High thermal conductivity high red hardness re-nb composite microalloyed hot work die steel and preparation method thereof

Abstract

The application relates to the technical field of metal materials, in particular to a high-thermal-conductivity high-red-hard RE-Nb composite microalloyed hot work die steel and a preparation method thereof. The hot work die steel contains C 0.30%-0.40%, Si 0.05%-0.10%, Mn 0.65%-0.95%, Cr 0.03%-0.07%, Mo 3.0%-3.6%, V 0.30%-0.60%, Nb 0.01%-0.02%, Ce 0.02%-0.03%, and the balance is Fe and inevitable impurity elements in a metallurgical process, and O in the inevitable impurity elements is less than or equal to 0.002%. The high-thermal-conductivity high-red-hard hot work die steel is obtained by combining component proportioning and process optimization.

Description

Technical Field

[0001] This application relates to the field of metallic materials technology, specifically to a high thermal conductivity, high red hardness RE-Nb composite microalloyed hot work die steel and its preparation method. Background Technology

[0002] With the continuous development of technologies such as die casting, hot forging, and extrusion forming, higher requirements are placed on the performance and service life of dies. Hot work dies come into contact with high-temperature metals during the hot forming process, with local temperatures reaching 500–700℃. Especially in the forming of difficult-to-deform materials, the insufficient thermal conductivity and red hardness of domestically produced hot work die steels lead to temperature differences in different parts of the die, easily generating significant thermal stress during thermal cycling, resulting in high-temperature wear and fatigue failure. To address these issues, it is necessary to develop hot work die steels with high thermal conductivity and high red hardness to improve their thermal fatigue performance and extend the service life of hot work dies.

[0003] Currently, the most commonly used hot work die steel in China is 4Cr5MoSiV1 (H13) steel. The chemical composition of H13 steel, expressed as a percentage by mass, is: C 0.32%–0.45%, Si 0.80%–1.20%, Mn 0.20%–0.50%, Cr 4.75%–5.50%, Mo 1.10%–1.75%, V 0.80%–1.20%, P≤0.03%, S≤0.03%. H13 steel has good hardenability and good comprehensive mechanical properties, but once the working temperature is high, the strength and thermal stability of H13 steel will decrease significantly, and the life cycle of the die will be reduced under high temperature conditions.

[0004] The existing technology has the following improvements:

[0005] The Spanish company Rovalma has developed a new high thermal conductivity hot work die steel, HTCS130. HTCS130 steel contains 0.17% Si, 0.16% Mn, <0.003% V, 0.08% Cr, 3.1% Mo, and 1.85% W. HTCS130 steel exhibits high thermal conductivity, approximately 54.9 W / m·K at 100°C (2.3 times that of H13 steel) and approximately 32.5 W / m·K at 700°C (1.2 times that of H13 steel). However, the 1.85% W content in HTCS130 steel increases its cost and may also affect its toughness.

[0006] Universities in Hebei and Shanghai have jointly developed a new type of hot-work die steel. The experimental steel contains 0.25% Si, 0.24% Mn, 2.26% Cr, 1.0% V, and 2.3% Mo. This die steel exhibits high thermal conductivity, approximately 33.9 W / m·K at 100℃, 1.4 times that of H13 steel, and approximately 28.8 W / m·K at 700℃, 1.1 times that of H13. However, the Cr and Si contents in this steel are still relatively high, and its thermal conductivity needs further improvement.

[0007] Baoshan Iron & Steel and Shandong University jointly developed SDK1 steel, a martensitic age-hardening hot stamping die steel. SDK1 steel contains 0.07–0.11% C, 0.07–0.12% Si, 1.53% Mn, 0.33% Cr, 3.4–4.5% Ni, 0.32–0.45% Mo, 1.1% Al, and 1.0% Cu. SDK1 steel exhibits high thermal conductivity, approximately 27.9 W / m·K at 100℃, 1.4 times that of H13 steel, and approximately 26.0 W / m·K at 700℃, close to that of H13. However, the relatively high content of Mn, Ni, Al, and Cu in this steel is detrimental to further improving its thermal conductivity.

[0008] Anhui Hart 3D Technology Co., Ltd. has developed a high-toughness, high-thermal-conductivity mold steel, obtained through a combination of melting, casting, and solution aging treatment. The steel contains 0.04–0.06% carbon, 0.35–0.45% silicon, 0.65–0.75% manganese, 0.7–0.8% nickel, 2.8–3.2% molybdenum, 1.8–2.2% watts (W), and 1.4–1.6% copper (Cu). This mold steel exhibits high thermal conductivity, approximately 33.9 W / m·K at 100℃ (1.4 times that of H13 steel) and approximately 36.3 W / m·K at 500℃ (1.3 times that of H13 steel). However, the high Cu and Ni content, coupled with the melting and casting process, hinders the improvement of thermal conductivity and mechanical properties.

[0009] Improving the thermal conductivity of steel is the core issue in developing high thermal conductivity die steels, while also considering overall performance factors such as cost and mechanical properties. Developing high thermal conductivity, high red hardness hot work die steels, improving their thermal fatigue performance, and extending the service life of hot work dies are the research and development directions for hot work die steels.

