post-forging pretreatment

[0057] The forging billet obtained in step S6 is air-cooled to a surface temperature of 700°C, and then air-cooled to room temperature.

[0058] S8. Final Processing:

[0059] The workpiece obtained in step S7 is placed in a resistance heating furnace and heated to 860°C, held for 10 hours, then air-cooled to a surface temperature of 700°C, and then air-cooled to 240°C. After cooling, the workpiece is placed in a resistance annealing furnace, heated to 630°C, held for 25 hours, and then cooled to 290°C in the furnace before being air-cooled to room temperature. The entire process is protected by inert nitrogen gas with circulating stirring.

[0060] Example 2

[0061] A high-temperature resistant forging fixture steel, by mass fraction, is basically composed of the elements shown in Table 1:

[0062] Table 2

[0063]

[0064] Its preparation method includes the following steps;

[0065] S1, Electric furnace smelting:

[0066] Based on the chemical composition of the steel grade to be smelted, scrap steel and alloy materials are prepared in advance. Scrap steel is smelted in an electric furnace at a temperature of 1670℃. Oxidation slag removal is performed. After slag removal, alloy materials are added and completely melted. Then, lime and fluorite are added to form alkaline slag. The molten steel in the electric furnace is dephosphorized and desulfurized. When the temperature of the molten steel reaches 1670℃, aluminum wire is added for deoxidation, and then the steel is tapped.

[0067] S2, Ladle refining furnace refining:

[0068] After smelting in the electric arc furnace, the molten steel is transferred to a ladle, hoisted onto the refining furnace base, and reduced with slag materials CaO, CaF2, and C-Si powder to create primary white slag. Based on the deviation between the actual composition and the target composition of the molten steel in the refining furnace base, corresponding alloy materials are added to complete the composition fine-tuning, desulfurization, and deoxidation operations. After the operation, the white slag is removed, and then the steel is reheated to a temperature of 1670℃. CaO, CaF2, C-Si powder, and red bricks are added to create secondary white slag. Al wire is fed (the finished product is controlled at 0.015-0.035%), and Ca wire is also fed at 0.5 kg / ton of steel.

[0069] S3. Vacuum refining furnace refining: The vacuum refining furnace has a four-stage inlet pump, with a final vacuum of 40Pa. The vacuum time is maintained for more than 20 minutes in both stages, and the residual gas nitrogen target value is ≤80ppm. After degassing, samples are taken for analysis. After the composition is qualified, argon gas is blown into the hoisting bag.

[0070] S4, Ingot casting in electric furnace:

[0071] Preheat the ingot mold to 40–60°C, then fill the mold with argon gas for 5 minutes per mold. Afterward, remove the argon gas pipe, cover the mold with a lid, and proceed with casting. Throughout the casting process, the casting is protected with argon gas using an asbestos-lined cloth, and the argon gas flow rate is 20 m³ / h. 3 / h, casting time 6min, demolding after 4h;

[0072] S5. Ingot annealing:

[0073] The electrode blank after demolding in step S4 is annealed at a temperature of 850℃ and a holding time of 1.5 min / mm, and then furnace cooled to 340℃ before being removed from the furnace.

[0074] S6, Forging:

[0075] The electroslag ingot obtained in step S5 is heated to 1230℃ and held for 25 hours for diffusion homogenization. Then, it is furnace cooled to 1200℃ and held for 3 hours before being taken out of the furnace for forging. The first forging completes the Z and X-axis upset drawing, and the second forging completes the Y and Z-axis upset drawing. It is then returned to the furnace and reheated to 1200℃, held for ≥3 hours, and then drawn along the Z-axis to the finished size. The theoretical drawing ratio for the last forging is 3.

[0076] S7. Post-forging pretreatment

[0077] The forging billet obtained in step S6 is air-cooled to a surface temperature of 695°C, and then air-cooled to room temperature.

[0078] S8. Final Processing:

[0079] The workpiece obtained in step S7 is placed in a resistance heating furnace and heated to 860°C, held for 10 hours, then air-cooled to a surface temperature of 705°C, and then air-cooled to 245°C. After cooling, the workpiece is placed in a resistance annealing furnace, heated to 630°C, held for 25 hours, and then cooled in the furnace to 290°C before being air-cooled to room temperature. The entire process is carried out under inert nitrogen protection with circulating stirring.

