A high-purity high-toughness cold work die steel and a method for manufacturing a wide and thick plate

Abstract

This invention relates to the field of steel rolling technology and discloses a high-purity, high-toughness cold work die steel, comprising, by mass percentage: C 0.85–1.15%, Si 0.80–1.10%, Mn 0.20–0.50%, Cr 7.00–9.0%, W 0.40–0.80%, Mo 2.0–3.0%, V 0.4–1.0%, Nb 0.2–0.5%, S 0.005–0.012%, Al 0.20–0.50%, P ≤ 0.010%, La + Ce ≤ 0.08%, with the balance being Fe and unavoidable impurities. This invention also provides a method for preparing thick plates using this cold work die steel. The high-purity, high-toughness cold work die steel provided by this invention can improve the purity, carbide uniformity, and impact toughness of steel, overcoming the limitations of existing processes that can only use small ingots and are difficult to produce large-scale thick plates.

Description

Technical Field

[0001] This invention relates to the field of steel rolling technology, and in particular to a high-purity, high-toughness cold work die steel and its preparation method. Background Technology

[0002] Cold work die steel is a key material for manufacturing dies for cold heading, cold extrusion, and stamping. Its performance directly determines the die life and processing quality, and it is widely used in the automotive, electronics, and home appliance manufacturing industries. As stamping technology develops towards high efficiency, high speed, and high precision, the strength of the processed materials is constantly increasing, placing higher demands on the hardness, strength, toughness, and wear resistance of dies.

[0003] Currently, the high-carbon, high-chromium Cr12 type cold work die steel widely used in China is mainly geared towards low-end dies, produced using a process of "electric furnace + LF + VD + forging / rolling + heat treatment". To avoid coarsening of the fishbone-like ledeburite structure, production is typically limited to small ingots of less than 1 ton, resulting in low production efficiency, low yield, and weak market competitiveness. More importantly, this process is difficult to produce large-format, thick plate products. For example, cold work die steel plates with a width of over 300mm and a thickness of over 40mm cannot be stably produced domestically due to limitations in microstructure control and deformation conditions. Existing technologies, unable to achieve large deformation rolling while ensuring high purity and high toughness, result in thick plate products exhibiting problems such as uneven microstructure, severe carbide segregation, and insufficient impact toughness, failing to meet the actual needs of large precision dies for wide and thick plates.

[0004] Therefore, there is a need to improve the preparation methods of high-purity, high-toughness cold work die steel and thick plates in the existing technology. Summary of the Invention

[0005] In view of this, the purpose of this invention is to propose a method for preparing high-purity, high-toughness cold work die steel and thick plates, so as to improve the purity, carbide uniformity and impact toughness of the steel, and overcome the limitation of existing processes that can only use small ingots and are difficult to produce large-size thick plates.

[0006] To achieve the above objectives, embodiments of the present invention provide a high-purity, high-toughness cold work die steel, comprising, by mass percentage: C 0.85–1.15%, Si 0.80–1.10%, Mn 0.20–0.50%, Cr 7.00–9.0%, W 0.40–0.80%, Mo 2.0–3.0%, V 0.4–1.0%, Nb 0.2–0.5%, S 0.005–0.012%, Al 0.20–0.50%, P ≤ 0.010%, La + Ce ≤ 0.08%, with the balance being Fe and unavoidable impurities.

[0007] Another aspect of the present invention provides a method for preparing thick plates using the above-mentioned high-purity, high-toughness cold work die steel, comprising the following steps: S1 places the raw material according to the predetermined chemical composition ratio of the cold work die steel into a vacuum induction furnace for melting and casting into an electrode rod; S2 uses an electrode rod as a consumable electrode and performs electroslag remelting under a protective atmosphere to obtain an electroslag ingot. S3 anneals the electroslag ingot and heats the annealed electroslag ingot to the rolling temperature; S4 uses a roughing mill to reciprocate and multi-pass roll the heated electroslag ingot to obtain a wide and thick plate with a width of ≥300mm and a thickness of ≥40mm. S5 is used to recrystallize and anneal the rolled thick plate to obtain the finished thick plate blank.

