High toughness hot work die steel for die casting and method of manufacturing the same

Abstract

The application discloses a high-toughness hot work die steel for die casting, which comprises the following chemical components in percentage by weight: C: 0.33-0.40%, Si: 0.10-0.40%, Mn: 0.20-0.60%, Cr: 4.50-5.50%, V: 0.30-0.60%, Mo: 1.70-2.80%, Co: 0.10-1.00%, Ni: 0.10-1.00%, Cu: <=0.25%, P: <=0.015, S: <=0.05, and the balance of Fe and inevitable impurities. The application further discloses a manufacturing method of the high-toughness hot work die steel for die casting. The application meets the material selection, material use and long service life requirements of the high-end hot work die steel for die casting.

Description

Technical Field

[0001] This invention relates to alloy steel for die-casting products in the metallurgical industry, and more specifically, to a high-toughness hot work die steel for die casting and its manufacturing method. Background Technology

[0002] With the transformation and upgrading of my country's manufacturing industry, the mold manufacturing industry is gradually developing towards large-scale and precision. Meanwhile, the stable growth demand from industries such as automobiles, home appliances, and 3C communications has put forward higher quality requirements for high-end mold steel in my country. Among them, hot work mold steel products for die casting, which have complex service conditions, high material performance requirements, and long mold service life, have problems such as a lack of high-quality, stable and reliable applicable materials.

[0003] Hot work die steel is mainly used to manufacture mold materials for forming metals or liquid metals heated to above the recrystallization temperature (such as zinc, magnesium, aluminum, copper, etc.). Its characteristics are that it is in contact with hot metal during operation, the mold cavity temperature is high, and the stress is complex. For example, when aluminum alloy die casting molds are in service, the temperature of aluminum alloy liquid is usually 650-700℃, and it is pressed into the cavity at a speed of 40-180mm / s, with a pressure of 20-120MPa, a holding time of 5-20s, and an interval of 20-75s between each injection. That is, it is often under high temperature and high pressure conditions during service, and is repeatedly heated and cooled. The main failures of the die casting mold are thermal cracking, melting, and cracking, which seriously affect the service life of the mold.

[0004] Among the common failure modes of die-casting molds, hot cracking is a defect caused by thermal fatigue due to repeated heating and cooling of the mold surface; erosion is a surface spalling phenomenon caused by the contact between the mold surface and molten metal; cracking is influenced by many factors, such as cracks originating from hot cracking and fatigue-promoted cracks caused by alternating stress. Currently, with the increasing demand for larger die-casting mold sizes and the annual increase in the tonnage of new die-casting machines, cracking of large molds due to factors such as microsegregation, insufficient hardenability, and poor heat resistance causes significant economic losses for mold users. Therefore, under high-temperature and complex stress conditions, improving material toughness, preventing mold cracking, and enhancing mold lifespan, developing high-toughness materials for hot-working die-casting molds is becoming increasingly important.

[0005] In an existing patent application, CN103334061B discloses a hot work die steel with the following chemical composition: C: 0.30-0.45%, Mn: 0.20-0.30%, Si: 0.10-0.30%, Cr: 2.00-3.50%, Ni: 2.00-6.00%, W: 2.50-4.00%, Mo: 1.00-1.50%, V: 0.35-0.65%, P<0.025%, S<0.025%, with the balance being Fe and unavoidable impurities.

[0006] CN104046915B discloses a die-casting hot-work die steel with the following chemical composition: C: 0.45-0.47%, Si: 0.30-1.00%, Mn: 0.30-1.00%, Cr: 4.80-5.50%, Mo: 2.00-3.00%, V: 0.40-0.80%, P<0.02%, S<0.01%, Ni: 1.00-2.00%, Nb: ≥0.15%, with the balance being Fe and unavoidable impurities.

[0007] CN107557667A discloses a hot-work die steel for large die-casting molds, with the following chemical composition: C: 0.20–0.30%, Si ≤ 0.40%, Mn: 0.30–0.60%, Cr: 4.10–4.50%, Mo: 2.00–2.30%, W: 0.10–0.20%, V: 0.40–0.80%, P < 0.01%, S < 0.005%, Nb: 0.02–0.04%, with the balance being Fe and unavoidable impurities.

