Partitioned strengthening and toughening treatment method for additive remanufacturing hot forging die

Abstract

The invention provides a partitioned strengthening and toughening treatment method for an additive remanufacturing hot forging die, which comprises the following steps of: firstly, deeply cleaning a cavity of a failed forging die to remove impurities, residues and the like in the cavity, and creating a good basic condition for subsequent remanufacturing treatment; secondly, the repairing area of the forging die is subjected to remanufacturing treatment, so that the basic toughness requirement of the additive remanufacturing hot forging die is met, and cracking is prevented; afterwards, selective surface nitriding or carburizing strengthening treatment is conducted on the strengthening area of the additive remanufacturing hot forging die, so that the strength and hardness of the strengthening area are improved, the abrasion resistance is guaranteed, the strength and toughness partition of the surface of a cavity of the additive remanufacturing hot forging die is achieved, and then the comprehensive performance of the strengthened hot forging die is comprehensively improved; and finally, the service life of the reinforced hot forging die is prolonged.

Description

Technical Field

[0001] The invention relates to the field of chemical heat treatment strengthening of mold surfaces, and in particular to a partition strengthening and toughening treatment method for additive remanufacturing hot forging molds. Background Art

[0002] As an important basic process equipment, hot forging dies are widely used in the automotive industry, aerospace industry and other fields. The production of hot forging dies has the advantages of low cost, good quality and high efficiency. Since hot forging dies are repeatedly subjected to high temperature and heavy load impact during the forging process, they are prone to failure forms such as wear, thermal fatigue cracking, plastic deformation and fracture, which seriously shortens the service life of hot forging dies. For failed forging dies, additive remanufacturing technology is generally used to repair them, which can effectively improve material utilization, save production costs and improve economic benefits.

[0003] However, although the additive remanufacturing technology can effectively repair and remanufacture the mold, there are also some process limitations, such as the heat treatment characteristics of the material, welding residual stress, interlayer bonding strength, shape accuracy, etc. The above process limitations lead to different failure modes in different parts of the cavity of the forging die, which leads to the deterioration of the comprehensive performance of the repaired hot forging die, thereby reducing the service life of the repaired hot forging die.

[0004] Therefore, there is an urgent need for a partitioned strengthening and toughening treatment method for additive remanufacturing hot forging dies to solve the above technical problems. Summary of the invention

[0005] The purpose of the present invention is to overcome the above-mentioned technical deficiencies and provide a partitioned strengthening and toughening treatment method for additively remanufactured hot forging dies, so as to improve the technical problems of the prior art that the comprehensive performance of the repaired hot forging dies deteriorates and the service life is reduced due to the limitations of the repair process.

[0006] In order to achieve the above technical objectives, the technical solution of the present invention provides a partition toughening treatment method for additive remanufacturing hot forging dies, comprising: S10, deep cleaning of the cavity of the failed forging die; S20, performing remanufacturing processing on the repaired area of ​​the forging die to obtain an additively remanufactured hot forging die; S30, performing a zoned chemical heat treatment on the cavity surface of the additive remanufactured hot forging die, wherein the zoned chemical heat treatment includes performing a selective surface nitriding or carburizing strengthening treatment on the strengthening area of ​​the additive remanufactured hot forging die; S40, performing coloring flaw detection and polishing treatment on the cavity surface of the additively remanufactured hot forging die to obtain a strengthened hot forging die.

[0007] Preferably, step S20 specifically includes: S201, using a first arc additive manufacturing process to form a transition layer on the surface of the cavity located in the repair area; S202, using a second arc additive manufacturing process to form an intermediate layer on the transition layer; S203, using a third arc additive manufacturing process to form a strengthening layer on the middle layer; Among them, the first arc additive manufacturing process uses RMD535 welding wire and RMD142 welding wire, the second arc additive manufacturing process uses RMD545 welding wire and RMD248 welding wire, and the third arc additive manufacturing process uses RMD545 welding wire and RMD248 welding wire.

[0008] Preferably, step S30 specifically includes: S301, deep cleaning of the cavity surface of the additive remanufacturing hot forging die; S302, evenly applying a solid nitriding agent and / or a solid carburizing agent to the surface of the cavity located in the strengthening area; S303, chemically heat treating the cavity surface of the additively manufactured hot forging die, and chemically cleaning it after natural cooling.