[0008] In some embodiments, in S1, all alloy raw materials are first polished to remove surface oxides and deposits, and then the materials are mixed according to a predetermined chemical composition ratio; during smelting, low-power melting is used, the melting time is ≥4h, and the vacuum degree in the furnace is ≤5Pa.

[0009] In some embodiments, in S1, after melting and clearing, the molten steel is heated to 150-200°C above the material's melting point, and the stirring and refining time is ≥35 minutes. Then, it is cooled to 60-90°C above the material's melting point before tapping and casting. The casting speed of the ingot body is 60-120 kg / s, and the casting speed at the riser end is 5-20 kg / s. After casting, it is kept at a temperature of ≥120 minutes before demolding.

[0010] In some embodiments, in S2, the electroslag remelting uses CaF2 and Al2O3 as the base slag system, and adds magnesium oxide and mixes it evenly; the electroslag remelting voltage is controlled at 50~80V, the current is controlled at 25000A~15000A, and the maximum current fluctuation range is ±1000A.

[0011] In some embodiments, in S2, the average melting rate of electroslag remelting is controlled at 4.0~8.0 kg / min, the melting rate of the feeding section is controlled at 0.5~2.0 kg / min, and after remelting, the material is cooled for ≥120 min before demolding.

[0012] In some embodiments, in S3, the electroslag ingot annealing temperature is 800-850℃, and the annealing time is calculated using the following formula: T 退火 =K×D Where K is 0.2~5 and D is the diameter of the electroslag ingot.

[0013] In some embodiments, in S3, after annealing, the electroslag ingot is heated in stages to the rolling temperature using a ring furnace, including: Heat for one stage, with the temperature controlled between 700 and 850℃; The heating stage is controlled at 1120–1160℃. The heating system has three stages, with the temperature controlled between 1130 and 1260℃. The temperature in the heat spreader is controlled between 1120 and 1150℃. The formula for calculating the walking cycle of a ring furnace is: T 步进周期 =S×t / n Where S is the billet diameter or maximum thickness, t is the thickness time coefficient, ranging from 5 to 20, and n is the total number of teeth in the walking beam furnace; the soaking time is ≥3.5h.

[0014] In some embodiments, in S4, a 3t or larger ingot billet is used for single-fire rolling. During the rolling process, there are at least two passes with a relative deformation rate ≥40%, a final rolling temperature ≥950℃, and the rolling speed is controlled in segments, with the bite-in stage speed being 0.5~2m / s and the rolling stage speed being 3~10m / s.

[0015] In some embodiments, in S5, the thick plates are first stacked and slowly cooled to 350~500°C before being loaded into the furnace. The recrystallization annealing temperature is 850~900°C, and the temperature is held for 10~20 hours. The plates are then cooled with the furnace to ≤350°C at a cooling rate of ≤30°C / h before being removed from the furnace and air-cooled.

[0016] The present invention has at least the following beneficial technical effects: This invention achieves an optimal balance between high purity, high toughness, high hardness, and high wear resistance in cold work die steel through a multi-component composite system with specific proportions. The method employs a dual high-purity smelting combination: vacuum induction furnace melting and casting of electrode rods, followed by protective atmosphere electroslag remelting. This significantly improves the purity of molten steel from the source, reducing harmful impurities and gas content. Electroslag ingot annealing and rolling heating pretreatment eliminate residual ingot stress and ensure uniform billet temperature. Further, multiple passes on a roughing mill break down coarse carbides and refine the matrix structure. Finally, recrystallization annealing eliminates rolling stress and stabilizes the microstructure, resulting in the stable production of high-purity, high-toughness cold work die steel plates. This solves the core problems of low purity, uneven microstructure, and insufficient toughness inherent in traditional processes. Attached Figure Description

[0017] 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 embodiments can be obtained based on these drawings without creative effort.

[0018] Figure 1This is a schematic diagram of an embodiment of the method for preparing thick plates using high-purity, high-toughness cold work die steel provided by the present invention. Detailed Implementation

[0019] 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.

[0020] The terms "comprising" and "having," and any variations thereof, used in the specification, claims, and accompanying drawings of this invention are intended to cover non-exclusive inclusion; the terms "first," "second," etc., used in the specification, claims, and accompanying drawings are used to distinguish different objects, not to describe a particular order. "A plurality of" means two or more, unless otherwise explicitly specified.