[0008] CN107653416A discloses a hot work die steel with the following chemical composition: C: 0.35-0.40%, Si≤0.25%, Mn: 0.30-0.50%, Cr: 5.00-5.30%, Mo: 2.20-2.40%, V: 0.50-0.65%, P≤0.010%, S≤0.001%, Ni≤0.20%, Cu≤0.10%, Nb: 0.005-0.020%, with the balance being Fe and unavoidable impurities.

[0009] CN111057933A discloses a hot-work die steel for die casting molds, with the chemical composition of C: 0.33-0.46%, Si: 1.5-2.3%, Mn: 0.32-0.45%, Mo: 1.6-2.3%, W: 2.6-3.6%, Nb: 0.16-0.27%, Cr: 2.8-3.7%, Sr: 0.21-0.53%, Ti: 0.16-0.31%, Ce: 0.05-0.09%, S ≤0.003%, P ≤0.03%, and the balance being Fe and unavoidable impurities.

[0010] CN103334061B, CN104046915B, CN107557667A, CN107653416A, and CN111057933A are all based on the composition of 4Cr5MoSiV steel. By adjusting and adding alloying elements such as Si, Cr, Wo, Ni, and Nb, the hardenability, heat resistance, and toughness of the material are improved. However, CN103334061B improves thermal conductivity by reducing Si and Cr, improves processability by reducing V, and increases high-temperature strength by adding W, but the high W content makes carbide control difficult. CN104046915B increases hardenability and hot strength by appropriately increasing C and Mo, and increases hardenability and refines grain size by adding Ni and Nb, but the high Ni content makes production control difficult. CN107557667A... By appropriately reducing C to improve hardness uniformity and appropriately increasing Mo to improve hot strength, and by adding W and Nb to improve thermal stability, CN111057933A improves its overall performance through high Si, high Mo, reduced Cr, and added W and Nb. However, the simultaneous addition of W, Mo, and Nb in CN107557667A and CN111057933A will form a large number of carbides, which will affect the toughness of the steel. CN107653416A only reduces the Si and V content and increases the Mo content on the basis of H13, while adding a trace amount of Nb to improve the overall performance of the material. Summary of the Invention

[0011] In view of the above-mentioned defects in the existing technology, the purpose of this invention is to provide a high-toughness hot work die steel for die casting and its manufacturing method, so as to meet the requirements of material selection, material usage and long service life of high-end hot work die steel for die casting.

[0012] To achieve the above objectives, the present invention adopts the following technical solution:

[0013] On the one hand, a high-toughness hot work die steel for die casting comprises the following chemical composition by weight percentage:

[0014] C: 0.33–0.40%, Si: 0.10–0.40%, Mn: 0.20–0.60%, Cr: 4.50–5.50%, V: 0.30–0.60%, Mo: 1.70–2.80%, Co: 0.10–1.00%, Ni: 0.10–1.00%, Cu: ≤0.25%, P: ≤0.015%, S: ≤0.05%, with the balance being Fe and unavoidable impurities.

[0015] On the other hand, a method for manufacturing high-toughness die-casting hot work die steel involves, according to the chemical composition ratio, smelting and casting electrode rods in an electric furnace with ladle refining, then electroslag forming electroslag ingots, and finally preparing the electroslag ingots through high-temperature homogenization, rapid forging, solution treatment, spheroidizing annealing, quenching, and tempering heat treatment.

[0016] Preferably, the slag-forming voltage of the electric furnace is 45V~65V / current is 6000A~18000A, the smelting voltage is 43V~52V / current is 14000A~17000A, and the feeding voltage is 9000V~16000V / current is 36A~44A.

[0017] Preferably, the electroslag remelting filling ratio is 0.75 to 0.80.

[0018] Preferably, the electroslag ingot undergoes high-temperature homogenization, which further includes:

[0019] The temperature is increased at 700℃~800℃ in a fast forging furnace at a rate of 80℃ / h~120℃ / h, and then held at 1210℃~1300℃ for 10 hours~12 hours.

[0020] Preferably, the forging start temperature of the electroslag ingot forging into finished product by fast forging is 1020℃~1100℃, and the forging stop temperature is 850℃~950℃.

[0021] Preferably, the electroslag ingot is water-cooled or mist-cooled after being forged by rapid forging, with a cooling rate greater than 0.5℃ / min, until the temperature drops below 200℃ for hot annealing.