[0009] Preferably, in step S302: the solid nitriding agent comprises the following components in weight percentage: 60% to 70% charcoal, 25% to 35% urea and 5% to 15% ammonium nitride.

[0010] Preferably, in step S303: when performing selective surface nitriding strengthening treatment on the strengthening area of ​​the additively remanufactured hot forging die, the cavity surface of the additively remanufactured hot forging die is heated to 550° C. to 600° C. and then kept warm for 4 h to 6 h.

[0011] Preferably, in step S302: the solid carburizing agent comprises the following components in weight percentage: 10% to 20% barium carbonate, 5% to 10% calcium carbonate and 70% to 85% charcoal.

[0012] Preferably, in step S303: when the reinforced area of ​​the additively remanufactured hot forging die is subjected to selective surface carburizing strengthening treatment, the cavity surface of the additively remanufactured hot forging die is heated to 750°C to 850°C and then kept warm for 2h to 3h, then continued to be heated to 900°C to 950°C and then kept warm for 2h to 3h, and finally cooled to 750 to 850°C at a rate of 50 to 60°C / h.

[0013] Preferably, step S302 further includes: using a coating to isolate the non-reinforced area of ​​the additively remanufactured hot forging die.

[0014] Preferably, the step of using a coating to isolate the non-reinforced area of ​​the additively remanufactured hot forging die specifically comprises: The material obtained by mixing lead, copper and rosin is dissolved in alcohol to form a paste, and then applied to the non-reinforced area of ​​the additive manufacturing hot forging die with a brush to obtain an insulating coating.

[0015] Preferably, the lead-copper material includes red lead and cupric chloride, and the mass ratio of red lead to cupric chloride is 1:2; the mass of rosin is 10% to 15% of the mass of the lead-copper material; and the thickness of the insulating coating is 1.4 mm to 2.0 mm.

[0016] Compared with the prior art, the beneficial effects of the present invention include: the present invention provides a partitioned strengthening and toughening treatment method for additive remanufacturing hot forging dies, the above method firstly deeply cleans the cavity of the failed forging die to remove impurities, residues, etc. in the cavity, so as to create good basic conditions for subsequent remanufacturing treatment; secondly, the repaired area of ​​the forging die is remanufactured to ensure the basic toughness requirements of the additive remanufactured hot forging die and prevent cracking; thereafter, the strengthened area of ​​the additive remanufactured hot forging die is selectively surface nitrided or carburized to strengthen the area to improve the strength and hardness of the strengthened area and ensure wear resistance, thereby realizing the strength and toughness zoning of the cavity surface of the additive remanufactured hot forging die, thereby comprehensively improving the comprehensive performance of the strengthened hot forging die, and finally improving the service life of the strengthened hot forging die. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 A flow chart of a partition toughening treatment method for additive remanufacturing hot forging dies provided by the present invention; Figure 2 It is a schematic diagram of a specific process flow of strengthening and toughening treatment of the partitions of the additively remanufactured forging die in Examples 1 and 2 of the present invention; Figure 3 The cavity structure and typical failure position of the additively remanufactured forging die in Examples 1 and 2 of the present invention. DETAILED DESCRIPTION

[0018] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0019] In view of the difference of the existing technology, the purpose of the present invention is to provide a method for repairing hot forging dies using additive remanufacturing technology to solve the process limitations. In the process of repairing the failed forging die, welding materials with good toughness are specially selected to repair the strengthening layer, so that the repaired forging die has good toughness. Subsequently, the forging die is subjected to surface partition chemical heat treatment to achieve the effect of forging die surface strength, toughness partition and partition surface strengthening.

[0020] See also Figure 1 , Figure 1 The present invention provides a flow chart of a partition toughening treatment method for additive remanufacturing hot forging dies; wherein the partition toughening treatment method for additive remanufacturing hot forging dies comprises the following steps: S10, deep cleaning of the cavity of the failed forging die.

