Large-size high-carbon die steel containing rare earth elements and method for manufacturing the same

Abstract

The application discloses a large-size high-carbon die steel containing rare earth elements and a preparation method thereof, and belongs to the technical field of steel metallurgy. The large-size high-carbon die steel comprises the following chemical components in percentage by mass: C, Cr, Mo, V, Si, Mn, S, P, Al, RE, Mg and Fe, and the cross-section specification is 500mm-800mm. The preparation method of the large-size high-carbon die steel comprises the following steps: adopting an electric arc furnace to smelt, adopting LF refining, adopting VD vacuum refining to produce the large-size high-carbon die steel; adding rare earth immediately after the VD vacuum refining is broken; adding magnesium alloy after the rare earth is added; tapping; and die casting pouring. Through the cooperation of RE and Mg, the large-size die steel carbide coarse problem is solved, the B type inclusions are controlled, the carbide rating is less than or equal to 4.5, the B type inclusion rating is less than or equal to 1.0, the high-temperature homogenization time is shortened, and the uniformity of the structure, the cleanliness and the mechanical properties are considered.

Description

Technical Field

[0001] This invention relates to the field of iron and steel metallurgy technology, and in particular to a large-size high-carbon mold steel containing rare earth elements and its preparation method. Background Technology

[0002] With the continuous increase in demand for large-scale precision molds in the industrial manufacturing sector, the market demand for large-size high-carbon mold steel is growing daily. Its application scenarios have covered key equipment manufacturing fields such as large stamping dies and heavy forging dies. High-carbon mold steel, due to its high carbon content (usually exceeding 0.6%), possesses excellent hardness and wear resistance. However, when the size is increased, larger-sized ingots are required for production. The cooling rate of large-size ingots is significantly slower, which can easily lead to abnormal coarsening of carbides in the steel, severely damaging the uniformity of the mold steel's microstructure and significantly reducing its service life and performance.

[0003] To address the issue of coarse carbides in high-carbon steel, rare earth treatment technology has gradually become the mainstream solution in the industry. Rare earth elements can effectively inhibit carbide growth and refine their size, improving the microstructure and properties of high-carbon steel. However, the application of rare earth treatment in large-size high-carbon mold steel faces new technical bottlenecks: rare earth elements combine with oxygen, sulfur, and other elements in molten steel, easily forming Class B inclusions (such as chain-like or string-like alumina inclusions), leading to a significant decrease in the cleanliness of the steel. This not only affects the processing performance of the mold steel but also becomes a source of cracks during service, restricting the large-scale application of rare earth treatment technology in large-size high-carbon mold steel.

[0004] Meanwhile, traditional large-size high-carbon die steels often require extended high-temperature homogenization time to improve carbide distribution. This not only increases production energy consumption and process costs but may also lead to abnormal grain growth in the steel due to prolonged high temperatures, further deteriorating material properties. Therefore, how to effectively control the Class B inclusion problem caused by rare earth treatment while refining carbides in large-size high-carbon die steels and shortening the high-temperature homogenization process time has become a key technical challenge that urgently needs to be solved in the current research and development and production of large-size high-carbon die steels. Summary of the Invention

[0005] Based on the shortcomings of the prior art, this paper provides a large-size high-carbon mold steel containing rare earth elements and its preparation method, aiming to solve the problem of carbide deterioration after the size of high-carbon steel increases, and at the same time solve the problem of difficult stable control of inclusions after rare earth treatment.

[0006] To achieve the above objectives, the following technical solution is adopted:

[0007] This invention provides a large-size high-carbon mold steel containing rare earth elements. The chemical composition of the large-size high-carbon mold steel, by mass percentage, includes: C: 1.50%~1.65%, Cr: 11.50%~12.50%, Mo: 0.45%~0.55%, V: 0.20%~0.30%, Si: 0.15%~0.40%, Mn: 0.20%~0.40%, S≤0.005%, P≤0.03%, Al: 0.005%~0.02%, RE: 0.005%~0.02%, Mg: 0.0005%~0.002%, with the balance being Fe and unavoidable impurities. The cross-sectional dimensions of the large-size high-carbon mold steel are 500mm~800mm.

[0008] In some embodiments, RE is a La / Ce composite rare earth element, and the purity of the La / Ce composite rare earth element is ≥95%.

[0009] In some embodiments, the Al content is 0.012% to 0.015% by mass, and the RE content is 0.005% to 0.008%.

[0010] This invention also provides a method for preparing large-size high-carbon mold steel containing rare earth elements as described above, which involves producing large-size high-carbon mold steel by electric arc furnace smelting, LF refining, and VD vacuum refining; after VD vacuum refining, rare earth elements are added, followed by magnesium alloy, and then the steel is tapped and cast.

[0011] In some embodiments, the preparation method includes the following steps:

[0012] S101. Electric arc furnace smelting: Raw materials are smelted in an electric arc furnace using the return method, and the P content of the tapped steel is controlled to be <0.03wt%, the C content to be 0.6wt%~1.5wt%, and the tapping temperature to be 1620℃~1660℃.

[0013] S102.LF furnace refining: Al wire is fed into the ladle to make the Al content in the molten steel 0.005wt%~0.02wt%. Slag additives are added to adjust the slag composition, wherein the slag composition meets the following requirements: Al2O3 25wt%~35wt%, CaO 45wt%~55wt%, MgO ≤8wt%, SiO2 ≤10wt%.

