Hot-work die steel easy for additive manufacturing, additive manufacturing method therefor, and use thereof

Abstract

The present invention belongs to the technical field of additive manufacturing die steel, and provides a hot-work die steel easy for additive manufacturing, an additive manufacturing method therefor, and a use thereof. The hot-work die steel provided by the present invention comprises the following chemical components by mass percentage: C 0.12-0.26%, Cr 4.5-5.8%, Mo 0.8-1.5%, V 0.2-1.2%, Si 0.02-0.15%, Mn 0.2-0.5%, Ni 0-2.45%, Al 0-0.80%, Cu 0-1.25%, P < 0.015%, S < 0.01%, the balance being Fe. The present invention improves the mechanical properties by forming carbides and introducing a β-NiAl phase and / or Cu-rich phase; reducing the content of C and Si not only improves the strength-plasticity / toughness ratio and avoids the cracking tendency during additive manufacturing, but also enhances thermal conductivity and service life and reduces cyclic thermal fatigue cracking.

Description

A hot working die steel easy for additive manufacturing and its additive manufacturing method and application

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on February 4, 2024, with application number 2024101538513 and invention name “A hot working die steel easy for additive manufacturing and its additive manufacturing method and application”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present invention relates to the technical field of additive manufacturing die steel, and in particular to a hot working die steel that is easy to additively manufacture, and an additive manufacturing method and application thereof. Background Art

[0003] At present, the quality of high-end molds in my country still has many shortcomings, such as relatively unstable microstructure and mechanical properties, short service life, poor reliability and other problems, so many high-end molds still rely on imports. The emerging additive manufacturing technology has changed the traditional mold manufacturing method. It not only greatly reduces or even avoids the adverse effects of harmful impurity elements and component segregation on raw materials (mold steel), but also the conformal water channels provided by additive manufacturing greatly improve the cooling capacity of the mold, thereby improving the product surface quality and production efficiency. At the same time, it can also compensate for the increase in mold material costs, making the quality of my country's additive manufacturing molds close to or even exceeding the foreign level, with high cost performance and competitiveness. Despite this, under repeated thermal fatigue loads, compared with traditional casting manufacturing methods, additive manufacturing mold steel often cracks and leads to premature failure, and there is still much room for improvement in service life.

[0004] H13 steel is a typical hot-work die steel, commonly used in die-casting molds. However, H13 steel powder is not suitable for additive manufacturing (AM). This is primarily due to the non-equilibrium martensitic transformation that occurs during repeated rapid melting and solidification cooling. The resulting lattice distortion creates very high thermal stresses. Furthermore, H13 steel's inherent hardness can exceed 50 HRC, resulting in poor toughness and ductility. Furthermore, coarse, chain-like carbides easily form in the final microstructure, acting as a source of crack initiation and promoting rapid crack propagation. Consequently, additively manufactured H13 steel is often accompanied by printing defects such as pores, cracks, and lack of fusion. These not only reduce mechanical properties but also significantly compromise service performance, such as friction, wear, and thermal fatigue resistance, limiting its widespread application in molds. Furthermore, H13 steel has a relatively low thermal conductivity, ranging from 24 to 27 W / (mK). This leads to high thermal stresses during service, particularly when the surface roughness of conformal cooling channels is high. This can easily cause cracking of the cooling channel surface, leading to overall mold failure.

[0005] Currently, to address the shortcomings of H13 steel, additively manufactured maraging steels (such as 18Ni300) are often used as die-casting mold materials. This improves print formability and avoids defects to a certain extent, primarily due to their low as-printed hardness (~35 HRC), which can be adjusted to the target hardness through subsequent heat treatment. However, maraging steels still have the following shortcomings: 1. Their thermal conductivity is lower than that of H13 steel, further increasing the risk of cracking during service; 2. They contain high levels of elements such as Co, Ni, and Mo, which increases material cost to a certain extent; 3. Their low carbon content results in low friction and wear properties, limiting fatigue life.

[0006] In addition to H13 steel and maraging steel, several materials for additive manufacturing die-casting molds are currently in the research and development stage. These include a Fe-0.24C-7.6Cr-3.8Mo-0.67V-0.65W-0.29Ti-0.12La-0.09N (mass fraction, wt.%) alloy steel. This not only refines the final microstructure (average grain size approximately 4.3 μm) by utilizing in-situ TiN nanoparticles generated during atomization, but also enhances the final mechanical properties (hardness approximately 47 HRC, impact energy approximately 26 J) by utilizing the M2C type (M primarily Mo) formed during tempering. This also successfully avoids solidification defects during printing and stress defects during cooling. However, both the in-situ formation of uniform, fine TiN particles and the three heat treatment steps involved narrow the process window in actual production and increase process costs. In addition, CN116855852A discloses an alloy steel of Fe-9.8Cr-8.0Co-2.6Mo-7.2Ni-2.4W-1.5Al-0.8Cu-0.02Re (mass fraction, wt.%), which can meet the mechanical properties of the die-casting mold by directly tempering once after printing, especially having excellent high-temperature performance and good printing process formability. However, due to the high Co and Ni content, the material cost is greatly increased.

[0007] Therefore, there is currently no alloy steel for die-casting molds suitable for additive manufacturing that combines mechanical properties and service performance while taking into account material and process costs. Providing a hot working die steel that combines mechanical properties and service performance while being low in cost and easy to manufacture has become a technical problem that needs to be urgently solved in this field.

[0008] Summary of the Invention

[0009] The present invention aims to provide a hot work die steel that is easily additively manufactured, as well as a method and application thereof. The hot work die steel provided by the present invention exhibits excellent mechanical properties at room temperature and high-temperature resistance, ensuring good service performance. Furthermore, the hot work die steel contains a low content of precious metal elements, reducing production costs.

[0010] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0011] The present invention provides a hot working die steel which is easy to be manufactured by additive manufacturing. The hot working die steel comprises the following chemical components, calculated by mass percentage: C 0.12-0.26%, Cr 4.5-5.8%, Mo 0.8-1.5%, V 0.2-1.2%, Si 0.02-0.15%, Mn 0.2-0.5%, Ni 0-2.45%, Al 0-0.80%, Cu 0-1.25%, P < 0.015%, S < 0.01% and the balance Fe.

[0012] Preferably, the hot working die steel that is easy to additively manufacture includes the following chemical composition, by mass percentage: C 0.18-0.26%, Cr4.8-5.8%, Mo 1.0-1.5%, V 0.5-1.2%, Si 0.02-0.1%, Mn 0.3-0.5%, Ni 0.02-2.45%, Al 0-0.60%, Cu 0-1.0%, P <0.015%, S <0.01% and the balance Fe.

[0013] Preferably, the hot working die steel that is easy to additively manufacture includes the following chemical composition, by mass percentage: C 0.2-0.26%, Cr 5.0-5.4%, Mo 1.2-1.5%, V 0.8-1.0%, Si 0.02-0.05%, Mn 0.45-0.5%, Ni 0.5-2.4%, Al 0.2-0.5%, Cu 0.1-0.8%, P < 0.015%, S < 0.01% and the balance Fe.

