High-toughness ledeburite-free cold work die steel and preparation method thereof

Abstract

The invention discloses high-toughness ledeburite-free cold work die steel and a preparation method thereof. The high-toughness ledeburite-free cold work die steel comprises the following components in percentage by weight: 0.45-0.65% of C, less than or equal to 0.20% of Si, 0.35-0.55% of Mn, 3.50-5.00% of Cr, 1.00-2.00% of Mo, 0.20-0.50% of V, 0.20-1.00% of Ni, less than or equal to 0.008% of P, less than or equal to 0.003% of S, less than or equal to 0.0008% of O, less than or equal to 0.0002% of H, less than or equal to 0.003% of N and the balance of Fe and inevitable impurities. The cold work die steel has good cooperation of strength and impact toughness, the impact toughness of the cold work die steel is 201-355J / cm < 2 >, the hardness is 57-59 HRC, the tensile strength is 2105-2422 MPa, the unevenness of eutectic carbides is smaller than or equal to grade 1, the content of Cr, Mo and V alloy is low, the cost is low, and the cold work die steel is suitable for manufacturing cold stamping, cold extruding, cold heading and other dies.

Description

Technical Field

[0001] The invention relates to the technical field of cold working die steel, in particular to a high-strength and toughness ledeburite-free cold working die steel and a preparation method thereof. Background Art

[0002] Cold working die steel is mainly used for cold working dies that deform metals in a cold state. Such as: cold punching dies, cold stamping dies, cold drawing dies, stamping dies, cold extrusion dies, thread pressing dies, powder pressing dies, cold heading dies, cold extrusion dies, bending dies and wire drawing dies. Cold working die steel is generally required to have high hardness, strength and wear resistance, certain toughness and hot hardness.

[0003] At present, the commonly used cold working die steel in my country is still high carbon and high chromium die steel Cr12MoV, D2, etc. Cr12MoV, D2, etc. are ledeburite steels with high C and Cr contents. Although Cr12MoV and D2 have high hardness and wear resistance, their carbide segregation is serious, which can easily lead to directional deformation and reduced toughness, and can easily lead to early failure of the die. If the carbide segregation is too serious, it is easy to cause the die to break after heat treatment.

[0004] In order to solve the above problems, researchers at home and abroad have adopted the following methods:

[0005] (1) Reducing the content of C and Cr can reduce the content and size of eutectic carbides, such as DC53 (Datong, Japan), SDC90 (Shanghai University), SDC99 (Shanghai University), etc., but there are still many large carbides in DC53, SDC90 and SDC99;

[0006] (2) Powder metallurgy process is used to produce high alloy powder tool steel. Powder metallurgy process can significantly refine carbides. Purification technology is also used in the latest powder metallurgy process to further improve the purity of powder metallurgy materials, such as Vanadis 4Extra (hereinafter referred to as V4E, Yishengbai), Vanadis 8SuperClean (Yishengbai), etc. V4E and Vanadis 8SuperClean have excellent performance, but the price is very expensive, up to 400,000 yuan / ton, which is 25 to 30 times that of Cr12MoV;

[0007] (3) Using multiple multi-directional upsetting and stretching forging processes to fully crush the carbides, but this will also significantly increase the manufacturing cost.

[0008] Chinese patent application No. 201610315651.9 discloses a cold working die steel and its manufacturing process, the chemical composition weight percentage content of which is: C 0.6-1%, Si≤0.3%, Mn≤0.4%, Cr5-6%, Mo 0.5-1%, V 0.5-1%, P≤0.03%, S≤0.03%, W 0.2-0.5% and the balance Fe. The patent appropriately reduces the Cr content in the steel and increases the strong carbide forming element W, ensuring the hardenability of the steel while improving the strength and wear resistance of the steel, and has good plasticity and toughness. The patent adopts electric furnace smelting, electroslag remelting, high temperature diffusion heat treatment (1150-1200℃ insulation for 10-20h), multi-directional forging hot processing and high quenching and high heat recovery treatment to obtain a tempered martensite structure with a hardness of 55-62HRC, and has low cost, high hardenability, high hardness, high strength and wear resistance. However, the patent does not mention the performance indicators of cold working die steel such as hardness, strength, and impact toughness, making it impossible to judge its true performance.

[0009] Chinese patent application No. 202110702497.1 discloses a cold working die steel material and its manufacturing process, and its chemical composition weight percentage content is: C 0.7-0.8%, Si 0.7-1.2%, Mn 0.1-0.5%, Cr 6.5-7%, Mo2-2.5%, Ni 1.8-2.2%, V 1.7-2.2%, W 0.9-1.3% and the balance Fe. The patent appropriately reduces the content of C and Cr, and adopts vacuum induction melting, forging, spheroidizing annealing, hardening quenching and toughness back quenching preparation process. The patented steel has a high hardness (59.7-63.4HRC) and an impact toughness of (73-118J / cm 2 ), the impact toughness is greatly improved compared with Cr12 series cold working die steel, but for the molds with high requirements on impact performance, its impact toughness needs to be improved.

[0010] Chinese patent application No. 202010896482.9 discloses a high-toughness and high-hardness die steel, whose chemical composition by weight percentage is: C 0.7-0.85%, Si 0.1-0.4%, Mn 0.3-0.7%, Cr4.85-5.3%, Mo 2.25-2.55%, V 0.4-0.7%, P <0.02%, S <0.003% and the balance Fe. The patent sets the C content between the components of hot-working and cold-working die steels, which can improve the material's hardenability and hardenability while also forming alloy carbides to improve wear resistance; reduce the Si content to improve the material's toughness; keep the Cr content the same as that in the hot-working die steel H13, while reducing the V content and increasing the Mo content to reduce the formation of V-containing eutectic carbides, reduce the impact on toughness, and ensure that the material has good resistance to tempering softening; the patent adopts preparation processes such as electric furnace melting, LF furnace refining, VD degassing, electroslag remelting, forging, and heat treatment. The patented steel has a high hardness (58-64HRC) and an impact toughness of (50-140J / cm 2 ), the impact toughness is greatly improved compared with Cr12 series cold working die steel, but for the molds with high requirements on impact performance, its impact toughness needs to be improved.