[0021] Specifically, step S10 also includes: Deeply clean the cavity of the failed forging die. Remove the fatigue layer of the failed forging die and the areas with wear, cracks and plastic deformation by grinding and machining, and appropriately expand the cavity surface of the failed forging die to prevent minor defects that cause the forging die to fail quickly. In the process of removal, the area with large curvature is smoothed to facilitate the subsequent additive remanufacturing of the cavity of the forging die.

[0022] Specifically, by cleaning the cavity, impurities, dirt, etc. that may affect the quality of remanufacturing can be removed. Targeted removal of the fatigue layer of the failed forging die and the areas where wear, cracks and plastic deformation occur is to eliminate the damaged parts of the forging die and provide a relatively intact foundation for remanufacturing. Appropriate expansion of the cavity surface can further ensure that no minor defects remain, because minor defects may gradually expand during subsequent use, causing the forging die to fail again more quickly. During the removal process, the areas with larger curvature are smoothed, which is conducive to subsequent additive remanufacturing. The smoothed area can better combine with the additive material, improving the quality and stability of the remanufactured mold.

[0023] S20, performing remanufacturing processing on the repaired area of ​​the forging die to obtain an additively remanufactured hot forging die.

[0024] Specifically, step S20 also includes: The arc additive manufacturing technology is used to remanufacture the cavity surface of the repair area of ​​the forging die, and the arc additive manufacturing technology can realize the gradient material structure design of the cavity surface of the forging die.

[0025] Furthermore, the selection of welding materials is very important in the repair process. In the process of repairing the failed forging die, high-toughness welding materials need to be selected for repair to ensure the basic toughness requirements of the forging die and prevent cracking.

[0026] In one embodiment, step S20 specifically includes: S201, using a first arc additive manufacturing process to form a transition layer on the surface of the cavity located in the repair area; S202, using a second arc additive manufacturing process to form an intermediate layer on the transition layer; S203, using a third arc additive manufacturing process to form a strengthening layer on the middle layer; Specifically, the transition layer is located at the bottom of the repair area, and the temperature and stress it is subjected to are relatively low and gradually tend to equilibrium. The first arc additive manufacturing process can use RMD535 welding wire and RMD142 welding wire.

[0027] Specifically, the middle layer is located in the middle of the repair area and is subjected to certain high temperatures and high stresses, but the fluctuations are small. The corresponding material should have good impact toughness and high-temperature strength at the same time. The second arc additive manufacturing process can use RMD545 welding wire and RMD248 welding wire.

[0028] Specifically, the strengthening layer is located on the outer surface of the repair area, in direct contact with the workpiece, and is subjected to periodically changing high temperatures, high pressures, and severe friction loads. The thermal effects vary greatly, and the corresponding materials should have high thermal stability and high-temperature wear resistance. Since the cavity surface of the additive remanufacturing hot forging die will be chemically heat treated to improve the surface wear resistance and fatigue strength, when repairing the forging die, the third arc additive manufacturing process can select materials with good toughness such as RMD545 welding wire and RMD248 welding wire.

[0029] S30, performing a zoned chemical heat treatment on the cavity surface of the additive remanufactured hot forging die, wherein the zoned chemical heat treatment includes performing a selective surface nitriding or carburizing strengthening treatment on the strengthening area of ​​the additive remanufactured hot forging die.

[0030] Specifically, step S30 also includes: S301, deep cleaning of the cavity surface of the additive remanufacturing hot forging die; S302, evenly applying a solid nitriding agent and / or a solid carburizing agent to the surface of the cavity located in the strengthening area (typical failure position); S303, chemically heat treating the cavity surface of the additively manufactured hot forging die, and chemically cleaning it after natural cooling.

[0031] Furthermore, when selective surface nitriding strengthening treatment is performed on the strengthening area of ​​the additive remanufacturing hot forging die, the surface nitriding strengthening method adopts solid nitriding treatment, and the specific steps are as follows: (1) Surface cleaning: Before nitriding, the workpiece surface needs to be cleaned to remove oil, rust and other impurities. Common methods include: Mechanical cleaning: using sandpaper, brushes and other tools to remove surface dirt; Chemical cleaning: using detergents or pickling solutions to remove surface oxides and grease.

[0032] (2) Preparation of solid nitriding agent: According to weight percentage, 60% to 70% charcoal, 25% to 35% urea and 5% to 15% ammonium nitride are mixed evenly to obtain a solid nitriding agent.