[0022] Preferably, the electroslag ingot undergoes solution treatment, which further includes:

[0023] The heating temperature is 950℃~1150℃, the holding time is 10 hours~15 hours, and then the temperature is cooled to below 250℃ by oil cooling or water cooling before being sent to the annealing furnace.

[0024] Preferably, the electroslag ingot undergoes spheroidizing annealing, which further includes:

[0025] The first stage of isothermal annealing is at a temperature of 830℃~850℃ and an annealing time of 5 hours~10 hours; the second stage of isothermal annealing is at a temperature of 730℃~750℃ and an annealing time of 10 hours~20 hours.

[0026] Preferably, the electroslag ingot undergoing quenching and tempering heat treatment further includes:

[0027] Heat to 950℃~1100℃, cool with oil or water mist to below 250℃, and then temper at above 590℃, tempering 2 to 3 times, holding each tempering for 2 to 4 hours.

[0028] The high-toughness hot work die steel for die casting and its manufacturing method provided by this invention have the following beneficial effects:

[0029] 1) The chemical composition is more rationally proportioned, with reduced carbon, silicon, and vanadium content, increased molybdenum content, and the addition of appropriate amounts of nickel and cobalt. The solid solution strengthening and precipitation strengthening effects of alloying elements such as Ni, Co, Cr, Mo, and V improve the material's high-temperature strength and thermal stability. Specifically, reducing Si content improves banded structure formation and thermal conductivity; reducing V content improves toughness; increasing Mo content increases the formation of Mo2C and MoC carbides, delaying their transformation to Mo23C6, thereby further improving high-temperature strength and thermal stability; and the addition of non-carbide-forming elements Ni and Co, which dissolve in ferrite and austenite, respectively improves hardenability and heat resistance.

[0030] 2) The hot work die steel used in this invention has a high alloy content. To fully utilize the material's inherent performance advantages, advanced manufacturing processes are needed to ensure the steel's performance. Therefore, metallurgical manufacturing methods such as electroslag remelting and high-temperature homogenization are employed. Electroslag remelting utilizes the resistance heat generated by current passing through the electroslag layer to melt the consumable electrode alloy steel ingot base material. The liquid metal falls as droplets through the slag layer into the water-cooled crystallizer below, where it resolidifies into a steel ingot. The steel ingot crystallizes gradually from bottom to top. Electroslag remelting can reduce gas inclusions and residual oxygen content in the steel ingot, improving its macroscopic and microscopic structure. Simultaneously, the high-temperature homogenization technology eliminates large, difficult-to-dissolve eutectic carbides, improves the segregation of alloying elements, and enhances the internal quality of the steel.

[0031] 3) The reasonable chemical composition ratio and advanced manufacturing process ensure the high performance of the steel. The hot work die steel of this invention has excellent key performance indicators, including the level of non-metallic inclusions and the level of annealed microstructure. After quenching at 1050℃ and tempering twice (tempering temperature ≥590℃), the impact toughness of the material is significantly improved compared with 4Cr5MoSiV1 steel under the same hardness conditions, making it more suitable for the manufacture of hot work dies for die casting with high service life requirements. Attached Figure Description

[0032] Figure 1 This is an annealed microstructure of the high-toughness die-casting hot work die steel of this invention;

[0033] Figure 2 This is a metallographic diagram of the high-toughness die-casting hot work die steel of this invention after quenching at 1050℃;

[0034] Figure 3This is a metallographic microstructure of the high-toughness die-casting hot work die steel of the present invention after quenching at 1050℃ and then tempering twice (tempering temperature ≥590℃).

[0035] Figure 4 This is a comparison chart of the room temperature transverse unnotched impact energy of the high-toughness die-casting hot work die steel produced in Example 1 of this invention and 4Cr5MoSiV1 steel.

