Large-size high-performance hot work die steel and its smelting process

Abstract

The present application relates to a kind of big specification high-performance hot die steel and its smelting process, including following chemical components by weight percentage: [C]:0.33~0.42%、[Si]:0.20~0.40%、[Mn]:0.30~0.60%、[Cr]:4.90~5.50%、[Ni]:0.40~0.80%、[Mo]:2.10~2.30%、[V]:0.70~0.80%、[Co]:0.60~0.80%、[P]≤0.012%、[S]≤0.002%、[Cu]≤0.10%、La+Ce:20~50ppm、(As+Sn+Pb+Sb+Bi)≤0.020%, the balance is [Fe];Using "electric furnace smelting+ladle refining+vacuum refining→continuous casting→annealing / hot delivery→finishing→detection" method, realize high-performance hot die steel big specification continuous casting billet center loose ≤0.5 level, center crack ≤1.0 level, same section carbon difference ≤0.02%, non-metallic inclusion total can reach ≤2.5 level, cost is lower than original process route 200~500 yuan / t, the method is realized with lower cost and shorter production cycle while high performance.

Description

Technical Field

[0001] This invention belongs to the field of steelmaking process technology, and relates to a large-size high-performance hot work die steel and its smelting process. Background Technology

[0002] Hot work die steel is a cornerstone material in modern manufacturing, particularly in the automotive, aerospace, home appliance, and electronics and communications industries. With the development of industrial technology, all sectors are driving the development of hot work die steel materials towards higher purity, higher quality, higher uniformity, longer service life, and lower cost. To meet these high standards, the traditional process for high-performance die steel typically involves electric arc furnace (EAF) → ladle refining (LF) → vacuum refining (VD) → ingot casting (IF) → electroslag remelting → forging. While this process ensures material quality, it has significant drawbacks: long production cycles, low ingot casting yield, and high product costs, making it difficult to meet the current development needs of hot work die steel.

[0003] Therefore, while ensuring the high purity, high quality, and long service life of mold steel, the industry is actively exploring new routes to replace ingot casting with continuous casting in order to reduce costs and improve the microstructure and compositional uniformity of the products. However, the production of high-performance hot work mold steel by continuous casting still faces technical challenges, especially the ring-shaped cracks in the continuously cast billets of high-performance hot work mold steel, which urgently need to be addressed. How to control and improve the problem of central crack defects in continuously cast billets throughout the entire hot work mold steel smelting process, so as to reduce the cost of high-performance hot work mold steel and improve the compositional uniformity, is a technical problem that urgently needs to be solved. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide a large-size, high-performance hot work die steel and its smelting process. The high-performance hot work die steel continuous casting billet produced by this process has a central porosity of ≤1.0 grade, a central crack of ≤1.0 grade, and a carbon difference of ≤0.010% in the same cross section. After forging and heat treatment, its mechanical properties meet the requirements for use, and its service life is longer than that of ordinary hot work die steel and its cost is lower than that of the original process route.

[0005] The objective of this invention is achieved as follows: a large-size, high-performance hot work die steel, comprising the following chemical composition by weight percentage: [C]: 0.33–0.42%, [Si]: 0.20–0.40%, [Mn]: 0.30–0.60%, [Cr]: 4.90–5.50%, [Ni]: 0.40–0.80%, [Mo]: 2.10–2.30%, [V]: 0.70–0.80%, [Co]: 0.60–0.80%, [Al]: 0.010–0.030%, [P] ≤ 0.012%, [S] ≤ 0.002%, […]. Cu]≤0.10%, total rare earth alloy La+Ce: 20~50ppm, (As+Sn+Pb+Sb+Bi)≤0.020%, balance is [Fe], where the mass ratio of La:Ce is 1:1.5~2.5; using scrap steel, pig iron, ferromanganese, ferrochrome, nickel plate, ferromolybdenum, ferrovanadium, metallic cobalt and rare earth alloy raw materials, as well as aluminum blocks and lime auxiliary materials, through electric furnace (EAF) → ladle refining (LF) → vacuum refining (VD) → continuous casting (CC) → electroslag remelting → forging to obtain a continuously cast electrode billet with quality and performance meeting the requirements, so as to reduce the cost of high-performance hot work die steel and improve the uniformity of composition and structure.