[0033] (3) Partition nitriding: First, evenly apply the obtained solid nitriding agent to the strengthening area (the area that needs surface strengthening) of the additive remanufactured hot forging die. For the non-strengthening area (the area that does not need carburizing strengthening), the coating method is used for isolation. Mix 1 / 3 red lead and 2 / 3 copper chloride with rosin accounting for 10% to 15% of the total amount of the two materials, dissolve in alcohol to form a paste, and apply it to the area that does not need carburizing with a brush. The thickness is about 0.7 to 1.0 mm. After drying, apply another layer. After completion, place the additive remanufactured hot forging die in the nitriding furnace to ensure that there is enough space between the workpieces so that the nitriding medium can be evenly distributed. Heat the nitriding furnace to between 550℃ and 600℃. The temperature should be kept uniform during the heating process to avoid temperature fluctuations and keep warm for 4h to 6h.

[0034] (4) Cooling: After nitriding is completed, natural cooling is usually used to allow the workpiece to slowly cool down in the furnace to reduce internal stress and deformation.

[0035] (5) Post-treatment: After cooling, the workpiece needs to be cleaned to remove the nitriding medium and oxides remaining on the surface. Cleaning agents or pickling solutions can be used for treatment.

[0036] Furthermore, when selective surface carburizing and strengthening treatment is performed on the strengthening area of ​​the additive remanufacturing hot forging die, the surface carburizing and strengthening method adopts solid carbonization treatment, and the specific steps are as follows: (1) Surface cleaning: Before carburizing, the workpiece surface needs to be cleaned to remove oil, rust and other impurities. Common methods include: Mechanical cleaning: using tools such as sandpaper and brushes to remove surface dirt; Chemical cleaning: using detergents or pickling solutions to remove surface oxides and grease.

[0037] (2) Preparation of solid carburizing agent: The solid carburizing agent is prepared according to weight percentage, and the solid carburizing agent includes 10% to 20% barium carbonate, 5% to 10% calcium carbonate, and 70% to 85% charcoal.

[0038] (3) Partition carburizing: First, evenly apply the obtained solid carburizing agent to the reinforced area of ​​the additive manufacturing hot forging die. For the non-reinforced area, the coating method is used for isolation. Mix 1 / 3 red lead and 2 / 3 cupric chloride with rosin accounting for 10% to 15% of the total amount of the two materials, dissolve in alcohol to form a paste, and apply it to the part that does not need carburizing with a brush. The thickness is about 0.7mm to 1.0mm. After drying, apply another layer. After completion, put the additive manufacturing hot forging die into the carburizing furnace. Heat the carburizing furnace to 750℃ to 850℃, keep it warm for 2h to 3h, continue to heat it to 900℃ to 950℃, keep it warm for 6h to 7h, and then cool it down to 750℃ to 850℃ at a rate of 50 to 60℃ per hour, so that carbon atoms can fully penetrate into the forging die surface of the additive manufacturing hot forging die.

[0039] (3) Cooling: After carburizing is completed, natural cooling is used to allow the workpiece to slowly cool down in the furnace to reduce internal stress and deformation.

[0040] (4) Post-processing: After cooling, the workpiece needs to be cleaned to remove the carbon residue and dirt remaining on the surface. Cleaning agents or pickling liquids can be used for treatment.

[0041] In the process of repairing the failed forging die in step S20, the present invention specially selects a welding material with good toughness to repair the strengthening layer, so that the repaired additive remanufactured hot forging die has good toughness. Subsequently, in step S30, the surface chemical heat treatment of the additive remanufactured hot forging die is performed to achieve the surface strength and toughness zoning of the forging die.

[0042] S40, performing coloring flaw detection and polishing treatment on the cavity surface of the additively remanufactured hot forging die to obtain a strengthened hot forging die.

[0043] Specifically, step S40 also includes: After the surface strengthening treatment of the cavity of the additively manufactured hot forging die is performed, surface coloring flaw detection is performed to detect whether there are defects, and the cavity surface is polished to finally obtain the strengthened hot forging die.

[0044] The following is a detailed description of the partition toughening treatment method for additive remanufacturing hot forging dies provided by the present invention through specific embodiments.