[0036] Figure 5 This is a comparison chart of the room temperature transverse unnotched impact energy of the high-toughness hot work die steel for die casting produced in Examples 1 to 5 of this invention and 4Cr5MoSiV1 steel. Detailed Implementation

[0037] To better understand the above-mentioned technical solutions of the present invention, the technical solutions of the present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0038] This invention provides a high-toughness hot-work die steel for die casting, which improves the non-metallic inclusions and annealed microstructure of large-section die steel. Simultaneously, it enhances the hardness and impact toughness of the material after quenching at 1050℃ followed by secondary tempering (tempering temperatures ≥ 590℃), significantly improving the overall performance of the material. The chemical composition includes the following by weight percentage:

[0039] C: 0.33–0.40%, Si: 0.10–0.40%, Mn: 0.20–0.60%, Cr: 4.50–5.50%, V: 0.30–0.60%, Mo: 1.70–2.80%, Co: 0.10–1.00%, Ni: 0.10–1.00%, Cu: ≤0.25%, P: ≤0.015%, S: ≤0.05%, with the balance being Fe and unavoidable impurities.

[0040] In this invention, carbon content is 0.33–0.40%. Carbon is the most effective element for improving the hardness and strength of steel, and it also affects the segregation and microstructure uniformity of steel. Furthermore, the various types of carbides, such as chromium, molybdenum, and vanadium, precipitated during tempering, which provide dispersion strengthening, are fundamental to ensuring the performance of hot work die steel meets specifications. The carbon content in this invention is lower than that of the existing 4Cr5MoSiV1, aiming to improve the grade and distribution of liquid carbides in the steel, improve the distribution and properties of carbides in the microstructure, and enhance the toughness of the material. The relatively low carbon content prevents segregation during solidification, thus avoiding uneven hardness and reduced impact toughness.

[0041] Si (0.10-0.40%) can improve hardenability and tempering resistance in quenched and tempered steel. However, silicon tends to form banded structures in steel, reducing isotropic properties (transverse properties are lower than longitudinal properties). At the same time, the outer electron structure of Si differs significantly from that of Fe, and higher Si content will severely reduce the thermal conductivity of steel.

[0042] Mn: 0.20~0.60%. Manganese dissolved in austenite can increase the hardenability of steel and lower the Ms point of steel. At the same time, an appropriate amount of manganese can increase the matrix strengthening effect of steel and delay the transformation of martensite structure, thereby improving the steel's resistance to tempering softening.

[0043] Cr: 4.50–5.50%; Chromium can improve hardenability and tempering resistance, and easily form stable carbides. Specifically, chromium can strongly delay the pearlite transformation, which is beneficial for improving the hardenability and tempering stability of martensite in materials. When Cr is around 5%, it forms (Fe,Cr)7C3 and (Fe,Cr)27C6 type carbides, producing a secondary hardening effect and increasing strength.

[0044] V: 0.30–0.60%; Vanadium is a strong carbide-forming element. Vanadium carbides have high hardness, and when the particles are fine and dispersed, they can strongly promote the secondary hardening effect and tempering resistance of steel, thereby improving the heat resistance of steel. At the same time, a small amount of V can refine the grains and improve the toughness of the material.

[0045] Mo: 1.70–2.80%. Vanadium readily forms stable carbides, improving tempering resistance. Its effect is even better when used in combination with Cr. Even a small amount of Mo can improve hardenability, increase grain coarsening temperature, and prevent temper brittleness.

[0046] Co: 0.10~1.00%. Cobalt is a non-carbide-forming element. When it melts into the matrix, it can hinder grain growth; when it melts into carbides, it can improve the stability of carbides, both of which contribute to improving the heat resistance of steel. However, excessive Co content will reduce the hardenability of the material, so it is advisable to add it in small amounts.

[0047] Ni: 0.10~1.00%, improves hardenability, making heat treatment of large workpieces easier. It can prevent low-temperature brittleness and improve corrosion resistance.

[0048] Phosphorus (P): ≤0.015; Sulfur (S): ≤0.05. Both P and S are harmful elements in steel. Phosphorus increases the brittleness of steel and reduces its impact toughness; sulfur increases the risk of hot brittleness defects in steel and also significantly reduces its weldability, causing high-temperature cracking. Therefore, the lower the P and S content in steel, the more beneficial it is to improving the material's performance indicators.

[0049] This invention also discloses a method for manufacturing high-toughness hot work die steel for die casting. According to the chemical composition ratio, the steel is smelted and cast into Φ740mm electrode rods using an electric furnace and ladle refining, then electroslag-refined into Φ900mm electroslag ingots. These ingots are then subjected to high-temperature homogenization, rapid forging, solution treatment, spheroidizing annealing, quenching, and tempering heat treatment to obtain the final product. Details are as follows:

[0050] Electroslag remelting process parameter control: The filling ratio of electroslag remelting is 0.75 to 0.80. A larger filling ratio can reduce the electroslag power consumption and increase the process capacity.