[0010] In view of the above, this application is hereby submitted. Summary of the Invention

[0011] The purpose of this application is to provide a high thermal conductivity, high red hardness RE-Nb composite microalloyed hot work die steel, so as to provide a material with high thermal conductivity, effectively improve product performance, enhance the service stability of hot work dies, and extend service life.

[0012] To achieve the above objectives, this application adopts the following technical solution.

[0013] A high thermal conductivity, high red hardness RE-Nb composite microalloyed hot work die steel, comprising, by mass percentage, 0.30%–0.40% C, 0.05%–0.10% Si, 0.65%–0.95% Mn, 0.03%–0.07% Cr, 3.0%–3.6% Mo, 0.30%–0.60% V, 0.01%–0.02% Nb, and 0.02%–0.03% Ce, with the balance being Fe and unavoidable impurity elements from the metallurgical process, wherein O ≤ 0.002% of the unavoidable impurity elements.

[0014] In some embodiments, the unavoidable impurity elements are Ni 0.01%–0.04%, Cu 0.03%–0.07%, Al 0.005%–0.010%, N ≤0.005%, P ≤0.005%, S ≤0.0015%, and Ti ≤0.0015%.

[0015] In some embodiments, the hot work die steel contains, by mass percentage, 0.31%–0.35% C, 0.069%–0.076% Si, 0.74%–0.83% Mn, 0.041%–0.051% Cr, 3.31%–3.44% Mo, 0.44%–0.51% V, 0.01%–0.02% Nb, and 0.02%–0.03% Ce, with the balance being Fe and unavoidable impurity elements from the metallurgical process, wherein O ≤ 0.002% of the unavoidable impurity elements.

[0016] In some embodiments, the hot work die steel contains, by mass percentage, 0.31% C, 0.076% Si, 0.74% Mn, 0.041% Cr, 3.44% Mo, 0.51% V, 0.018% Nb, and 0.024% Ce.

[0017] In some embodiments, the hot work die steel contains, by mass percentage, 0.35% C, 0.069% Si, 0.83% Mn, 0.051% Cr, 3.31% Mo, 0.44% V, 0.017% Nb, and 0.022% Ce.

[0018] The preparation method of the above-mentioned hot work die steel includes the following process steps:

[0019] S1: Vacuum Induction Melting: According to the composition ratio, vacuum induction melting is carried out to control the content of active elements in the alloy, such as Al 0.005%~0.010% and Ti≤0.0015%. Gas and non-metallic inclusions and impurities in the alloy are removed, and the purity is improved by double-layer slag blocking and ceramic filtration. When tapping the steel, P≤0.005%, Si≤0.10%, O≤0.002%, N≤0.005%, and S≤0.0015% are controlled.

[0020] S2: Electroslag remelting: The mother electrode is subjected to electroslag remelting refining treatment under a protective atmosphere to obtain electroslag ingots, reducing the burn-off of easily oxidized elements, controlling the increase of O, N and H element content, and annealing at 720℃~760℃ for 6~10h. After annealing, it is slowly cooled to 400℃~500℃ for further processing.

[0021] S3: High-temperature homogenization treatment: High-temperature homogenization treatment is carried out on electroslag ingots to improve the banded structure. The holding temperature is 1240℃~1280℃ and the holding time is 20~30h.

[0022] S4: Forging process: After high-temperature homogenization treatment, furnace cooling is carried out to 1150℃~2000℃ and forging is started using a high-speed forging machine. The final forging temperature is 850℃~900℃, the forging ratio is >4, the original coarse grains are broken and new fine equiaxed grains are obtained.

[0023] S5: Ultrafine treatment: After forging, ultrafine treatment is performed to refine the grains. The holding temperature is 1000℃~1050℃ and the holding time is 3~5h. After exiting the furnace, the grains are cooled by water.

[0024] S6: Spheroidizing Annealing Treatment: After ultrafine treatment, spheroidizing annealing is performed. The temperature is heated to 830℃~880℃ and held for 15~20h. The temperature is then furnace cooled to 720℃~760℃ and held for 30~40h to spheroidize the carbides in the structure. The temperature is then furnace cooled to 400℃~500℃ and then air cooled.

[0025] The above-mentioned hot work die steels are used in die casting, hot forging or hot stamping.

[0026] A steel product comprising the aforementioned hot work die steel.

[0027] Compared with the prior art, the technical effects of this application are as follows:

[0028] First, high thermal conductivity and high red hardness RE (rare earth element)-Nb composite microalloyed hot work die steel can improve the heat conduction efficiency of the die. The die needs to undergo repeated heating and cooling during the working process. The improved heat conduction efficiency shortens the hot and cold cycle time and improves the production efficiency.

[0029] Secondly, the use of high thermal conductivity and high red hardness RE-Nb composite microalloyed hot work die steel in molds can reduce the temperature difference at different locations caused by dimensional changes in large and complex molds, improve the surface temperature uniformity during product forming, and enhance the surface quality and precision of the formed products.

