Preparation method of ultra-large high-quality 4Cr5MoSiV1 die steel

Abstract

The invention relates to a preparation method of ultra-large high-quality 4Cr5MoSiV1 die steel, belongs to the technical field of die steel, and aims to solve at least one of the problems of macrosegregation, uneven structure, easiness in cracking, short service life, poor mechanical property, poor cold and hot fatigue performance and the like in the existing large and ultra-large manufacturing process. According to the method, smelting, forging and other processes in the production process of the large-size high-quality die steel are finely controlled, and the structure uniformity and the mechanical property are improved. And a subsequent forge piece product has a good initial homogenization state, so that the aim of homogenizing the performance of the large forge piece is fulfilled.

Description

Technical Field

[0001] This invention relates to the field of mold steel technology, and in particular to a method for preparing ultra-large, high-quality 4Cr5MoSiV1 mold steel. Background Technology

[0002] With the rapid development of manufacturing industries such as automobiles, aerospace, and home appliances, the increasing size of molded parts and the growing demand for multi-cavity molds with high productivity have led to a more pronounced trend towards larger molds. Currently, large-tonnage molds weigh over 100 tons. While the market demand for large hot-work die steel continues to grow, the significant increase in mold value necessitates enhanced mold safety. Users are also continuously raising their requirements for the metallurgical quality (such as material purity and microstructure uniformity), dimensions, and performance (strength, toughness, fatigue, and wear resistance) of die steel. Simultaneously, research and application of die steel are developing towards high alloys, high quality, large specifications, and high performance.

[0003] Numerous problems exist in the production of ultra-large, high-quality 4Cr5MoSiV1 mold steel. For example, as the diameter of large-section high-quality mold steel increases, severe segregation occurs due to the size effect. Furthermore, the presence of large inclusions and liquid carbides within the mold steel billet can lead to uneven stress in the billet or the mold itself during subsequent performance heat treatment and use, resulting in mold failure. The difficulty in guaranteeing the quality of large-size mold steel products and the failure of large molds are mainly related to key preparation processes such as alloy composition design, smelting, forging, and heat treatment. Secondly, insufficient equipment capacity during forging leads to incomplete forging penetration and edge cracking, and the heat treatment process, particularly quenching and annealing, presents challenges in controlling the uniformity of heating and cooling. The key to developing large-scale, high-quality 4Cr5MoSiV1 hot work die steel lies in how to refine the processes of smelting, forging, and heat treatment in the production of ultra-large-sized, high-quality 4Cr5MoSiV1 die steel, improve and enhance the microstructure and uniformity of the die steel, and solve problems such as macrosegregation, uneven microstructure, and easy cracking that easily occur during its processing, ultimately achieving the goal of improving the service life and reliability of the die steel. Summary of the Invention

[0004] Based on the above analysis, the present invention aims to provide a method for preparing ultra-large high-quality 4Cr5MoSiV1 mold steel, in order to solve at least one of the following problems that are prone to occur in existing large and ultra-large mold manufacturing processes: macroscopic segregation, uneven microstructure, easy cracking, short service life, poor mechanical properties, and poor thermal fatigue performance.

[0005] In a first aspect, the present invention provides a method for preparing ultra-large, high-quality 4Cr5MoSiV1 mold steel, comprising the following steps: (1) The scrap steel raw material is smelted in an electric furnace and refined in a refining furnace in sequence. CaO, CaF2 and aluminum powder are added to the refining furnace for smelting. The vacuum degree is ≤2 Torr, the degassing time is ≥20 min, the total vacuum treatment time is ≤50 min, and the steel is tapped. (2) Molten steel is poured, demolded, and electroslag remelted to obtain electroslag ingots; (3) The electroslag ingot is homogenized at a temperature of 1230-1250℃ for 30-45h, and then subjected to three upsetting and three drawing processes to obtain a mold steel billet of finished size; (4) The mold steel billet is air-cooled to a core temperature of 400-500℃, annealed, and then subjected to an ultra-fine solution treatment at a temperature of 1020-1040℃. After solution treatment, it is rapidly cooled to a core temperature of 400-500℃. After ball annealing, the surface is rough-machined to obtain the ultra-large high-quality 4Cr5MoSiV1 mold steel.