[0021] Furthermore, the reference to "embodiment" herein means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of the invention. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0022] This invention proposes a high-purity, high-toughness cold work die steel, comprising, by mass percentage: C 0.85–1.15%, Si 0.80–1.10%, Mn 0.20–0.50%, Cr 7.00–9.0%, W 0.40–0.80%, Mo 2.0–3.0%, V 0.4–1.0%, Nb 0.2–0.5%, S 0.005–0.012%, Al 0.20–0.50%, P ≤0.010%, La+Ce ≤0.08%, with the balance being Fe and unavoidable impurities. The high-purity properties of this invention are achieved through strict control of harmful impurities, enhanced deoxidation, and rare-earth modification; and through carbon-chromium optimization to suppress brittle carbides, vanadium-niobium grain refinement for strengthening, molybdenum-tungsten solid solution for toughness, and rare-earth element elimination for stress concentration. By controlling C to 0.85~1.15% and Cr to 7.0~9.0%, coarse network / fishbone-like ledeburite carbides are avoided, reducing brittleness at the compositional level while ensuring hardness and wear resistance. Nb and V strongly refine grains and pin grain boundaries, representing the only mechanism that simultaneously improves strength and toughness. Rare earth elements La and Ce spheroidize and refine brittle inclusions, purify grain boundaries, reduce stress concentration, and significantly improve toughness. Al strongly deoxidizes and purifies the molten steel; S is controlled at 0.005~0.012%, improving machinability without reducing toughness. Strictly controlling P ≤0.010%, low impurities, and low gases eliminates grain boundary embrittlement and compositional segregation, achieving a high-purity matrix. These synergistic effects result in high toughness in the steel, ultimately enabling the mold steel to possess both high purity and high toughness as its dual core properties.

[0023] This invention also proposes a method for preparing thick plates using the high-purity, high-toughness cold work die steel described above, wherein the width-to-thickness ratio of the thick plates is (300-780) × (40-120), comprising the following steps: S1 places raw materials according to the predetermined chemical composition ratio of cold work die steel into a vacuum induction furnace for melting and casting into electrode rods; S2 uses an electrode rod as a consumable electrode and performs electroslag remelting under a protective atmosphere to obtain an electroslag ingot. S3 anneals the electroslag ingot and heats the annealed electroslag ingot to the rolling temperature; S4 uses a roughing mill to reciprocate and multi-pass roll the heated electroslag ingot to obtain a wide and thick plate with a width of ≥300mm and a thickness of ≥40mm. S5 is used to recrystallize and anneal the rolled thick plate to obtain the finished thick plate blank.

[0024] Further, in S1, all alloy raw materials are first polished to remove surface oxides and adhering substances, and then mixed according to a predetermined chemical composition ratio. By mass percentage, the components include: C 0.85–1.15%, Si 0.80–1.10%, Mn 0.20–0.50%, Cr 7.00–9.0%, W 0.40–0.80%, Mo 2.0–3.0%, V 0.4–1.0%, Nb 0.2–0.5%, S 0.005–0.012%, Al 0.20–0.50%, P ≤0.010%, La+Ce ≤0.08%, with the balance being Fe and unavoidable impurities. Low-power melting is used during smelting, with a melting time ≥4 hours, and the vacuum degree inside the furnace ≤5 Pa throughout the melting process.

[0025] Furthermore, in S1, the steel is first melted at a low power for ≥4 hours. After melting, the molten steel is heated to 150-200°C above the material's melting point and stirred and refined for ≥35 minutes. Then, it is cooled to 60-90°C above the material's melting point before being tapped and cast. The casting speed of the ingot body is 60-120 kg / s, and the casting speed at the riser end is 5-20 kg / s. After casting, the ingot is held at the temperature for ≥120 minutes before demolding.

[0026] Furthermore, in S2, the electroslag remelting uses CaF2 and Al2O3 as the base slag system, and adds magnesium oxide to mix evenly; the electroslag remelting voltage is controlled at 50~80V, the current is controlled at 25000A~15000A, and the maximum current fluctuation range is ±1000A.