[0030] Third, the use of high thermal conductivity and high red hardness RE-Nb composite microalloyed hot work die steel in molds can reduce the content of low melting point elements such as sulfur, phosphorus, lead, and tin in the die steel by utilizing the purification effect of rare earth elements, improve grain boundary segregation, reduce the content of non-metallic inclusions, and improve the red hardness of hot work die steel through the organic combination of toughening mechanisms such as fine grain strengthening and precipitation strengthening, thereby enhancing the service stability of hot work dies, extending service life, and reducing production costs. Attached Figure Description

[0031] To more clearly illustrate the technical solutions in the specific embodiments of this application or the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0032] Figure 1 This is a metallographic photograph (200x magnification) of the microstructure of the high thermal conductivity, high red hardness RE-Nb composite microalloyed hot work die steel of this application.

[0033] Figure 2 This is a thermal conductivity diagram of FC-50-1 mold steel and H13 steel at different temperatures in Example 1 of this application;

[0034] Figure 3 This is a thermal conductivity diagram of FC-50-2 mold steel and H13 steel at different temperatures in Example 2 of this application. Detailed Implementation

[0035] The technical solutions of this application will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0036] Thermal conductivity: Thermal conductivity, also known as the thermal conductivity coefficient, reflects a material's ability to conduct heat. The formula for calculating the thermal conductivity of alloy materials is: λ = αρC p .

[0037] Where λ is the thermal conductivity, in W / m·K, and α is the thermal diffusivity, in m. 2 / s, ρ is the density of the alloy material, in kg / m³. 3 C p Specific heat capacity at constant pressure, expressed in J / kg·K. The thermal conductivity of steel is related to its material composition, microstructure, impurities, and defects; thermal conductivity is positively correlated with grain size.

[0038] Red hardness: Red hardness refers to a material's ability to retain its hardness after a certain period of time at a certain temperature. It represents the stability of a material's structure and properties under thermal conditions.

[0039] This application, through a combination of adjusting the chemical composition ratio of the material and optimizing the process, reduces the content of Cr, Si, and V elements and increases the content of Mo and Mn elements compared to H13, thereby improving the thermal conductivity of the die steel and enhancing its heat transfer efficiency and temperature uniformity during operation. Furthermore, the introduction of Nb and rare earth element Ce controls the oxygen content of the die steel. Microalloying refines the grains, improving the morphology of precipitated phases. The purification effect of rare earth elements reduces the content of low-melting-point impurities in the steel, improves grain boundary conditions, reduces element segregation, and enhances the hardness and fatigue performance of the die steel. Its high thermal conductivity and high red hardness make it suitable for more complex working environments, especially for forging processes of difficult-to-deform metals requiring high wear resistance, red hardness, and processing efficiency. The manufacturing process employs a combination of vacuum induction melting, electroslag remelting, high-temperature homogenization, multi-directional forging, ultra-fine refining treatment, and spheroidizing annealing. Vacuum induction melting utilizes induction heating, avoiding the carbonization of graphite electrodes used in arc heating and producing less smoke and dust. Electromagnetic stirring in the molten pool helps improve the uniformity of steel composition, and the vacuum environment prevents the introduction of impurities from the air. Electroslag remelting helps remove sulfur and non-metallic inclusions. The molten metal pool can fill shrinkage cavities generated during solidification, and gases and inclusions float to the surface during remelting, ensuring the uniformity and density of the ingot structure. High-temperature homogenization processes eliminate dendrites and elemental segregation in the ingot. Multi-directional forging effectively breaks down coarse columnar crystals in the ingot, promoting recrystallization to form fine grains. Ultrafine processing refines the grains, allowing carbides to dissolve back into the matrix and precipitate during spheroidizing annealing, forming uniformly dispersed carbides, ultimately yielding homogenized high-performance die steel.

[0040] Introducing appropriate amounts of nitrogen (Nb) into die steel can refine austenite grains and reduce the volume fraction of eutectic carbides. Nb can improve the ductility and impact toughness of die steel without reducing its hardness. Rare earth elements (REs) can form high-melting-point rare earth compounds with elements such as oxygen, sulfur, and hydrogen, thereby reducing the content of non-metallic inclusions in steel. Simultaneously, rare earth microalloying compounds can play a role in solid solution strengthening. Rare earth elements can control the morphology of oxygen (O) and sulfur (S) inclusions in steel, contributing to improved fatigue performance of die steel. During smelting, rare earth elements form high-melting-point compounds that precipitate before the molten steel solidifies, acting as nucleation centers, reducing supercooling, and thus refining the solidification structure. The introduction of rare earth elements can increase the solubility of alloying elements such as Nb and v in steel, facilitating the precipitation of carbides in ferrite, improving the dispersion strengthening effect of carbides, and increasing the strength of die steel. Hardness reflects a material's ability to resist localized plastic deformation; the hardness level of hot-work die steel during service is crucial to the service life of the die. Introducing appropriate amounts of rare earth elements can refine grains and strengthen through solid solution, thereby increasing the red hardness of the material. High red hardness helps hot work die steel maintain a high hardness value during service, improves its performance stability during service, and extends its service life.