[0006] Furthermore, in step (1), the scrap steel raw materials, by mass percentage, include scrap steel + steel scrap ≥ 70% and pig iron ≤ 30%.

[0007] Furthermore, in step (1), the mass ratio of CaO, CaF2 and aluminum powder is 6-8:2-1:2-1, and the total mass of CaO, CaF2 and aluminum powder used in the refining furnace is 6.4-8.0% of the mass of scrap steel raw materials.

[0008] Furthermore, in step (1), the tapping temperature is 1555-1565℃.

[0009] Furthermore, in step (1), the H content in the molten steel before tapping is ≤0.0001%, the O content is ≤0.0015%, and the N content is ≤0.0074%.

[0010] Furthermore, in step (2), the average melting rate during electroslag remelting is 700-800 kg / h.

[0011] Furthermore, in step (2), the quaternary slag system of CaF2-Al2O3-CaO-MgO is used in the electroslag remelting process.

[0012] Furthermore, in step (3), the forging ratio is ≥6.

[0013] Furthermore, in step (4), the ultrafine solid solution treatment time is 2-5 hours.

[0014] Furthermore, in step (4), the annealing temperature is 700-780℃ and the annealing time is 8-15h.

[0015] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects: 1. The method of this invention achieves deep deoxidation through refining with CaO, CaF2, and aluminum powder, and uses specific raw materials to ensure that the H content in the molten steel before tapping is ≤0.0001%, O content is ≤0.0015%, N content is ≤0.0074%, and P content is ≤0.001%, solving the problem of low purity of scrap steel raw materials and achieving ultra-high purity control with low-cost scrap steel raw materials. This breaks through the dependence on high proportion of molten iron in traditional high-purity mold steel. The homogenization treatment temperature is the same as the forging heating temperature, and the ultra-fine process is carried out at 1020-1040℃, which can avoid overheating and achieve grain refinement and segregation elimination through multiple austenitic recrystallization. Slow cooling to 400-500℃ after forging and rapid cooling to 400-500℃ after ultra-fine solution treatment avoid cracking problems. The control of network carbides is transferred to the ultra-fine heat treatment stage, and the precipitation of carbides along the grain is precisely suppressed by "lower temperature austenitization + rapid cooling". The method of this invention solves the two contradictory issues of "cracking prevention" and "microstructure control", ensuring uniform spheroidization of carbides and fundamentally improving the strength, toughness and fatigue life of the material.

[0016] 2. The present invention has a moderate tapping temperature, which avoids the problems caused by excessively high tapping temperatures, such as (1) increased molten steel fluidity, which can easily lead to shrinkage cavities, cracks, segregation, etc.; (2) increased gas solubility, which can lead to porosity after cooling; and (3) increased oxidation reaction due to high temperature, which can increase impurity content and ultimately reduce the quality of steel ingots. At the same time, it avoids the problems caused by excessively low tapping temperatures, such as (1) decreased molten steel fluidity, which can easily lead to cold shuts, inclusions and residues, which can affect the integrity of the ingot; and (2) blockage of the sprue, which can lead to casting interruption and increased scrap rate.

[0017] 3. The method of this invention provides refined control over the smelting and forging processes in the production of large-size, high-quality mold steel, improving and enhancing the uniformity of the microstructure and mechanical properties. This ensures that subsequent forgings have a good initial homogenization state, thereby meeting the goal of achieving uniform performance in large forgings.