[0014] The present invention provides an additive manufacturing method for hot working die steel that is easy to additively manufacture as described in the above technical solution, comprising the following steps:

[0015] (1) preparing a hot working die steel alloy powder from an alloy raw material by gas atomization or a rotating electrode method; the chemical composition of the hot working die steel alloy powder is the same as the chemical composition of the hot working die steel that is easy to additively manufacture as described in the above technical solution;

[0016] (2) performing additive manufacturing using the hot working die steel alloy powder obtained in step (1) as a raw material to obtain a molded component;

[0017] (3) Post-processing the formed component obtained in step (2) to obtain hot working die steel.

[0018] Preferably, the particle size of the hot working die steel alloy powder in step (1) is 15 to 75 μm, and the packing density is 3.8 to 4.4 g / cm 3, the tap density is 4.6~5.0g / cm 3 , Hall flow rate ≤15s / 50g.

[0019] Preferably, the process parameters of the additive manufacturing in step (2) include: laser power of 200-450W, scanning rate of 0.5-1.0m / s, scanning spacing of 50-150μm, powder layer thickness of 20-100μm, interlayer scanning path angle of 65-70°, and substrate preheating temperature of 120-200℃.

[0020] Preferably, the post-treatment in step (3) includes one, two or a combination of three of solution treatment, cryogenic treatment and tempering treatment.

[0021] Preferably, the post-treatment is any one of tempering treatment, solution treatment + tempering treatment, cryogenic treatment + tempering treatment and solution treatment + cryogenic treatment + tempering treatment.

[0022] Preferably, the temperature of the solution treatment is 1020-1050° C., the holding time of the solution treatment is 0.5-5 h, the cooling rate of the solution treatment is 2-50° C. / s, and the cooling method of the solution treatment is water quenching.

[0023] Preferably, the temperature of the solution treatment is 1020-1050° C., the holding time of the solution treatment is 1-4 h, the cooling rate of the solution treatment is 5-50° C. / s, and the cooling method of the solution treatment is water quenching.

[0024] Preferably, the temperature of the solution treatment is 1020-1050° C., the holding time of the solution treatment is 2-3 h, the cooling rate of the solution treatment is 20-50° C. / s, and the cooling method of the solution treatment is water quenching.

[0025] Preferably, the temperature of the cryogenic treatment is -196 to -120°C, the holding time of the cryogenic treatment is 0.5 to 3 hours, and the return to temperature of the cryogenic treatment is to place the product at room temperature for 10 to 60 minutes.

[0026] Preferably, the temperature of the cryogenic treatment is -196 to -150°C, the holding time of the cryogenic treatment is 1 to 2.5 hours, and the return to temperature of the cryogenic treatment is to place the product at room temperature for 20 to 50 minutes.

[0027] Preferably, the temperature of the cryogenic treatment is -196°C, the holding time of the cryogenic treatment is 1.5 to 2 hours, and the return to temperature of the cryogenic treatment is to place the product at room temperature for 30 to 40 minutes.

[0028] Preferably, the temperature of the tempering treatment is 400-750° C., and the holding time of the tempering treatment is 0.5-7 h.

[0029] Preferably, the temperature of the tempering treatment is 460-650° C., and the holding time of the tempering treatment is 3-7 hours.

[0030] Preferably, the temperature of the tempering treatment is 500-600° C., and the holding time of the tempering treatment is 3-5 hours.

[0031] The present invention provides the application of the hot working die steel that is easy to additively manufacture as described in the above technical solution or the hot working die steel prepared by the additive manufacturing method as described in the above technical solution in a mold.

[0032] Preferably, the mold comprises a die-casting mold and / or an injection mold.

[0033] The present invention provides a hot-working die steel that is easily additively manufactured. The steel comprises, by mass percentage, the following chemical composition: C 0.12-0.26%, Cr 4.5-5.8%, Mo 0.8-1.5%, V 0.2-1.2%, Si 0.02-0.15%, Mn 0.2-0.5%, Ni 0-2.45%, Al 0-0.80%, Cu 0-1.25%, P < 0.015%, S < 0.01%, and the balance Fe. Based on H13 steel for die-casting molds, the present invention reduces the C content (adjusting its upper limit to 0.26 wt.%) to improve additive manufacturing processability and reduce the risk of cracking, while also enhancing plasticity and toughness. Furthermore, the Si content is reduced (adjusting its upper limit to 0.15 wt.%) to improve thermal conductivity. Depending on the actual alloy composition or element additions, the thermal conductivity ranges from 18 to 38 W / (m·K). At the same time, in order to compensate for the reduction in solid solution strengthening effect or strength caused by the reduction of C and Si, appropriate amounts of Cu, Ni and / or Al are selectively added to form potential Cu-rich phase and / or nano-β-NiAl phase during heat treatment, thereby improving the precipitation strengthening effect. The Cu-rich phase and / or β-NiAl phase as well as MC type (M is mainly V) and M2C (M is mainly Mo) are mainly distributed in the martensite matrix, with a size between 2.5 and 50 nm and a number density of 10 24 m -3 The MC and M2C carbides are uniformly and dispersedly distributed, and the precipitation reactions of MC and M2C carbides with β-NiAl phase and / or Cu-rich phase promote each other, often co-precipitating or adjacently precipitating. The main function is to produce precipitation strengthening through the dislocation cutting mechanism to improve the room temperature and high temperature strength; Cr 23C6 carbides are distributed relatively evenly at the interfaces of martensite laths and the original austenite grain boundaries. Their main function is to stabilize the hierarchical martensite structure to ensure high-temperature strength and durability, while improving fatigue resistance. The results of the embodiment show that the hot working die steel prepared by the present invention has a hardness of 35-53 HRC, a room temperature yield strength of 1240-1700 MPa, a tensile strength of 1535-1835 MPa, an elongation of 5.2-19.5%, a V-notch room temperature impact energy of 11-60 J, and a thermal conductivity of 18-38 W / (m·K); a high-temperature yield strength of 1100-1340 MPa at 300°C, a high-temperature tensile strength of 1310-1530 MPa, and an elongation of 9.2-19.5%; a high-temperature yield strength of 690-840 MPa at 600°C, a high-temperature tensile strength of 850-1080 MPa, and an elongation of 11.2-20.5%. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] FIG1 is a hardness variation curve of the formed component obtained in step (2) of Example 1, the alloy after deep cryogenic treatment in step (3) of Example 3, and the alloy after solid solution treatment in step (3) of Example 11 as the tempering treatment temperature changes;

[0035] FIG2 is a hardness variation curve of the molded component obtained in step (2) of Example 4 and the alloy after deep cryogenic treatment in step (3) of Example 6 as the tempering temperature changes;

[0036] FIG3 is a hardness change curve of the hot working die steel prepared in Example 14, Example 6 and Comparative Example 1 at 550° C. for 100 hours;

[0037] FIG4 is the metallographic microstructure of the hot working die steel prepared in Examples 1 to 6;

[0038] FIG5 is the SEM microstructure of the molded component obtained in step (2) of Example 1, and the hot working die steel obtained in Examples 1 to 3 and Examples 7 to 14;

[0039] FIG6 is the EBSD microstructure of the molded component obtained in step (2) of Example 1, and the hot working die steel obtained in Examples 1 to 3 and Examples 10 to 11;

[0040] FIG7 is a TEM microstructure of the hot working die steel obtained in Examples 1 to 3;

[0041] FIG8 is a TEM micrograph of carbide of the hot working die steel obtained in Example 2;

[0042] FIG9 is an APT three-dimensional atomic distribution diagram of the hot working die steel obtained in Example 1;

[0043] FIG10 is an APT three-dimensional atomic distribution diagram of the hot working die steel obtained in Example 2;