[0011] Chinese patent application No. 202011030378.8 discloses a hot and cold die steel with high toughness and high hardness, the chemical composition weight percentage of which is: C 0.75-0.85%, Si 0.8-1.2%, Mn 0.3-0.7%, Cr 5-6%, Mo 2.2-2.6%, V 0.4-0.7%, P < 0.025%, S < 0.003% and the balance of Fe. The invention sets the C content between the components of hot and cold die steels, which can improve the hardenability and hardenability of the material while also forming alloy carbides to improve wear resistance; reduce the Si content to improve the toughness of the material; reduce the V content and increase the Mo content to reduce the formation of V-containing eutectic carbides, reduce the impact on toughness, and ensure that the material has good resistance to temper softening. The patent adopts preparation processes such as electric furnace smelting, electroslag remelting, forging, fine grain heat treatment and spheroidizing annealing. The patented steel has a high hardness (56-64HRC) and an impact toughness (80-140J / cm 2 ), the impact toughness is greatly improved compared with Cr12 series cold working die steel, but for the molds with high requirements on impact performance, its impact toughness needs to be improved.

[0012] Chinese patent application No. 200710061402.2 discloses a high-toughness and high-wear-resistant cold-working die steel, whose chemical composition weight percentage is: C 0.95-1.15%, Si 0.2-1.2%, Mn 0.2-0.5%, Cr 6.5-8%, Mo 1-2%, V 1.8-2.6%, W 0.5-1.5%, Nb 0.1-1%, and the balance Fe. The patent controls the carbon content according to the alloying principle, C=0.033W+0.063Mo+0.06Cr+0.2V+0.13Nb, effectively plays the role of alloy elements, and makes the material have higher comprehensive performance. Adding more Nb can partially replace V to form NbC carbide, making the carbide more uniform and improving the toughness of the material. The patent adopts medium frequency furnace smelting and electroslag remelting method, rapid forging + precision forging to open the blank and rolling into finished products, followed by annealing and finishing, as well as high quenching and high heat recovery treatment. The patented steel has a high hardness (60-65HRC) and an impact toughness of (70-140J / cm 2 ), the impact toughness is greatly improved compared with Cr12 series cold working die steel, but for the molds with high requirements on impact performance, its impact toughness needs to be improved.

[0013] Chinese patent application No. 200710171694.5 discloses a high-strength and toughness cold-working die steel and its manufacturing method, the chemical composition weight percentage of which is: C 0.9-1%, Si 1%, Cr 9-10%, Mo 2%, V 0.8-1%, P <0.02%, S <0.02% and the balance Fe. The patent appropriately reduces the content of carbon and chromium, increases the content of molybdenum and vanadium, reduces and refines the eutectic carbide, and refines the grains to improve toughness. The patent adopts medium-frequency induction furnace or arc furnace smelting, electroslag remelting for secondary refining, forging, spheroidizing annealing and low quenching and low heat recovery treatment. The patented steel has a high hardness (61-63HRC) and an impact toughness of (61-85J / cm 2 ), the impact toughness is greatly improved compared with Cr12 series cold working die steel, but for the molds with high requirements on impact performance, its impact toughness needs to be improved.

[0014] Chinese patent application No. 201310165533.0 discloses a powder metallurgy high-toughness cold-working die steel and a manufacturing method thereof, wherein the chemical composition weight percentage is: C 0.5-2%, Si≤2%, Mn 0.2-1.5%, Cr 4-5.6%, Mo≤3%, V 2.5-6%, Nb 0.2-2.5%, and the balance Fe. The patent optimizes the design of alloy elements and cooperates with appropriate heat treatment to make the matrix structure mainly martensite. Adding more Nb, the solid solution of Nb in MC-type carbides can make the precipitated MC carbides finer, which is conducive to improving the toughness of cold-working die steel. Cold-working die steel is prepared by powder metallurgy process. The rapid cooling characteristics of powder metallurgy process avoid the segregation of alloy elements and make the structure uniform. The alloy powder is formed by hot isostatic pressing process to form a pressed blank, and the pressure is forged to obtain a forging, and finally annealing, high quenching and high heat recovery treatment are performed. The patented steel has a high hardness (60-61HRC) and an impact toughness (40-85J / cm 2 ), the impact toughness is greatly improved compared with Cr12 series cold working die steel, but for molds with high impact performance requirements, its impact toughness needs to be improved. And the powder metallurgy process cost is relatively high. Summary of the invention

[0015] The object of the present invention is to provide a high-strength and toughness-free ledeburite cold working die steel and a preparation method thereof, wherein the cold working die steel has a good combination of strength and impact toughness, and its impact toughness is 201-355 J / cm 2 The hardness is 57-59HRC, the tensile strength is 2105-2422MPa, the eutectic carbide unevenness is ≤1 level, and the Cr, Mo, and V alloy content is low, the cost is low, and it is suitable for manufacturing cold stamping, cold extrusion, cold heading and other molds.

[0016] To achieve the above object, the technical solution of the present invention is:

[0017] The composition design of the mold steel of the present invention adopts: reducing the content of C and Cr, so that no ledeburite is formed in the steel, reducing the formation of large carbides from the source, thereby improving the comprehensive performance of the material. Adding a proper amount of Ni element to the steel, Ni is an austenite stabilizing element, can reduce the ductile-brittle transition temperature, and can maintain good plasticity and toughness while improving the strength of the steel.

[0018] Specifically, a high-strength and toughness-free ledeburite cold-working die steel, whose components by weight percentage are: C: 0.45-0.65%, Si: ≤0.20%, Mn: 0.35-0.55%, Cr: 3.50-5.00%, Mo: 1.00-2.00%, V: 0.20-0.50%, Ni: 0.20-1.00%, P≤0.008%, S≤0.003%, O≤0.0008%, H≤0.0002%, N≤0.003%, the balance includes Fe and other unavoidable impurities, and must meet the following requirements:

[0019] 5≤[Cr] / [C]≤10,

[0020] 2≤[C]×[Cr]≤4,

[0021] 5≤[Cr] / 5+2[Mo]+2[V]+2 / [Ni]≤16.

[0022] Furthermore, the remainder is Fe and other inevitable impurities.

[0023] Preferably, 7≤[Cr] / 5+2[Mo]+2[V]+2 / [Ni]≤10.

[0024] Preferably, C: 0.55-0.60%, or Cr: 4.50-5.00%, or Mo: 1.50-2.00%, or V: 0.30-0.45%, or Ni: 0.40-0.60%.

[0025] The annealed structure of the cold working die steel of the present invention is pearlite + granular carbide, the size of the granular carbide is very small, and there is no ledeburite structure that is often present in conventional Cr12 series cold working die steel; after quenching and tempering treatment, the structure of the cold working die steel is tempered martensite + dispersed fine carbide particles + a small amount of residual austenite, and there is no large eutectic carbide that is often present in conventional Cr12 series cold working die steel.

[0026] The impact toughness of the cold working die steel of the present invention is 201-355 J / cm 2 , hardness is 57~59HRC, tensile strength is 2105~2422MPa, and eutectic carbide unevenness is ≤level 1.