[0018] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objects and other advantages of this invention can be realized and obtained from what is particularly pointed out in the description and drawings. Attached Figure Description

[0019] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts. Figure 1 This is a physical image of the 4Cr5MoSiV1 mold steel prepared in Example 1 of the present invention. Detailed Implementation

[0020] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which constitute a part of the present invention and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0021] A specific embodiment of the present invention discloses a method for preparing ultra-large, high-quality 4Cr5MoSiV1 mold steel, comprising the following steps: (1) The scrap steel raw material is smelted in an electric furnace and refined in a refining furnace in sequence. CaO, CaF2 and aluminum powder are added to the refining furnace for smelting. The vacuum degree is ≤2 Torr, the degassing time is ≥20 min, the total vacuum treatment time is ≤50 min, and the steel is tapped. (2) Molten steel is poured, demolded, and electroslag remelted to obtain electroslag ingots; (3) The electroslag ingot is homogenized at a temperature of 1230-1250℃ for 30-45h, and then subjected to three upsetting and three drawing processes to obtain a mold steel billet of finished size; (4) The mold steel billet is air-cooled to a core temperature of 400-500℃, annealed, and then subjected to an ultra-fine solution treatment at a temperature of 1020-1040℃. After solution treatment, it is rapidly cooled to a core temperature of 400-500℃. After ball annealing, the surface is rough-machined to obtain the ultra-large high-quality 4Cr5MoSiV1 mold steel.

[0022] Compared with existing technologies, the method of this invention achieves deep deoxidation through refining with CaO, CaF2, and aluminum powder, and uses specific raw materials to ensure that the H content in the molten steel before tapping is ≤0.0001%, O content is ≤0.0015%, N content is ≤0.0074%, and P content is ≤0.001%, solving the problem of low purity of scrap steel raw materials and achieving ultra-high purity control with low-cost scrap steel raw materials. This breaks through the dependence on high proportion of molten iron in traditional high-purity mold steel. The homogenization treatment temperature is the same as the forging heating temperature, and the ultra-fine process is carried out at 1020-1040℃, which can avoid overheating and achieve grain refinement and segregation elimination through multiple austenitic recrystallization. Slow cooling to 400-500℃ after forging and rapid cooling to 400-500℃ after ultra-fine solution treatment avoid cracking problems. The control of network carbides is transferred to the ultra-fine heat treatment stage, and the precipitation of carbides along the grain is precisely suppressed by "lower temperature austenitization + rapid cooling". The method of this invention solves the two contradictory issues of "cracking prevention" and "microstructure control", ensuring uniform spheroidization of carbides and fundamentally improving the strength, toughness and fatigue life of the material.

[0023] In one specific implementation, in step (1), the scrap steel raw material includes, by mass percentage, scrap steel + steel scrap ≥ 70% and pig iron ≤ 30%.

[0024] It should be noted that the ratio of scrap steel and steel scrap can be arbitrary, as long as the ratio of scrap steel + steel scrap is ≥70%. The raw materials used in this invention can ensure that the residual elements meet the requirements, guarantee that the P content of the electric furnace steel is ≤0.001%, reduce the use of alloys with high P content in refining, and make the final die steel ≤0.008%, while reducing production costs.

[0025] In one specific implementation, in step (1), the mass ratio of CaO, CaF2 and aluminum powder is 6-8:2-1:2-1, and the total mass of CaO, CaF2 and aluminum powder used in the refining furnace is 6.4-8.0% of the mass of scrap steel raw materials.

[0026] It should be noted that in this invention, CaO, CaF2 and aluminum powder are selected as slag-forming materials, and the deoxidation process control is optimized to ultimately achieve consistency between theoretical calculations and actual production, forming a new technology for stable control of slag components.

[0027] In one specific implementation, in step (1), the tapping temperature is 1555-1565℃.

[0028] It should be noted that excessively high tapping temperatures increase the fluidity of molten steel, making it prone to problems such as shrinkage cavities, cracks, and segregation. Simultaneously, increased gas solubility leads to the formation of porosity upon cooling; high temperatures also increase oxidation reactions, resulting in higher impurity content and ultimately a decline in ingot quality. Conversely, excessively low tapping temperatures reduce the fluidity of molten steel, making it prone to problems such as cold shuts and inclusions, affecting ingot integrity; they may also cause nozzle blockage, leading to casting interruptions and increased scrap rates. In one specific implementation, in step (1), the H content in the molten steel before tapping is ≤0.0001%, the O content is ≤0.0015%, and the N content is ≤0.0074%.