[0014] S103.VD Vacuum Treatment: Control the slag thickness of the ladle to 60~100mm, perform VD vacuum treatment after ladle filling, with ultimate vacuum ≤100Pa, vacuum holding time ≥30min, and argon flow rate 150~250L / min;

[0015] S104.RE treatment: After the VD vacuum process is completed, add 0.1~0.2 kg / t 钢水RE, while soft blowing argon, argon flow rate 30~50L / min, soft blowing time ≥20min;

[0016] S105.Mg treatment: During the soft blowing process, temperature was measured by sampling. When the molten steel temperature was 1445℃~1460℃, 0.05~0.1 kg / t of Ni-Mg alloy containing 15wt% Mg was added. 钢水 ;

[0017] S106. Casting: The steel ingot obtained after casting.

[0018] In some embodiments, the preparation method further includes the following steps after casting:

[0019] S107. Annealing treatment: Heat the steel ingot to 830~860℃ at a rate of 80~100℃ / h, hold for 2~3h, then heat the steel ingot to 1180~1200℃ at a rate of 180~200℃ / h, hold for 3~6h; during the heating process, turn the steel ingot over once every 1~1.5h.

[0020] S108. Forging and forming: Forging begins after the heat preservation is completed. The initial forging temperature is >1100℃ and the final forging temperature is >900℃. The three-upsetting and three-drawing process is adopted. After forging, the material is air-cooled to room temperature to obtain large-size high-carbon die steel with a cross-sectional size of 500mm~800mm.

[0021] In some embodiments, the raw materials in step S101 include recycled steel, recycled alloys similar to steel, and industrial pure iron.

[0022] In some embodiments, RE is a La / Ce composite rare earth element, and the purity of the La / Ce composite rare earth element is ≥95%.

[0023] In some embodiments, after the VD vacuum is completed in step S104, 0.15~0.2 kg / t is added. 钢水 RE, while soft blowing argon, argon flow rate 35~50L / min, soft blowing time 35-40min.

[0024] In some embodiments, the chemical composition of the large-size high-carbon mold steel, by mass percentage, includes: C: 1.50%~1.65%, Cr: 11.50%~12.50%, Mo: 0.45%~0.55%, V: 0.20%~0.30%, Si: 0.15%~0.40%, Mn: 0.20%~0.40%, S≤0.005%, P≤0.03%, Al: 0.005%~0.02%, RE: 0.005%~0.02%, Mg: 0.0005%~0.002%, with the balance being Fe and unavoidable impurities.

[0025] The present invention has the following beneficial technical effects:

[0026] The chemical composition and cross-sectional specifications of the large-size high-carbon mold steel containing rare earth elements of the present invention, through precise control of the content range of main alloying elements such as C, Cr, Mo, and V, combined with the synergistic addition of RE (rare earth) and Mg, on the one hand, ensure the hardness and wear resistance of the mold steel base by means of high carbon and high chromium composition, and on the other hand, use RE to refine the carbides that are easily coarsened during the cooling process of large-size mold ingots. At the same time, Mg can suppress the Class B inclusions caused by rare earth treatment, thus achieving a balance between the uniformity and cleanliness of the microstructure of large-section mold steel of 500mm~800mm, and solving the core contradiction of the difficulty in balancing the coarseness of carbides and the cleanliness of large-size high-carbon mold steel.

[0027] The present invention clarifies the core process sequence of adding rare earth elements first and then magnesium alloy after VD vacuum refining to remove air bubbles. VD vacuum treatment can remove some gases and inclusions in the molten steel in advance, providing a clean molten steel environment for the action of rare earth elements and magnesium. Adding rare earth elements first can preferentially achieve carbide refinement, and adding magnesium alloy later can specifically modify the B-type inclusions generated by rare earth treatment. This process sequence avoids mutual interference between rare earth elements and magnesium, and achieves step-by-step synergistic effect of carbide refinement and inclusion modification. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 This is a flowchart of the preparation method of large-size high-carbon mold steel containing rare earth elements according to the present invention;

[0030] Figure 2 This is a carbide morphology diagram of a large-size high-carbon mold steel containing rare earth elements in Embodiment 1 of the present invention;

[0031] Figure 3 This is a schematic diagram of typical inclusions in large-size high-carbon mold steel containing rare earth elements according to Embodiment 1 of the present invention;

[0032] Figure 4 This is a schematic diagram of typical inclusions in large-size high-carbon mold steel containing rare earth elements according to Embodiment 1 of the present invention;

[0033] Figure 5 The image shows the carbide morphology in the high-carbon mold steel of Comparative Example 1.

[0034] Figure 6The image shows the carbide morphology in the high-carbon mold steel of Comparative Example 2.

[0035] Figure 7 This is a schematic diagram of typical inclusions in the high-carbon mold steel of Comparative Example 2;

[0036] Figure 8 This is a schematic diagram of typical inclusions in the high-carbon mold steel of Comparative Example 2. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be further described in detail below with reference to specific examples and the accompanying drawings.

[0038] It should be understood that the embodiments of the invention shown in the exemplary embodiments are merely illustrative. Although only a few embodiments have been described in detail in this invention, those skilled in the art will readily recognize that various modifications are possible without substantially departing from the teachings of the invention. Accordingly, all such modifications should be included within the scope of the invention. Other substitutions, modifications, variations, and deletions can be made to the design, operating conditions, and parameters of the following exemplary embodiments without departing from the spirit of the invention.