[0027] In the composition design of the mold steel of the present invention:

[0028] Carbon is one of the main chemical elements of high-strength and tough cold-working die steel. It is an indispensable basic element for the formation of various carbides and an important element that affects the composition segregation of steel and the uniformity of its structure. As the carbon content in steel increases, the yield point and tensile strength increase, but excessive carbon will lead to the formation of coarse chromium carbides, which will lead to reduced plasticity and impact properties. Compared with the retrieved patent, the carbon content of the steel composition of the present invention is much lower, and its purpose is to improve the distribution and properties of carbides in the microstructure of the steel and reduce the level of network carbides. If the carbon content is higher than the upper limit of the design of this component, it will lead to the formation of too many carbides and the generation of organizational segregation, resulting in reduced impact toughness of the steel; however, if the carbon content is lower than the design range of this component, it will also cause the equivalent of carbon and other alloy elements to form carbides to deviate, and stable fine carbides cannot be effectively formed, affecting the strength and hardenability of the steel. The present invention controls C 0.45-0.65%, preferably, C: 0.55-0.60%.

[0029] Si, dissolved in the matrix, can improve the strength of the matrix, hinder the decomposition of martensite during tempering, improve the tempering stability of steel, and can also act as a reducing agent and deoxidizer in the steelmaking process. However, Si tends to make the steel present a banded structure, increase segregation after heat treatment, so that the transverse performance of the steel is worse than the longitudinal performance, and also increase the brittle transition temperature of the steel, reducing the toughness and plasticity of the steel to a certain extent. Therefore, compared with the patented steels such as CN 112080704A and CN 113718170A, the Si content of the steel composition of this design is reduced, in order to minimize the influence of the Si content on toughness. The present invention controls Si≤0.20%.

[0030] Mn, during the austenitization process, is mostly dissolved into the matrix, increasing the alloy content in the matrix, playing a role of solid solution strengthening, thereby improving the strength of the matrix. Mn has a greater affinity with S, which can avoid the formation of low-melting-point sulfides FeS on the grain boundaries, thereby eliminating the harmful effects of sulfur. In addition, Mn can also delay and slow down the pearlite transformation, improve hardenability, and improve the toughness of steel. However, the content of Mn should not be too high. Mn is an austenitization stabilizing element. Excessive Mn will cause the increase of residual austenite and the required hardness cannot be obtained. Therefore, the upper limit of Mn is designed to be 0.55%. The present invention controls Mn0.35~0.55%.

[0031] Cr, a strong carbide-forming element, can improve the hardenability of the material and is also inexpensive. However, Cr is also the main reason for the formation of network carbides, which affects the toughness of the material, so the Cr content should not be too high. The effect of the chromium element causes serious macro-element segregation during the cooling process of the ingot. The segregated Cr and C will form unevenly distributed network ledeburite carbides, which seriously reduce the impact toughness of the steel. Compared with the retrieved patented steel, the steel composition of this design reduces the Cr content, prevents the precipitation of coarse network eutectic carbides, makes the material structure uniform, and improves the toughness of the material. However, in order to ensure the hardness and hardenability of the material, the Cr content cannot be too low, and the lower limit is designed to be 3.50%. The present invention controls Cr 3.50~5.00%, preferably, Cr: 4.50~5.00%.

[0032] Mo is an efficient element for improving hardenability. It has a strong affinity with C atoms and can form carbides, including Mo2C, MC, Mo3Fe3C and Fe2MoC. Due to the strong affinity of Mo with carbon atoms, the decomposition rate of martensite is reduced during tempering, the stability of steel is improved, and carbides are precipitated during tempering to produce secondary hardening. Mo can increase the toughness, hardenability and thermal cracking resistance of steel, and improve the high temperature strength and creep strength of steel. However, excessive Mo increases the material cost on the one hand, and on the other hand, it will lead to the formation of excessive carbides, thereby reducing toughness. Combined with the content of carbon and other alloying elements, the content of Mo is limited to no more than 2.0%. The present invention controls Mo 1.00-2.00%, preferably, Mo: 1.50-2.00%.

[0033] V and C can form highly stable carbides, which contribute to the grain refinement and precipitation strengthening of steel. V can improve hardenability and produce secondary hardening during tempering, and the secondary hardening effect of V is more significant than that of Mo. Appropriate addition of V can improve the hardenability of steel, but too much V will consume C in the matrix, reduce the C content in martensite, and thus reduce the strength of the material. The present invention controls V to 0.20-0.50%, preferably, V: 0.30-0.45%.

[0034] Ni can delay the transformation of pearlite, thereby increasing hardenability. Ni can reduce the toughness-brittle transition temperature and improve the toughness of steel to a certain extent. In addition, the addition of Ni can also prevent forging cracking caused by Cu brittleness. The steel type designed by the present invention adds an appropriate amount of nickel element compared with Chinese patents CN 105861942B and CN 112011740A, which can improve the strength without damaging the toughness and can strengthen the matrix well. However, too much nickel element will cause the bonding effect of intermetallic compounds, and too much nickel will lead to an increase in residual austenite, thereby reducing the strength and hardness of the steel. Therefore, the present invention controls Ni0.20~1.00%, preferably, Ni: 0.40~0.60%.

[0035] Phosphorus is a harmful element in steel, which increases the brittleness of steel and reduces the impact toughness of steel. Therefore, controlling the phosphorus content to a lower level has a certain effect on improving the performance index value. The present invention controls P≤0.008%.

[0036] Sulfur, to a certain extent, can easily deteriorate the processing performance of steel and easily cause overheating of steel during hot working. Therefore, controlling the sulfur content to a lower level can improve the processing performance and mechanical properties of steel. The present invention controls S≤0.003%.

[0037] O is a harmful element in steel. It enters the steel naturally during the steelmaking process. Although manganese, silicon, iron and aluminum are added for deoxidation at the end of steelmaking, it is impossible to remove it completely. During the solidification of molten steel, oxygen and carbon in the solution react to generate carbon monoxide, which can cause bubbles. Oxygen mainly exists in steel in the form of inclusions such as FeO, MnO, SiO2, Al2O3, etc., which reduces the strength and plasticity of steel. In particular, it has a serious impact on fatigue strength, impact toughness, etc. The lower the oxygen content, the better. The present invention controls O≤0.0008%.

[0038] H is the most harmful element in general steel. Dissolved hydrogen in steel can cause defects such as hydrogen embrittlement and white spots. Like oxygen and nitrogen, hydrogen has very low solubility in solid steel. It dissolves into molten steel at high temperature and does not have time to escape during cooling, so it accumulates in the structure to form high-pressure fine pores, which sharply reduce the plasticity, toughness and fatigue strength of the steel. In severe cases, it can cause cracks and brittle fractures. Therefore, the hydrogen content in steel should be reduced as much as possible. The present invention controls H≤0.0002%.