[0051] The slag-smelting voltage of the electric furnace is 45V~65V / current 6000A~18000A, the melting voltage is 43V~52V / current 14000A~17000A, and the feeding voltage is 9000V~16000V / current 36A~44A. Through the electroslag process, the internal crystalline structure of the electroslag steel ingot is made finer and more uniform, while the segregation of components and the level of inclusions are reduced.

[0052] Forging process parameter control: The electroslag ingot is heated in a fast forging furnace at 700℃~800℃ with a temperature rise rate of 80℃ / h~120℃ / h, and then held at 1210℃~1300℃ for 10 hours~12 hours.

[0053] The starting forging temperature for electroslag ingots to be forged into finished products by fast forging is 1020℃~1100℃, and the stopping forging temperature is 850℃~950℃.

[0054] The electroslag ingot is introduced into the rapid forging furnace at 700℃~800℃ and heated at a rate of 80℃ / h~120℃ / h. Since the Φ900mm electroslag ingot is a large round ingot, there will be a large surface stress during heating, which increases the thermal stress sensitivity of the ingot and makes it easy to generate stress cracks during the heating process. Therefore, controlling the furnace temperature of the electroslag ingot at 700℃~800℃ and the heating rate at 80℃ / h~120℃ / h can prevent the ingot from generating thermal stress cracks during the heating process and prevent the risk of cracking caused by thermal stress in the electroslag ingot.

[0055] Heating to 1210℃~1300℃ and holding for 10 to 20 hours: This ensures uniform temperature from the surface to the core of the steel ingot, improves its forgeability, and prevents cracking during the forging process of the electroslag ingot. At the same time, the long-term high-temperature homogenization treatment can eliminate large, difficult-to-dissolve eutectic carbides, thereby achieving a uniform as-cast structure and reducing component segregation.

[0056] The initial forging temperature for fast forging is 1020℃~1100℃: This temperature range represents the austenitic single-phase microstructure of the steel, exhibiting optimal high-temperature hot plasticity. This facilitates high-temperature deformation processing and reduces the likelihood of high-temperature working cracks. Exceeding the upper temperature limit may lead to overheating due to compositional segregation, resulting in coarse grains and negatively impacting the product's internal quality.

[0057] The stopping temperature of the high-speed forging mill is 850℃~950℃: Since the final forging temperature of the electroslag ingot has a significant impact on the final forging quality of the steel ingot, if the stopping temperature of the high-speed forging mill is lower than the specified control range, it is very easy to cause cracking of the finished product during the forging process. However, if the stopping temperature is higher than the control range, it is easy to cause coarse grains in the steel structure after the initial forging in the high-speed forging mill, and the formation of severe network carbides, which reduces the performance of the steel. Therefore, selecting this appropriate final forging temperature can further ensure the internal quality of the product.

[0058] Post-forging cooling: After the electroslag ingot is forged into a material by fast forging, it is cooled by water or mist at a rate greater than 0.5℃ / min until the temperature drops below 200℃ for hot annealing.

[0059] Solution treatment: The electroslag ingot is heated to 950℃~1150℃ and held for 10 hours~15 hours. Then it is rapidly cooled to below 250℃ by oil or water cooling and then sent to the annealing furnace.

[0060] Spheroidizing annealing: The electroslag ingot undergoes a first-stage isothermal annealing at 830℃~850℃ for 5 to 10 hours; the second-stage isothermal annealing is performed at 730℃~750℃ for 10 to 20 hours. This process results in a microstructure with spheroidal or granular carbides uniformly distributed in the ferrite matrix, achieving a good annealed microstructure and preparing the microstructure for further quenching.

[0061] like Figure 1 As shown, the annealed microstructure consists of ferrite and alloy carbides. The carbides are uniformly dispersed in the matrix in spherical or granular form, without carbide segregation or large eutectic carbides. This uniformly distributed spheroidized annealed microstructure provides a microstructure guarantee for obtaining tempered hardness and high impact toughness in the next step.