[0044] FIG11 is an APT three-dimensional atomic distribution diagram of the hot working die steel obtained in Example 3;

[0045] FIG12 is a 2at.% C isoconcentration distribution diagram of the hot work die steel provided in Example 1;

[0046] FIG13 is a 2at.% C isoconcentration distribution diagram of the hot working die steel provided in Example 2;

[0047] FIG14 is a 2at.% C isoconcentration distribution diagram of the hot work die steel provided in Example 3;

[0048] FIG15 is a one-dimensional concentration distribution diagram of the carbide phase P1 in FIG12;

[0049] FIG16 is a one-dimensional concentration distribution diagram of the carbide phase P2 in FIG12;

[0050] FIG17 is a one-dimensional concentration distribution diagram of the carbide phase P3 in FIG13 ;

[0051] FIG18 is a one-dimensional concentration distribution diagram of the carbide phase P4 in FIG13;

[0052] FIG19 is a one-dimensional concentration distribution diagram of the carbide phase P5 in FIG14 ;

[0053] FIG20 is a one-dimensional concentration distribution diagram of the carbide phase P6 in FIG14;

[0054] FIG21 is a three-dimensional spatial distribution diagram of the atomic distribution of the hot working die steel and the corresponding element isoconcentration surface provided in Example 4;

[0055] FIG22 is a composition analysis diagram of the region of interest (ROI) of the hot working die steel provided in Example 4;

[0056] FIG23 is a composition analysis diagram of the Cu-rich phase of the hot working die steel provided in Example 4;

[0057] FIG24 is a composition analysis diagram near the interface of the hot working die steel provided in Example 4;

[0058] FIG25 is a composition analysis diagram of carbides in the hot working die steel matrix provided in Example 4;

[0059] FIG26 is an SEM morphology of the tensile and impact fracture surfaces of the hot working die steels prepared in Examples 1 to 3. DETAILED DESCRIPTION

[0060] The present invention provides a hot working die steel which is easy to be manufactured by additive manufacturing. The hot working die steel comprises the following chemical components, calculated by mass percentage: C 0.12-0.26%, Cr 4.5-5.8%, Mo 0.8-1.5%, V 0.2-1.2%, Si 0.02-0.15%, Mn 0.2-0.5%, Ni 0-2.45%, Al 0-0.80%, Cu 0-1.25%, P < 0.015%, S < 0.01% S and the balance Fe.

[0061] The hot work die steel provided by the present invention, which is easy to manufacture using additive manufacturing, comprises 0.12-0.26% C by mass, preferably 0.18-0.26%, and more preferably 0.2-0.26%. By controlling the carbon content, the present invention maintains the carbon content in the hot work die steel within a moderate range. This allows the formation of different types of carbides, stabilizes the hierarchical structure of martensite, produces precipitation strengthening, and achieves interstitial solid solution strengthening. Furthermore, the present invention reduces the degree of lattice distortion during the martensitic phase transformation during additive manufacturing, thereby reducing stress and cracking risks and minimizing printing defects.

[0062] The hot working die steel provided by the present invention, which is easy to manufacture by additive manufacturing, comprises 4.5-5.8% Cr, preferably 4.8-5.8%, more preferably 5.0-5.4% Cr, by mass percentage. 23 C6 carbides are relatively evenly distributed at the interfaces of martensite laths and the original austenite grain boundaries. Their main function is to stabilize the hierarchical martensite structure to ensure high temperature strength and durability, while improving fatigue resistance.

[0063] The hot-working die steel provided by the present invention, which is easily additively manufactured, comprises 0.8-1.5% Mo by mass, preferably 1.0-1.5%, and more preferably 1.2-1.5%. The present invention introduces Mo to form Mo-based M2C carbides, which are needle- or rod-shaped, exhibit strong thermal stability and are less susceptible to growth and coarsening at high temperatures. This is primarily used to improve high-temperature durability.

[0064] The hot working die steel provided by the present invention, which is easy to manufacture by additive manufacturing, includes 0.2-1.2% V, preferably 0.5-1.2%, and more preferably 0.8-1.0%. The present invention introduces V to form MC-type carbides mainly composed of V and can enrich a certain amount of Mo, which is mainly distributed in the martensite matrix and has a size between 2.5 and 50 nm and a number density of 10 24 m -3 The nanostructured phase is uniform and dispersed, and can form a composite nanophase with the Cu-rich phase and / or β-NiAl phase to further improve the strength.

[0065] The hot work die steel provided by the present invention, which is easy to manufacture using additive manufacturing, includes 0.02-0.15% Si by mass, preferably 0.02-0.1%, and more preferably 0.02-0.05%. By controlling the Si content, the present invention can further improve thermal conductivity, and the reduction in solid solution strengthening can be compensated by precipitation strengthening.

[0066] The hot-working die steel provided by the present invention, which is easy to manufacture with additive manufacturing, includes 0.2-0.5% Mn by mass, preferably 0.3-0.5%, and more preferably 0.45-0.5%. By adding a small amount of Mn, in addition to producing solid solution strengthening, the addition can also diffuse into other precipitated phases (such as a Cu-rich phase) or segregate at the interface between the precipitated phase and the matrix, thereby inhibiting the growth of the precipitated phase and increasing its dispersion, thereby indirectly producing strengthening.

[0067] The hot-working die steel provided by the present invention, which is easy to manufacture using additive manufacturing, includes 0 to 2.45% Ni, preferably 0.02 to 2.45%, and more preferably 0.5 to 2.4%. By adding Ni and controlling its content, the present invention can form a β-NiAl phase with Al, or segregate at the interface between the Cu-rich phase and the matrix, thereby inhibiting its growth and increasing its dispersion, further enhancing the strengthening effect and overall mechanical properties of the nano-precipitated phase, while also improving toughness to a certain extent.

[0068] The hot-working die steel provided by the present invention, which is easy to manufacture with additive manufacturing, comprises 0-0.80% Al, preferably 0-0.60% Al, and more preferably 0.2-0.5% Al by mass percentage. By adding and controlling the Al content, the present invention can promote the formation of a nano-β-NiAl phase or inhibit the growth and coarsening of a Cu-rich phase, thereby achieving a better strengthening effect.

[0069] The hot-working die steel provided by the present invention, which is easy to manufacture with additive manufacturing, comprises 0-1.25% Cu, preferably 0-1.0%, and more preferably 0.1-0.8% Cu by mass percentage. By adding Cu and controlling its amount, the present invention can form a Cu-rich phase. The Cu-rich phase, the potential β-NiAl phase, and the dispersed precipitation of VC mutually promote each other, further improving the strengthening effect and overall mechanical properties of the nano-precipitated phase.

[0070] The hot working die steel provided by the present invention, which is easy to manufacture by additive manufacturing, comprises P < 0.015% by mass. In the present invention, the P element is an impurity element.

[0071] The hot working die steel provided by the present invention, which is easy to manufacture by additive manufacturing, comprises S less than 0.01% by mass. In the present invention, the S element is an impurity element.

[0072] The hot working die steel provided by the present invention and easy for additive manufacturing includes a balance of Fe in terms of mass percentage. In the present invention, Fe is used as a matrix element.