[0045] Embodiment 1: See also Figures 2 to 3 , Figure 2 It is a schematic diagram of a specific process flow of strengthening and toughening treatment of the partitions of the additively remanufactured forging die in Examples 1 and 2 of the present invention; Figure 3The cavity structure and typical failure position of the additively remanufactured forging die in Examples 1 and 2 of the present invention are shown; wherein, the flash bridge portion (i.e., the strengthening area) of the additively remanufactured hot forging die needs to be selectively surface nitrided and strengthened. The surface nitriding and strengthening method adopts solid nitriding treatment, and the specific steps are as follows: Step 1: Use mechanical processing to remove the fatigue layer of the cavity of the failed forging die and the areas where wear, cracks and plastic deformation occur, and appropriately expand the cavity surface of the forging die, and smooth the area with larger curvature during the removal process.

[0046] Step 2: Use arc additive manufacturing technology to remanufacture the cavity surface of the forging die. When repairing the forging die, the temperature and stress of the transition layer are relatively low, so RMD535 welding wire is selected. The middle layer is subjected to a certain high temperature and high stress, but the fluctuation is small, so RMD545 welding wire is selected. The strengthening layer uses RMD248 welding wire with good toughness. Ensure the basic toughness requirements of the forging die and prevent cracking. In order to facilitate the subsequent partition heat treatment and strengthening of the surface of the forging die, improve the partition strength and hardness, and ensure wear resistance.

[0047] Step three: clean the surface of the repaired additive remanufacturing hot forging die to remove oil, rust and other impurities.

[0048] Step 4: According to weight percentage, 60% to 70% of charcoal, 25% to 35% of urea and 5% to 15% of ammonium nitride are mixed evenly to obtain a solid nitriding agent.

[0049] Step 5. Since the additive remanufacturing hot forging die needs to be strengthened by chemical heat treatment in different areas, it is necessary to isolate the parts of the additive remanufacturing hot forging die that do not need to be strengthened by coating. First, evenly apply the obtained solid nitriding agent to the flash bridge part of the additive remanufacturing hot forging die. For the parts that do not need nitriding strengthening (except the flash bridge part), the coating method is used for isolation. The isolation coating is made by mixing 30% red lead, 60% copper chloride and 10% rosin by mass percentage, dissolving it in alcohol, and applying it to the parts that do not need carburizing with a brush. The thickness is about 1.0 mm, and then another layer is applied after drying. After the coating isolation is completed, the forging die is placed in the nitriding furnace to ensure that there is enough space between the workpieces so that the nitriding medium can be evenly distributed. Heat the nitriding furnace to between 550℃ and 600℃. The temperature should be kept uniform during the heating process to avoid temperature fluctuations and keep warm for 4h to 6h.

[0050] Step 6: After the nitriding treatment is completed, the workpiece is cooled slowly in the furnace by natural cooling to reduce internal stress and deformation.

[0051] Step seven, use a cleaning agent to clean the cooled additive remanufacturing hot forging die to remove the nitriding medium and oxides remaining on the surface.

[0052] Step 8: Perform surface coloring flaw detection on the surface of the additive remanufactured hot forging die to detect whether there are defects. Polish the surface of the additive remanufactured hot forging die to obtain the additive remanufactured hot forging die after surface heat treatment and strengthening.

[0053] Embodiment 2: In Example 2 of the present invention, it is necessary to perform selective surface carburizing strengthening treatment on the inner fillet and bottom part (i.e., strengthening area) of the cavity of the additive remanufacturing hot forging die. The surface carburizing strengthening method adopts solid carbonization treatment, and the specific steps are as follows: Step 1: Use mechanical processing to remove the fatigue layer of the cavity of the failed forging die and the areas where wear, cracks and plastic deformation occur, and appropriately expand the cavity surface of the forging die, and smooth the area with larger curvature during the removal process.

[0054] Step 2: Use arc additive manufacturing technology to remanufacture the cavity surface of the forging die. When repairing the forging die, the temperature and stress of the transition layer are relatively low, so RMD535 welding wire is selected. The middle layer is subjected to a certain high temperature and high stress, but the fluctuation is small, so RMD545 welding wire is selected. The strengthening layer uses RMD248 welding wire with good toughness. Ensure the basic toughness requirements of the forging die and prevent cracking. In order to facilitate the subsequent partition heat treatment and strengthening of the surface of the forging die, improve the partition strength and hardness, and ensure wear resistance.