[0006] A smelting process for large-size, high-performance hot work die steel, wherein the steel is smelted using a short-process steelmaking method, specifically the following technical route: electric arc furnace (EAF) smelting + ladle refining (LF) + vacuum refining (VD) → continuous casting (CC) → annealing / hot delivery → finishing → testing. The implementation steps of this technical route are as follows: Step 1) Batching: The furnace charge includes 400-700 kg / t of high-quality steel scrap or waste steel, 200-400 kg / t of pig iron or waste steel ingot molds, 30-50 kg / t of ferromolybdenum, and 5-8 kg / t of metallic nickel. The sum of the five harmful elements in the raw materials, As, Sn, Pb, Sb, and Bi, should be controlled to be ≤0.020%. Step 2) Electric Arc Furnace Smelting: Raw materials entering the furnace should be clean and dry. When the temperature of the molten steel is 1550~1580℃, the slag should be dephosphorized. The weight percentage of the steel tapped from the electric furnace should be controlled as [C]≥0.08% and [P]≤0.006%, and the tapping temperature should be 1630~1660℃. During the tapping process, carbon powder 0~3.0kg / t, ferrosilicon 2~4kg / t, ferromanganese alloy 1~6kg / t, ferrochrome alloy 10~30kg / t, aluminum blocks 2~4kg / t, and grade 1 lime 4~7kg / t should be added to the ladle along with the steel flow. Step 3) Ladle Refining: After the ladle furnace is in place, argon gas is connected, and graphite electrodes are inserted for heating and refining. The bottom-blowing argon system is turned on throughout the refining process, and the argon flow rate is adjusted to 60~120L / min. 2~4kg / t of Grade I lime is added. After slag formation, 1~2kg / t of calcium carbide, 1.0~2kg / t of carbon powder, and 1~2kg / t of ferrosilicon powder are added for deoxidation and slag adjustment. After the slag turns white, 1~4kg / t of high-carbon ferromanganese, 1~4kg / t of medium-carbon ferromanganese, 20~40kg / t of high-carbon ferrochrome, 40~60kg / t of medium-carbon ferrochrome, 15~30kg / t of low-carbon ferrochrome, and 5~8kg / t of metallic cobalt are added to adjust the alloy composition. During the refining process, the color and consistency of the refined slag should be checked every 10 minutes, and 1.0~2.0kg / t of deoxidizer should be added accordingly. After the steel composition and temperature are adjusted, the steel is tapped. Before tapping, the chemical composition by mass percentage should meet the following requirements: [C]: 0.33~0.42%, [Si]: 0.20~0.40%, [Mn]: 0.30~0.60%, [Cr]: 4.90~5.50%, [Ni]: 0.40~0.80%, [Mo]: 2.10~2.30%, [V]: 0.70~0.80%, [Co]: 0.60~0.80%, [Al]: 0.010~0.030%, [P]≤0.012%, [S]≤0.002%, [Cu]≤0.10%, (As+Sn+Pb+Sb+Bi)≤0.020%, with the balance being [Fe]. The tapping temperature is 1640~1660℃. Step 4) Vacuum degassing: After the ladle is in place, argon gas is turned on. The argon gas flow rate is adjusted to 50L / min~80L / min according to the slag quantity and condition, and maintained at ≤0.67mbar for more than 20 minutes. After vacuum degassing, hydrogen and oxygen are determined, and [H] is controlled to ≤1.0ppm, [O] to ≤5.0ppm, and [N] to ≤70ppm; the residual [Al] is controlled to ≤0.015%. Before lifting the ladle, 0.05kg / t~0.10kg / t of rare earth alloy La+Ce and 0~3.0m / t of silicon-calcium wire are fed in. The argon gas flow rate is adjusted to 20L / min~40L / min for stirring, and the stirring time is ≥15 minutes. The ladle temperature is 1550~1570℃. The total amount of rare earth alloy La+Ce is controlled to be 20~50ppm, and the La:Ce mass ratio is 1:1.5~2.5. Step 5) Continuous casting: The continuous casting machine adopts a two-machine two-strand vertical continuous casting machine. Before continuous casting, the continuous casting equipment, cooling system and heat preservation equipment should be inspected. After the ladle is in place, the temperature is measured and the superheat is controlled at 15~30℃. The ladle is rotated to the continuous casting station on the rotary table and the casting speed is 0.10~0.25m / min. The electromagnetic stirring adopts a three-stage linkage electromagnetic stirring and the secondary cooling system is controlled as medium cooling. Step 6) Annealing: The annealing temperature is 530~630℃, the annealing time is 3~4h, the holding temperature is 760~800℃, the holding time is 8~13h, the billet is cooled with the furnace, the temperature is ≤170℃, and after annealing, it is transferred to electroslag remelting.