[0080] Example 3

[0081] A high-temperature resistant forging fixture steel, by mass fraction, is basically composed of the elements shown in Table 1:

[0082] Table 3

[0083]

[0084] Its preparation method includes the following steps;

[0085] S1, Electric furnace smelting:

[0086] Based on the chemical composition of the steel grade to be smelted, scrap steel and alloy materials are prepared in advance. Scrap steel is smelted in an electric furnace at a temperature of 1670℃. Oxidation slag removal is performed. After slag removal, alloy materials are added and completely melted. Then, lime and fluorite are added to form alkaline slag. The molten steel in the electric furnace is dephosphorized and desulfurized. When the temperature of the molten steel reaches 1670℃, aluminum wire is added for deoxidation, and then the steel is tapped.

[0087] S2, Ladle refining furnace refining:

[0088] After smelting in the electric arc furnace, the molten steel is transferred to a ladle, hoisted onto the refining furnace base, and reduced with slag materials CaO, CaF2, and C-Si powder to create primary white slag. Based on the deviation between the actual composition and the target composition of the molten steel in the refining furnace base, corresponding alloy materials are added to complete the composition fine-tuning, desulfurization, and deoxidation operations. After the operation, the white slag is removed, and then the steel is reheated to a temperature of 1670℃. CaO, CaF2, C-Si powder, and red bricks are added to create secondary white slag. Al wire is fed (the finished product is controlled at 0.015-0.035%), and Ca wire is also fed at 0.5 kg / ton of steel.

[0089] S3. Vacuum refining furnace refining: The vacuum refining furnace has a four-stage inlet pump, with a final vacuum of 40Pa. The vacuum time is maintained for more than 20 minutes in both stages, and the residual gas nitrogen target value is ≤80ppm. After degassing, samples are taken for analysis. After the composition is qualified, argon gas is blown into the hoisting bag.

[0090] S4, Ingot casting in electric furnace:

[0091] Preheat the ingot mold to 40–60°C, then fill the mold with argon gas for 5 minutes per mold. Afterward, remove the argon gas pipe, cover the mold with a lid, and proceed with casting. Throughout the casting process, the casting is protected with argon gas using an asbestos-lined cloth, and the argon gas flow rate is 20 m³ / h. 3 / h, casting time 6min, demolding after 4h;

[0092] S5. Ingot annealing:

[0093] The electrode blank after demolding in step S4 is annealed at a temperature of 850℃ and a holding time of 1.5 min / mm, and then furnace cooled to 340℃ before being removed from the furnace.

[0094] S6, Forging:

[0095] The electroslag ingot obtained in step S5 is heated to 1230℃ and held for 25 hours for diffusion homogenization. Then, it is furnace cooled to 1200℃ and held for 3 hours before being taken out of the furnace for forging. The first forging completes the Z and X-axis upset drawing, and the second forging completes the Y and Z-axis upset drawing. It is then returned to the furnace and reheated to 1200℃, held for ≥3 hours, and then drawn along the Z-axis to the finished size. The theoretical drawing ratio for the last forging is 3.

[0096] S7. Post-forging pretreatment

[0097] The forging billet obtained in step S6 is air-cooled to a surface temperature of 690°C, and then air-cooled to room temperature.

[0098] S8. Final Processing:

[0099] The workpiece obtained in step S7 is placed in a resistance heating furnace and heated to 860°C, held for 10 hours, then air-cooled to a surface temperature of 685°C, and then air-cooled to 240°C. After cooling, the workpiece is placed in a resistance annealing furnace, heated to 630°C, held for 25 hours, and then air-cooled to 290°C before being removed from the furnace and air-cooled to room temperature. The entire process is carried out under inert nitrogen protection with circulating stirring.

[0100] To verify the mechanical properties of the plastic mold steel provided by the preparation method of the present invention, the inventors took samples of the fixture steel obtained in Examples 1 to 3 for microstructure analysis, such as... Figures 1 to 6 As shown; the test data for mechanical performance testing are shown in Tables 4 and 5.