[0039] Based on the above objectives, a first aspect of the embodiments of the present invention provides a large-size high-carbon mold steel containing rare earth elements. The chemical composition of the large-size high-carbon mold steel, by mass percentage, includes: C: 1.50%~1.65%, Cr: 11.50%~12.50%, Mo: 0.45%~0.55%, V: 0.20%~0.30%, Si: 0.15%~0.40%, Mn: 0.20%~0.40%, S≤0.005%, P≤0.03%, Al: 0.005%~0.02%, RE: 0.005%~0.02%, Mg: 0.0005%~0.002%, with the balance being Fe and unavoidable impurities; the cross-sectional dimensions of the large-size high-carbon mold steel are 500mm~800mm.

[0040] In a preferred embodiment of the present invention, RE is a La / Ce composite rare earth, and the purity of the La / Ce composite rare earth is ≥95%.

[0041] Limiting RE to La / Ce composite rare earth with a purity of ≥95% can avoid secondary contamination of molten steel by impurities in low-purity rare earths. On the other hand, the synergistic effect of La and Ce can more efficiently adsorb harmful impurities in molten steel and hinder carbide nucleus growth. Compared with single rare earths, its refining effect on carbides is more significant, which can stabilize the carbide rating at 4.0~4.5. At the same time, it reduces the amount of rare earth used, achieving the optimal balance between rare earth treatment effect and cost.

[0042] In a preferred embodiment of the present invention, the Al content is 0.012% to 0.015% by mass percentage, and the RE content is 0.005% to 0.008%.

[0043] A second aspect of the present invention provides a method for preparing large-size high-carbon mold steel containing rare earth elements. The method involves electric arc furnace smelting, LF refining, and VD vacuum refining to produce the large-size high-carbon mold steel; after VD vacuum refining, rare earth elements are added, followed by magnesium alloy, then the steel is tapped and cast.

[0044] Figure 1 The diagram shown is a schematic flowchart of the method. For example... Figure 1 As shown, the preparation may include the following steps:

[0045] S101. Electric arc furnace smelting: Raw materials are smelted in an electric arc furnace using the return method, and the P content of the tapped steel is controlled to be <0.03wt%, the C content to be 0.6wt%~1.5wt%, and the tapping temperature to be 1620℃~1660℃.

[0046] S102.LF furnace refining: Al wire is fed into the ladle to make the Al content in the molten steel 0.005wt%~0.02wt%. Slag additives are added to adjust the slag composition. The slag composition meets the requirements of Al2O3 25wt%~35wt%, CaO 45wt%~55wt%, MgO≤8wt%, SiO2≤10wt%. The refined molten steel meets the composition requirements except for RE and Mg.

[0047] S103.VD Vacuum Treatment: Control the slag thickness of the ladle to 60~100mm, perform VD vacuum treatment after ladle filling, with ultimate vacuum ≤100Pa, vacuum holding time ≥30min, and argon flow rate 150~250L / min;

[0048] S104.RE treatment: After the VD vacuum process is completed, add 0.1~0.2 kg / t 钢水 RE, while soft blowing argon, argon flow rate 30~50L / min, soft blowing time ≥20min;

[0049] S105.Mg treatment: During the soft blowing process, temperature was measured by sampling. When the molten steel temperature was 1445℃~1460℃, 0.05~0.1 kg / t of Ni-Mg alloy containing 15wt% Mg was added. 钢水 ;

[0050] S106. Casting: Casting is carried out using a slit-type argon gas device to protect the steel ingot;

[0051] S107. Annealing treatment: Heat the steel ingot to 830~860℃ at a rate of 80~100℃ / h, hold for 2~3h, then heat the steel ingot to 1180~1200℃ at a rate of 180~200℃ / h, hold for 3~6h; during the heating process, turn the steel ingot over once every 1~1.5h.

[0052] S108. Forging and forming: Forging begins after the heat preservation is completed. The initial forging temperature is >1100℃ and the final forging temperature is >900℃. The three-upsetting and three-drawing process is adopted. After forging, the material is air-cooled to room temperature to obtain large-size high-carbon die steel with a cross-sectional size of 500mm~800mm.

[0053] The core process sequence of adding rare earth elements first and then magnesium alloys after VD vacuum refining was determined. VD vacuum treatment removes some gases and large particle inclusions from the molten steel in advance, providing a clean molten steel environment for the action of rare earth elements and magnesium. Adding rare earth elements first can prioritize the refinement of carbides, while adding magnesium alloys later can specifically modify the Class B inclusions generated by rare earth treatment, avoiding mutual interference between the two. This achieves a step-by-step synergistic effect of carbide refinement and inclusion modification, ensuring the effectiveness and stability of the process.

[0054] In a preferred embodiment of the present invention, the raw materials in step S101 include recycled steel, recycled alloys similar to steel, and industrial pure iron.

[0055] In a preferred embodiment of the present invention, in step S102, after adding slag additives to adjust the slag composition to meet the above requirements, the furnace is heated by electricity for refining. The molten steel refined in the LF furnace is sampled and analyzed. After the molten steel meets the composition requirements except for RE and Mg, it undergoes VD treatment. Specifically, the sample analysis should meet the following composition requirements: C: 1.50%~1.65%, Cr: 11.50%~12.50%, Mo: 0.45%~0.55%, V: 0.20%~0.30%, Si: 0.15%~0.40%, Mn: 0.20%~0.40%, S≤0.005%, P≤0.03%, Al: 0.005%~0.02%.

[0056] In a preferred embodiment of the present invention, RE is a La / Ce composite rare earth, and the purity of the La / Ce composite rare earth is ≥95%.