[0039] The influence of N on the properties of steel is similar to that of carbon and phosphorus. With the increase of nitrogen content, the strength of steel can be significantly improved, the plasticity, especially toughness, can be significantly reduced, the weldability can be deteriorated, and the cold brittleness can be aggravated; at the same time, N can increase the aging tendency, cold brittleness and hot brittleness, and damage the welding performance and cold bending performance of steel. Therefore, the nitrogen content in steel should be reduced as much as possible. In the present invention, N is controlled to be ≤0.003%.

[0040] In particular, the content of the chemical elements in the present invention should also conform to the following two relationships:

[0041] 1)5≤[Cr] / [C]≤10, and, 2≤[C]×[Cr]≤4.

[0042] This is because it is necessary to suppress the formation of large chromium-containing carbides. When the C content and Cr content are high, coarse network eutectic carbides are easily formed. However, the C content and Cr content cannot be too low, because the addition of C and Cr is beneficial to improve the hardness and wear resistance of the material, so [C]×[Cr]≥2 and [Cr] / [C]≤10 should be limited.

[0043] 2) 5≤[Cr] / 5+2[Mo]+2[V]+2 / [Ni]≤16, preferably:

[0044] 7≤[Cr] / 5+2[Mo]+2[V]+2 / [Ni]≤10.

[0045] This is because Cr, Mo, and V are all ferrite stabilizing elements, while Ni is an austenite stabilizing element. When the value of this relationship is greater than 16, the toughness of the mold steel will be insufficient. Similarly, considering the effect of the addition of Cr, Mo, and V on the hardness and strength of the material, the value of this relationship should not be less than 5.

[0046] [M] in the above formula is 100 times the mass fraction of element M. For example, if the mass fraction of M is 0.6%, then [M] = 0.6.

[0047] The method for preparing the high-strength and toughness-free ledeburite cold-working die material of the present invention comprises the following steps:

[0048] 1) Vacuum induction melting and casting

[0049] According to the above composition, vacuum induction furnace is used for smelting, and two refinings are carried out after dissolving. The ingot mold is preheated to 250-300℃, and molten steel is poured in. The pouring temperature is 1550±10℃. During pouring, the mold chamber must be filled with Ar gas for protective pouring. After pouring, the mold chamber continues to be filled with Ar gas for ≥50min until the molten steel solidifies. The electrode rod is cooled with the mold, and the cooling time is ≥6h, and then annealed.

[0050] 2) Vacuum consumable remelting

[0051] The steel ingot is used as a consumable electrode and put into a vacuum consumable furnace for refining.

[0052] ≤0.133Pa / min; melting voltage 20~26V, average melting speed 3.5~4.5kg / min. Cooling process is furnace cooling for 40~60min, and hot annealing after stripping;

[0053] 3) High temperature diffusion and heating

[0054] High temperature diffusion, heating the consumable ingot to 1180-1220℃ at a heating rate of ≤100℃ / h and keeping it at that temperature for 8-12h. The heating process is to keep it at 1150-1180℃ for 4-6h.

[0055] 4) Hot rolling and annealing

[0056] Initial rolling, the rolling temperature is 1100-1140℃, the final rolling temperature is 900-1000℃, and the rolling deformation ratio is ≥7;

[0057] The intermediate billet is heated to 1150-1180°C and kept warm for 4-6 hours;

[0058] The start rolling temperature of finishing rolling is 1100~1140℃, the final rolling temperature is 900~1000℃, and the rolling deformation ratio is ≥7;

[0059] After rolling, spheroidizing annealing is performed. Preferably, hot spheroidizing annealing is performed after rolling. If hot annealing is not possible, slow cooling must be performed in a slow cooling box before entering the annealing furnace. The average cooling rate should be ≤20°C / h, and the cooling end temperature should be ≥200°C.

[0060] The spheroidizing annealing of the finished product adopts canning annealing, and the annealing process is: heating the rolled bar to 830±10℃ at a heating rate of ≤100℃ / h and keeping it for 3-5h, then cooling it to 670±10℃ at a rate of ≤50℃ / h and keeping it for 4-6h, then cooling it to below 500℃ at a rate of ≤50℃ / h, and air cooling it to room temperature after being taken out of the furnace; preferably, finishing processes such as straightening and polishing are performed after annealing;

[0061] 5) Heat treatment

[0062] The quenching temperature is 960-1020℃, the holding time is 1-2h, and the oil quenching is used;

[0063] Temper twice, the tempering temperature is 180-250℃, each tempering time is 1.5-2.5h, and air cooling.

[0064] Preferably, in step 5), a cryogenic treatment is added after tempering, at -110°C to -196°C for 1 to 2 hours.

[0065] Preferably, it is characterized in that, in step 1), the annealing process is to heat the electrode rod to 830±10°C and keep it for 3-5h, then cool it to below 300°C in the furnace at a cooling rate of ≤50°C / h, and then air-cool it to room temperature.

[0066] Preferably, it is characterized in that, in step 2), the annealing process is to heat the consumable ingot to 830±10°C and keep it for 4-6h, then cool it to below 300°C in the furnace at a cooling rate of ≤50°C / h, and then air-cool it to room temperature.

[0067] In the preparation method of the present invention:

[0068] The smelting adopts vacuum induction melting and vacuum consumable remelting to reduce the content of P, S, O, H, and N, reduce the formation of non-metallic inclusions, and improve the purity of the matrix, thereby reducing the temper brittleness of the steel.

[0069] A high-temperature diffusion process is carried out before rolling, and the temperature is kept at 1180-1220°C for 8-12 hours to dissolve the carbides into the matrix, thereby improving the uniformity of element distribution and organization.

[0070] The rolling process adopts two-fire rolling. The first fire is the initial rolling to roll the consumable ingot into an intermediate billet, and the second fire is the finished product rolling. The deformation ratio of the two rollings must be ≥7 (the deformation ratio is the cross-sectional area before rolling ÷ the cross-sectional area after rolling). A sufficiently large deformation ratio can ensure that the carbides are broken more thoroughly. If the forging process of multiple multi-directional upsetting and drawing is used, the manufacturing cost is too high to achieve the same deformation ratio. The rolling process can reduce the processing cost and can also achieve the purpose of fully breaking the carbides.

[0071] The heat treatment process adopts low quenching and low tempering (960-1020℃ quenching, 180-250℃ double tempering) and deep cryogenic treatment.