[0029] It should be noted that vacuum treatment is one of the important steps in achieving clean steelmaking. During the smelting of electrode billet steel, the molten steel is degassed under vacuum at a level less than 2 Torr for 20 minutes. After vacuuming, no alloy adjustments are made, which helps to shorten the smelting time and improve the purity of the molten steel. Degasting is performed using argon soft blowing, which mainly uses small amounts of gas. This is an important way to achieve uniform composition and temperature in the refining ladle before tapping and to promote the flotation and removal of inclusions. The steel is tapped immediately after soft blowing. The ingot mold is preheated with a hot blast furnace before casting. Enhanced protection is provided during the molten steel casting process. The molten steel stream is protected by an argon gas protective cover until the casting is completed to prevent the stream from absorbing gas and avoid secondary oxidation of the molten steel.

[0030] Aluminum powder is added during the refining process to form slag. The aluminum powder diffuses and deoxidizes, thereby stabilizing the slag composition, improving the purity of the molten steel, and reducing smelting costs. Enhanced protection is implemented during the steel pouring process. The pouring stream is protected by an argon gas shield until the pouring is complete, preventing air intake and secondary oxidation of the molten steel. During pouring, the molten steel level rises steadily, promoting the floating and removal of inclusions.

[0031] In this invention, by selecting specific slag-forming materials and controlling the vacuum degree, degassing time, and total vacuum treatment time, the H content in the molten steel before tapping is ≤0.0001%, the O content is ≤0.0015%, and the N content is ≤0.0074%, thus achieving precise control of H, O, and N in the molten steel.

[0032] In one specific implementation, in step (2), the average melting rate during electroslag remelting is 700-800 kg / h.

[0033] In the electroslag remelting stage, this invention strictly controls the smelting speed to ensure that the molten pool filling ratio is 0.45-0.6, and ensures that the riser end of the steel ingot is fully fed during the feeding period, thereby improving the metallurgical quality of the electroslag ingot.

[0034] In one specific implementation, in step (2), the electroslag remelting process uses a CaF2-Al2O3-CaO-MgO quaternary slag system.

[0035] It should be noted that in this invention, a CaF2-Al2O3-CaO-MgO quaternary slag system deep desulfurization process is used to control the P and S element content in the electroslag billet. After cooling in the electric furnace for 80-100 minutes, the billet is sent to the forging process. The electroslag remelting process can further enhance desulfurization. At the electrode melting end – droplet formation stage, the steel and slag are in full contact. The addition of CaO and MgO to the slag system increases the slag basicity, thereby removing a large amount of S from the steel.

[0036] The ultra-fine heat treatment process after forging in this invention fully homogenizes the microstructure and refines the grains, preparing the microstructure for the final performance heat treatment, achieving grain size control of level 9 or above, and meeting the requirements for high strength and toughness, good high-temperature strength, and resistance to softening and thermal fatigue.

[0037] In one specific implementation, in step (3), the forging ratio is ≥6.

[0038] It should be noted that, in order to increase the core deformation during forging and ensure the density and uniformity of the steel, auxiliary tools are fully utilized, and multiple upsetting and drawing processes are adopted, with a forging ratio of ≥6. In order to prevent crack defects on the surface of the forging billet, especially at the edges and corners, during the forging process, the final forging temperature must be strictly controlled.

[0039] During the casting process, medium-carbon protective slag is used to ensure that the molten steel surface is not exposed, and the molten steel is protected by an argon gas shield until the casting is completed. The steel ingot is then demolded and hot-annealed as required, with a demolding time of 3-4 hours.

[0040] In one specific implementation, in step (3), the diameter of the mold steel billet is 900-1200mm and the height is 1000-2000mm.

[0041] In one specific implementation, in step (4), the ultrafine processing time is 2-5 hours.