[0007] The beneficial effects of this invention are as follows: the high-performance hot work die steel large-size continuous casting billets produced by this invention can achieve a central porosity of ≤0.5 grade, a central crack of ≤1.0 grade, a carbon difference of ≤0.02% in the same cross section, and a total non-metallic inclusion of ≤2.5 grade. The cost is reduced by 200~500 yuan / t compared with the original process route. Detailed Implementation

[0008] Example 1: This invention provides a hot-work die steel and its smelting process that can meet the requirements of high quality, high purity, and long service life. The process involves using an electric furnace, LF refining, and VD refining to obtain molten steel that meets the quality requirements. This molten steel is then transported to the continuous casting station by an overhead crane and cast using the appropriate continuous casting process, ultimately yielding a continuously cast billet that meets the quality requirements. This invention achieves the goals of improving the quality of the electrode billet and reducing costs by controlling key aspects of the production process, such as the deoxidation process, bottom-blown argon flow rate, VD refining vacuum degree, vacuum time, continuous casting cooling process, casting speed, electromagnetic stirring, and rare earth addition. The specific technical solution is as follows: Step 1) Batching: The furnace charge should be divided into 40-60% steel scrap, 30-50% pig iron, and 10-30% recycled steel scrap by weight. Mixed scrap steel, as well as raw materials containing oil or paint, are not allowed. The sum of the five harmful elements in the raw materials (As, Sn, Pb, Sb, Bi) should be controlled to ≤0.010%. Step 2) Electric Arc Furnace Smelting: The raw materials fed into the furnace should be clean and dry. The weight percentage of the steel tapped from the electric furnace should be controlled as follows: [C] ≥ 0.08%, [P] ≤ 0.006%, and the tapping temperature ≥ 1640℃. During the tapping process, carbon powder 0.5~1kg / t, aluminum blocks 2.0~4.0kg / t, grade 1 lime 4.0~6.0kg / t, high carbon ferrochrome 10~12kg / t, and high carbon ferromanganese 1.0~2.0kg / t should be added with the steel stream for deoxidation and slag formation. Step 3) Ladle refining: After the ladle furnace is in place, argon gas is first turned on for stirring and heating refining, and the argon gas flow rate is adjusted to 60~70L / min; deoxidizers such as calcium carbide 1~2.0kg / t, carbon powder deoxidizer 1.0~2.0kg / t, and ferrosilicon powder 1.0~2.0kg / t are added for deoxidation. According to the slag quantity and slag condition, grade 1 lime 3.0~5.0kg / t and fluorite 0~2.0kg / t are added. After the slag turns white, the composition is adjusted according to the target value; argon is purged throughout the refining process. The flow rate is adjusted at any time according to the requirements of argon gas stirring at different stages of refining, and should not exceed 120L / min to ensure uniform stirring and no leakage of molten steel; Step 4) Vacuum degassing: Degas the steel in a vacuum tank from the LF furnace ladle at a temperature of 1640-1660℃, maintaining the temperature at ≤0.67mbar for ≥20 minutes. After vacuum degassing, determine the hydrogen and oxygen content online, controlling [H] ≤1.0ppm, [O] ≤5.0ppm, and [N] ≤70ppm; control the residual [Al] ≤0.015%; before ladle loading, feed in 0.06kg / t~0.07kg / t of rare earth alloy (La+Ce) and 1~1.5m / t of silicon-calcium wire, and blow argon with weak stirring for ≥15min before tapping, with ladle temperature of 1552-1567℃; control the total amount of rare earth alloy La+Ce to be 20-50ppm, and the La:Ce mass ratio to be 1:1.5-2.5; Step 5) Continuous Casting: Before scheduling continuous casting production, check the crystallizer (including the inner wall of the copper tube and the filter screen), the alignment of the continuous casting billet roller, and the tightness of the stopper rod to ensure a stable liquid level in the crystallizer; check and maintain the cutting torch; check the secondary cooling water spray system, and carefully check the spray frame and nozzles before casting, replacing any clogged nozzles promptly; check the insulation plates of the continuous casting machine for integrity. After the ladle is in place, measure the temperature and control the superheat to 15~25℃. Rotate the ladle to the continuous casting station on the rotary table, with a casting speed of 0.13m / min. Use a three-stage linkage electromagnetic stirring system, controlling the primary cooling regime as strong cooling with a water flow rate of 3600~3800L / min, and the secondary cooling regime as medium cooling with water flow rates of 30~32L / min, 18~20L / min, and 7~9L / min.