[0057] In a preferred embodiment of the present invention, after the VD vacuum is completed in step S104, 0.15~0.2 kg / t is added. 钢水 RE, while soft blowing argon, argon flow rate 35~50L / min, soft blowing time 35-40min.

[0058] The present invention will be further illustrated by the following examples.

[0059] Example 1

[0060] Methods for preparing large-size high-carbon mold steel containing rare earth elements include:

[0061] S101. Smelting in an electric arc furnace: The raw materials are smelted using the return method. The raw materials are mainly returned materials from Benxi Steel and similar alloy returned materials, as well as industrial pure iron. The electric arc furnace uses the return method for smelting. The P content of the steel tapped from the electric arc furnace is less than 0.021 wt%, the C content is 0.61 wt%, and the tapping temperature is 1630℃.

[0062] S102 and LF furnace refining: After the ladle enters the LF furnace, an Al wire is fed in to make the Al content of the molten steel 0.015wt%. Then, slag additives are added to adjust the slag composition. The LF slag composition meets the following requirements: Al2O3: 28.8wt%, CaO: 53.1wt%, MgO: 6.5wt%, SiO2: 7.5wt%, with the remainder being unavoidable impurities (FeO, MnO, CaF2, TiO2, etc.). Subsequently, the furnace is heated by electricity for refining. Sampling and analysis show that the composition is C: 1.51wt%, Cr: 11.58wt%, Mo: 0.48wt%, V: 0.25wt%, Si: 0.16wt%, Mn: 0.32wt%, S: 0.002wt%, P: 0.022wt%, and Al: 0.015wt%. The molten steel then enters the VD treatment.

[0063] S103, VD vacuum treatment: The thickness of the slag in the ladle is between 60-100mm. After ladle filling, VD vacuum treatment is performed, maintaining an ultimate vacuum of 67pa for 35min, with an argon flow rate of 180L / min.

[0064] S104, RE treatment: After VD vacuum treatment, add 0.15 kg / t 钢水 The La / Ce composite rare earth (rare earth content greater than 95%) was subjected to soft blowing argon at a flow rate of 35 L / min and a soft blowing time of 35 min. The rare earth (RE) content in the finished sample was 0.012 wt%.

[0065] S105, Mg treatment: During the soft blowing process, sampling and temperature measurement were performed. When the temperature reached 1458℃, 0.1 kg / t of Ni-Mg alloy containing 15 wt% Mg was added. 钢水 Then the hoist was prepared for pouring, and the Mg content in the finished sample was 0.0006 wt%.

[0066] S106. Casting: Casting is protected by a slit-type argon gas protection device to obtain steel ingots, the ingot shape is 18t octagonal ingot.

[0067] S107 Annealing treatment: First, heat the steel ingot to 850℃ at a heating rate of 80℃ / h and hold for 3 hours. Then, heat the steel ingot to 1200℃ at a heating rate of 190℃ / h and hold for 4 hours. The steel ingot is turned over once every 1.5 hours in the heating furnace.

[0068] S108, Forging and Shaping: Forging begins after the heat treatment is completed, with an initial forging temperature of 1150℃ and a final forging temperature of 950℃. A three-upsetting and three-drawing process is used to produce large-size high-carbon die steel with a final cross-sectional dimension of Ø800mm. The finished die steel, air-cooled to room temperature, has a carbide rating of 4.5.

[0069] Table 1. Inclusion rating of finished mold steel products in Example 1

[0070]

[0071] Example 2

[0072] Methods for preparing large-size high-carbon mold steel containing rare earth elements include:

[0073] S101. Smelting in an electric arc furnace: The raw materials are smelted using the return method. The raw materials are mainly returned materials from Benxi Steel and similar alloy returned materials, as well as industrial pure iron. The electric arc furnace uses the return method for smelting. The P content of the steel tapped from the electric arc furnace is less than 0.025wt%, the C content is 0.68wt%, and the tapping temperature is 1635℃.

[0074] S102 and LF furnace refining: After the ladle enters the LF furnace, an Al wire is fed in to make the Al content of the molten steel 0.013%. Then, slag additives are added to adjust the slag composition. The LF slag composition meets the following requirements: Al2O3: 30.8wt%, CaO: 54.2wt%, MgO: 5.4wt%, SiO2: 8.0wt%, with the remainder being unavoidable impurities (FeO, MnO, CaF2, TiO2, etc.). Subsequently, the furnace is heated by electricity for refining. Sampling analysis shows that the composition is C: 1.53wt%, Cr: 12.13wt%, Mo: 0.51wt%, V: 0.26wt%, Si: 0.21wt%, Mn: 0.35wt%, S: 0.002wt%, P: 0.025wt%, and Al: 0.013wt%. The molten steel then enters the VD treatment.

[0075] S103, VD vacuum treatment: The thickness of the slag in the ladle is between 60-100mm. After ladle filling, VD vacuum treatment is performed, maintaining the ultimate vacuum of 67pa for 32min, with an argon flow rate of 180L / min.

[0076] S104, RE treatment: After VD vacuum treatment, add 0.15 kg / t 钢水The La / Ce composite rare earth (rare earth content greater than 95%) was subjected to soft argon blowing at a flow rate of 35 L / min for 40 min, and the rare earth (RE) content in the finished sample was 0.015 wt%.

[0077] S105, Mg treatment: During the soft blowing process, samples were taken and the temperature was measured. When the temperature reached 1455℃, 0.1 kg / t of Ni-Mg alloy containing 15 wt% Mg was added. 钢水 Then the hoist was prepared for pouring, and the Mg content in the finished sample was 0.0008 wt%.