[0073] Based on the H13 steel used for die-casting molds, the present invention reduces the C content (adjusts its upper limit to 0.26wt.%) on the one hand to improve the additive manufacturing processability and reduce the risk of cracking, while improving plasticity and toughness; on the other hand, it reduces the Si content (adjusts its upper limit to 0.15wt.%) to improve thermal conductivity. Depending on the actual composition of the alloy or the amount of element addition, the thermal conductivity varies between 18 and 38W / (m·K). At the same time, in order to compensate for the solid solution strengthening effect or the reduction in strength caused by the reduction of C and Si, appropriate amounts of elements such as Cu, Ni and / or Al are selectively added, thereby forming a potential Cu-rich phase and / or nano-β-NiAl phase during the heat treatment process, thereby improving the precipitation strengthening effect. The Cu-rich phase and / or β-NiAl phase, as well as the MC type (M is mainly V) and M2C (M is mainly Mo) are mainly distributed in the martensite matrix, with a size between 2.5 and 50nm and a number density of 10 24 m -3 The precipitation reaction of MC and M2C carbides with β-NiAl phase and / or Cu-rich phase promotes each other, often co-precipitating or adjacent precipitation. The main function is to produce precipitation strengthening through the dislocation cutting mechanism to improve the room temperature and high temperature strength. 23 C6 carbides are distributed relatively evenly at the interfaces of martensite laths and the original austenite grain boundaries. Their main function is to stabilize the hierarchical martensite structure to ensure high-temperature strength and durability, while improving fatigue resistance.

[0074] The present invention provides an additive manufacturing method for hot working die steel that is easy to additively manufacture as described in the above technical solution, comprising the following steps:

[0075] (1) preparing a hot working die steel alloy powder from an alloy raw material by gas atomization or a rotating electrode method; the chemical composition of the hot working die steel alloy powder is the same as the chemical composition of the hot working die steel that is easy to additively manufacture as described in the above technical solution;

[0076] (2) performing additive manufacturing using the hot working die steel alloy powder obtained in step (1) as a raw material to obtain a molded component;

[0077] (3) Post-processing the formed component obtained in step (2) to obtain hot working die steel.

[0078] The present invention uses gas atomization or rotating electrode method to prepare hot working die steel alloy powder from alloy raw materials. The present invention has no particular restrictions on the specific type and source of the alloy raw materials, as long as the chemical composition of the hot working die steel alloy powder meets the requirements.

[0079] In the present invention, the chemical composition of the hot working die steel alloy powder is the same as the chemical composition of the hot working die steel that is easy to be additively manufactured as described in the above technical solution.

[0080] In the present invention, the particle size of the hot working die steel alloy powder is preferably 15 to 75 μm, more preferably 30 to 75 μm; the particle size of the hot working die steel alloy powder is preferably normally distributed; the packing density of the hot working die steel alloy powder is preferably 3.8 to 4.4 g / cm 3 , more preferably 4.0 to 4.4 g / cm 3 The tap density of the hot working die steel alloy powder is preferably 4.6 to 5.0 g / cm 3 , more preferably 4.8 to 5.0 g / cm 3 The Hall flow velocity of the hot-working die steel alloy powder is preferably ≤15 s / 50 g, more preferably ≤14 s / 50 g. The hot-working die steel alloy powder is preferably spherical in shape. The hot-working die steel alloy powder preferably has a fine-grained martensitic structure. By controlling the parameters of the spherical alloy powder, the present invention further improves the performance of formed components during additive manufacturing.

[0081] The present invention does not specifically limit the specific operations and process parameters for preparing the hot working die steel alloy powder by the gas atomization or rotating electrode method. The specific operations of the gas atomization or rotating electrode method well known to those skilled in the art can be used to ensure that the parameters of the hot working die steel alloy powder meet the requirements.

[0082] After obtaining the hot working die steel alloy powder, the present invention uses the hot working die steel alloy powder as a raw material to perform additive manufacturing to obtain a molded component.

[0083] In the present invention, the process parameters of the additive manufacturing preferably include: laser power of 200-450W, scanning rate of 0.5-1.0m / s, scanning spacing of 50-150μm, powder layer thickness of 20-100μm, interlayer scanning path at an angle of 65-70°, substrate preheating temperature of 120-200°C, more preferably: laser power of 250-400W, scanning rate of 0.5-1.0m / s, scanning spacing of 50-150μm, powder layer thickness of 20-100μm, interlayer scanning path at an angle of 65-70°, substrate preheating temperature of 120-200°C. The thickness of the powder layer is 50-120 μm, the thickness of the powder layer is 40-80 μm, the interlayer scanning path is at an angle of 65-70°, and the substrate preheating temperature is 120-200°C. More preferably, the laser power is 300-350 W, the scanning rate is 0.5-1.0 m / s, the scanning pitch is 80-120 μm, the thickness of the powder layer is 50-80 μm, the interlayer scanning path is at an angle of 65-70°, and the substrate preheating temperature is 150-180°C. The present invention can further improve the strength of hot working die steel by controlling the parameters of the additive manufacturing process.

[0084] The present invention has no special limitation on the specific structure and size of the molding component, which can be set according to product requirements.

[0085] After obtaining the formed component, the present invention performs post-processing on the formed component to obtain hot working die steel.

[0086] In the present invention, the post-treatment preferably includes one, two or three of solution treatment, cryogenic treatment and tempering treatment, more preferably any one of tempering treatment, solution treatment + tempering treatment, cryogenic treatment + tempering treatment and solution treatment + cryogenic treatment + tempering treatment.

[0087] In the present invention, the temperature of the solution treatment is preferably 1020-1050°C; the holding time of the solution treatment is preferably 0.5-5 hours, more preferably 1-4 hours, and even more preferably 2-3 hours; the cooling rate of the solution treatment is preferably 2-50°C / s, more preferably 5-50°C / s, and even more preferably 20-50°C / s; and the cooling method of the solution treatment is preferably water quenching. The room temperature microstructure of the hot work die steel obtained by solution treatment of the present invention is equiaxed grains (original austenite grains), and the grains have a hierarchical martensitic lath structure, similar to the as-cast microstructure.

[0088] In the present invention, the temperature of the cryogenic treatment is preferably -196 to -120°C, more preferably -196 to -150°C, and further preferably -196°C; the holding time of the cryogenic treatment is preferably 0.5 to 3 hours, more preferably 1 to 2.5 hours, and further preferably 1.5 to 2 hours; the temperature recovery method of the cryogenic treatment is preferably placed at room temperature for 10 to 60 minutes, more preferably 20 to 50 minutes, and further preferably 30 to 40 minutes. The present invention does not change the layered structure of the microstructure of the additive manufacturing hot working die steel by adding cryogenic treatment; in the subsequent tempering structure, except for the α-phase matrix of the body-centered cubic structure, there is basically no γ-phase (austenite phase) of the face-centered cubic structure. That is to say, the cryogenic treatment promotes the transformation of potential retained austenite into martensite, increases crystal defects (such as dislocation density), and better controls the distribution morphology of the precipitated phase in the tempered structure.

[0089] In the present invention, the tempering temperature is preferably 400-750°C, more preferably 460-650°C, further preferably 500-600°C, and most preferably 550-575°C. The holding time for the tempering is preferably 0.5-7 hours, more preferably 3-7 hours, further preferably 3-5 hours, and most preferably 3 hours. Through the tempering treatment, the microstructure of the hot-working die steel can be transformed into a layered structure with alternating cellular and columnar grains, resulting in refined equivalent grains and a better strength-toughness ratio.