[0072] Usually the heat treatment process of mold steel adopts low quenching and low recovery or high quenching and high recovery.

[0073] The quenching temperature of high quenching and high tempering is usually 1100-1150℃ quenching, and 500-520℃ tempering three to four times. Its advantages are that the alloy elements are fully dissolved, the mold has good red hardness, and the alloy elements are fully exerted. Moreover, after high temperature tempering, the stress is completely eliminated, and the residual austenite is small and stable. However, the disadvantages are that there is a tendency to overheat, the grains are easy to be coarse, and the toughness is poor. It is suitable for molds with high working temperatures and small impact loads during operation.

[0074] The quenching temperature of low quenching and low tempering is usually 960-1020℃ quenching, and 180-250℃ secondary tempering. Its advantages are energy saving, small quenching deformation, simple process, good strength and toughness, but the disadvantage is that the residual austenite is large and unstable. After the cold working die steel is heated to 960-1020℃ for austenitization, a large amount of alloy elements are dissolved into the matrix to enhance the solid solution strengthening effect. At the same time, during the secondary tempering process, the dispersed and precipitated small and uniform second phase particles are strengthened by precipitation, which improves the strength and impact toughness of the material.

[0075] For molds that need to withstand large impact loads during operation, a low quenching and low return heat treatment process can achieve higher toughness.

[0076] Adding cryogenic treatment can transform part of the retained austenite into martensite, thereby improving the strength and hardness of the material to a certain extent without affecting the toughness of the material.

[0077] Compared with the prior art, the present invention has the following advantages:

[0078] 1. Reasonable chemical composition ratio: 1) Reducing the content of carbon and chromium elements significantly improves the uniformity of the steel structure and greatly improves the segregation condition, thereby improving the performance indicators such as impact toughness and eutectic carbide non-uniformity of high-strength and toughness-free ledeburite cold working die steel; 2) Nickel is added to the invention steel, which can improve the strength of the steel while maintaining good plasticity and toughness; 3) Reducing the content of phosphorus, sulfur, oxygen and nitrogen can make the molten steel purer, reduce the tendency of non-metallic inclusions in the steel to form, and reduce the brittleness of the steel after quenching and tempering; 4) Reducing the hydrogen content can prevent defects such as hydrogen embrittlement and white spots.

[0079] 2. The steel of the present invention adopts a double vacuum smelting method of vacuum induction melting + vacuum consumable remelting, which can obtain a uniform and dense structure, greatly reduce the gas content, make the molten steel purer, reduce non-metallic inclusions, reduce the temper brittleness of the steel after quenching and tempering treatment, and greatly improve the mechanical properties and microstructure of the steel.

[0080] 3. The steel of the present invention adopts high-temperature diffusion treatment to improve the non-uniformity of the original structure and composition of the consumable ingot. The hot rolling process is subsequently used to form the material in two heats, and rolling instead of forging can reduce the process cost; during the initial rolling and rolling process, the deformation ratio of each rolling is required to be ≥7, ensuring a sufficiently large deformation ratio, so that the carbides are fully broken, the structure is fine and uniform, and it has a significant effect on improving the performance of the steel.

[0081] 4. The steel of the present invention adopts low quenching and low heat recovery treatment process and deep cryogenic treatment, which improves the strength and hardness of the material to a certain extent without affecting the toughness of the material.

[0082] In summary, the present invention enables the steel to have excellent comprehensive properties through reasonable chemical composition ratio, advanced smelting process, reasonable thermal processing process and heat treatment process.

[0083] The performance index of the steel of the present invention is compared with that of the most commonly used cold working die steel Cr12MoV. After quenching at 1020℃ and tempering at 200℃, the longitudinal unnotched impact toughness of Cr12MoV steel is 11.2J / cm 2 , hardness is 61HRC, tensile strength is 1730MPa, eutectic carbide unevenness is 3.5 level; and after quenching at 960-1020℃ and tempering twice at 180-250℃ and adding cryogenic treatment, the impact toughness of the steel is 201-355J / cm 2, hardness is 57-59HRC, tensile strength is 2105-2422MPa, and eutectic carbide unevenness is ≤ level 1. The hardness of the steel of the present invention is slightly lower than that of Cr12MoV, but the strength and toughness are much higher than those of Cr12MoV.

[0084] Compared with the prior art, the advantages of the present invention are:

[0085] (1) From the comparison of components, it can be seen that the C content of the comparative patents is generally above 0.6%, and the upper limit is basically between 0.8% and 2%. The Cr content is generally higher than 5%, the Mo content is generally higher than 2%, and some are lower than 1%. The V content is generally higher than 0.5%. Some patents also add appropriate amounts of Nb, W or Ni to improve strength and toughness. The carbon content and chromium content in the element content of the chemical composition of the present invention are lower than those of the above-mentioned comparative patents. Chromium is one of the main reasons for the unevenness of carbides, which is easy to form a network of carbides and reduce the toughness of the material. Compared with Chinese patents CN 105861942B, CN112011740A, CN112080704A, etc., the steel of the present invention adds an appropriate amount of nickel, but the content of Ni is lower than the amount added in Chinese patent CN113718170A. Ni is an austenite stabilizing element, which can reduce the ductile-brittle transition temperature, and can maintain good plasticity and toughness while improving the strength of steel; however, the C content and other alloying elements in the steel of the present invention are not high. In order to achieve a good combination of various elements and thus achieve the best comprehensive performance, the upper limit design value of the Ni element in the steel of the present invention is 1%. In addition, the steel of the present invention controls P, S, O, H, and N at very low levels, reduces non-metallic inclusions in the steel, can reduce the temper brittleness of the steel after quenching and tempering, and is conducive to improving the comprehensive performance of the steel.

[0086] (2) About the manufacturing process

[0087] First of all, the smelting process. The comparative patents all use non-vacuum or single-vacuum smelting methods, such as electric furnace or medium-frequency furnace smelting + electroslag remelting, or only vacuum induction melting. Compared with other patents, the present invention uses double vacuum smelting, which can greatly reduce the content of P, S, O, H, and N, and obtain a pure, uniform and dense structure; in addition, the Chinese patent CN103233168A uses a powder metallurgy process, which is relatively expensive;

[0088] The second is the high-temperature diffusion process. Among the comparative patents, only the Chinese patent CN105861942B adopts the "high-temperature diffusion process of keeping warm at 1150-1200°C for 10-20h". Although the present invention also adopts the high-temperature diffusion process to uniform the element composition and organization, the process is to keep warm at 1180-1220°C for 8-12h. Compared with the comparative patent, i.e. the Chinese patent CN105861942B, the present invention appropriately increases the high-temperature diffusion temperature and shortens the insulation time, which can also achieve the purpose of uniform element distribution and organization, and can save energy and cost.