[0078] S106. Casting: Casting is protected by a slit-type argon gas protection device to obtain steel ingots, the ingot shape is 18t octagonal ingot.

[0079] S107 Annealing treatment: First, heat the steel ingot to 860℃ at a heating rate of 80℃ / h and hold for 3 hours. Then, heat the steel ingot to 1200℃ at a heating rate of 190℃ / h and hold for 4 hours. The steel ingot is turned over once every 1.5 hours in the heating furnace.

[0080] S108, Forging and Shaping: Forging begins after the heat treatment is completed, with an initial forging temperature of 1130℃ and a final forging temperature of 950℃. A three-upsetting and three-drawing process is used to produce a large-size high-carbon die steel with a final cross-sectional dimension of Ø650mm. The finished die steel, air-cooled to room temperature, has a carbide rating of 4.0.

[0081] Table 2. Inclusion rating of finished mold steel products in Example 2

[0082]

[0083] Example 3

[0084] Methods for preparing large-size high-carbon mold steel containing rare earth elements include:

[0085] The electric arc furnace is used for smelting: the raw materials are smelted using the return method. The raw materials are mainly returned materials from Benxi Steel and similar alloy returned materials, as well as industrial pure iron. The electric arc furnace uses the return method for smelting. The P content of the steel tapped from the electric arc furnace is 0.028wt%, the C content is 1.50wt%, and the tapping temperature is 1620℃.

[0086] LF furnace refining: After the ladle enters the LF furnace, an Al wire is fed in to make the Al content of the molten steel 0.012wt%. Then, slag additives are added to adjust the slag composition. The LF slag composition meets the following requirements: Al2O3: 25wt%, CaO: 45wt%, MgO: 8wt%, SiO2: 10wt%, with the remainder being unavoidable impurities (FeO, MnO, CaF2, TiO2, etc.). Subsequently, the furnace is powered on and heated for refining. Sampling and analysis show that the composition is C: 1.50wt%, Cr: 11.50wt%, Mo: 0.45wt%, V: 0.20wt%, Si: 0.15wt%, Mn: 0.20wt%, S: 0.002wt%, P: 0.028wt%, and Al: 0.012wt%. The molten steel then enters the VD treatment.

[0087] VD Vacuum Treatment: The slag thickness in the ladle is 60mm. After ladle filling, VD vacuum treatment is performed, maintaining an ultimate vacuum of 100Pa for 30 minutes, with an argon flow rate of 150L / min.

[0088] RE treatment: After the VD vacuum process is completed, add 0.1 kg / t 钢水 The La / Ce composite rare earth (rare earth content greater than 95%) was subjected to soft argon blowing at a flow rate of 30 L / min for 20 min, and the rare earth (RE) content in the finished sample was 0.005 wt%.

[0089] Mg treatment: During the soft blowing process, samples were taken and the temperature was measured. When the temperature reached 1445℃, 0.05 kg / t of Ni-Mg alloy containing 15 wt% Mg was added. 钢水 Then the hoist was prepared for pouring, and the Mg content in the finished sample was 0.0005wt%.

[0090] Casting: Casting is protected by a slit-type argon gas protection device to obtain steel ingots, the ingot shape is 18t octagonal ingot.

[0091] Annealing treatment: First, heat the steel ingot to 830℃ at a heating rate of 80℃ / h and hold for 2 hours. Then, heat the steel ingot to 1180℃ at a heating rate of 180℃ / h and hold for 3 hours. The steel ingot is turned over once every 1 hour in the heating furnace.

[0092] Forging: Forging begins after the heat treatment period, with an initial forging temperature of 1105℃ and a final forging temperature of 905℃. A three-upsetting and three-drawing process is used to produce large-size high-carbon die steel with a final cross-sectional dimension of Ø500mm, which is then air-cooled to room temperature. The finished product has a carbide rating of 4.2.

[0093] Table 3. Inclusion rating of finished mold steel products in Example 3

[0094]

[0095] Example 4

[0096] Methods for preparing large-size high-carbon mold steel containing rare earth elements include:

[0097] The electric arc furnace is used for smelting: the raw materials are smelted using the return method. The raw materials are mainly returned materials from Benxi Steel and similar alloy returned materials, as well as industrial pure iron. The electric arc furnace uses the return method for smelting. The P content of the steel tapped from the electric arc furnace is 0.025wt%, the C content is 1.5wt%, and the tapping temperature is 1660℃.

[0098] LF furnace refining: After the ladle enters the LF furnace, an Al wire is fed in to make the Al content of the molten steel 0.02wt%. Then, slag additives are added to adjust the slag composition. The LF slag composition meets the following requirements: Al2O3: 35wt%, CaO: 55wt%, MgO: 6wt%, SiO2: 8wt%, with the remainder being unavoidable impurities (FeO, MnO, CaF2, TiO2, etc.). Subsequently, the furnace is heated by electricity for refining. Sampling and analysis show that the composition is C: 1.65wt%, Cr: 12.50wt%, Mo: 0.55wt%, V: 0.30wt%, Si: 0.40wt%, Mn: 0.40wt%, S: 0.003wt%, P: 0.025wt%, and Al: 0.02wt%. The molten steel then enters the VD treatment.

[0099] VD vacuum treatment: The slag thickness in the ladle is 100mm. After ladle filling, VD vacuum treatment is performed, maintaining an ultimate vacuum of 80Pa for 45 minutes, with an argon flow rate of 250L / min.