[0009] Step 6) Annealing: After annealing, clean the easily peelable oxide scale and cutting slag on the surface of the billet, and then transfer it to electroslag remelting.

[0010] Step 7) Inspection: Perform cross-sectional inspection on the annealed billet. The central porosity should be ≤0.5 grade, the central crack should be ≤1.0 grade, and the carbon difference in the same cross section should be 0.09%.

[0011] Appendix: The chemical composition of high-performance hot work die steel is shown in Table 1 below. Table 1 Chemical composition (m%) C 0.33-0.42 0.38 Si 0.20-0.40 0.32 Mn 0.30-0.60 0.46 P ≤0.012 0.007 S ≤0.003 0.001 Cr 4.90-5.50 5.15 Ni 0.40-0.80 0.52 Mo 2.10-2.30 2.15 V 0.70-0.80 0.73 Co 0.60-0.80 0.68 Cu ≤0.10 0.08 As ≤0.010 0.006 Sn ≤0.010 0.003 Pb ≤0.010 0.001 Sb ≤0.010 0.001 Bi ≤0.010 0.001 Rare earth alloys (La+Ce) 20~50ppm 30ppm Appendix: Gas composition for high-performance hot work die steels is shown in Table 2 below. Table 2 Gases (ppm) [H] ≤1.0 0.86 [O] ≤10 5.0 [N] ≤90 62 .

Claims

1. A large-size, high-performance hot work die steel, characterized in that: The chemical composition, by weight percentage, includes the following: [C]: 0.33–0.42%, [Si]: 0.20–0.40%, [Mn]: 0.30–0.60%, [Cr]: 4.90–5.50%, [Ni]: 0.40–0.80%, [Mo]: 2.10–2.30%, [V]: 0.70–0.80%, [Co]: 0.60–0.80%, [Al]: 0.010–0.030%, [P] ≤0.012%, [S] ≤0.002%, [Cu] ≤0.10%, rare earth elements. The total content of gold (La+Ce) is 20-50 ppm, (As+Sn+Pb+Sb+Bi) ≤ 0.020%, and the balance is [Fe]. The mass ratio of La:Ce is 1:1.5-2.

5. The process involves using scrap steel, pig iron, ferromanganese, ferrochrome, nickel plates, ferromolybdenum, ferrovanadium, metallic cobalt, rare earth alloys, aluminum blocks, and lime as auxiliary materials. The process is carried out in an electric arc furnace (EAF) → ladle refining (LF) → vacuum refining (VD) → continuous casting (CC) → electroslag remelting → forging to obtain continuously cast electrode billets that meet the required quality and performance. This reduces the cost of high-performance hot work die steel and improves the uniformity of composition and microstructure.