[0089] The third is the hot working process. Other patents all use forging process, while the present invention uses rolling blanking and rolling process, while ensuring a large deformation ratio. The rolling deformation ratio of each fire should be ≥7, which can ensure the full crushing of carbides and reduce processing costs.

[0090] The fourth is the heat treatment process. The patent mentioned that the heat treatment process is high quenching and high tempering or low quenching and low tempering. The Chinese patent CN113718170A uses toughness tempering, but none of the patents adds cryogenic treatment after tempering. The present invention proposes to add cryogenic treatment after tempering to promote the transformation of retained austenite to martensite and ensure the strength and hardness of the material. BRIEF DESCRIPTION OF THE DRAWINGS

[0091] Figure 1 This is a metallographic structure photograph of the annealed state of steel Example 1 of the present invention.

[0092] Figure 2 This is a metallographic structure photograph of steel Example 1 of the present invention after quenching at 980°C and tempering at 200°C.

[0093] Figure 3 This is a metallographic structure photograph of steel Example 1 of the present invention after quenching at 980°C, tempering at 200°C and cryogenic treatment.

[0094] Figure 4 This is a photograph of the inhomogeneous eutectic carbide of Example 1 of the steel of the present invention.

[0095] Figure 5 This is a photograph of the inhomogeneous eutectic carbide of Example 2 of the steel of the present invention. DETAILED DESCRIPTION

[0096] The present invention will be further described below in conjunction with the embodiments and drawings.

[0097] The chemical composition of die steel embodiments 1 to 8 of the present invention and comparative example Cr12MoV is shown in Table 1, and the remainder is Fe and unavoidable impurities. The preparation methods of the embodiments of the present invention are shown in Tables 2 to 4, and the mechanical properties including hardness, tensile strength and longitudinal unnotched impact toughness (unnotched impact specimen size is 7×10×55 (mm)) are shown in Table 5.

[0098] Example 1

[0099] A method for producing high-strength and toughness ledeburite-free cold-working die steel comprises the following steps:

[0100] 1) Double vacuum smelting

[0101] A vacuum induction furnace was used for smelting. The ingot mold was preheated to 250°C before pouring. The pouring temperature was 1546°C. Ar gas was used for pouring. After pouring, the mold chamber was filled with Ar gas for 50 minutes until the steel liquid solidified. The electrode rod was cooled along with the mold. The cooling time was 6.3 hours. The cast ingot was annealed at 820°C for 4 hours.

[0102] 2) Vacuum consumable remelting, gas leakage rate 0.121Pa / min, average melting rate 4kg / min; cooling process is furnace cooling for 50min, ingot stripping and hot annealing; consumable ingot annealing process is 830℃ insulation for 4.5h;

[0103] 3) High temperature diffusion is performed before rolling; the high temperature diffusion process of the consumable ingot is to heat the consumable ingot to 1180°C at a heating rate of 80°C / h and keep it warm for 12 hours, and the heating process is to keep it warm at 1165°C for 5 hours;

[0104] 4) Hot rolling and annealing

[0105] Initial rolling, the starting temperature is 1100℃, the final rolling temperature is 900℃, and the rolling deformation ratio is 7.17;

[0106] The heating process of the rolling intermediate billet is to keep the temperature at 1160℃ for 5h;

[0107] The start rolling temperature of finishing rolling is 1100℃, the final rolling temperature is 920℃, and the rolling deformation ratio is 27.7;

[0108] The spheroidizing annealing of the finished product adopts canning annealing. The annealing process is to heat the rolled bar to 830℃ at a heating rate of 80℃ / h and keep it at that temperature for 4.2h, and then cool it to 678℃ at a rate of 40℃ / h and keep it at that temperature for 4.3h; after annealing, straightening, polishing and other finishing processes are carried out, and the finished product specification is Φ30mm round steel;

[0109] 5) Heat treatment

[0110] The low quenching and low tempering heat treatment method is adopted, that is, quenching at 980℃, tempering twice at 200℃, each tempering for 2h; after tempering, deep cooling treatment is performed at -196℃ for 2 hours.

[0111] Example 2

[0112] A method for producing high-strength and toughness ledeburite-free cold-working die steel comprises the following steps:

[0113] 1) Double vacuum smelting

[0114] A vacuum induction furnace was used for smelting. The ingot mold was preheated to 270°C before pouring, and the pouring temperature was 1553°C. Ar gas was used for pouring. After pouring, the mold chamber was continuously filled with Ar gas for 52 minutes until the molten steel solidified. The electrode rod was cooled along with the mold, and the cooling time was 8 hours. The cast ingot was annealed at 832°C for 4.5 hours.

[0115] 2) Vacuum consumable remelting, gas leakage rate 0.132Pa / min, average melting rate 3.9kg / min; cooling process is furnace cooling for 58min, ingot stripping and hot annealing; consumable ingot annealing process is 835℃ insulation for 4.8h;

[0116] 3) High temperature diffusion before rolling; the high temperature diffusion process of the consumable ingot is to heat the consumable ingot to 1200°C at a heating rate of 100°C / h and keep it at that temperature for 8.5h, and the heating process is to keep it at 1170°C for 4.5h;

[0117] 4) Hot rolling and annealing

[0118] Initial rolling, the starting temperature is 1120℃, the final rolling temperature is 960℃, and the rolling deformation ratio is 7.7;

[0119] The heating process of the rolling intermediate billet is to keep the temperature at 1165℃ for 4.8h, and the rolling deformation ratio is 9.98;

[0120] The starting temperature of finishing rolling is 1120℃, and the final rolling temperature is 950℃;

[0121] The spheroidizing annealing of the finished product adopts canning annealing. The annealing process is to heat the rolled bar to 820℃ at a heating rate of 90℃ / h and keep it for 4.5h, then cool it to 670℃ at a rate of 40℃ / h and keep it for 5.7h; after annealing, straightening, polishing and other finishing processes are carried out, and the finished product specification is Φ50mm round steel;

[0122] 5) Heat treatment

[0123] The low quenching and low tempering heat treatment method is adopted, that is, quenching at 1000℃ and tempering twice at 220℃, each tempering for 1.9h.

[0124] Example 3

[0125] A method for producing high-strength and toughness ledeburite-free cold-working die steel comprises the following steps:

[0126] 1) Double vacuum smelting

[0127] A vacuum induction furnace was used for smelting. The ingot mold was preheated to 280°C before pouring. The pouring temperature was 1544°C. Ar gas was used for pouring. After pouring, the mold chamber was continuously filled with Ar gas for 51 minutes until the molten steel solidified. The electrode rod was cooled along with the mold. The cooling time was 6.2 hours. The cast ingot was annealed at 835°C for 3.2 hours.