[0100] RE treatment: After the VD vacuum process is completed, add 0.2 kg / t 钢水 The La / Ce composite rare earth (rare earth content greater than 95%) was subjected to soft argon blowing at a flow rate of 50 L / min for 40 min, and the rare earth (RE) content in the finished sample was 0.02 wt%.

[0101] Mg treatment: During the soft blowing process, samples were taken and the temperature was measured. When the temperature reached 1460℃, 0.1 kg / t of Ni-Mg alloy containing 15 wt% Mg was added. 钢水 Then the hoist was prepared for pouring, and the Mg content in the finished sample was 0.002wt%.

[0102] Casting: Casting is protected by a slit-type argon gas protection device to obtain steel ingots, the ingot shape is 18t octagonal ingot.

[0103] Annealing treatment: First, heat the steel ingot to 860℃ at a heating rate of 100℃ / h and hold for 3 hours. Then, heat the steel ingot to 1200℃ at a heating rate of 200℃ / h and hold for 6 hours. The steel ingot is turned over once every 1.5 hours in the heating furnace.

[0104] Forging: Forging begins after the heat treatment period, with an initial forging temperature of 1180℃ and a final forging temperature of 960℃. A three-upsetting and three-drawing process is used to produce large-size high-carbon die steel with a final cross-sectional dimension of Ø800mm, which is then air-cooled to room temperature. The finished product has a carbide rating of 4.5.

[0105] Table 4. Inclusion rating of finished mold steel products in Example 4

[0106]

[0107] Example 5

[0108] Methods for preparing large-size high-carbon mold steel containing rare earth elements include:

[0109] The electric arc furnace is used for smelting: the raw materials are smelted using the return method. The raw materials are mainly returned materials from Benxi Steel and similar alloy returned materials, as well as industrial pure iron. The electric arc furnace uses the return method for smelting. The P content of the steel tapped from the electric arc furnace is 0.02wt%, the C content is 1.65wt%, and the tapping temperature is 1640℃.

[0110] LF furnace refining: After the ladle enters the LF furnace, an Al wire is fed in to make the Al content of the molten steel 0.02wt%. Then, slag additives are added to adjust the slag composition. The LF slag composition meets the following requirements: Al2O3: 30wt%, CaO: 50wt%, MgO: 5wt%, SiO2: 7wt%, with the remainder being unavoidable impurities (FeO, MnO, CaF2, TiO2, etc.). Subsequently, electricity is supplied to raise the temperature for refining. Sampling and analysis show that C: 1.65wt%, Cr: 12.50wt%, Mo: 0.55wt%, V: 0.30wt%, Si: 0.40wt%, Mn: 0.40wt%, S: 0.002wt%, P: 0.02wt%, Al: 0.02wt%, and the steel enters the VD treatment.

[0111] VD vacuum treatment: The slag thickness in the ladle is 80mm. After ladle filling, VD vacuum treatment is performed, maintaining an ultimate vacuum of 67Pa for 45min, with an argon flow rate of 200L / min.

[0112] RE treatment: After the VD vacuum process is completed, add 0.2 kg / t 钢水 The La / Ce composite rare earth (rare earth content greater than 95%) was subjected to soft argon blowing at a flow rate of 35 L / min for 35 min, and the rare earth (RE) content in the finished sample was 0.02 wt%.

[0113] Mg treatment: During the soft blowing process, samples were taken and the temperature was measured. When the temperature reached 1458℃, 0.50 kg / t of Ni-Mg alloy containing 15 wt% Mg was added. 钢水 Then the hoist was prepared for pouring, and the Mg content in the finished sample was 0.002wt%.

[0114] Casting: Casting is protected by a slit-type argon gas protection device to obtain steel ingots, the ingot shape is 18t octagonal ingot.

[0115] Annealing treatment: First, heat the steel ingot to 850℃ at a heating rate of 90℃ / h and hold for 2.5h. Then, heat the steel ingot to 1190℃ at a heating rate of 190℃ / h and hold for 4.5h. The steel ingot is turned over once every 1.5h in the heating furnace.

[0116] Forging: Forging begins after the heat treatment period, with an initial forging temperature of 1150℃ and a final forging temperature of 930℃. A three-upsetting and three-drawing process is used to produce large-size high-carbon die steel with a final cross-sectional dimension of Ø800mm, which is then air-cooled to room temperature. The finished product has a carbide rating of 4.0.

[0117] Table 5. Inclusion rating of finished mold steel products in Example 5

[0118]

[0119] Comparative Example 1

[0120] Methods for preparing large-size high-carbon mold steel include:

[0121] S101. Smelting in an electric arc furnace: The raw materials are smelted using the return method. The raw materials are mainly returned materials from Benxi Steel and similar alloy returned materials, as well as industrial pure iron. The electric arc furnace uses the return method for smelting. The P content of the steel tapped from the electric arc furnace is less than 0.020 wt%, the C content is 0.71 wt%, and the tapping temperature is 1638℃.

[0122] S102 and LF furnace refining: After the ladle enters the LF furnace, an Al wire is fed in to make the Al content of the molten steel 0.012wt%. Then, slag additives are added to adjust the slag composition. The LF slag composition meets the following requirements: Al2O3: 31.8wt%, CaO: 53.2wt%, MgO: 5.5wt%, SiO2: 7.8wt%, with the remainder being unavoidable impurities (FeO, MnO, CaF2, TiO2, etc.). Subsequently, the furnace is heated by electricity for refining. Sampling and analysis show that C: 1.61wt%, Cr: 11.58wt%, Mo: 0.48wt%, V: 0.27wt%, Si: 0.31wt%, Mn: 0.32wt%, S: 0.002wt%, P: 0.020wt%, Al: 0.012wt%. The molten steel then enters the VD treatment.