[0090] In the present invention, when the post-treatment is tempering or cryogenic treatment plus tempering, the matrix structure of the hot work die steel is lath martensite with a lath width of 0.8 to 1.5 μm and a grain morphology of a layered structure with alternating cellular and columnar structures. In the present invention, when the post-treatment is solution treatment plus tempering or solution treatment plus cryogenic treatment plus tempering, the lath martensite in the hot work die steel transforms into fully equiaxed grains (original austenite grains), similar to the heat-treated microstructure of conventional cast alloys.

[0091] The precipitated phase of the hot working die steel prepared by the present invention includes Cr 23 C6 and VC type carbides and potential β-NiAl phase and Cu-rich phase; the Cr 23 C6 carbides are distributed relatively evenly at the interface of martensite laths and the original austenite grain boundaries. Their main function is to stabilize the hierarchical martensite structure to ensure high temperature strength and durability, while improving fatigue resistance. VC carbides, β-NiAl phases and Cu-rich phases are mainly distributed in the martensite matrix. Their sizes range from 2.5 to 50 nm, and their number density is 10 24 m -3The precipitates are uniform and dispersed, and two or more different types of precipitates are often co-precipitated or adjacent to each other. The main function is to produce precipitation strengthening through the dislocation cutting mechanism to improve the strength of hot working die steel.

[0092] Based on H13 steel and taking into account the operating temperature of the die-casting mold, the present invention optimizes the chemical composition of the hot working die steel, and through subsequent additive manufacturing and post-processing processes, regulates a flexible strength-plasticity / toughness ratio, providing technical support for the stable manufacturing and large-scale application of additive manufacturing molds.

[0093] The present invention also provides the use of the hot working die steel that is easy to additively manufacture as described in the above technical solution or the hot working die steel prepared according to the additive manufacturing method described in the above technical solution in a mold.

[0094] In the present invention, the mold preferably includes a die-casting mold and / or an injection mold.

[0095] The present invention does not specifically limit the specific manner of the application, and those skilled in the art may make conventional selections based on the heat treatment process and target mechanical properties.

[0096] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions of the present invention. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0097] Example 1

[0098] A hot work die steel that is easy to manufacture by additive manufacturing, comprising the following chemical composition by mass percentage: C 0.23%, Cr 5.14%, Mo 1.3%, V 0.38%, Si 0.11%, Mn 0.4%, P < 0.01%, S < 0.01% and the balance Fe; according to the chemical composition, it is an EM003 type alloy;

[0099] The additive manufacturing method for hot working die steel that is easy to additively manufacture comprises the following steps:

[0100] (1) preparing a hot working die steel alloy powder from an alloy raw material by gas atomization; the chemical composition of the hot working die steel alloy powder is the same as the chemical composition of the aforementioned hot working die steel that is easy to manufacture by additive manufacturing; the particle size of the hot working die steel alloy powder is 45±12 μm; the particle size of the hot working die steel alloy powder is normally distributed; the packing density of the hot working die steel alloy powder is 4.4 g / cm 3 The tap density of the hot working die steel alloy powder is 5.0g / cm3 The Hall flow rate of the hot working die steel alloy powder is 14s / 50g; the shape of the hot working die steel alloy powder is spherical; the structure of the hot working die steel alloy powder is a fine-grained martensitic structure;

[0101] (2) using the hot working die steel alloy powder obtained in step (1) as a raw material to perform additive manufacturing to obtain a molded component; the process parameters of the additive manufacturing are: laser power of 285W, scanning rate of 0.8m / s, scanning spacing of 110μm, powder layer thickness of 50μm, interlayer scanning path angle of 67°, and substrate preheating temperature of 150°C;

[0102] (3) The formed component obtained in step (2) is subjected to post-processing to obtain hot working die steel; the post-processing is tempering treatment; the temperature of the tempering treatment is 550°C; the holding time of the tempering treatment is 3 hours, recorded as T550.

[0103] Example 2

[0104] A hot work die steel that is easy to manufacture by additive manufacturing, comprising the following chemical composition by mass percentage: C 0.23%, Cr 5.14%, Mo 1.3%, V 0.38%, Si 0.11%, Mn 0.4%, P < 0.01%, S < 0.01% and the balance Fe; according to the chemical composition, it is an EM003 type alloy;

[0105] The temperature of the tempering treatment in the additive manufacturing method is 575° C., and other conditions are the same as those in Example 1, which is denoted as T575.

[0106] Example 3

[0107] A hot work die steel that is easy to manufacture by additive manufacturing, comprising the following chemical composition by mass percentage: C 0.23%, Cr 5.14%, Mo 1.3%, V 0.38%, Si 0.11%, Mn 0.4%, P < 0.01%, S < 0.01% and the balance Fe; according to the chemical composition, it is an EM003 type alloy;

[0108] In the additive manufacturing method, the post-treatment is cryogenic treatment + tempering treatment; the temperature of the cryogenic treatment is -196°C, the holding time of the cryogenic treatment is 2 hours, and the temperature return method of the cryogenic treatment is to place it at room temperature for 30 minutes; the temperature of the tempering treatment is 550°C, and the holding time of the tempering treatment is 3 hours; other conditions are the same as in Example 1, denoted as LNC+T550.

[0109] Example 4

[0110] A hot work die steel that is easy to manufacture using additive manufacturing, comprising, by mass percentage, the following chemical composition: C 0.26%, Cr 5.11%, Mo 1.3%, V 0.99%, Si 0.03%, Mn 0.42%, Al 0.64%, Ni 2.31%, Cu 1.08%, P < 0.01%, S < 0.01% and the balance Fe; the chemical composition is EM006 type alloy;

[0111] The additive manufacturing method for hot working die steel that is easy to additively manufacture comprises the following steps:

[0112] (1) A hot working die steel alloy powder is prepared from an alloy raw material by gas atomization; the chemical composition of the hot working die steel alloy powder is the same as the chemical composition of the aforementioned hot working die steel that is easy to manufacture by additive manufacturing; the particle size of the hot working die steel alloy powder is 45±12 μm; the particle size of the hot working die steel alloy powder is normally distributed; the packing density of the hot working die steel alloy powder is 4.3 g / cm 3 The tap density of the hot working die steel alloy powder is 4.9g / cm 3 The Hall flow rate of the hot working die steel alloy powder is 14.3s / 50g; the shape of the hot working die steel alloy powder is spherical; the structure of the hot working die steel alloy powder is a fine-grained martensitic structure;

[0113] (2) using the hot working die steel alloy powder obtained in step (1) as a raw material to perform additive manufacturing to obtain a molded component; the process parameters of the additive manufacturing are: laser power of 285W, scanning rate of 0.8m / s, scanning spacing of 110μm, powder layer thickness of 50μm, interlayer scanning path angle of 67°, and substrate preheating temperature of 150°C;

[0114] (3) The formed component obtained in step (2) is post-processed to obtain hot working die steel; the post-processing is tempering treatment; the tempering treatment temperature is 550°C, and the tempering treatment holding time is 3 hours, which is recorded as T550.

[0115] Example 5

[0116] A hot work die steel that is easy to manufacture using additive manufacturing, comprising, by mass percentage, the following chemical composition: C 0.26%, Cr 5.11%, Mo 1.3%, V 0.99%, Si 0.03%, Mn 0.42%, Al 0.64%, Ni 2.31%, Cu 1.08%, P < 0.01%, S < 0.01% and the balance Fe; the chemical composition is EM006 type alloy;

[0117] The temperature of the tempering treatment in the additive manufacturing method is 575° C., and other conditions are the same as those in Example 4, denoted as T575.