[0041] This application provides a high thermal conductivity, high red hardness RE-Nb composite microalloyed hot work die steel. By mass percentage, the hot work die steel contains 0.30%–0.40% C, 0.05%–0.10% Si, 0.65%–0.95% Mn, 0.03%–0.07% Cr, 3.0%–3.6% Mo, 0.30%–0.60% V, 0.01%–0.02% Nb, and 0.02%–0.03% Ce, with the balance being Fe and unavoidable impurity elements from the metallurgical process, wherein O ≤ 0.002% of the unavoidable impurity elements.

[0042] The hot work die steel obtained through reasonable composition design in this application has good thermal conductivity. The microstructure of this high thermal conductivity, high red hardness RE-Nb composite microalloyed hot work die steel is ferrite + pearlite + bainite + carbides (such as...). Figure 1 As shown, this high thermal conductivity, high red hardness RE-Nb composite microalloyed hot work die steel is suitable for hot forming processes such as injection molding, hot forging, and hot stamping, which require high thermal conductivity and wear resistance in die materials. This high thermal conductivity, high red hardness RE-Nb composite microalloyed hot work die steel exhibits a thermal conductivity of 43.7 W / m·K at 150℃, 36.0 W / m·K at 400℃, and 30.8 W / m·K at 650℃, demonstrating significantly higher thermal conductivity compared to H13 steel.

[0043] Carbon (C) is an essential element for strengthening the matrix structure and ensuring mechanical properties such as hardness and wear resistance. Therefore, the carbon content in mold steel cannot be too low. However, excessive carbon content in steel will be detrimental to thermal conductivity and lead to a decrease in toughness, thereby reducing the steel's resistance to thermal fatigue.

[0044] Silicon (Si) improves the hardenability and tempering resistance of mold steel, which is beneficial to the comprehensive mechanical properties of steel, especially the elastic limit. However, the atomic structure of silicon is very different from that of iron, which will significantly reduce its thermal conductivity.

[0045] Manganese (Mn) melts into ferrite and cementite in mold steel, increasing the steel's strength and hardness. Furthermore, because Mn has a greater affinity for sulfur than iron does for sulfur, it can remove some of the harmful sulfur, forming high-melting-point MnS (above 1600 degrees Celsius), thus mitigating the harmful effects of sulfur on the steel. However, excessively high manganese content significantly reduces the steel's thermal conductivity and increases its brittleness, reducing its corrosion resistance.

[0046] Chromium (Cr) increases the hardness and strength of die steel and punch stock (Cr is a strong carbide-forming element), and most importantly, it improves corrosion resistance. However, in Fe-Cr binary alloys, its thermal conductivity gradually decreases with increasing Cr content, which can affect the thermal conductivity of die steel. Therefore, in this application, the Cr content was reduced to 0.03-0.07%, and other alloying element carbides were used to replace the role of chromium carbides, which achieved good results and reduced the impact of chromium on thermal conductivity.

[0047] Molybdenum (Mo) can improve the hardenability of die steel, and at a content of about 0.5%, it can reduce or suppress temper brittleness caused by other alloying elements. At higher tempering temperatures, it forms a dispersed special carbide (Mo2C), which has a secondary hardening effect, improving the hot strength and creep strength of die steel.

[0048] Vanadium (V) enhances wear resistance and ductility, improving the service life of tool steels, but it can affect the thermal conductivity of die steels. V contributes to improved hardenability; VC carbides are stable strengthening phases.

[0049] Niobium (Nb) can refine grain size and reduce the overheating sensitivity and temper brittleness of steel, thus improving strength, but it also reduces plasticity and toughness. As a microalloying element (content in the range of 0.001–0.1%), Nb, being a strong carbide-forming element, combines with C to form NbC, which can control austenite grain growth and thus refine the grain size. Replacing part of the vanadium (V) element with trace amounts of Nb can ensure the hardness of die steel and improve its tempering stability.

[0050] Cerium (Ce) is a rare earth element that can form high-melting-point rare earth compounds with elements such as oxygen, sulfur, nitrogen, and carbon. Introducing a certain amount of Ce into mold steel can displace sulfur and oxygen elements from inclusions in the steel to form rare earth compounds, thereby reducing the sulfur and oxygen content. Rare earth elements can eliminate blocky liquid carbides at the grain boundaries of electroslag ingots, helping to purify the grain boundaries and refine the size of inclusions to reduce crack initiation sites.

[0051] Oxygen (O) has an adverse effect on the mechanical properties of steel. It is a significant impurity element in mold steel and needs to be strictly controlled.

[0052] It should be noted that, by mass percentage, the C content can be, but is not limited to, 0.30%, 0.31%, 0.32%, 0.33%, 0.34%, 0.35%, 0.36%, 0.37%, 0.38%, 0.39%, or 0.40%; the Si content can be, but is not limited to, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, or 0.10%; and the Mn content can be, but is not limited to, 0.65%, 0.7%, 0.75%, 0.8%, 0.85%, or 0.9%. The content of Cr may be, but is not limited to, 0.03%, 0.04%, 0.05%, 0.06%, or 0.07%; the content of Mo may be, but is not limited to, 3.0%, 3.1%, 3.2%, 3.3%, 3.4%, 3.5%, or 3.6%; the content of Ce may be, but is not limited to, 0.02%, 0.021%, 0.022%, 0.023%, 0.024%, 0.025%, 0.026%, 0.027%, 0.028%, 0.029%, or 0.03%.

