Hot forming tools for press hardening

Abstract

The present invention relates to a hot forming tool for press hardening, the tool comprising a body and a surface layer partially or entirely laser-metal deposited, the body containing 0.25-0.45 C, 0.10-1.50 Si, 0.2-1.0 Mn, 2-6 Cr, 1-3 Mo, 0.4-1.0 V, 0.001-0.06 Al, and ≤0.12 N, and the laser-metal deposited surface layer containing 0.27-0.40 C, 0.10-0.35 Si, 0.2-0.8 Mn, 4.0-6.0 Cr, 2.0-3.0 Mo, 0.4-1.0 V, 0.001-0.06 Al, and 0.003-0.12 N. The laser-metal deposited surface layer has a hardness of 53-59 HRC.

Description

Technical Field

[0001] The present invention relates to a hot forming tool for press hardening.

Background Art

[0002] Press hardening or hot stamping is a hot forming method in which a blank is hot formed and quenched at the same time in a water-cooled mold to achieve high strength. By using press hardening, lightweight parts with very high mechanical properties and complex shapes can be manufactured. Press hardening of advanced high-strength steel (AHSS) and ultra-high-strength steel (UHSS) with a tensile strength of up to 2000 MPa is used in the manufacture of high-strength body parts to reduce the weight of automobile bodies, and at the same time, collision safety can be maintained or improved.

[0003] However, when press hardening AHSS or UHSS sheet materials, significant abrasive wear and adhesive wear may occur on the press forming tool. In the past, many attempts have been made to reduce wear by using wear-resistant tool materials and applying surface treatments such as laser hardening, nitriding treatment, and various types of PVD coatings. Furthermore, since hot forming tools are subjected to severe thermal cycles, they may cause thermal fatigue.

Summary of the Invention

[0004] The object of the present invention is to improve the performance of hot forming tools and thereby extend tool life. This object is achieved to a considerable extent by providing a surface layer made of a specific vanadium alloy matrix tool steel having high toughness and hardness on a body made of hot working tool steel by laser metal deposition (LMD). The present invention is defined in the claims.

Modes for Carrying Out the Invention

[0005] Detailed Description Vanadium alloy matrix tool steel has been on the market for decades and has attracted considerable attention due to its high wear resistance, excellent dimensional stability, and superior toughness.

[0006] The hot forming tool of the present invention consists of a body and a surface layer, and the body has a composition within the following range (wt%). C 0.25 - 0.45 Si 0.10 - 1.50 Mn 0.2 - 1.0 Cr 2 - 6 Mo 1 - 3 V 0.4 - 1.0 Al 0.001 - 0.06 N ≤ 0.12 The material optionally contains one or more of Ni, Cu, Co, W, and Nb in amounts up to 1% each, and optionally contains one or more of Zr, Ta, Ti, and B in amounts up to 0.1%, preferably up to 0.05%, each, with the remainder being Fe, excluding impurities.

[0007] The body of the hot forming tool can be manufactured by any technique known in the art. Then, conventional quenching and tempering are performed to give the body the desired hardness. The hardness can be in the range of 40-55 HRC.

[0008] Subsequently, a surface layer is formed on the main body, either partially or entirely, using laser metal deposition (LMD). At this time, the laser beam is focused onto the surface of the main body, where a molten pool is formed. A pre-alloy metal powder with the desired composition is simultaneously supplied to the melt pool under a protective atmosphere, thereby forming a strong metallurgical bond between the additive material and the main body. Rapid solidification increases the hardness of the deposited material, while the mechanical properties of the main body are largely unaffected. Laser metal deposition (LMD) can be carried out by ultra-high-speed laser cladding (EHLC), also known as ultra-high-speed laser cladding (UHSLC), with a coating thickness of 10 to 500 μm, preferably 10 to 250 μm. The result is a low dilution ratio, a very fine and dense microstructure, and requires only grinding and / or polishing as post-treatment.

[0009] The vanadium alloy matrix tool steel used in laser metal deposition (LMD) in this invention has the following composition in weight percent (wt%). C 0.27 - 0.40 Si 0.10 - 0.35 Mn 0.2 - 0.8 Cr 4.0 - 6.0 Mo 2.0 - 3.0 V 0.4 - 1.0 Al 0.001 - 0.06 N 0.003 - 0.12 Optionally, it contains up to 1% each of one or more of Ni, Cu, Co, W, and Nb, and optionally, up to 0.1% each of one or more of Zr, Ta, Ti, and B, with the remainder being Fe, excluding impurities.

[0010] According to one embodiment, the composition of the main body and the surface layer can have the same nominal composition within the above range. Preferably, the difference between the amounts of C, Cr, Mo, and V in the laser-metal-deposited surface layer and the main body is 15% or less.