[0118] Example 6

[0119] A hot work die steel that is easy to manufacture using additive manufacturing, comprising, by mass percentage, the following chemical composition: C 0.26%, Cr 5.11%, Mo 1.3%, V 0.99%, Si 0.03%, Mn 0.42%, Al 0.64%, Ni 2.31%, Cu 1.08%, P < 0.01%, S < 0.01% and the balance Fe; the chemical composition is EM006 type alloy;

[0120] In the additive manufacturing method, the post-treatment is cryogenic treatment + tempering treatment; the temperature of the cryogenic treatment is -196°C, the holding time of the cryogenic treatment is 2 hours, and the temperature return method of the cryogenic treatment is to place it at room temperature for 30 minutes; the temperature of the tempering treatment is 625°C, and the holding time of the tempering treatment is 3 hours; other conditions are the same as those in Example 4, denoted as LNC+T625.

[0121] Example 7

[0122] A hot working die steel that is easy to manufacture by additive manufacturing, wherein the temperature of the tempering treatment in step (3) is 500°C, and the other conditions are the same as those in Example 1, which is denoted as T500.

[0123] Example 8

[0124] A hot working die steel that is easy to manufacture by additive manufacturing, wherein the temperature of the tempering treatment in step (3) is 600°C, and the other conditions are the same as those in Example 1, which is denoted as T600.

[0125] Example 9

[0126] A hot working die steel that is easy to manufacture by additive manufacturing, wherein the temperature of the tempering treatment in step (3) is 650°C, and other conditions are the same as those in Example 1, denoted as T650.

[0127] Example 10

[0128] A hot working die steel that is easy to manufacture by additive manufacturing, wherein the post-treatment in step (3) is solution treatment, the solution treatment temperature is 1030°C, the solution treatment holding time is 1h, the solution treatment cooling rate is 50°C / s, the solution treatment cooling method is water quenching, and other conditions are the same as those in Example 1, and is recorded as Q1030.

[0129] Example 11

[0130] A hot working die steel that is easy to manufacture by additive manufacturing, wherein the post-treatment in step (3) is solution treatment + tempering treatment, the temperature of the solution treatment is 1030°C, the holding time of the solution treatment is 1 hour, the cooling rate of the solution treatment is 50°C / s, the cooling method of the solution treatment is water quenching, the temperature of the tempering treatment is 550°C, the holding time of the tempering treatment is 3 hours, and other conditions are the same as those in Example 1, and is recorded as QT550.

[0131] Example 12

[0132] A hot working die steel that is easy to manufacture by additive manufacturing, wherein the temperature of the tempering treatment in step (3) is 575°C, and other conditions are the same as those in Example 11, and is recorded as QT575.

[0133] Example 13

[0134] A hot working die steel that is easy to manufacture by additive manufacturing, wherein the temperature of the tempering treatment in step (3) is 600°C, and other conditions are the same as those in Example 11, and is denoted as QT600.

[0135] Example 14

[0136] A hot working die steel that is easy to manufacture by additive manufacturing, wherein the tempering temperature in step (3) is 575° C., and other conditions are the same as those in Example 3, and is denoted as QT575.

[0137] Comparative Example 1

[0138] A commercial solid hot working die steel, comprising, by mass percentage, the following chemical composition: C 0.35%, Cr 5.0%, Mo 2.3%, V 0.6%, Si 0.2%, Mn 0.5%, P < 0.01%, S < 0.01% and the balance Fe; denoted by the chemical composition as Dievar;

[0139] The method for preparing the commercial solid hot working die steel specifically comprises the following steps:

[0140] (1) melting and forging the alloy raw materials in sequence to obtain a formed component;

[0141] (2) The formed component obtained in step (1) is post-processed to obtain a commercial solid hot working die steel; the post-processing is solution treatment + tempering treatment; the temperature of the solution treatment is 1030°C, the holding time of the solution treatment is 30 minutes, and the cooling method of the solution treatment is air cooling; the temperature of the tempering treatment is 615°C, the holding time of the tempering treatment is 2 hours, and it is recorded as Q+T615.

[0142] The properties of the hot working die steels prepared in Examples 1 to 6 and Comparative Example 1 were tested, and the results are shown in Table 1:

[0143] Table 1 Properties of hot working die steels prepared in Examples 1 to 6 and Comparative Example 1

[0144] In Table 1, the values ​​in brackets are the minimum values ​​of impact energy; T is tempering treatment, LNC is cryogenic treatment, and Q is solution treatment.

[0145] As can be seen from Table 1, the hot work die steel prepared by the present invention has a hardness of 35-53 HRC, a room temperature yield strength of 1240-1700 MPa, a tensile strength of 1535-1835 MPa, an elongation of 5.2-19.5%, and a V-notch room temperature impact energy of 11-60 J. The high-temperature yield strength at 300°C is 1100-1340 MPa, the high-temperature tensile strength is 1310-1530 MPa, and the elongation is 9.2-19.5%. The high-temperature yield strength at 600°C is 690-840 MPa, the high-temperature tensile strength is 850-1080 MPa, and the elongation is 11.2-20.5%. This shows that the hot work die steel provided by the present invention has excellent mechanical properties at room temperature and excellent high-temperature resistance, ensuring good service performance.

[0146] FIG1 is a hardness curve of the molded component obtained in step (2) of Example 1, the alloy after cryogenic treatment in step (3) of Example 3, and the alloy after solution treatment in step (3) of Example 11 as the tempering temperature changes. FIG2 is a hardness curve of the molded component obtained in step (2) of Example 4 and the alloy after cryogenic treatment in step (3) of Example 6 as the tempering temperature changes. In FIG1 and FIG2, as-built represents the hardness of the alloy before tempering. As can be seen from FIG1 and FIG2, the initial printing hardness and subsequent tempering hardness at different temperatures of the EM006 alloy are higher than those of the EM003 alloy. This is due to the addition of alloying elements such as Ni, Cu, and Al and the strengthening of various complex precipitation phases such as carbides and Cu-rich phases in the former, which can be used in scenarios with higher hardness requirements. Both alloys have a hardness peak at around 550°C, showing a certain precipitation strengthening effect, but the strengthening of the EM006 alloy can be maintained to around 600°C, with better resistance to tempering softening. The introduction of cryogenic treatment (blue line) does not significantly affect the hardness of the two alloys and their tempering trends. However, solution treatment (red line) can significantly improve the hardness before tempering at 600°C, but at the same time causes a sharp drop in high-temperature tempering hardness. This may be attributed to the introduction of solution treatment, which, on the one hand, allows more alloying elements to be dissolved into austenite, while on the other hand, destroys the fine grain structure of printed columnar crystals + equiaxed crystals. The former is more conducive to the tempering precipitation of alloy carbides, resulting in a higher initial hardness, while the latter promotes the recrystallization of lath martensite, resulting in a rapid drop in hardness in the later stage.