[0101] Table 4

[0102]

[0103] Table 5

[0104]

[0105] Therefore,

[0106] 1. The C60+0.5Ni+0.2Mo fixture steel employs a segmented controlled cooling normalizing followed by stress-relief tempering as the final heat treatment process. The finished product exhibits a uniform and stable sorbitic matrix structure with fine, evenly dispersed pearlite, containing only a small amount of discontinuous intergranular ferrite, and free from defects such as continuous network ferrite and Widmanstätten structure. According to GB / T 13320-2007 standard, the rating is consistently controlled at level 2-3, with uniform microstructure, slight compositional segregation, and complete release of internal residual stress. This effectively ensures long-term stability of dimensional accuracy after finishing and minimizes aging deformation.

[0107] 2. This steel undergoes refined smelting, resulting in excellent matrix purity. The grades of A, B, and C non-metallic inclusions are all controlled within 0.5, with no large-sized DS-type spherical inclusions, significantly reducing crack initiation sources. The austenite grains are refined to grade 8.0–8.5, resulting in significant grain strengthening. A reasonable Ni / Mo alloy ratio further optimizes matrix properties; Ni improves the matrix's plasticity and toughness, while Mo effectively inhibits the coarsening and aggregation of cementite at grain boundaries, reducing grain boundary stress concentration and hindering microcrack initiation and propagation. The material's mechanical properties are stable and controllable, with a yield strength of 406–415 MPa, tensile strength of 815–832 MPa, and elongation after fracture ≥15.5%, achieving a good balance between high strength and excellent plasticity, and exhibiting excellent fatigue and crack resistance.

[0108] 3. This material is used in its final state after normal tempering. The matrix structure has moderate hardness and excellent uniformity, resulting in superior machinability. It is less prone to built-up edge, tool marks, and machining deformation during processing. A small amount of discontinuous ferrite does not disrupt the matrix continuity, and combined with the high-purity, fine-grained structure, it can be used directly as a finished product without additional tempering. 4. The normal tempered material has a dense, continuous microstructure with no significant component segregation, exhibiting excellent and stable thermal conductivity. Under long-term contact with steel materials at temperatures above 1200℃, heat from the workpiece surface can be quickly and evenly conducted towards the core, resulting in a gentle temperature gradient on the working surface. This effectively avoids surface softening and performance degradation caused by localized heat accumulation, demonstrating excellent high-temperature thermal stability.

[0109] 5. This nickel-molybdenum alloy system, combined with a refined grain structure, endows the material with excellent high-temperature creep resistance. Mo can significantly increase the resistance to atomic diffusion at grain boundaries, effectively suppressing grain boundary slip and dislocation movement at high temperatures; the 8.0-8.5 grade fine grains further enhance the stability of the high-temperature structure, significantly suppressing plastic flow during long-term high-temperature service, resulting in small creep on the tooling working surface, making it less prone to permanent failures such as collapse, bulging, and deformation, and exhibiting outstanding dimensional retention at high temperatures.

[0110] 6. The material undergoes thorough stress-relief tempering, resulting in extremely low overall residual stress. Ni enhances high-temperature plasticity reserves, while Mo prevents the precipitation and aggregation of brittle carbides at grain boundaries. Combined with the advantage of fine grains dispersing thermal stress, it effectively buffers the impact of alternating hot and cold temperatures. Under harsh conditions of repeated rapid heating and cooling, it significantly delays the initiation and propagation of thermal fatigue cracks, reducing the likelihood of defects such as cracking, peeling, and flaking. It exhibits excellent resistance to thermal shock cracking, greatly improving the service life and operational stability of high-temperature fixtures.

[0111] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited to the embodiments described. Those skilled in the art can make various equivalent modifications or substitutions without departing from the spirit of the present invention, and these equivalent modifications or substitutions are all included within the scope defined by the claims of this application.

Claims

1. A high-temperature resistant forging fixture steel, characterized in that, The chemical composition of the steel, by weight percentage, includes: C 0.57%~0.65%; Mn 0.60%~0.90%; Si 0.20%~0.30%; S≤0.010%; P≤0.020%; Cr≤0.25%; Mo 0.10%~0.30%; Ni 0.40%~0.60%; Al 0.015%~0.035%; the balance is Fe and unavoidable impurities, and the residual gas content is: H≤1.5ppm, O≤13ppm, N≤90ppm; the residual harmful element content is: Cu≤0.20%, Ti≤0.002%, Sn≤0.002%, Pb≤0.002%.