[0053] In some embodiments, the unavoidable impurity elements are Ni 0.01-0.04%, Cu 0.03-0.07%, Al 0.005-0.010%, N≤0.005%, P≤0.005%, S≤0.0015%, and Ti≤0.0015%.

[0054] Nickel (Ni) has the effects of solid solution strengthening and improving hardenability. It refines the ferrous element grains, improving the plasticity and toughness of steel, especially low-temperature toughness, under the same strength conditions. When used in combination with chromium, molybdenum, etc., it improves the hot strength and corrosion resistance of steel.

[0055] Copper (Cu) improves strength and toughness, especially in terms of atmospheric corrosion resistance. Its disadvantage is that it is prone to hot brittleness during hot working.

[0056] Aluminum (Al) is a commonly used deoxidizer in steel. Adding a small amount of aluminum to steel can refine the grain size and improve impact toughness. Aluminum also has antioxidant and corrosion-resistant properties. When used in combination with chromium and silicon, aluminum can significantly improve the high-temperature non-scaling properties and high-temperature corrosion resistance of steel. The disadvantages of aluminum are that it affects the hot working properties, weldability, and machinability of steel.

[0057] Nitrogen (N) can improve the strength, low-temperature toughness and weldability of steel, but also increase its aging sensitivity.

[0058] Phosphorus (P) is a harmful element in mold steel under normal circumstances. Phosphorus (P) can increase the cold brittleness of mold steel, which will worsen the welding performance of mold steel; it can also reduce the plasticity of mold steel, which will worsen the cold bending performance of mold steel.

[0059] Sulfur (S) is also a harmful element under normal circumstances. Sulfur (S) causes hot brittleness in die steel, reduces its ductility and toughness, and causes cracks during forging and rolling. Sulfur (S) is also detrimental to the weldability of die steel and reduces its corrosion resistance.

[0060] Titanium (Ti) is a strong deoxidizer in steel. It can make the internal structure of steel denser, refine grain strength, reduce aging sensitivity and cold brittleness, and improve weldability.

[0061] It should be noted that, by mass percentage, the Ni content may be, but is not limited to, 0.01%, 0.02%, 0.03%, or 0.04%; the Cu content may be, but is not limited to, 0.03%, 0.04%, 0.05%, 0.06%, or 0.07%; the Al content may be, but is not limited to, 0.005%, 0.007%, or 0.010%; and the N content may be, but is not limited to, ≤0.005% or ≤0.004%. The content of phosphorus (P) may be ≤0.005%, ≤0.004%, ≤0.003%, or ≤0.002%; the content of sulfur (S) may be ≤0.0015%, ≤0.0013%, ≤0.001%, or ≤0.0005%; the content of titanium (Ti) may be ≤0.0015%, ≤0.0013%, ≤0.001%, or ≤0.0005%.

[0062] In a preferred embodiment, the hot work die steel contains, by mass percentage, 0.31%–0.35% C, 0.069%–0.076% Si, 0.74%–0.83% Mn, 0.041%–0.051% Cr, 3.31%–3.44% Mo, 0.44%–0.51% V, 0.01%–0.02% Nb, and 0.02%–0.03% Ce, with the balance being Fe and unavoidable impurity elements from the metallurgical process, wherein O ≤ 0.002% of the unavoidable impurity elements.

[0063] In a preferred embodiment, the hot work die steel contains, by mass percentage: C 0.31%, Si 0.076%, Mn 0.74%, Cr 0.041%, Mo 3.44%, V 0.51%, Nb 0.018%, Ce 0.024%, O ≤0.002%, Ni 0.01–0.04%, Cu 0.03–0.07%, Al 0.005–0.010%, N ≤0.005%, P ≤0.005%, S ≤0.0015%, and Ti ≤0.0015%.

[0064] In a preferred embodiment, the hot work die steel contains, by mass percentage: C 0.35%, Si 0.069%, Mn 0.83%, Cr 0.051%, Mo 3.31%, V 0.44%, Nb 0.017%, Ce 0.022%, O ≤ 0.002%, Ni 0.01–0.04%, Cu 0.03–0.07%, Al 0.005–0.010%, N ≤ 0.005%, P ≤ 0.005%, S ≤ 0.0015%, and Ti ≤ 0.0015%.

[0065] This application proposes a method for manufacturing a high thermal conductivity, high red hardness RE-Nb composite microalloyed hot work die steel:

[0066] S1: Vacuum Induction Melting: Based on the composition ratio of the hot work die steel, select materials for vacuum induction melting, control the content of active elements in the alloy, such as Al 0.005~0.010%, Ti≤0.0015%, remove impurities such as gases and non-metallic inclusions from the alloy, and improve purity through double-layer slag blocking and ceramic filtration. When tapping the steel, control P≤0.005%, Si≤0.10%, O≤0.002%, N≤0.005%, S≤0.0015%;

[0067] S2: Electroslag remelting: The mother electrode is subjected to electroslag remelting refining treatment under a protective atmosphere to obtain electroslag ingots, reducing the burn-off of easily oxidized elements, controlling the increase of O, N and H element content, and annealing at 720℃~760℃ for 6~10h. After annealing, it is slowly cooled to 400℃~500℃ for further processing.