[0027] Furthermore, in S2, the average melting rate of electroslag remelting is controlled at 4.0~8.0 kg / min, the melting rate of the feeding section is controlled at 0.5~2.0 kg / min, and after remelting, the material is cooled for ≥120 min before demolding.

[0028] S1 and S2 employ a two-step purification process: vacuum induction furnace + protective atmosphere electroslag remelting, replacing the traditional electric furnace + LF + VD. The vacuum induction furnace degassing, removes impurities, and prevents oxidation; the electroslag remelting further purifies, eliminates segregation, and homogenizes the microstructure. The two steps combined achieve extremely high purity, minimizing impurities, gases, and inclusions from the source, reducing the root causes of brittleness to achieve high toughness.

[0029] Furthermore, in S3, the electroslag ingot annealing temperature is 800-850℃, and the annealing time is calculated using the following formula: T 退火 =K×D Where K is 0.2~5 and D is the diameter of the electroslag ingot.

[0030] Furthermore, in S3, after annealing, the electroslag ingot is heated in stages to the rolling temperature using a ring furnace, including: Heat for one stage, with the temperature controlled between 700 and 850℃; The heating stage is controlled at 1120–1160℃. The heating system has three stages, with the temperature controlled between 1130 and 1260℃. The temperature in the heat spreader is controlled between 1120 and 1150℃. The formula for calculating the walking cycle of a ring furnace is: T 步进周期 =S×t / n Where S is the billet diameter or maximum thickness, t is the thickness time coefficient, ranging from 5 to 20, and n is the total number of teeth in the walking beam furnace; the soaking time is ≥3.5h.

[0031] This step involves first annealing to release stress, and then segmented heating to ensure that the billet structure is uniform and the temperature is consistent before rolling. This avoids cracking during the rolling of large ingots and eliminates local brittle fracture caused by uneven structure, making it suitable for the production of large-size wide and thick plates.

[0032] Furthermore, in S4, 3t or larger ingot billets are used for single-fire rolling. During the rolling process, there are at least two passes with a relative deformation rate ≥40%, a final rolling temperature ≥950℃, and segmented speed control. The bite-in stage speed is 0.5~2m / s, and the rolling stage speed is 3~10m / s. A reciprocating multi-pass roughing mill is used, employing large deformation rate + variable speed control. The reciprocating large deformation forcefully breaks down coarse eutectic carbides, and the variable speed rolling ensures uniform deformation across the entire cross-section of the thick plate. Single-fire forming reduces energy consumption and oxidation, completely solving the problems of uneven carbides and insufficient toughness in traditional Cr8 steel. Simultaneously, it overcomes the limitations of small ingots, achieving efficient rolling of ≥3t large ingots.

[0033] Furthermore, in S5, the thick plates are first stacked and slowly cooled to 350~500℃ before being loaded into the furnace. The recrystallization annealing temperature is 850~900℃, held for 10~20 hours, and then cooled in the furnace at a cooling rate of ≤30℃ / h to ≤350℃ before being removed from the furnace and air-cooled to obtain qualified thick plate blanks. The recrystallization annealing process avoids thermal stress by first slow cooling, then holds the plate at the temperature to complete recrystallization and refine the microstructure, and finally slow cooling eliminates residual stress, stabilizes the microstructure and properties, and ensures that the thick plates meet the toughness requirements, have straight dimensions, and are free from deformation and cracking.

[0034] The present invention will be further explained below with reference to specific embodiments.

[0035] Example 1 This embodiment uses Φ650 / 3.5t electroslag ingots to roll 100×650 (thickness*width) cold work die steel wide and thick plates. The specific production steps include: S1 places raw materials according to a predetermined chemical composition ratio into a vacuum induction furnace for melting and then casts them into electrode rods; The raw materials are prepared according to the target composition of C 0.95%, Si 0.90%, Mn 0.30%, Cr 8.5%, W 0.65%, Mo 2.5%, V 0.70%, Nb 0.20%, Al 0.20%, and La+Ce=0.05%, and the W, Mo and V metal surfaces are polished before being loaded into the furnace.