[0011] According to another embodiment, the body is a low-chromium steel containing only 2.3 to 2.9% Cr to obtain a thermal conductivity of more than 30 W / mK at 600°C. The preferred composition also satisfies at least one of the following limitations (wt%). C 0.34 - 0.42 Si 0.10 - 0.50 Mn 0.5 - 1.0 Cr 2.3 - 2.9 Mo 2.0 - 2.5 V 0.7 - 1.0 Al 0.001 - 0.06 N ≤ 0.02 B 0.001 - 0.005 Optionally, it contains up to 1% each of one or more of Ni, Cu, Co, W, and Nb, and optionally, up to 0.05% each of one or more of Zr, Ta, and Ti, with the remainder being Fe, excluding impurities.

[0012] The particle size distribution (PSD) of conventional LMD supply materials is such that at least 95 vol% of the total particles have a particle size of 20 to 150 μm, and preferably 80 vol% or more of the total particles have a particle size of 50 to 150 μm. In a preferred embodiment, the pre-alloy powder satisfies at least one of the following requirements. D10 ≤ 50 μm D50 70±15μm D90 ≤ 130 μm However, the particle size distribution (PSD) of the (EHLC) or (UHSLC) feedstock may be much finer. The particle size distribution was analyzed using a Camsizer XT instrument.

[0013] The deposition process is repeated layer by layer until the desired thickness is reached. The hot-formed tool may then be tempered twice at 540°C for 2 hours each time to reduce the amount of retained austenite to less than 2 vol%, which is below the X-ray detection limit.

[0014] The importance of individual elements, their interactions, and the limits of the chemical composition of the claimed alloys will be briefly described below. All percentages of the chemical composition of the steel are given in weight % (wt%) throughout this specification. The amount of the hard phase is given in volume % (vol%). The upper and lower limits of the individual elements can be freely combined within the ranges described in the claims.

[0015] Composition of the LMD powder The LMD powder used satisfies the following conditions.

[0016] Carbon (0.27 - 0.40%) Carbon is present with a minimum content of 0.27%, preferably at least 0.28, 0.29, 0.30, 0.31, 0.32, 0.33 or 0.34%. The upper limit of carbon is 0.40% and can be set at 0.39, 0.38, 0.37, 0.36 or 0.35%. The preferred ranges are 0.30 - 0.38% and 0.33 - 0.37%. In any case, the amount of carbon should be controlled so that the amounts of M 23 The amounts of primary carbides of the C6 type, M7C3 type and M6C type are restricted, and preferably the steel does not contain such primary carbides.

[0017] Silicon (0.10 - 0.35%) Silicon is used for deoxidation. Si exists in a dissolved form in the steel. Si is a strong ferrite-forming element and increases the risk of forming undesirable carbides in order to increase carbon activity. Such carbides have an adverse effect on impact strength. Furthermore, silicon is prone to interfacial segregation, and as a result, toughness and thermal fatigue resistance may decrease. Therefore, Si is limited to 0.35%. The upper limit can be 0.34, 0.32, 0.30, 0.28, 0.26, 0.24 and 0.22%. The lower limit can be 0.12, 0.14, 0.16, 0.18 and 0.20%. The preferred ranges are 0.10 - 0.25% and 0.15 - 0.24%.

[0018] Manganese (0.2 - 0.8%) Manganese contributes to improving the hardenability of steel and, together with sulfur, forms manganese sulfides, which contribute to improved machinability. Therefore, manganese should be present in a minimum of 0.2%, preferably at least 0.3, 0.35, 0.4, 0.45, or 0.5%. When the sulfur content is high, manganese prevents red brittleness of steel. The steel should contain a maximum of 0.8%, preferably a maximum of 0.7, 0.6, 0.55, or 0.5%.

[0019] Chromium (4.0-6.0%) Chromium should be included at least 4.0% to obtain good hardenability in large cross-sections during heat treatment. Too high a chromium content can lead to the formation of high-temperature ferrite, reducing hot workability. The lower limit can be 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8, or 4.9%. The upper limit can be 6.0, 5.8, 5.6, 5.5, 5.4, 5.2, or 5.1%.

[0020] Molybdenum (2.0-3.0%) Mo is known to have a very favorable effect on hardenability. Molybdenum is essential for obtaining a good secondary hardening reaction. The minimum content is 2.0%, and can be set to 2.1%, 2.2%, 2.25%, or 2.3%. Molybdenum is both a strong carbide-forming element and a strong ferrite-forming element. Therefore, the maximum molybdenum content is 3.0%. Preferably, Mo is limited to 2.9%, 2.8%, 2.7%, 2.6%, 2.5%, 2.4%, or 2.35%.