2. A smelting process for large-size, high-performance hot work die steel, characterized in that, The steel smelting process adopts a short-process steelmaking method, and the specific technical route is as follows: electric arc furnace (EAF) smelting + ladle refining (LF) + vacuum refining (VD) → continuous casting (CC) → annealing / hot delivery → finishing → testing. The implementation steps of the technical route are as follows: Step 1) Batching: The furnace charge includes 400-700 kg / t of high-quality steel scrap or waste steel, 200-400 kg / t of pig iron or waste steel ingot molds, 30-50 kg / t of ferromolybdenum, and 5-8 kg / t of metallic nickel. The sum of the five harmful elements in the raw materials, As, Sn, Pb, Sb, and Bi, should be controlled to be ≤0.020%. Step 2) Electric Arc Furnace Smelting: Raw materials entering the furnace should be clean and dry. When the temperature of the molten steel is 1550~1580℃, the slag should be dephosphorized. The weight percentage of the steel tapped from the electric furnace should be controlled as [C]≥0.08% and [P]≤0.006%, and the tapping temperature should be 1630~1660℃. During the tapping process, carbon powder 0~3.0kg / t, ferrosilicon 2~4kg / t, ferromanganese alloy 1~6kg / t, ferrochrome alloy 10~30kg / t, aluminum blocks 2~4kg / t, and grade 1 lime 4~7kg / t should be added to the ladle along with the steel flow. Step 3) Ladle Refining: After the ladle furnace is in place, argon gas is connected, and graphite electrodes are inserted for heating and refining. The bottom-blowing argon system is turned on throughout the refining process, and the argon flow rate is adjusted to 60~120L / min. 2~4kg / t of Grade I lime is added. After slag formation, 1~2kg / t of calcium carbide, 1.0~2kg / t of carbon powder, and 1~2kg / t of ferrosilicon powder are added for deoxidation and slag adjustment. After the slag turns white, 1~4kg / t of high-carbon ferromanganese, 1~4kg / t of medium-carbon ferromanganese, 20~40kg / t of high-carbon ferrochrome, 40~60kg / t of medium-carbon ferrochrome, 15~30kg / t of low-carbon ferrochrome, and 5~8kg / t of metallic cobalt are added to adjust the alloy composition. During the refining process, the color and consistency of the refined slag should be checked every 10 minutes, and 1.0~2.0kg / t of deoxidizer should be added accordingly. After the steel composition and temperature are adjusted, the steel is tapped. Before tapping, the chemical composition by mass percentage should meet the following requirements: [C]: 0.33~0.42%, [Si]: 0.20~0.40%, [Mn]: 0.30~0.60%, [Cr]: 4.90~5.50%, [Ni]: 0.40~0.80%, [Mo]: 2.10~2.30%, [V]: 0.70~0.80%, [Co]: 0.60~0.80%, [Al]: 0.010~0.030%, [P]≤0.012%, [S]≤0.002%, [Cu]≤0.10%, (As+Sn+Pb+Sb+Bi)≤0.020%, with the balance being [Fe]. The tapping temperature is 1640~1660℃. Step 4) Vacuum degassing: After the ladle is in place, argon gas is turned on. The argon gas flow rate is adjusted to 50L / min~80L / min according to the slag quantity and condition, and maintained at ≤0.67mbar for more than 20 minutes. After vacuum degassing, hydrogen and oxygen are determined, and [H] is controlled to ≤1.0ppm, [O] to ≤5.0ppm, and [N] to ≤70ppm; the residual [Al] is controlled to ≤0.015%. Before lifting the ladle, 0.05kg / t~0.10kg / t of rare earth alloy La+Ce and 0~3.0m / t of silicon-calcium wire are fed in. The argon gas flow rate is adjusted to 20L / min~40L / min for stirring, and the stirring time is ≥15 minutes. The ladle temperature is 1550~1570℃. The total amount of rare earth alloy La+Ce is controlled to be 20~50ppm, and the La:Ce mass ratio is 1:1.5~2.

5. Step 5) Continuous casting: The continuous casting machine adopts a two-machine two-strand vertical continuous casting machine. Before continuous casting, the continuous casting equipment, cooling system and heat preservation equipment should be inspected. After the ladle is in place, the temperature is measured and the superheat is controlled at 15~30℃. The ladle is rotated to the continuous casting station on the rotary table and the casting speed is 0.10~0.25m / min. The electromagnetic stirring adopts a three-stage linkage electromagnetic stirring and the secondary cooling system is controlled as medium cooling. Step 6) Annealing: The annealing temperature is 530~630℃, the annealing time is 3~4h, the holding temperature is 760~800℃, the holding time is 8~13h, the billet is cooled with the furnace, the temperature is ≤170℃, and after annealing, it is transferred to electroslag remelting.