[0128] 2) Vacuum consumable remelting, gas leakage rate 0.131Pa / min, average melting rate 4.1kg / min; cooling process is furnace cooling for 40min, ingot stripping and hot annealing; consumable ingot annealing process is 840℃ insulation for 5h;

[0129] 3) High temperature diffusion is performed before rolling; the high temperature diffusion process of the consumable ingot is to heat the consumable ingot to 1210°C at a heating rate of 90°C / h and keep it warm for 8 hours, and the heating process is to keep it warm at 1175°C for 4.2 hours;

[0130] 4) Hot rolling and annealing

[0131] Initial rolling, the starting temperature is 1110℃, the final rolling temperature is 950℃, and the rolling deformation ratio is 7.23;

[0132] The heating process of the rolling intermediate billet is to keep the temperature at 1170℃ for 4.5h;

[0133] The start rolling temperature of finishing rolling is 1100℃, the final rolling temperature is 955℃, and the rolling deformation ratio is 12.3;

[0134] The spheroidizing annealing of the finished product adopts canning annealing. The annealing process is to heat the rolled bar to 835℃ at a heating rate of 100℃ / h and keep it for 4h, then cool it to 675℃ at a rate of 50℃ / h and keep it for 4.8h; after annealing, straightening, polishing and other finishing processes are carried out, and the finished product specification is Φ45mm round steel;

[0135] 5) Heat treatment

[0136] The low quenching and low tempering heat treatment method is adopted, that is, quenching at 990℃, tempering twice at 210℃, and each tempering is 2.1h; after tempering, deep cooling treatment is performed at -150℃ for 1 hour.

[0137] Example 4

[0138] A method for producing high-strength and toughness ledeburite-free cold-working die steel comprises the following steps:

[0139] 1) Double vacuum smelting

[0140] A vacuum induction furnace was used for smelting. The ingot mold was preheated to 260°C before pouring. The pouring temperature was 1557°C. Ar gas was used for pouring. After pouring, the mold chamber was continuously filled with Ar gas for 53 minutes until the molten steel solidified. The electrode rod was cooled along with the mold. The cooling time was 8.5 hours. The cast ingot was annealed at 830°C for 5 hours.

[0141] 2) Vacuum consumable remelting, gas leakage rate 0.116Pa / min, average melting rate 3.8kg / min; cooling process is furnace cooling for 60min, ingot stripping and hot annealing; consumable ingot annealing process is 832℃ insulation for 5.5h;

[0142] 3) High temperature diffusion is performed before rolling; the high temperature diffusion process of the consumable ingot is to heat the consumable ingot to 1190°C at a heating rate of 90°C / h and keep it warm for 10 hours, and the heating process is to keep it warm at 1160°C for 5.3 hours;

[0143] 4) Hot rolling and annealing

[0144] Initial rolling, the rolling temperature is 1105℃, the final rolling temperature is 920℃, and the rolling deformation ratio is 8.33;

[0145] The heating process of the rolling intermediate billet is to keep the temperature at 1155℃ for 5.5h;

[0146] The start rolling temperature of finishing rolling is 1105℃, the final rolling temperature is 945℃, and the rolling deformation ratio is 53.8;

[0147] The spheroidizing annealing of the finished product adopts canning annealing. The annealing process is to heat the rolled bar to 825℃ at a heating rate of 80℃ / h and keep it for 5h, then cool it to 660℃ at a rate of 50℃ / h and keep it for 6h; after annealing, straightening, polishing and other finishing processes are carried out, and the finished product specification is Φ20mm round steel;

[0148] 5) Heat treatment

[0149] The low quenching and low tempering heat treatment method is adopted, that is, quenching at 960℃ and tempering twice at 180℃, each tempering for 2.5h.

[0150] Example 5

[0151] A method for producing high-strength and toughness ledeburite-free cold-working die steel comprises the following steps:

[0152] 1) Double vacuum smelting

[0153] A vacuum induction furnace was used for smelting. The steel ingot mold was preheated to 300°C before pouring. The pouring temperature was 1543°C. Ar gas was used for pouring. After pouring, the mold chamber was continuously filled with Ar gas for 57 minutes until the steel liquid solidified. The electrode rod was cooled along with the mold. The cooling time was 6.5 hours. The cast steel ingot was annealed at 823°C for 3.5 hours.

[0154] 2) Vacuum consumable remelting, gas leakage rate 0.12Pa / min, average melting rate 3.7kg / min; cooling process is furnace cooling for 55min, ingot stripping and hot annealing; consumable ingot annealing process is 820℃ insulation for 6h;

[0155] 3) High temperature diffusion is performed before rolling; the high temperature diffusion process of the consumable ingot is to heat the consumable ingot to 1205°C at a heating rate of 100°C / h and keep it warm for 9 hours, and the heating process is to keep it warm at 1180°C for 4 hours;

[0156] 4) Hot rolling and annealing

[0157] Initial rolling, the starting temperature is 1140℃, the final rolling temperature is 1000℃, and the rolling deformation ratio is 7.71;

[0158] The heating process of the rolling intermediate billet is to keep the temperature at 1175℃ for 4.2h;

[0159] The finishing rolling temperature is 1140℃, the final rolling temperature is 980℃, and the rolling deformation ratio is 7.71;

[0160] The spheroidizing annealing of the finished product adopts canning annealing. The annealing process is to heat the rolled bar to 840℃ at a heating rate of 90℃ / h and keep it for 3.5h, then cool it to 680℃ at a rate of 50℃ / h and keep it for 4h; after annealing, straightening, polishing and other finishing processes are carried out, and the finished product specification is Φ55mm round steel;

[0161] 5) Heat treatment

[0162] The low quenching and low tempering heat treatment method is adopted, that is, quenching at 1020℃ and tempering twice at 250℃, each tempering for 1.5h.

[0163] Figure 1 This is a metallographic structure photo of the annealed state of the steel example 1 of the present invention. It can be seen that the structure of the steel of the present invention is very uniform, the carbide spheroidization effect is very good, the size of the granular carbide is very small, and the diameter is less than 1μm. The steel of the present invention does not contain the ledeburite structure that often appears in conventional Cr12 series cold working die steel.

[0164] Figure 2 This is a metallographic photograph of the steel example 1 of the present invention after the heat treatment process is quenching at 980°C and tempering at 200°C. The structure is tempered martensite + carbide + retained austenite. Figure 2 It can be seen that fine carbide particles are evenly distributed on the tempered martensite matrix. Such a structure ensures that the steel of the present invention has excellent strength and toughness combination.