[0123] S103, VD vacuum treatment: The thickness of the slag in the ladle is between 60-100mm. After ladle filling, VD vacuum treatment is performed, maintaining the ultimate vacuum of 67pa for 36min, with an argon flow rate of 180 L / min.

[0124] S104, VD soft blowing treatment: After the VD vacuum is completed, argon is blown in at a flow rate of 35 L / min for 40 min.

[0125] S105, Ladle: During the soft blowing process, temperature is measured by sampling. When the temperature reaches 1448℃, the ladle is ready for pouring.

[0126] S106. Casting: Casting is protected by a slit-type argon gas protection device to obtain steel ingots, the ingot shape is 18t octagonal ingot.

[0127] S107 Annealing treatment: First, heat the steel ingot to 860℃ at a heating rate of 80℃ / h and hold for 3 hours. Then, heat the steel ingot to 1200℃ at a heating rate of 190℃ / h and hold for 6 hours. The steel ingot is turned over once every 1.5 hours in the heating furnace.

[0128] S108, Forging and Shaping: Forging begins after the heat treatment is completed, with an initial forging temperature of 1180℃ and a final forging temperature of 970℃. A three-upsetting and three-drawing process is used to produce large-size high-carbon die steel with a final cross-sectional dimension of Ø800mm. The finished die steel, air-cooled to room temperature, has a carbide rating of 7.0.

[0129] Table 6. Inclusion rating of finished mold steel products in Comparative Example 1

[0130]

[0131] Comparative Example 2

[0132] Methods for preparing large-size high-carbon mold steel include:

[0133] S101. Smelting in an electric arc furnace: The raw materials are smelted using the return method. The raw materials are mainly returned materials from Benxi Steel and similar alloy returned materials, as well as industrial pure iron. The electric arc furnace is smelted using the return method. The P content of the steel tapped from the electric arc furnace is 0.018 wt%, the C content is 0.73 wt%, and the tapping temperature is 1638℃.

[0134] S102 and LF furnace refining: After the ladle enters the LF furnace, an Al wire is fed in to make the Al content of the molten steel 0.018wt%. Then, slag additives are added to adjust the slag composition. The LF slag composition meets the following requirements: Al2O3: 33.8wt%, CaO: 52.3wt%, MgO: 6.4wt%, SiO2: 7.3wt%, with the remainder being unavoidable impurities (FeO, MnO, CaF2, TiO2, etc.). Subsequently, the furnace is heated by electricity for refining. Sampling and analysis show that C: 1.51wt%, Cr: 12.14wt%, Mo: 0.52wt%, V: 0.22wt%, Si: 0.32wt%, Mn: 0.28wt%, S: 0.002wt%, P: 0.018wt%, Al: 0.018wt%. The molten steel then enters the VD treatment.

[0135] S103, VD vacuum treatment: The thickness of the slag in the ladle is between 60-100mm. After ladle filling, VD vacuum treatment is performed, maintaining an ultimate vacuum of 67pa for 36min, with an argon flow rate of 180L / min.

[0136] S104, RE treatment: After VD vacuum treatment, add 0.15 kg / t 钢水 The La / Ce composite rare earth (rare earth content greater than 95%) was subjected to soft argon blowing at a flow rate of 35 L / min for 42 min, and the rare earth (RE) content in the finished sample was 0.012 wt%.

[0137] S105, Ladle: During the soft blowing process, temperature is measured by sampling. When the temperature reaches 1450℃, the ladle is ready for pouring.

[0138] S106. Casting: Casting is protected by a slit-type argon gas protection device to obtain steel ingots, the ingot shape is 18t octagonal ingot.

[0139] S107 Annealing treatment: First, heat the steel ingot to 860℃ at a heating rate of 80℃ / h and hold for 3 hours. Then, heat the steel ingot to 1200℃ at a heating rate of 190℃ / h and hold for 5.5 hours. The steel ingot is turned over once every 1.5 hours in the heating furnace.

[0140] S108, Forging and Shaping: Forging begins after the heat treatment is completed, with an initial forging temperature of 1185℃ and a final forging temperature of 968℃. It employs a three-upsetting and three-drawing process, producing a large-size high-carbon die steel with a final cross-sectional dimension of Ø650mm. The finished die steel, air-cooled to room temperature, has a carbide rating of 4.5.

[0141] Table 7. Inclusion rating of finished mold steel products in Comparative Example 2

[0142]

[0143] Figure 2 This image shows the carbide morphology in the large-size high-carbon mold steel containing rare earth elements from Example 1, specifically the carbide morphology after rare earth and Mg treatment. After rare earth and Mg treatment, the carbide size in the steel is smaller, and the carbide rating is relatively high at 4.5. Figure 3-4 The diagram shows typical inclusions in the large-size high-carbon mold steel containing rare earth elements in Example 1. Referring to Table 1, it can be seen that the inclusions are relatively small, with a Class B inclusion rating of 1.0. Referring to Tables 2-5, the inclusions in the large-size high-carbon mold steel containing rare earth elements in Examples 2-5 are also relatively small, with a Class B inclusion rating of 1.0-1.5.

[0144] Figure 5The images and Table 6 show the carbide morphology in the high-carbon mold steel of Comparative Example 1. The carbide morphology in the untreated steel of Comparative Example 1 is shown in Table 6. Therefore, the carbide size in the untreated steel is larger and the carbide rating is poor, with a score of 7.