[0055] Step three: clean the surface of the repaired additive remanufacturing hot forging die to remove oil, rust and other impurities.

[0056] Step 4: Prepare a solid carburizing agent according to weight percentage, wherein the solid carburizing agent includes 10% to 20% barium carbonate, 5% to 10% calcium carbonate, and 70% to 85% charcoal.

[0057] Step 5: Since the additive remanufacturing hot forging die needs to be strengthened by chemical heat treatment in different areas, it is necessary to isolate the parts of the additive remanufacturing hot forging die that do not need to be strengthened by coating. First, evenly apply the obtained solid carburizing agent to the inner fillet and bottom of the cavity of the additive remanufacturing hot forging die. For the parts that do not need carburizing strengthening, the coating method is used for isolation. The isolation coating is made by mixing 30% red lead, 60% copper chloride and 10% rosin by mass, and dissolving it in alcohol. Apply it to the parts that do not need carburizing with a brush, with a thickness of about 1.0 mm, and apply another layer after drying. After the coating isolation is completed, the additive remanufacturing hot forging die is placed in the carburizing furnace, and the carburizing furnace is heated to 750℃~850℃. After keeping it warm for 2h~3h, it is continued to heat up to 900℃~950℃, keep it warm for 6h~7h, and then cool down to 750℃~850℃ at a rate of 50℃~60℃ per hour, so that the carbon atoms can fully penetrate into the surface of the forging die.

[0058] Step 6: After the carburizing treatment is completed, the workpiece is cooled slowly in the furnace by natural cooling to reduce internal stress and deformation.

[0059] Step seven, use a cleaning agent to clean the cooled additive remanufacturing hot forging die to remove the nitriding medium and oxides remaining on the surface.

[0060] Step 8: Perform surface coloring flaw detection on the surface of the additive remanufactured hot forging die to detect whether there are defects. Polish the surface of the additive remanufactured hot forging die to obtain the additive remanufactured hot forging die after surface heat treatment and strengthening.

[0061] The present invention, based on the use of additive remanufacturing technology to repair hot forging dies, performs toughening treatment on the surface of the forging dies, and develops hot forging dies with high wear resistance, high fatigue strength and toughness. Among them, chemical heat treatment can change the chemical composition and organizational structure of the surface layer of the hot forging die parts, improve the surface mechanical properties and physical and chemical properties, thereby greatly increasing the service life of the hot forging dies. Therefore, on the basis of hot forging dies based on additive remanufacturing, high-toughness welding materials are first used to repair the forging dies to ensure the basic toughness requirements of the hot forging dies and prevent cracking. Then, on the basis of ensuring toughness, different chemical heat treatment surface strengthening is performed on the strengthening area (typical failure position) of the hot forging die to improve the partition strength and hardness, ensure wear resistance, and specifically strengthen the surface of the hot forging die to increase the service life of the hot forging die.

[0062] Compared with the prior art, the present invention has the following advantages: First, the present invention performs surface chemical heat treatment on the hot forging die based on the additively remanufactured hot forging die cavity, which can further improve the wear resistance and fatigue strength of the surface of the additively remanufactured hot forging die.

[0063] Second, the present invention combines the additive remanufacturing hot forging die with the die surface strengthening technology, which not only effectively reduces the production cost and improves the material utilization rate, but also further improves the service life of the additive remanufacturing hot forging die.

[0064] Third, the present invention aims at the process limitations of hot forging dies repaired by additive remanufacturing technology, improves the comprehensive performance of hot forging dies, and performs targeted zoned chemical heat treatment strengthening on typical failure parts of hot forging dies. It can not only overcome the defects of hot forging dies repaired by additive remanufacturing, but also further improve the service life of the repaired hot forging dies.