[0042] The method of this invention uses auxiliary tool design and multi-directional flexible upsetting and drawing forging control technology to break up carbide dendrites, refine grains, and use Φ900mm-level electroslag ingots to realize the manufacturing of large-size forging round billets with a diameter of more than Φ900 mm and large forging modules with a width of more than 1m and a thickness of more than 600mm.

[0043] In one specific implementation, in step (4), the annealing temperature is 700-780℃ and the annealing time is 8-15h.

[0044] It should be noted that in step (4) of the present invention, the temperature of the cooling core is 400-500℃, the first cooling is slow air cooling, and the second cooling is rapid water cooling.

[0045] The method of this invention provides refined control over the smelting and forging processes in the production of large-size, high-quality mold steel, improving and enhancing the uniformity of the microstructure. This ensures that subsequent forgings have a good initial homogenization state, thereby achieving the goal of uniform performance in large forgings. The method of this invention refines the microstructure and grain size of large-size mold steel, improves the strength and toughness of mold steel materials at room temperature and high temperature, solves the problem of low performance of large-size mold steel products, and aims to achieve the goal of large-size and high-quality products.

[0046] It should be noted that the ultra-large, high-quality 4Cr5MoSiV1 mold steel of this invention refers to a thickness ≥ 600 mm. The technical solution of this invention will be further explained below with reference to specific embodiments.

[0047] Example 1 The preparation method of an ultra-large, high-quality 4Cr5MoSiV1 mold steel (Φ=1200mm) according to this embodiment includes the following steps: (1) The scrap steel raw material is smelted in an electric furnace and refined in a refining furnace in sequence. The scrap steel raw material is 70% scrap steel + steel scrap and 30% pig iron by mass percentage. The mass ratio of scrap steel to steel scrap is 1:1. CaO, CaF2 and aluminum powder are added to the refining furnace for smelting. The mass ratio of CaO, CaF2 and aluminum powder is 6:1:2. The total mass of CaO, CaF2 and aluminum powder is 8.0% of the mass of scrap steel raw material. The vacuum degree is 2 Torr, the degassing time is 20 min, the total vacuum treatment time is 50 min, and the steel is tapped. The tapping temperature is 1555℃. Before tapping, the H content in the molten steel is ≤0.0001%, the O content is ≤0.0015%, the N content is ≤0.0074%, and the P content is ≤0.001%. (2) The molten steel is poured, demolded, and electroslag remelted. The average melting rate during electroslag remelting is 700 kg / h, and an electroslag ingot is obtained. The quaternary slag system of CaF2-Al2O3-CaO-MgO is used in the electroslag remelting process. (3) The electroslag ingot is homogenized at 1230°C for 45 hours, and then subjected to three upsetting and three drawing processes with a forging ratio of 6.1 to obtain a mold steel billet of finished size. The diameter of the mold steel billet is 1200 mm and the height is 1000 mm. (4) The mold steel billet is air-cooled to a core temperature of 400°C, annealed at 700°C for 15 hours, subjected to ultra-fine solution treatment at 1020°C for 5 hours, rapidly cooled to a core temperature of 500°C by water cooling, and rough surface treatment is performed after ball annealing to obtain the ultra-large high-quality 4Cr5MoSiV1 mold steel.

[0048] The actual image of the 4Cr5MoSiV1 mold steel prepared in this embodiment is shown below. Figure 1 As shown.