2. The high-temperature resistant forging fixture steel as described in claim 1, characterized in that, The austenitic grain size of the steel is 8.0 to 8.5, and the mechanical properties of the steel are: yield strength 406 to 415 MPa, tensile strength 815 to 832 MPa, and elongation after fracture ≥15.5%.

3. A method for preparing high-temperature resistant forging fixture steel as described in claim 1 or 2, characterized in that, Includes the following steps, S1. Electric furnace smelting: Scrap steel and alloy materials are smelted in an electric furnace. The temperature of the molten steel is ≥1630℃. After oxidation and slag removal, alloy materials are added to make them completely melt. Lime and fluorite are added to form alkaline slag for dephosphorization and desulfurization treatment. Then, aluminum wire is added for deoxidation before tapping the steel. S2. Ladle refining: The molten steel after electric furnace smelting is transferred to the ladle, and slag materials CaO, CaF2 and C-Si powder are added to reduce and create white slag. According to the deviation between the actual composition and the target composition, alloy materials are added for composition fine-tuning, desulfurization and deoxidation. After removing the white slag, it is reheated to ≥1630℃, and CaO, CaF2, C-Si powder and red bricks are added for secondary white slag creation. Al wire is fed until the finished product Al content is 0.015~0.035%, and Ca wire is fed at 0.5Kg / ton of steel. S3. Vacuum refining furnace refining: Place the molten steel into the vacuum refining furnace, use a four-stage pump to evacuate to the final vacuum degree ≤67Pa, maintain the vacuum time twice for ≥20 minutes each time, so that the residual nitrogen is ≤80ppm. After degassing, take a sample for analysis. After the composition is qualified, blow argon gas into the ladle. S4. Molded electric furnace ingot: Preheat the ingot mold to 40-60°C, fill it with argon gas for 3-6 minutes, and then cover and cast. S5, steel ingot annealing; S6, Forging; S7. Pretreatment after forging; S8, Final Processing.

4. The method for preparing high-temperature resistant forging fixture steel as described in claim 3, characterized in that, In step S4, the casting is protected by argon gas with asbestos cloth attached throughout the casting process. The argon gas flow rate is 20 m³ / h, the casting time is 6 min, and the casting is demolded 4 h after casting.

5. The method for preparing high-temperature resistant forging fixture steel as described in claim 3, characterized in that, In step S5, the specific operation of annealing the steel ingot is to anneal the demolded steel ingot at a temperature of 830-860℃, with a holding time of 1.5 min / mm, and then furnace-cool it to below 350℃ before removing it from the furnace.

6. The method for preparing high-temperature resistant forging fixture steel as described in claim 3, characterized in that, In step S6, the specific forging operation is as follows: the annealed steel ingot is heated to 1220-1250°C, held at that temperature for 20-30 hours for diffusion homogenization, cooled in the furnace to 1200°C, held at that temperature for 3 hours, and then taken out of the furnace for forging.

7. The method for preparing high-temperature resistant forging fixture steel as described in claim 6, characterized in that, In step S6, after holding at the temperature for 3 hours, the billet is taken out of the furnace for forging. The first heat is used to complete the upsetting and drawing in both Z and X directions, and the second heat is used to complete the upsetting and drawing in both Y and Z directions. The billet is then returned to the furnace and reheated to 1200℃, held for ≥3 hours, and then drawn along the Z direction and rounded to the finished size. The final heat has a drawing ratio ≥3.

8. The method for preparing high-temperature resistant forging fixture steel as described in claim 3, characterized in that, In step S7, the specific operation of the post-forging pretreatment is to air-cool the forged billet to a surface temperature of 680-720°C, and then air-cool it to room temperature.

9. The method for preparing high-temperature resistant forging fixture steel as described in claim 3, characterized in that, In step S8, the specific steps of the final treatment are as follows: the forging billet is placed in a resistance heating furnace and heated to 840-880°C, held for 8-12 hours, cooled by air and mist to a surface temperature of 680-720°C, and then air-cooled to below 250°C; then it is placed in a resistance annealing furnace and heated to 600-650°C, held for 20-30 hours, cooled in the furnace to below 300°C, and then air-cooled to room temperature.

10. The method for preparing high-temperature resistant forging fixture steel as described in claim 9, characterized in that, In step S8, inert nitrogen gas is used for protection and the mixture is circulated and stirred throughout the process.

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