[0062] Quenching and tempering heat treatment: The electroslag ingot is heated to 950℃~1100℃, cooled to below 250℃ by oil cooling or water mist, and then tempered at above 590℃, tempered 2 to 3 times, and held at the tempering temperature for 2 to 4 hours each time.

[0063] like Figure 2As shown, the quenched structure can be seen as martensite + partially undissolved carbides + retained austenite, which can achieve high tempering hardness and high impact toughness.

[0064] like Figure 3 As shown, the uniform distribution of high-temperature tempered sorbite and more dispersed carbides in the microstructure ensures that the material obtains high toughness.

[0065] Example 1

[0066] The chemical composition of the steel by weight percentage is as follows: C: 0.37%, Si: 0.26%, Mn: 0.47%, P: 0.008%, S: 0.001%, Cr: 4.99%, Mo: 2.28%, V: 0.57%, Ni: 0.54%, Co: 0.51%, with the remainder being Fe and unavoidable impurities.

[0067] The steel ingot was cast into a Φ740mm electrode rod through an electric arc furnace and ladle refining process. The electroslag remelting voltage was 60V, and the electroslag remelting current was 1200A. The electroslag smelting voltage was 50V, and the smelting current was 15000A. The electroslag feeding voltage was 15000V, and the feeding current was 40A. The electroslag remelting resulted in a Φ900mm electroslag ingot. This ingot was then heated in a rapid forging furnace at 750℃ to 1220℃ at a rate of 100℃ / h, and held for 10 hours. The initial forging temperature for the rapidly forged steel was 1050℃, and the forging stop temperature was 870℃. Annealing heat treatment: the ingot was held at 850℃ for 8 hours, then cooled to 730℃ at a rate of 40℃ / h and held for 10 hours.

[0068] like Figure 4 As shown, the performance indicators of the die-casting mold steel produced using Example 1 are significantly improved. After quenching at 1050℃ and tempering twice (≥590℃), the Rockwell hardness of the material is 47.5HRC, and the average transverse unnotched impact energy at room temperature is 435J, which is higher than the 286J (average) of high-quality electroslag 4Cr5MoSiV1 steel under the same heat treatment conditions.

[0069] The specific chemical compositions (wt%) of Examples 1 to 5 and the comparative steel (4Cr5MoSiV1) are shown in Table 1 below, and the process parameter controls are shown in Table 2 below. The impact test results (room temperature transverse unnotched impact energy) of the samples from Examples 1 to 5 and the comparative steel (4Cr5MoSiV1) are compared as follows: Figure 5 As shown, the room temperature transverse unnotched impact energy of the samples is higher than that of the control steel (4Cr5MoSiV1) under the same heat treatment conditions. After quenching and tempering, the hardness of the samples is between 44 HRC and 46 HRC.

[0070] Table 1

[0071]

[0072] Table 2

[0073]

[0074] In summary, this invention provides a high-toughness hot work die steel for die casting and its manufacturing method. The aim is to improve the toughness of the material by optimizing the Si, V, and Mo alloying element ratios based on 4Cr5MoSiV1, while utilizing the micro-alloying composite strengthening effect of Co and Ni to enhance the hardenability and high-temperature performance. Combined with metallurgical manufacturing methods such as electric furnace vacuum refining, electroslag remelting, high-temperature homogenization, multi-directional forging technology, and special heat treatment, the invention improves the non-metallic inclusions and annealed microstructure levels. It also enhances the hardness and impact toughness of the material after quenching at 1050℃ followed by secondary tempering (tempering temperatures ≥590℃), thereby improving hardenability, toughness, and high-temperature strength. This significantly improves the overall performance of the material, making it more suitable for manufacturing hot work dies for aluminum-magnesium alloy die casting with high service life requirements. Furthermore, it improves the quality of high-performance hot work die steel products produced by metallurgical enterprises, achieving domestic substitution of imported materials and enhancing the competitiveness of enterprises in the die casting die steel market.

[0075] Those skilled in the art should recognize that the above embodiments are merely illustrative of the present invention and are not intended to limit the present invention. Any variations or modifications to the above embodiments that are within the spirit and essence of the present invention will fall within the scope of the claims of the present invention.