[0068] S3: High-temperature homogenization treatment: High-temperature homogenization treatment is carried out on electroslag ingots to improve the banded structure. The holding temperature is 1240℃~1280℃ and the holding time is 20~30h.

[0069] S4: Forging process: After high-temperature homogenization treatment, furnace cooling is carried out to 1150℃~2000℃ and forging is started using a high-speed forging machine. The final forging temperature is 850℃~900℃, the forging ratio is >4, the original coarse grains are broken and new fine equiaxed grains are obtained.

[0070] S5: Ultrafine treatment: After forging, ultrafine treatment is performed to refine the grains. The holding temperature is 1000℃~1050℃ and the holding time is 3~5h. After exiting the furnace, the grains are cooled by water.

[0071] S6: Spheroidizing Annealing Treatment: After ultrafine treatment, spheroidizing annealing is performed. The temperature is heated to 830℃~880℃ and held for 15~20h. The temperature is then furnace cooled to 720℃~760℃ and held for 30~40h to spheroidize the carbides in the structure. The temperature is then furnace cooled to 400℃~500℃ and then air cooled.

[0072] This method employs vacuum induction melting and electroslag remelting, resulting in less segregation and improved microstructure uniformity in the mold steel. Figure 1 )better.

[0073] The present application will be further illustrated below through examples. Unless otherwise specified, the materials in the examples are prepared according to existing methods or purchased directly from the market.

[0074] Example 1

[0075] A high thermal conductivity, high red hardness RE-Nb composite microalloyed hot work die steel is manufactured using the following process:

[0076] Step 1: Vacuum Induction Melting: Based on the composition ratio of the high thermal conductivity, high red hardness RE-Nb composite microalloyed hot work die steel, the material is selected for vacuum induction melting. The content of active elements in the alloy is controlled, such as Al 0.005~0.010%, Ti≤0.0015%, to remove impurities such as gases and non-metallic inclusions from the alloy. The purity is improved by double-layer slag blocking and ceramic filtration. When tapping the steel, P≤0.005%, Si≤0.10%, O≤0.002%, N≤0.005%, S≤0.0015%.

[0077] Step 2: Electroslag remelting: The mother electrode is subjected to electroslag remelting and refining treatment under a protective atmosphere to obtain electroslag ingots, reducing the burn-off of easily oxidized elements, controlling the increase of O, N and H element content, and annealing at 760℃ for 6 hours. After annealing, it is slowly cooled to 480℃ for the next step of processing.

[0078] Step 3: High-temperature homogenization treatment: High-temperature homogenization treatment is carried out on the electroslag ingot to improve the banded structure. The holding temperature is 1280℃ and the holding time is 20h.

[0079] Step 4: Forging treatment: After high-temperature homogenization treatment, furnace cooling is carried out to 1170℃ and forging is started using a high-speed forging machine. The final forging temperature is 880℃ and the forging ratio is >4. The original coarse grains are broken to obtain new fine equiaxed grains.

[0080] Step 5: Ultrafine treatment: After forging, ultrafine treatment is carried out to refine the grains. The holding temperature is 1050℃ and the holding time is 3h. After being taken out of the furnace, it is water-cooled.

[0081] Step 6: Spheroidizing Annealing Treatment: After ultrafine treatment, spheroidizing annealing is performed. The temperature is heated to 860℃ and held for 16 hours. The temperature is then furnace cooled to 760℃ and held for 32 hours to spheroidize the carbides in the microstructure. The temperature is then furnace cooled to 480℃ and air cooled.

[0082] FC-50-1 high thermal conductivity, high red hardness RE-Nb composite microalloyed hot work die steel was obtained (microstructure and metallographic images are shown below). Figure 1 As shown in Table 1, the chemical composition of this steel is as follows. Compared with H13 steel, this steel has lower Si, Cr, and V content, with Si content of 0.076%, Cr content of 0.041%, and V content of 0.51%, while increasing the Mo content to 3.44% and the Mn content to 0.74%.

[0083] Table 1. Main Chemical Composition of FC-50-1 Steel (wt%) FC-50-1 0.31 0.076 0.74 0.041 3.44 0.51 0.024 0.0013 H13 0.38 0.95 0.39 5.01 1.40 1.02 / 0.0016

[0084] Comparing the impurity element content of this high thermal conductivity, high red hardness RE-Nb composite microalloyed hot work die steel (FC-50-1) with H13 steel (as shown in Table 2), it can be found that Ce significantly reduces the impurity element content in the steel, improves the cleanliness of the die steel, thereby inhibiting impurity element segregation and improving the mechanical properties of the die steel. The Rockwell hardness of the tempered FC-50-1 high thermal conductivity rare earth hot work die steel is 53.5 HRC, which is relatively high.