[0147] Figure 3 shows the hardness curves of the hot work die steels prepared in Example 14, Example 6, and Comparative Example 1 after holding at 550°C for 100 hours. As shown in Figure 3, the hardness of the three hot work die steels after various heat treatments remained around 46 HRC, meeting the hardness requirements for practical applications. Overall, the hardness of the three hot work die steels decreased with increasing holding time. However, after 100 hours of holding, the hardness of the hot work die steel obtained in Example 6 was significantly higher than that of Example 3 and Comparative Example 1, demonstrating its superior resistance to temper softening and improved service performance, such as resistance to thermal fatigue. It is important to note that after 1 hour of tempering, the hardness of EM003 was higher than that of EM006 and Dievar. This is attributed to the lower tempering temperature (575°C) of the former, which prevented the complete precipitation of the second phase and achieved optimal strengthening. In contrast, the higher tempering temperatures (625°C and 615°C) of the latter two stabilized their microstructures, resulting in only a decrease in hardness due to softening during long holding times.

[0148] Figure 4 shows the metallographic microstructures of the hot work die steels prepared in Examples 1 to 6. As can be seen from Figure 4, direct tempering or tempering after deep cooling does not change the initial printed layered structure of cellular and columnar structures (i.e., the structure of the molded component), and all of the heat treatments result in martensitic structures. The structure after deep cooling appears to be more uniform, and the microstructures of the two hot work die steels are not significantly different. In addition, no obvious defects, including pores, unfused materials, or cracks, were found in the microstructures, indicating that this type of hot work die steel (with a chemical composition range from EM003 to EM006) has good printability within the additive manufacturing process parameter range, eliminating chain-like carbides similar to those in H13 steel and avoiding the risk of cracking.

[0149] FIG5 is the SEM microstructure of the molded component obtained in step (2) of Example 1, and the hot working die steel obtained in Examples 1 to 3 and Examples 7 to 14. As can be seen from FIG5, the printed cellular + columnar interlayer structure in the molded component is maintained until 575°C. At 600°C and 650°C, the grain morphology changes significantly, and obvious second phase particles (T650) appear. This indicates that the initial lath martensite structure has partially recrystallized, the equivalent grain size increases, and the second phase grows and coarsens, the strengthening effect decreases, and ultimately the overall hardness decreases, which is consistent with the results in FIG1. ​​After solution treatment, the printed initial cellular + columnar interlayer structure completely disappears, and the tempered structure is different from that of the sample without solution treatment, and the equivalent grain size increases. Although cryogenic treatment does not change the cellular + columnar interlayer structure, the grains appear to be finer.

[0150] Figure 6 shows the EBSD microstructures of the molded component obtained in step (2) of Example 1, and the hot work die steel obtained in Examples 1-3 and Examples 10-11. As can be seen from Figure 6, the EBSD microstructure further confirms that the printed and tempered (including cryogenically treated) samples mainly have a layered structure with alternating cellular and columnar structures. However, after solution treatment, they transform into completely equiaxed grains (original austenite grains), which are similar to the heat-treated microstructure of traditional cast alloys, and the hierarchical structure of the martensite is more obvious. In addition, the introduction of solution treatment significantly increases the equivalent grain size, which weakens the fine grain strengthening to a certain extent, but also has two advantages: 1. The stress and anisotropy of the printed structure are almost completely eliminated; 2. The alloy elements are more fully dissolved and are conducive to precipitation strengthening during tempering. It is worth noting that the orientation of the grains of the alloy after printing is random, without obvious preferred orientation, which is beneficial to the application of the hot work die steel.

[0151] Figure 7 shows the TEM microstructures of the hot-working die steels obtained in Examples 1-3. As shown in Figure 7, while additive manufacturing effectively refines the grains, the cellular or columnar grains are still composed of lath martensite, containing numerous dislocations and a small amount of observable carbide precipitation. Tempering (550°C and 575°C) does not completely eliminate these small-angle lath interfaces, nor does it significantly accelerate carbide growth. Furthermore, varying the tempering temperature and cryogenic treatment do not significantly alter the microstructure.

[0152] Figure 8 shows the TEM micromorphology of the carbides of the hot work die steel obtained in Example 2, including bright field images (BF), selected area electron diffraction (SAED), and dark field images (DF) of the corresponding carbides (P1 and P2). As can be seen from Figure 8, there are mainly two types of carbides in the large amount of dislocation martensite matrix contained in the hot work die steel. The first type has the same orientation and growth direction, is short rod-shaped, and is Cr-rich M 23 Type C6 mainly stabilizes the martensite hierarchical structure and improves high-temperature endurance performance (DF-P1); the second type has mutually perpendicular morphological characteristics and is needle-shaped. It is a V- and Mo-rich MC or M2C type carbide, which mainly improves the comprehensive mechanical properties of the alloy through precipitation strengthening.

[0153] Figure 9 is an APT three-dimensional atomic distribution diagram of the hot work die steel obtained in Example 1. Figure 10 is an APT three-dimensional atomic distribution diagram of the hot work die steel obtained in Example 2. Figure 11 is an APT three-dimensional atomic distribution diagram of the hot work die steel obtained in Example 3. As can be seen from Figures 9 to 11, the carbon atoms in the hot work die steel are unevenly distributed, with different enrichment levels and morphologies. Strong carbide-forming elements Cr, V, and Mo, as well as weak carbide-forming element Mn, are segregated or enriched to varying degrees at corresponding locations, confirming the presence of different types of carbides. At the same time, the non-carbide-forming element Si is also segregated, likely due to its diffusion to the carbide / matrix interface or the martensite lath interface. In terms of morphological characteristics, the distribution of carbon and carbide-forming elements is similar during different heat treatments.

[0154] Figure 12 is a 2at.%C isoconcentration surface distribution diagram of the hot work die steel provided in Example 1. Figure 13 is a 2at.%C isoconcentration surface distribution diagram of the hot work die steel provided in Example 2. Figure 14 is a 2at.%C isoconcentration surface distribution diagram of the hot work die steel provided in Example 3. In Figures 12 to 14, P1 to P6 are potential carbide phases. It can be seen from Figures 12 to 14 that, from the distribution morphology, P5 is marked as grain boundary (GB) carbide or C segregation; the distribution of C atoms or carbides is related to the interface and other structures. During tempering, C is more likely to diffuse preferentially into crystal defects and promote the nucleation of carbides.

[0155] Figure 15 shows the one-dimensional concentration distribution of carbide phase P1 in Figure 12. Figure 16 shows the one-dimensional concentration distribution of carbide phase P2 in Figure 12. Figure 17 shows the one-dimensional concentration distribution of carbide phase P3 in Figure 13. Figure 18 shows the one-dimensional concentration distribution of carbide phase P4 in Figure 13. Figure 19 shows the one-dimensional concentration distribution of carbide phase P5 in Figure 14. Figure 20 shows the one-dimensional concentration distribution of carbide phase P6 in Figure 14. Figures 15-20 show that different types of carbides are enriched in Cr, Mo, and V, but their specific concentrations vary. This indicates that the nucleation locations of the carbides differ, resulting in differences in their size, morphology, and composition, and thus in their strengthening effects. Based on the compositional characteristics of the carbides, the initial alloy composition can be further optimized to control the carbide formation process, thereby obtaining more uniformly dispersed carbides and improving the overall performance of the alloy.

[0156] Figure 21 shows the atomic distribution of the hot work die steel provided in Example 4, along with a three-dimensional spatial distribution diagram of the corresponding element isoconcentration surfaces. As can be seen from Figure 21, the entire region of the hot work die steel is divided into two parts: the upper part is almost free of precipitates, with various alloying elements evenly distributed. The lower part contains a dispersed Cu-rich phase and carbides. The Cu-rich phase is spherical, and the carbides grow adjacent to it, thus changing their morphology and quantity. In comparison, the addition of elements such as Ni, Cu, and Al to EM003 not only forms a more dispersed and fine Cu-rich phase, but also influences the nucleation and growth of carbides, forming a composite precipitate phase with the carbides, further enhancing the precipitation strengthening effect.