[0036] Evacuate the vacuum; power supply begins when the vacuum level is ≤10 Pa. First, melt at a low power. Once melting appears at the bottom of the crucible, increase the power while maintaining a vacuum of ≤5 Pa. Melt for 6.5 hours. After melting and cleaning, adjust the temperature to 1570℃~1590℃, stir and refine for 50 minutes, then cool down to 1450℃~1455℃ and tap out the steel. The casting speed of the ingot body is 70~80kg / s, and the casting speed of the riser end is 5~20kg / s, casting Φ500 electrode rods.

[0037] S2 uses an electrode rod as a consumable electrode and performs electroslag remelting under a protective atmosphere to obtain an electroslag ingot.

[0038] Heat the Φ500 electrode rod at 860-880℃ and hold for 10 hours; The slag system of CaF2, Al2O3 and MgO mixed evenly in a ratio of 70:25:5 is heated until it melts; Prepare a Φ650 crystallizer, install electrodes, and use an argon atmosphere for protection inside the furnace.

[0039] The process conditions for electroslag remelting are as follows: voltage is controlled at 70~55V, current is controlled at 24000A~23000A, the maximum fluctuation range of current is ±1000A, the average melting rate is controlled at 5.5~7.0kg / min, and the melting rate of the feeding section is 0.9~1.05kg / min. During the electroslag remelting process, the temperature of the cooling water from the crystallizer is 40~45℃. During the electroslag remelting process, C powder, Al particles and Si-Ca powder are used for deoxidation, fine-tuning of composition and slowing down the burning loss of the original composition of the billet. S3 performs annealing on the electroslag ingot, and then heats the electroslag ingot to the rolling temperature. After 180 minutes of electroslag remelting, the product is demolded and then annealed. The annealing process involves raising the temperature at a rate of 60℃ / h and controlling it at 500±10℃, holding it at that temperature for 6 hours, then raising the temperature at a rate of 80℃ / h to 820±10℃, holding it at that temperature for 18 hours, and then cooling it in the furnace at a rate of 20℃ / h to approximately 300℃ before removing it from the furnace and air cooling.

[0040] Heating of electroslag ingots: The temperature of the first heating stage is controlled at 750±10℃, the temperature of the second heating stage is controlled at 1100±10℃, the temperature of the third heating stage is controlled at 1150±10℃, the temperature of the heat soaking stage is controlled at 1130±10℃, the heating time is 10h, and the heat soaking time is 13h. S4 uses a roughing mill to perform reciprocating multi-pass rolling on heated electroslag ingots to obtain wide and thick plates. Roughing mill rolling: 19 passes are used (vertical rolling - vertical rolling - horizontal rolling - horizontal rolling - horizontal rolling - horizontal rolling - horizontal rolling - horizontal rolling - horizontal rolling - vertical rolling - vertical rolling - horizontal rolling - horizontal rolling - horizontal rolling - vertical rolling - horizontal rolling - horizontal rolling - vertical rolling - horizontal rolling), with the relative reduction rates of the 10th and 13th passes being 45% and 42% respectively, the bite speed being 1m / s, the stable rolling speed being 6m / s, the roll cooling water being turned off during the entire rolling process, and the final rolling temperature being 1010~1025℃; S5 is used to recrystallize and anneal the rolled thick plate to obtain the finished thick plate billet. For the 100×660 cold work die steel wide and thick plates, the stacks are slowly cooled. After the temperature drops to 430~450℃, they are loaded into the furnace. The furnace temperature is controlled at 885±10℃. After holding at the temperature for 12 hours, they are slowly cooled to 250℃ with the furnace at a cooling rate of 20℃ / h before being removed from the empty furnace to obtain qualified wide and thick slabs.

[0041] Example 2 This embodiment uses Φ550 / 3.2t electroslag ingots to roll 70×430 (thickness*width) cold work die steel wide and thick plates. The specific production steps include: S1 places raw materials according to a predetermined chemical composition ratio into a vacuum induction furnace for melting and then casts them into electrode rods. The raw materials were prepared according to the target composition of C 1.05%, Si 0.95%, Mn 0.35%, Cr 8.0%, W 0.60%, Mo 2.5%, V 0.75%, Nb 0.25%, Al 0.25%, and La+Ce=0.04%, and the W, Mo and V metal surfaces were polished before being loaded into the furnace.