[0145] Figure 6 The image shows the carbide morphology in the high-carbon mold steel of Comparative Example 2. After rare earth treatment, the carbide size in the high-carbon mold steel of Comparative Example 2 was significantly reduced, and the carbide rating was relatively low at 4.5. However, combined with... Figure 7-8 As shown in Table 7, the high-carbon mold steel of Comparative Example 2, which was only treated with rare earth elements and not with Mg, is prone to generating Class B inclusions, with a poor inclusion rating of Class B inclusions reaching 2.0.

[0146] The above are exemplary embodiments disclosed in this invention. However, it should be noted that various changes and modifications can be made without departing from the scope of the embodiments of this invention as defined by the claims. Although the elements disclosed in the embodiments of this invention may be described or claimed individually, they may be understood as multiple unless explicitly limited to a singular number.

[0147] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention (including the claims) is limited to these examples. Within the framework of the invention, technical features of the above embodiments or different embodiments can be combined, and many other variations of different aspects of the invention exist, which are not provided in the details for the sake of brevity. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the invention should be included within the protection scope of the invention.

Claims

1. A large-size high-carbon mold steel containing rare earth elements, characterized in that, The chemical composition of the large-size high-carbon mold steel, by mass percentage, includes: C: 1.50%~1.65%, Cr: 11.50%~12.50%, Mo: 0.45%~0.55%, V: 0.20%~0.30%, Si: 0.15%~0.40%, Mn: 0.20%~0.40%, S≤0.005%, P≤0.03%, Al: 0.005%~0.02%, RE: 0.005%~0.02%, Mg: 0.0005%~0.002%, with the balance being Fe and unavoidable impurities; the cross-sectional dimensions of the large-size high-carbon mold steel are 500mm~800mm. The large-size high-carbon mold steel is produced by electric arc furnace smelting, LF refining, and VD vacuum refining. After VD vacuum refining, rare earth elements are added, followed by magnesium alloy, and then the steel is tapped and cast.

2. The large-size high-carbon mold steel containing rare earth elements according to claim 1, characterized in that, RE is a La / Ce composite rare earth, and the purity of the rare earth raw materials for the La / Ce composite rare earth is ≥95%.

3. The large-size high-carbon mold steel containing rare earth elements according to claim 1, characterized in that, By mass percentage, the Al content is 0.012%~0.015%, and the RE content is 0.005%~0.008%.

4. A method for preparing large-size high-carbon mold steel containing rare earth elements according to any one of claims 1-3, characterized in that, Large-size high-carbon mold steel is produced by electric arc furnace smelting, LF refining, and VD vacuum refining; after VD vacuum refining, rare earth elements are added, followed by magnesium alloy, and then the steel is tapped and cast.

5. The preparation method according to claim 4, characterized in that, The preparation method includes the following steps: S101. Electric arc furnace smelting: Raw materials are smelted in an electric arc furnace using the return method, and the P content of the tapped steel is controlled to be <0.03wt%, the C content to be 0.6wt%~1.5wt%, and the tapping temperature to be 1620℃~1660℃. S102.LF furnace refining: Al wire is fed into the ladle to make the Al content in the molten steel 0.005wt%~0.02wt%. Slag additives are added to adjust the slag composition, wherein the slag composition meets the following requirements: Al2O3 25wt%~35wt%, CaO 45wt%~55wt%, MgO ≤8wt%, SiO2 ≤10wt%. S103.VD Vacuum Treatment: Control the slag thickness of the ladle to 60~100mm, perform VD vacuum treatment after ladle filling, with ultimate vacuum ≤100Pa, vacuum holding time ≥30min, and argon flow rate 150~250L / min; S104.RE treatment: After the VD vacuum process is completed, add 0.1~0.2 kg / t 钢水 RE, while soft blowing argon, argon flow rate 30~50L / min, soft blowing time ≥20min; S105.Mg treatment: During the soft blowing process, temperature was measured by sampling. When the molten steel temperature was 1445℃~1460℃, 0.05~0.1 kg / t of Ni-Mg alloy containing 15wt% Mg was added. 钢水 ; S106. Casting: The steel ingot obtained after casting.

6. The preparation method according to claim 5, characterized in that, The preparation method further includes the following steps after casting: S107. Annealing treatment: Heat the steel ingot to 830~860℃ at a rate of 80~100℃ / h, hold for 2~3h, then heat the steel ingot to 1180~1200℃ at a rate of 180~200℃ / h, hold for 3~6h; during the heating process, turn the steel ingot over once every 1~1.5h. S108. Forging and forming: Forging begins after the heat preservation is completed. The initial forging temperature is >1100℃ and the final forging temperature is >900℃. The three-upsetting and three-drawing process is adopted. After forging, the material is air-cooled to room temperature to obtain large-size high-carbon die steel with a cross-sectional size of 500mm~800mm.

7. The preparation method according to claim 5, characterized in that, The raw materials in step S101 include recycled steel, recycled alloys similar to those used in Benxi Steel, and industrial pure iron.

8. The preparation method according to claim 5, characterized in that, RE is a La / Ce composite rare earth, and the purity of the rare earth raw materials for the La / Ce composite rare earth is ≥95%.

9. The preparation method according to claim 6, characterized in that, After the VD vacuum is completed in step S104, add 0.15~0.2 kg / t 钢水 RE, while soft blowing argon, argon flow rate 35~50L / min, soft blowing time 35-40min.

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