[0165] Figure 3 This is a metallographic photograph of the steel example 1 of the present invention after the heat treatment process is 980℃ quenching, 200℃ tempering and then cryogenic treatment, and Figure 2In comparison, the structure after cryogenic treatment is finer and the amount of retained austenite is reduced, which is beneficial to improving the hardness and strength of the material.

[0166] Figure 4 and Figure 5 The following are photos of the inhomogeneous eutectic carbides of the steel examples 1 and 2 of the present invention. The inhomogeneous carbide levels of the two examples are both ≤ level 1. In addition, since the diameter of the finished round steel of example 1 is smaller than that of example 2, the processing deformation ratio is larger, and the crushing effect of the eutectic carbide is better.

[0167]

[0168]

[0169]

[0170]

[0171]

Claims

1. A high-strength and toughness non-ledeburite cold-working die steel, the composition weight percentage of which is: C: 0.45-0.65%, Si: ≤0.20%, Mn: 0.35-0.55%, Cr: 3.50-5.00%, Mo: 1.00-2.00%, V: 0.20-0.50%, Ni: 0.20-1.00%, P≤0.008%, S≤0.003%, O≤0.0008%, H≤0.0002%, N≤0.003%, the balance includes Fe and other unavoidable impurities, and must meet the following requirements: 5≤[Cr] / [C]≤10, 2≤[C]×[Cr]≤4, 5≤[Cr] / 5+2[Mo]+2[V]+2 / [Ni]≤16.

2. The high-strength and toughness non-ledburite cold-working die steel according to claim 1, characterized in that: The remainder is Fe and other inevitable impurities.

3. The high-strength and toughness non-ledburite cold-working die steel according to claim 1 or 2, characterized in that: 7≤[Cr] / 5+2[Mo]+2[V]+2 / [Ni]≤10.

4. The high-strength and toughness non-ledeburite cold-working die steel according to claim 1, 2 or 3, characterized in that: C: 0.55-0.60%, or Cr: 4.50-5.00%, or Mo: 1.50-2.00%, or V: 0.30-0.45%, or Ni: 0.40-0.60%.

5. The high-strength and toughness non-ledeburite cold-working die steel according to claim 1, 2, 3 or 4, characterized in that: The annealed structure of the cold working die steel is pearlite + granular carbide, the size of the granular carbide is very small, the diameter is less than 1 μm, and there is no ledeburite structure that is often present in conventional Cr12 series cold working die steel; after quenching and tempering treatment, the structure of the cold working die steel is tempered martensite + dispersed fine carbide particles + a small amount of residual austenite, and there is no large eutectic carbide that is often present in conventional Cr12 series cold working die steel.

6. The high-strength and toughness non-ledeburite cold-working die steel according to claim 1, 2, 3, 4 or 5, characterized in that: The impact toughness of the cold working die steel is 201-355 J / cm 2 , hardness is 57~59HRC, tensile strength is 2105~2422MPa, and eutectic carbide unevenness is ≤level 1.

7. The method for preparing the high-strength and toughness non-ledburite cold-working die material according to any one of claims 1 to 6, characterized in that: The steps include: 1) Vacuum induction melting and casting According to the composition of claim 1 or 2 or 3 or 4, a vacuum induction furnace is used for smelting, and after dissolving, two refinings are performed, the ingot mold is preheated to 250-300°C, and molten steel is injected, and the pouring temperature is 1550±10°C; during pouring, the mold chamber must be filled with Ar gas for protective pouring; after pouring, the mold chamber continues to be filled with Ar gas for ≥50min until the molten steel solidifies; the electrode rod is cooled with the mold, and the cooling time is ≥6h, and then annealed; 2) Vacuum consumable remelting The steel ingot is used as a consumable electrode and put into a vacuum consumable furnace for refining, with a gas leakage rate of ≤0.133Pa / min; the melting voltage is 20-26V, and the average melting speed is 3.5-4.5kg / min; the cooling process is furnace cooling for 40-60min, and the ingot is removed and hot annealed; 3) High temperature diffusion and heating High temperature diffusion, heating the consumable ingot to 1180-1220℃ at a heating rate of ≤100℃ / h and keeping it at that temperature for 8-12h. The heating process is to keep it at 1150-1180℃ for 4-6h. 4) Hot rolling and annealing Initial rolling, the rolling temperature is 1100-1140℃, the final rolling temperature is 900-1000℃, and the rolling deformation ratio is ≥7; The intermediate billet is heated to 1150-1180°C and kept warm for 4-6 hours; The start rolling temperature of finishing rolling is 1100~1140℃, the final rolling temperature is 900~1000℃, and the rolling deformation ratio is ≥7; After rolling, spheroidizing annealing is performed. Preferably, hot spheroidizing annealing is performed after rolling. If hot annealing is not possible, slow cooling must be performed in a slow cooling box before entering the annealing furnace. The average cooling rate should be ≤20°C / h, and the cooling end temperature should be ≥200°C. The spheroidizing annealing of the finished product adopts canning annealing, and the annealing process is: heating the rolled bar to 830±10℃ at a heating rate of ≤100℃ / h and keeping it for 3-5h, then cooling it to 670±10℃ at a rate of ≤50℃ / h and keeping it for 4-6h, then cooling it to below 500℃ at a rate of ≤50℃ / h, and air cooling it to room temperature after being taken out of the furnace; preferably, finishing processes such as straightening and polishing are performed after annealing; 5) Heat treatment The quenching temperature is 960-1020℃, the holding time is 1-2h, and the oil quenching is used; Temper twice, the tempering temperature is 180-250℃, each tempering time is 1.5-2.5h, and air cooling.

8. The method for preparing high-strength and toughness non-ledeburite cold-working die steel according to claim 7, characterized in that: Step 5) After tempering, a cryogenic treatment is added at -110°C to -196°C for 1 to 2 hours.

9. The method for preparing high-strength and toughness non-ledeburite cold-working die steel according to claim 7, characterized in that: Its characteristics are: In step 1), the annealing process is to heat the electrode rod to 830±10°C and keep it at that temperature for 3-5h, then cool it to below 300°C at a cooling rate of ≤50°C / h, and then air cool it to room temperature.

10. The method for preparing high-strength and toughness non-ledeburite cold-working die steel according to claim 7, characterized in that: Its characteristics are: In step 2), the annealing process is to heat the consumable ingot to 830±10°C and keep it at that temperature for 4 to 6 hours, then cool it to below 300°C at a cooling rate of ≤50°C / h, and then air cool it to room temperature.

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