[0042] Evacuate the vacuum; power supply begins when the vacuum level is ≤10 Pa. First, melt at a low power. Once the bottom of the crucible shows signs of melting, increase the power while maintaining a vacuum of ≤5Pa. Melt for 5 hours. After melting and cleaning, adjust the temperature to 1560℃~1580℃, stir and refine for 45 minutes, then cool down to 1460℃~1470℃ and tap out the steel. The casting speed of the ingot body is 60~75kg / s, and the casting speed of the riser end is 5~20kg / s, casting Φ400 electrode rods.

[0043] S2 uses an electrode rod as a consumable electrode and performs electroslag remelting under a protective atmosphere to obtain an electroslag ingot. Heat the Φ400 electrode rod at 850-900℃ and hold it at that temperature for 6-8 hours. The slag system of CaF2, Al2O3 and MgO mixed evenly in a ratio of 70:25:5 is heated until it melts; Prepare a Φ550 crystallizer, install electrodes, and use an argon atmosphere for protection inside the furnace.

[0044] The process conditions for electroslag remelting are as follows: voltage is controlled at 70~55V, current is controlled at 22000A~10000A, the maximum fluctuation range of current is ±1000A, the average melting rate is controlled at 4.0~6.0kg / min, and the melting rate of the feeding section is 0.75~0.85kg / min. During the electroslag remelting process, the temperature of the cooling water from the crystallizer is 40~45℃. During the electroslag remelting process, C powder, Al particles and Si-Ca powder are used for deoxidation, fine-tuning of composition and slowing down the burning loss of the original composition of the billet. S3 performs annealing on the electroslag ingot, and after annealing, the electroslag ingot is heated to the rolling temperature; After 150 minutes of electroslag remelting, the product is demolded and then annealed. The annealing process involves raising the temperature at a rate of 60℃ / h and controlling it at 500±10℃, holding it at that temperature for 4 hours, then raising the temperature at a rate of 80℃ / h to 820±10℃, holding it at that temperature for 15 hours, and then cooling it in the furnace at a rate of 20℃ / h to approximately 300℃ before removing it from the furnace and air cooling.

[0045] Heating of electroslag ingots: The temperature of the first heating stage is controlled at 750±10℃, the temperature of the second heating stage is controlled at 1100±10℃, the temperature of the third heating stage is controlled at 1150±10℃, the temperature of the heat soaking stage is controlled at 1130±10℃, the heating time is 8 hours, and the heat soaking time is 11 hours. S4 uses a roughing mill to perform reciprocating multi-pass rolling on heated electroslag ingots to obtain wide and thick plates. Roughing mill rolling: 15 passes are used (vertical rolling - vertical rolling - horizontal rolling - horizontal rolling - horizontal rolling - horizontal rolling - horizontal rolling - vertical rolling - vertical rolling - horizontal rolling - vertical rolling - horizontal rolling - vertical rolling - horizontal rolling), with the relative reduction rates of the 8th and 12th passes being 44% and 41% respectively, the bite speed being 1.0 m / s, the stable rolling speed being 5 m / s, the roll cooling water being turned off during the entire rolling process, and the final rolling temperature being 1020~1035℃; S5 is used to recrystallize and anneal the rolled thick plate to obtain the finished thick plate billet. The 70×430 cold work die steel wide and thick plates are stacked and slowly cooled. After the temperature drops to 450~470℃, they are loaded into the furnace. The furnace temperature is controlled at 890±10℃. After holding at the temperature for 10 hours, they are slowly cooled to 250℃ with the furnace at a cooling rate of 20℃ / h before being taken out of the furnace empty, thus obtaining qualified wide and thick slab billets.

[0046] 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. The functions, steps, and / or actions of the methods according to the disclosed embodiments described herein do not need to be performed in any particular order. Furthermore, 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.

[0047] It should be understood that, as used herein, unless the context clearly supports an exception. It should also be understood that, as used herein, "and / or" means any and all possible combinations of one or more of the associated listed items.

[0048] The embodiment numbers disclosed in the above embodiments of the present invention are for descriptive purposes only and do not represent the superiority or inferiority of the embodiments.