Claims

1. A high-toughness hot work die steel for die casting, characterized in that, Chemical composition in percentage by weight: C: 0.33-0.40%, Si: 0.10-0.40%, Mn: 0.20-0.60%, Cr: 4.50-5.50%, V: 0.30-0.60%, Mo: 1.70-2.80%, Co: 0.10-1.00%, Ni: 0.10-1.00%, Cu: ≤0.25%, P: ≤0.015, S: ≤0.05, balance Fe and inevitable impurities, The high-toughness hot-work die steel for die casting is prepared by the following manufacturing method: according to the proportion of chemical components, an electrode rod is smelted and cast by using an electric furnace plus external refining, then an electroslag ingot is formed, the electroslag ingot is further subjected to high-temperature homogenization, fast forging, solid solution treatment, spheroidizing annealing, quenching and tempering heat treatment, The filling ratio of the electroslag remelting is 0.75-0.80; The high-temperature homogenization of the electroslag ingot further comprises: When the temperature is 700-800 DEG C, the fast forging heating furnace is entered to perform temperature rising at a temperature rising speed of 80-120 DEG C / h, and after heating to 1210-1300 DEG C, the temperature is kept for 10-12 hours; The open forging temperature of the electroslag ingot for fast forging into a finished product is 1020-1100 DEG C, and the stop forging temperature is 850-950 DEG C; The spheroidizing annealing of the electroslag ingot further comprises: The first stage isothermal annealing temperature is 830-850 DEG C, and the annealing time is 5-10 hours; the second stage isothermal annealing temperature is 730-750 DEG C, and the annealing time is 10-20 hours; The quenching and tempering heat treatment of the electroslag ingot further comprises: Heating to 950-1100 DEG C, oil cooling or water mist cooling to below 250 DEG C, and then tempering treatment above 590 DEG C, tempering 2-3 times, and keeping the temperature for 2-4 hours each time, The average value of the room temperature transverse unnotched impact energy of the high-toughness hot-work die steel for die casting is 435 J.

2. A method of manufacturing a hot work die steel for high toughness die casting as claimed in claim 1, characterized in that: According to the proportion of chemical components, an electrode rod is smelted and cast by using an electric furnace plus external refining, then an electroslag ingot is formed, the electroslag ingot is further subjected to high-temperature homogenization, fast forging, solid solution treatment, spheroidizing annealing, quenching and tempering heat treatment, The filling ratio of the electroslag remelting is 0.75-0.80; The high-temperature homogenization of the electroslag ingot further comprises: When the temperature is 700-800 DEG C, the fast forging heating furnace is entered to perform temperature rising at a temperature rising speed of 80-120 DEG C / h, and after heating to 1210-1300 DEG C, the temperature is kept for 10-12 hours; The open forging temperature of the electroslag ingot for fast forging into a finished product is 1020-1100 DEG C, and the stop forging temperature is 850-950 DEG C; The spheroidizing annealing of the electroslag ingot further comprises: The first stage isothermal annealing temperature is 830-850 DEG C, and the annealing time is 5-10 hours; the second stage isothermal annealing temperature is 730-750 DEG C, and the annealing time is 10-20 hours; The quenching and tempering heat treatment of the electroslag ingot further comprises: Heating to 950-1100℃, using oil cooling or water mist cooling to 250℃ or below, and then tempering at 590℃ or above, tempering 2-3 times, each time for 2-4 hours, The average value of the high-toughness hot-work die steel for die casting is 435 J in the room-temperature transverse unnotched impact energy.

3. The method of manufacturing a hot work die steel for high toughness die casting according to claim 2, characterized by: The slag melting voltage of the electric furnace is 45-65 V / 6000-18000 A, the melting voltage is 43-52 V / 14000-17000 A, and the feeding voltage is 9000-16000 V / 36-44 A.

4. The method of producing a hot work die steel for high-toughness die casting according to claim 2, characterized by: After the electric slag ingot is forged into a material by fast forging, water cooling or mist cooling is used, the cooling speed is greater than 0.5 ℃ / min, and hot charging annealing is performed until the temperature is reduced to 200 ℃ or below.

5. The method of producing a hot work die steel for high-toughness die casting according to claim 2, characterized by, The electric slag ingot further comprises solid solution treatment after the electric slag ingot is forged into a material by fast forging. The heating temperature is 950-1150℃, the holding time is 10-15 hours, then oil cooling or water cooling is used to cool to 250℃ or below, and then the annealing furnace is used.

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