[0049] Example 2 The preparation method of an ultra-large, high-quality 4Cr5MoSiV1 mold steel (Φ=900mm) according to this embodiment includes the following steps: (1) The scrap steel raw material is smelted in an electric furnace and refined in a refining furnace in sequence. The scrap steel raw material is 70% scrap steel + steel scrap and 30% pig iron by mass percentage. The mass ratio of scrap steel to steel scrap is 2:1. CaO, CaF2 and aluminum powder are added to the refining furnace for smelting. The mass ratio of CaO, CaF2 and aluminum powder is 7:1.5:1.5. The total mass of CaO, CaF2 and aluminum powder is 6.4% of the mass of scrap steel raw material. The vacuum degree is 1.5 Torr, the degassing time is 25 min, the total vacuum treatment time is 45 min, and the steel is tapped. The tapping temperature is 1560℃. Before tapping, the H content in the molten steel is ≤0.0001%, the O content is ≤0.0015%, the N content is ≤0.0074%, and the P content is ≤0.001%. (2) The molten steel is poured, demolded, and electroslag remelted. The average melting rate during electroslag remelting is 750 kg / h, and an electroslag ingot is obtained. The quaternary slag system of CaF2-Al2O3-CaO-MgO is used in the electroslag remelting process. (3) The electroslag ingot is homogenized at 1240°C for 37 hours, and then subjected to three upsetting and three drawing processes with a forging ratio of 6.5 to obtain a mold steel billet of finished size. The diameter of the mold steel billet is 900 mm and the height is 2000 mm. (4) The mold steel billet is air-cooled to a core temperature of 450°C, annealed at 730°C for 11 hours, and then subjected to an ultra-fine solution treatment at 1030°C for 3.5 hours. After water cooling to 450°C, the surface is rough-machined after ball annealing to obtain the ultra-large high-quality 4Cr5MoSiV1 mold steel.

[0050] Example 3 The preparation method of an ultra-large, high-quality 4Cr5MoSiV1 mold steel (1000mm wide, 600mm thick) according to this embodiment includes the following steps: (1) The scrap steel raw material is smelted in an electric furnace and refined in a refining furnace in sequence. The scrap steel raw material is 75% scrap steel + steel scrap and 25% pig iron by mass percentage. The mass ratio of scrap steel to steel scrap is 3:1. CaO, CaF2 and aluminum powder are added to the refining furnace for smelting. The mass ratio of CaO, CaF2 and aluminum powder is 8:2:1. The total mass of CaO, CaF2 and aluminum powder is 7.2% of the mass of scrap steel raw material. The vacuum degree is 1.8 Torr, the degassing time is 30 min, the total vacuum treatment time is 30 min, and the steel is tapped. The tapping temperature is 1565℃. Before tapping, the H content in the molten steel is ≤0.0001%, the O content is ≤0.0015%, the N content is ≤0.0074%, and the P content is ≤0.001%. (2) The molten steel is poured, demolded, and electroslag remelted. The average melting rate during electroslag remelting is 800 kg / h, and an electroslag ingot is obtained. The quaternary slag system of CaF2-Al2O3-CaO-MgO is used in the electroslag remelting process. (3) The electroslag ingot is homogenized at 1250°C for 30 hours, and then subjected to three upsetting and three drawing processes with a forging ratio of 7 to obtain a mold steel billet of finished size. The mold steel billet has a width of 1000 mm and a thickness of 600 mm. (4) The mold steel billet is air-cooled to a core temperature of 500°C, annealed at 780°C for 8 hours, subjected to ultra-fine solution treatment at 1040°C for 2 hours, water-cooled to a core temperature of 450°C, and rough-machined on the surface after ball annealing to obtain the ultra-large high-quality 4Cr5MoSiV1 mold steel.

[0051] Comparative Example 1 The preparation method of the 4Cr5MoSiV1 mold steel in this comparative example is similar to that in Example 1, except that in step (1), the vacuum degree is 2.5 Torr and the degassing time is 15 min.

[0052] Comparative Example 2 The preparation method of the 4Cr5MoSiV1 mold steel in this comparative example is similar to that in Example 1, except that CaO, CaF2 and aluminum powder are not added in step (1).

[0053] Comparative Example 3 The preparation method of the 4Cr5MoSiV1 mold steel in this comparative example is similar to that in Example 1, except that in step (2), the average melting rate during electroslag remelting is 600 kg / h.

[0054] Comparative Example 4 The preparation method of the 4Cr5MoSiV1 mold steel in this comparative example is similar to that in Example 1, except that in step (3), the homogenization treatment is carried out at a temperature of 1290℃ for 40h.

[0055] Comparative Example 5 The preparation method of the 4Cr5MoSiV1 mold steel in this comparative example is similar to that in Example 1, except that in step (4), the core temperature is air-cooled to 350°C.