[0085] Table 2. Composition of Impurity Elements and Microalloying Elements in FC-50-1 Steel (wt%) FC-50-1 0.0022 0.0008 0.0030 0.018 0.050 0.0008 0.023 0.0069 H13 0.0210 0.0013 0.0160 0.003 0.081 0.0031 0.20 0.0098

[0086] Thermal conductivity of FC-50-1 steel was tested, and the test results are as follows: Figure 2 As shown, and compared with the thermal conductivity of domestic H13 steel, the thermal conductivity of FC-50-1 steel at 200℃ is 40.6W / m·K, which is about 1.6 times that of H13 steel. At 750℃, the thermal conductivity of FC-50-1 steel is 24.5W / m·K, which is about 1.4 times that of H13 steel.

[0087] Example 2

[0088] A high thermal conductivity, high red hardness RE-Nb composite microalloyed hot work die steel is manufactured using the following process:

[0089] Step 1: Vacuum Induction Melting: Based on the composition ratio of the high thermal conductivity, high red hardness RE-Nb composite microalloyed hot work die steel, the material is selected for vacuum induction melting. The content of active elements in the alloy is controlled, such as Al 0.005~0.010%, Ti≤0.0015%, to remove impurities such as gases and non-metallic inclusions from the alloy. The purity is improved by double-layer slag blocking and ceramic filtration. When tapping the steel, P≤0.005%, Si≤0.10%, O≤0.002%, N≤0.005%, S≤0.0015%.

[0090] Step 2: Electroslag remelting: The mother electrode is subjected to electroslag remelting and refining treatment under a protective atmosphere to obtain electroslag ingots, reducing the burn-off of easily oxidized elements, controlling the increase of O, N and H element content, and annealing at 740℃ for 8 hours. After annealing, it is slowly cooled to 450℃ for the next step of processing.

[0091] Step 3: High-temperature homogenization treatment: High-temperature homogenization treatment is carried out on the electroslag ingot to improve the banded structure. The holding temperature is 1250℃ and the holding time is 28h.

[0092] Step 4: Forging treatment: After high-temperature homogenization treatment, furnace cooling is carried out to 1180℃ and forging is started using a high-speed forging machine. The final forging temperature is 870℃ and the forging ratio is >4. The original coarse grains are broken to obtain new fine equiaxed grains.

[0093] Step 5: Ultrafine treatment: After forging, ultrafine treatment is carried out to refine the grains. The holding temperature is 1030℃ and the holding time is 5h. After being taken out of the furnace, it is water-cooled.

[0094] Step 6: Spheroidizing Annealing Treatment: After ultrafine treatment, spheroidizing annealing is performed. The temperature is heated to 840℃ and held for 18 hours. The temperature is then furnace cooled to 750℃ and held for 36 hours to spheroidize the carbides in the microstructure. The temperature is then furnace cooled to 450℃ and air cooled.

[0095] FC-50-2, a high thermal conductivity, high red hardness RE-Nb composite microalloyed hot work die steel, was obtained. Its chemical composition is shown in Table 3. Compared to H13 steel, this steel has lower Si, Cr, and V content (0.069% Si, 0.051% Cr, 0.44% V), and increases the Mo content to 3.31% and the Mn content to 0.83%.

[0096] Table 3. Main Chemical Composition of FC-50-2 Mold Steel (wt%) FC-50-2 0.35 0.069 0.83 0.051 3.31 0.44 0.022 0.0015 H13 0.38 0.95 0.39 5.01 1.40 1.02 / 0.0016

[0097] Comparing the impurity element content of this high thermal conductivity, high red hardness RE-Nb composite microalloyed hot work die steel with H13 steel (as shown in Table 4), it can be found that Ce significantly reduces the impurity element content in the steel, improves the cleanliness of the die steel, thereby inhibiting impurity element segregation and improving the mechanical properties of the die steel. The Rockwell hardness of the tempered FC-50-2 high thermal conductivity, high red hardness RE-Nb composite microalloyed hot work die steel is 54.1 HRC, which is relatively high.

[0098] Table 4. Composition of Impurity Elements and Microalloying Elements in FC-50-2 Steel (wt%) FC-50-2 0.0033 0.0009 0.0035 0.017 0.048 0.0010 0.026 0.0074 H13 0.0210 0.0013 0.0160 0.003 0.081 0.0031 0.20 0.0098

[0099] The thermal conductivity test results of FC-50-2 are as follows: Figure 3 As shown, the thermal conductivity of FC-50-2 steel is 41.32 W / m·K at 200℃, which is about 1.6 times that of H13 steel. At 750℃, the thermal conductivity of FC-50-2 steel is 26.23 W / m·K, which is about 1.5 times that of H13 steel.

[0100] Note that the above are merely preferred embodiments and the technical principles employed in this application. Those skilled in the art will understand that this application is not limited to the specific embodiments described herein, and various obvious changes, readjustments, and substitutions can be made without departing from the scope of protection of this application. Therefore, although this application has been described in detail through the above embodiments, this application is not limited to the above embodiments. Many other equivalent embodiments may be included without departing from the technical concept of this application, all of which fall within the scope of protection of this application.