[0157] Figure 22 is a composition analysis diagram of the region of interest (ROI) of the hot work die steel provided in Example 4. Figure 23 is a composition analysis diagram of the Cu-rich phase of the hot work die steel provided in Example 4. Figure 24 is a composition analysis diagram near the interface of the hot work die steel provided in Example 4. Figure 25 is a composition analysis diagram of the carbide in the hot work die steel matrix provided in Example 4. It can be seen from Figures 22 to 25 that a large number of second phases such as Cu-rich phases and carbides are present near the interface of the hot work die steel. This is attributed to the fact that defects such as interfaces serve as element diffusion channels that are more conducive to the nucleation of second phases; the Cu-rich phase contains almost no elements such as Cr, V, and Mo, while the carbides contain almost no elements such as Cu and Ni. This is the physical basis for the "adjacent growth" of the two types of precipitated phases and is also the basis for optimizing the chemical composition and improving the mechanical properties of the hot work die steel.

[0158] Figure 26 shows the SEM images of the tensile and impact fracture surfaces of the hot working die steels prepared in Examples 1 to 3. As can be seen from Figure 26, all samples subjected to different heat treatments exhibited ductile fracture, which is consistent with the mechanical properties listed in Table 1.

[0159] The description of the above embodiments is only intended to help understand the method of the present invention and its core concept. It should be noted that for those skilled in the art, without departing from the principles of the present invention, several improvements and modifications may be made to the present invention, and these improvements and modifications also fall within the scope of protection of the claims of the present invention. Various modifications to these embodiments are obvious to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A hot working die steel that is easy to manufacture by additive manufacturing, comprising the following chemical composition, calculated by mass percentage: C 0.12-0.26%, Cr 4.5-5.8%, Mo 0.8-1.5%, V 0.2-1.2%, Si 0.02-0.15%, Mn 0.2-0.5%, Ni 0-2.45%, Al 0-0.80%, Cu 0-1.25%, P < 0.015%, S < 0.01% and the balance Fe.

2. The hot working die steel easy for additive manufacturing according to claim 1, characterized in that: Calculated by mass percentage, it includes the following chemical components: C 0.18-0.26%, Cr 4.8-5.8%, Mo 1.0-1.5%, V 0.5-1.2%, Si 0.02-0.1%, Mn 0.3-0.5%, Ni 0.02-2.45%, Al 0-0.60%, Cu 0-1.0%, P <0.015%, S <0.01% and the balance Fe.

3. The hot working die steel easy for additive manufacturing according to claim 1, characterized in that: Calculated by mass percentage, it includes the following chemical components: C 0.2-0.26%, Cr 5.0-5.4%, Mo 1.2-1.5%, V 0.8-1.0%, Si 0.02-0.05%, Mn 0.45-0.5%, Ni 0.5-2.4%, Al 0.2-0.5%, Cu 0.1-0.8%, P < 0.015%, S < 0.01% and the balance Fe.

4. The additive manufacturing method for the hot working die steel easy for additive manufacturing according to any one of claims 1 to 3, comprising the following steps: (1) preparing a hot working die steel alloy powder from an alloy raw material by gas atomization or a rotating electrode method; the chemical composition of the hot working die steel alloy powder is the same as the chemical composition of the hot working die steel that is easy to additively manufacture as described in claim 1, 2 or 3; (2) performing additive manufacturing using the hot working die steel alloy powder obtained in step (1) as a raw material to obtain a molded component; (3) Post-processing the formed component obtained in step (2) to obtain hot working die steel.

5. The additive manufacturing method according to claim 4, characterized in that: The particle size of the hot working die steel alloy powder in step (1) is 15 to 75 μm, and the packing density is 3.8 to 4.4 g / cm 3 , the tap density is 4.6~5.0g / cm 3 , Hall flow rate ≤15s / 50g.

6. The additive manufacturing method according to claim 4, characterized in that The process parameters of the additive manufacturing in step (2) include: laser power of 200-450W, scanning rate of 0.5-1.0m / s, scanning spacing of 50-150μm, powder layer thickness of 20-100μm, interlayer scanning path angle of 65-70°, and substrate preheating temperature of 120-200℃.

7. The additive manufacturing method according to claim 4, characterized in that: The post-treatment in step (3) includes one, two or a combination of three of solution treatment, cryogenic treatment and tempering treatment.

8. The additive manufacturing method according to claim 7, characterized in that: The post-treatment is any one of tempering treatment, solution treatment + tempering treatment, cryogenic treatment + tempering treatment and solution treatment + cryogenic treatment + tempering treatment.

9. The additive manufacturing method according to claim 7 or 8, characterized in that: The temperature of the solution treatment is 1020-1050° C., the holding time of the solution treatment is 0.5-5 h, the cooling rate of the solution treatment is 2-50° C. / s, and the cooling method of the solution treatment is water quenching.

10. The additive manufacturing method according to claim 9, characterized in that: The temperature of the solution treatment is 1020-1050° C., the holding time of the solution treatment is 1-4 hours, the cooling rate of the solution treatment is 5-50° C. / s, and the cooling method of the solution treatment is water quenching.

11. The additive manufacturing method according to claim 10, characterized in that: The temperature of the solution treatment is 1020-1050° C., the holding time of the solution treatment is 2-3 hours, the cooling rate of the solution treatment is 20-50° C. / s, and the cooling method of the solution treatment is water quenching.

12. The additive manufacturing method according to claim 7 or 8, characterized in that: The temperature of the cryogenic treatment is -196 to -120° C., the holding time of the cryogenic treatment is 0.5 to 3 hours, and the return to temperature of the cryogenic treatment is to place the cryogenic treatment at room temperature for 10 to 60 minutes.

13. The additive manufacturing method according to claim 12, characterized in that: The temperature of the cryogenic treatment is -196 to -150° C., the holding time of the cryogenic treatment is 1 to 2.5 hours, and the return to temperature of the cryogenic treatment is to place the cryogenic treatment at room temperature for 20 to 50 minutes.

14. The additive manufacturing method according to claim 13, characterized in that: The temperature of the cryogenic treatment is -196°C, the holding time of the cryogenic treatment is 1.5 to 2 hours, and the return to temperature of the cryogenic treatment is to place the cryogenic treatment at room temperature for 30 to 40 minutes.

15. The additive manufacturing method according to claim 7 or 8, characterized in that: The temperature of the tempering treatment is 400-750° C., and the holding time of the tempering treatment is 0.5-7 hours.

16. The additive manufacturing method according to claim 15, characterized in that: The temperature of the tempering treatment is 460-650° C., and the holding time of the tempering treatment is 3-7 hours.

17. The additive manufacturing method according to claim 16, characterized in that: The temperature of the tempering treatment is 500-600° C., and the holding time of the tempering treatment is 3-5 hours.

18. Use of the hot working die steel that is easy to additively manufacture according to any one of claims 1 to 3 or the hot working die steel prepared according to the additive manufacturing method according to any one of claims 4 to 17 in a die.

19. The use according to claim 18, characterized in that The mold includes a die-casting mold and / or an injection mold.

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