[0065] The specific implementation of the present invention described above does not constitute a limitation on the protection scope of the present invention. Any other corresponding changes and modifications made based on the technical concept of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A method for zone toughening treatment of hot forging dies for additive remanufacturing, characterized in that: include: S10, deep cleaning of the cavity of the failed forging die; S20, performing a remanufacturing process on the repaired area of ​​the forging die to obtain an additively remanufactured hot forging die; S30, performing a zoned chemical heat treatment on the cavity surface of the additively remanufactured hot forging die, wherein the zoned chemical heat treatment includes performing a selective surface nitriding or carburizing strengthening treatment on the strengthening area of ​​the additively remanufactured hot forging die; S40, performing coloring, flaw detection and polishing treatment on the cavity surface of the additively remanufactured hot forging die to obtain a strengthened hot forging die.

2. The method for zone toughening treatment of hot forging dies for additive remanufacturing according to claim 1 is characterized in that: The step S20 specifically includes: S201, using a first arc additive manufacturing process to form a transition layer on the surface of the cavity located in the repair area; S202, using a second arc additive manufacturing process to form an intermediate layer on the transition layer; S203, selecting a third arc additive manufacturing process to form a strengthening layer on the intermediate layer; Among them, the first arc additive manufacturing process uses RMD535 welding wire and RMD142 welding wire, the second arc additive manufacturing process uses RMD545 welding wire and RMD248 welding wire, and the third arc additive manufacturing process uses RMD545 welding wire and RMD248 welding wire.

3. The method for zone toughening treatment of hot forging dies for additive remanufacturing according to claim 1 is characterized in that: The step S30 specifically includes: S301, deeply cleaning the cavity surface of the additively remanufactured hot forging die; S302, evenly applying a solid nitriding agent and / or a solid carburizing agent to the surface of the cavity located in the strengthening area; S303, performing chemical heat treatment on the cavity surface of the additively remanufactured hot forging die, and performing chemical cleaning treatment after natural cooling.

4. The method for zone toughening treatment of hot forging dies for additive remanufacturing according to claim 3 is characterized in that: In the step S302: the solid nitriding agent comprises the following components in weight percentage: 60% to 70% charcoal, 25% to 35% urea and 5% to 15% ammonium nitride.

5. The method for zone toughening treatment of hot forging dies for additive remanufacturing according to claim 4 is characterized in that: In the step S303: when the strengthening area of ​​the additively remanufactured hot forging die is subjected to selective surface nitriding strengthening treatment, the cavity surface of the additively remanufactured hot forging die is heated to 550° C. to 600° C. and then kept warm for 4 h to 6 h.

6. The method for zone toughening treatment of hot forging dies for additive remanufacturing according to claim 3 is characterized in that: In the step S302: the solid carburizing agent comprises the following components in weight percentage: 10% to 20% barium carbonate, 5% to 10% calcium carbonate and 70% to 85% charcoal.

7. The method for zone toughening treatment of hot forging dies for additive remanufacturing according to claim 6 is characterized in that: In the step S303: when the strengthening area of ​​the additively manufactured hot forging die is subjected to selective surface carburizing strengthening treatment, the cavity surface of the additively manufactured hot forging die is heated to 750°C to 850°C and then kept warm for 2h to 3h, then continued to be heated to 900°C to 950°C and then kept warm for 2h to 3h, and finally cooled to 750 to 850°C at a rate of 50 to 60°C / h.

8. The method for zone toughening treatment of hot forging dies for additive remanufacturing according to claim 3 is characterized in that: The step S302 further includes: using a coating to isolate the non-reinforced area of ​​the additively remanufactured hot forging die.

9. The method for zone toughening treatment of hot forging dies for additive remanufacturing according to claim 8, characterized in that: The step of using a coating to isolate the non-reinforced area of ​​the additively remanufactured hot forging die specifically comprises: The lead-copper material and the rosin mixed material are dissolved in alcohol to form a paste, and then applied to the non-reinforced area of ​​the additively manufactured hot forging die with a brush to obtain an insulating coating.

10. The method for zone toughening treatment of hot forging dies for additive remanufacturing according to claim 9, characterized in that: The lead-copper material includes red lead and cupric chloride, and the mass ratio of red lead to cupric chloride is 1:2; the mass of the rosin is 10% to 15% of the mass of the lead-copper material; and the thickness of the insulating coating is 1.4 mm to 2.0 mm.

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