Claims

1. A high thermal conductivity, high red hardness RE-Nb composite microalloyed hot work die steel, characterized in that, By mass percentage, hot work die steel contains 0.31%~0.35% C, 0.069%~0.076% Si, 0.74%~0.83% Mn, 0.041%~0.051% Cr, 3.31%~3.44% Mo, 0.44%~0.51% V, 0.01%~0.02% Nb, and 0.02%~0.03% Ce, with the balance being Fe and unavoidable impurity elements from the metallurgical process, of which O ≤ 0.002%. The preparation method of the hot work die steel includes the following process steps: S1: Vacuum Induction Melting: According to the composition ratio, vacuum induction melting is carried out to control the content of active elements in the alloy, such as Al 0.005%~0.010%, Ti≤0.0015%, to remove gaseous and non-metallic inclusions and impurities from the alloy, and to improve purity through double-layer slag blocking and ceramic filtration. When tapping the steel, P≤0.005%, Si≤0.10%, O≤0.002%, N≤0.005%, S≤0.0015% are controlled. S2: Electroslag remelting: The mother electrode is subjected to electroslag remelting and refining treatment under a protective atmosphere to obtain electroslag ingots, reducing the burn-off of easily oxidized elements, controlling the increase of O, N and H element content, and annealing at 720℃~760℃ for 6~10h. After annealing, it is slowly cooled to 400℃~500℃ for further processing. S3: High-temperature homogenization treatment: High-temperature homogenization treatment is carried out on the electroslag ingot to improve the banded structure. The holding temperature is 1240℃~1280℃ and the holding time is 20~30h. S4: Forging process: After high-temperature homogenization treatment, furnace cooling is carried out to 1150℃~2000℃ and forging is started using a high-speed forging machine. The final forging temperature is 850℃~900℃, the forging ratio is >4, the original coarse grains are broken and new fine equiaxed grains are obtained. S5: Ultrafine treatment: After forging, ultrafine treatment is performed to refine the grains. The holding temperature is 1000℃~1050℃ and the holding time is 3~5h. After exiting the furnace, the grains are cooled by water. S6: Spheroidizing Annealing Treatment: After ultrafine treatment, spheroidizing annealing is performed. The temperature is heated to 830℃~880℃ and held for 15~20h. The temperature is then furnace cooled to 720℃~760℃ and held for 30~40h to spheroidize the carbides in the microstructure. The temperature is then furnace cooled to 400℃~500℃ and air cooled after removal from the furnace.

2. The hot work die steel according to claim 1, characterized in that, The unavoidable impurity elements are Ni 0.01%~0.04%, Cu 0.03%~0.07%, Al 0.005%~0.010%, N≤0.005%, P≤0.005%, S≤0.0015%, and Ti≤0.0015%.

3. The hot work die steel according to claim 1 or 2, characterized in that, By mass percentage, hot work die steel contains 0.31% C, 0.076% Si, 0.74% Mn, 0.041% Cr, 3.44% Mo, 0.51% V, 0.018% Nb, and 0.024% Ce.

4. The hot work die steel according to claim 1 or 2, characterized in that, By mass percentage, hot work die steel contains 0.35% C, 0.069% Si, 0.83% Mn, 0.051% Cr, 3.31% Mo, 0.44% V, 0.017% Nb, and 0.022% Ce.

5. The method for preparing hot work die steel according to any one of claims 1 to 4, characterized in that, The process includes the following steps: S1: Vacuum Induction Melting: According to the composition ratio, vacuum induction melting is carried out to control the content of active elements in the alloy, such as Al 0.005%~0.010%, Ti≤0.0015%, to remove gaseous and non-metallic inclusions and impurities from the alloy, and to improve purity through double-layer slag blocking and ceramic filtration. When tapping the steel, P≤0.005%, Si≤0.10%, O≤0.002%, N≤0.005%, S≤0.0015% are controlled. S2: Electroslag remelting: The mother electrode is subjected to electroslag remelting and refining treatment under a protective atmosphere to obtain electroslag ingots, reducing the burn-off of easily oxidized elements, controlling the increase of O, N and H element content, and annealing at 720℃~760℃ for 6~10h. After annealing, it is slowly cooled to 400℃~500℃ for further processing. S3: High-temperature homogenization treatment: High-temperature homogenization treatment is carried out on the electroslag ingot to improve the banded structure. The holding temperature is 1240℃~1280℃ and the holding time is 20~30h. S4: Forging process: After high-temperature homogenization treatment, furnace cooling is carried out to 1150℃~2000℃ and forging is started using a high-speed forging machine. The final forging temperature is 850℃~900℃, the forging ratio is >4, the original coarse grains are broken and new fine equiaxed grains are obtained. S5: Ultrafine treatment: After forging, ultrafine treatment is performed to refine the grains. The holding temperature is 1000℃~1050℃ and the holding time is 3~5h. After exiting the furnace, the grains are cooled by water. S6: Spheroidizing Annealing Treatment: After ultrafine treatment, spheroidizing annealing is performed. The temperature is heated to 830℃~880℃ and held for 15~20h. The temperature is then furnace cooled to 720℃~760℃ and held for 30~40h to spheroidize the carbides in the microstructure. The temperature is then furnace cooled to 400℃~500℃ and air cooled after removal from the furnace.

6. The application of the hot work die steel according to any one of claims 1 to 4 in die casting, hot forging or hot stamping.

7. A steel product, characterized in that, It includes the hot work die steel as described in any one of claims 1 to 4.

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