[0049] 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 high-purity, high-toughness cold work die steel, characterized in that, By mass percentage, it includes: C 0.85–1.15%, Si 0.80–1.10%, Mn 0.20–0.50%, Cr 7.00–9.0%, W 0.40–0.80%, Mo 2.0–3.0%, V 0.4–1.0%, Nb 0.2–0.5%, S 0.005–0.012%, Al 0.20–0.50%, P ≤0.010%, La+Ce ≤0.08%, with the balance being Fe and unavoidable impurities.

2. A method for preparing a thick plate of high-purity, high-toughness cold work die steel, characterized in that, The preparation method using the cold work die steel as described in claim 1 includes: S1 places the raw material according to the predetermined chemical composition ratio of the cold work die steel into a vacuum induction furnace for melting and casting into an electrode rod; S2 uses the electrode rod as a consumable electrode and performs electroslag remelting under a protective atmosphere to obtain an electroslag ingot. S3 performs annealing on the electroslag ingot and heats the annealed electroslag ingot to the rolling temperature; S4 uses a roughing mill to reciprocate and multi-pass roll the heated electroslag ingot to obtain a wide and thick plate with a width of ≥300mm and a thickness of ≥40mm. S5 performs recrystallization annealing on the rolled thick plate to obtain the finished thick plate blank.

3. The preparation method according to claim 2, characterized in that, In S1, all alloy raw materials are first polished to remove surface oxides and deposits, and then the predetermined chemical composition ratio is used. During smelting, low-power melting is used, the melting time is ≥4h, and the vacuum degree in the furnace is ≤5Pa.

4. The preparation method according to claim 2, characterized in that, In S1, after melting and clearing, the molten steel is heated to 150-200℃ above the material's melting point, and the stirring and refining time is ≥35min. Then, it is cooled to 60-90℃ above the material's melting point before being tapped and cast. The casting speed of the ingot body is 60~120kg / s, and the casting speed of the riser end is 5~20kg / s. After casting, it is held at the temperature for ≥120min before demolding.

5. The preparation method according to claim 2, characterized in that, In S2, the electroslag remelting uses CaF2 and Al2O3 as the base slag system, and adds magnesium oxide and mixes it evenly; the electroslag remelting voltage is controlled at 50~80V, the current is controlled at 25000A~15000A, and the maximum current fluctuation range is ±1000A.

6. The preparation method according to claim 5, characterized in that, In S2, the average melting rate of electroslag remelting is controlled at 4.0~8.0 kg / min, the melting rate of the feeding section is controlled at 0.5~2.0 kg / min, and the demolding is performed after cooling for ≥120 min after remelting.

7. The preparation method according to claim 2, characterized in that, In S3, the annealing temperature of the electroslag ingot is 800-850℃, and the calculation formula for the annealing time is: T 退火 =K×D Where K is 0.2~5 and D is the diameter of the electroslag ingot.

8. The preparation method according to claim 2, characterized in that, In S3, after annealing, the electroslag ingot is heated in sections to the rolling temperature using a ring furnace, including: Heat for one stage, with the temperature controlled between 700 and 850℃; The heating stage is controlled at 1120–1160℃. The heating system has three stages, with the temperature controlled between 1130 and 1260℃. The temperature in the heat spreader is controlled between 1120 and 1150℃. The formula for calculating the stepping cycle of the ring furnace is as follows: T 步进周期 =S×t / n Where S is the billet diameter or maximum thickness, t is the thickness time coefficient, ranging from 5 to 20, and n is the total number of teeth in the walking beam furnace; the soaking time is ≥3.5h.

9. The preparation method according to claim 2, characterized in that, In S4, 3t or larger ingot billets are used for single-fire rolling. During the rolling process, there are at least two passes with a relative deformation rate of ≥40%, and the final rolling temperature is ≥950℃. The rolling speed is controlled in segments, with the bite-in stage speed being 0.5~2m / s and the rolling stage speed being 3~10m / s.

10. The preparation method according to claim 2, characterized in that, In S5, the thick plates are first stacked and slowly cooled to 350~500℃ before being loaded into the furnace. The recrystallization annealing temperature is 850~900℃, and the temperature is held for 10~20h. The plates are then cooled with the furnace to ≤350℃ at a cooling rate of ≤30℃ / h before being removed from the furnace and air-cooled.

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