[0056] Comparative Example 6 The preparation method of the 4Cr5MoSiV1 mold steel in this comparative example is similar to that in Example 1, except that in step (4), the temperature of the ultrafine process is 1000℃ and the time is 6h.

[0057] Experimental Example 1 The 4Cr5MoSiV1 mold steels prepared in the examples and comparative examples were subjected to microstructure analysis according to NADCA-207-2016 standard, banded structure analysis according to NADCA-207-2003 standard, and room temperature unnotched impact mechanical property test, respectively. The results are shown in Table 1.

[0058] Table 1

[0059] As shown in Table 1, the 4Cr5MoSiV1 die steel prepared by the method of the present invention has a room temperature unnotched impact strength ≥246J, preferably 246-282J. The microstructure grade is AS4 or higher, and the banded structure grade is SA1.

[0060] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing ultra-large, high-quality 4Cr5MoSiV1 mold steel, characterized in that, Includes the following steps: (1) The scrap steel raw material is smelted in an electric furnace and refined in a refining furnace in sequence. CaO, CaF2 and aluminum powder are added to the refining furnace for smelting. The vacuum degree is ≤2 Torr, the degassing time is ≥20 min, the total vacuum treatment time is ≤50 min, and the steel is tapped. (2) Molten steel is poured, demolded, and electroslag remelted to obtain electroslag ingots; (3) The electroslag ingot is homogenized at a temperature of 1230-1250℃ for 30-45h, and then subjected to three upsetting and three drawing processes to obtain a mold steel billet of finished size; (4) The mold steel billet is air-cooled to a core temperature of 400-500℃, annealed, and then subjected to an ultra-fine solution treatment at a temperature of 1020-1040℃. After solution treatment, it is rapidly cooled to a core temperature of 400-500℃. After ball annealing, the surface is rough-machined to obtain the ultra-large high-quality 4Cr5MoSiV1 mold steel.

2. The method for preparing ultra-large high-quality 4Cr5MoSiV1 mold steel according to claim 1, characterized in that, In step (1), the scrap steel raw materials, by mass percentage, include scrap steel + steel scrap ≥ 70% and pig iron ≤ 30%.

3. The method for preparing ultra-large high-quality 4Cr5MoSiV1 mold steel according to claim 1, characterized in that, In step (1), the mass ratio of CaO, CaF2 and aluminum powder is 6-8:2-1:2-1, and the total mass of CaO, CaF2 and aluminum powder used in the refining furnace is 6.4-8.0% of the mass of scrap steel raw materials.

4. A method for preparing ultra-large high-quality 4Cr5MoSiV1 mold steel according to any one of claims 1-3, characterized in that, In step (1), the tapping temperature is 1555-1565℃.

5. A method for preparing an ultra-large, high-quality 4Cr5MoSiV1 mold steel according to any one of claims 1-3, characterized in that, In step (1), the H content in the molten steel before tapping is ≤0.0001%, the O content is ≤0.0015%, and the N content is ≤0.0074%.

6. The method for preparing an ultra-large, high-quality 4Cr5MoSiV1 mold steel according to claim 1, characterized in that, In step (2), the average melting rate during electroslag remelting is 700-800 kg / h.

7. The method for preparing an ultra-large, high-quality 4Cr5MoSiV1 mold steel according to claim 1, characterized in that, In step (2), the quaternary slag system of CaF2-Al2O3-CaO-MgO is used in the electroslag remelting process.

8. The method for preparing ultra-large high-quality 4Cr5MoSiV1 mold steel according to claim 1, characterized in that, In step (3), the forging ratio is ≥6.

9. The method for preparing ultra-large high-quality 4Cr5MoSiV1 mold steel according to claim 1, characterized in that, In step (4), the ultrafine solid solution treatment time is 2-5 hours.

10. The method for preparing an ultra-large, high-quality 4Cr5MoSiV1 mold steel according to claim 1, characterized in that, In step (4), the annealing temperature is 700-780℃ and the annealing time is 8-15h.

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