[0021] Vanadium (0.4-1.0%) Vanadium forms V(N,C) type primary precipitate carbides and carbonitrides uniformly dispersed in the steel matrix. This hard phase is also denoted as MX, where M is mainly V, but Cr and Mo may also be present, and X is one or more of C, N, and B. Therefore, vanadium is present in an amount of 0.4–1.0%. The upper limit can be set to 0.9, 0.8, 0.7, 0.6, 0.58, 0.56, or 0.55%. The lower limit can be 0.42, 0.44, 0.46, 0.48, 0.50, or 0.52%. The preferred range is 0.4–0.6%.

[0022] Aluminum (0.001-0.06%) Aluminum is used in combination with Si and Mn for deoxidation. To ensure good deoxidation, the lower limit is set to 0.001, 0.003, 0.005, or 0.007%. The upper limit is restricted to 0.06% to avoid precipitation of undesirable phases such as AlN. The upper limit can also be set to 0.05, 0.04, 0.03, 0.02, or 0.015%.

[0023] Nitrogen (0.003~0.12%) Nitrogen content is limited to 0.003–0.08% to obtain the desired type and amount of hard phase, particularly V(C,N). When the balance between nitrogen and vanadium content is appropriate, vanadium-rich carbonitrides V(C,N) are formed. These partially dissolve in the austenitization process and then precipitate as nanometer-sized particles in the tempering process. The thermal stability of vanadium carbonitrides is considered to be superior to that of vanadium carbides, improving the tempering resistance of tool steels and enhancing resistance to grain growth at high austenitization temperatures. The lower limit can be 0.003, 0.004, 0.007, 0.011, 0.012, 0.013, 0.014, 0.015, 0.016, or 0.017%. The upper limit can be 0.12, 0.10, 0.08, 0.07, 0.06, 0.05, 0.04, or 0.03%.

[0024] Nickel (≤1%) Nickel may be present in steel up to a maximum of 1%. Nickel imparts good hardenability and toughness to steel. However, due to its cost, the nickel content in steel should be limited. Therefore, the upper limit may be set at 0.8%, 0.5%, or 0.3%. However, nickel is not usually added intentionally.

[0025] Copper (≦1.0%) Cu is an optional element that contributes to improving the hardness and corrosion resistance of steel. When used, the preferred range is 0.02 to 1%. However, it is impossible to extract copper from steel once it has been added. Therefore, handling the scrap becomes very difficult. For this reason, copper is not usually added intentionally.

[0026] Cobalt (≤1%) Co is an optional element. Because Co increases the solid-state temperature, it provides an opportunity to increase the hardening temperature, which is 15-30°C higher than without Co. Therefore, more carbides can be dissolved during austenitization, improving hardenability. Co also increases the Ms temperature. However, large amounts of Co can reduce toughness and wear resistance. The maximum amount is 1. However, due to practical reasons such as scrap processing, intentional addition of Co is not performed. Therefore, the upper limit of the impurity content can be set to 0.3%, 0.2%, or 0.1%.

[0027] Tungsten (≤1%) In principle, due to chemical similarity, molybdenum can be replaced with twice the amount of tungsten. However, tungsten is expensive and complicates the handling of metal scrap. Therefore, the maximum amount is limited to 1%, preferably 0.5%, more preferably 0.3%, and most preferably no intentional addition is made.

[0028] Niobium (≤1%) Niobium is similar to vanadium in that it forms M(N,C) type carbonitrides, and in principle can be used to replace part of vanadium, but this requires twice the amount of niobium. However, Nb makes the M(N,C) shape more angular. The maximum amount is 1%, preferably 0.1%, more preferably 0.05%, and most preferably no intentional addition is made.

[0029] Ti, Zr, and Ta These elements are carbide-forming elements and may be present in the alloy in the ranges defined in the claims to alter the composition of the hard phase. However, these elements are not usually added. Therefore, the maximum amount is 0.1%, preferably 0.05%, and most preferably no intentional addition is made.

[0030] Boron (≤0.1%) B can be used to further increase the hardness of the steel. Its amount is limited to 0.1%, preferably 0.05%, more preferably 0.01%, even more preferably 0.005%, and most preferably ≤0.0035%. When used, the preferred range for the addition of B is 0.001 to 0.004%.

[0031] Impurity elements P, S, and O are the main impurities that adversely affect the mechanical properties of steel. Therefore, P may be limited to 0.03%, preferably 0.01%. S may be limited to 0.03%, 0.01%, 0.003%, 0.001%, 0.0008%, 0.0005%, or 0.0001%. O may be limited to 0.015%, 0.012%, 0.010%, or 0.008%.

[0032] Main body composition The main body is made of hot work tool steel, and the influence of alloying elements is basically the same as in the case of LMD powder. However, a wider limit may be acceptable for the main body.

[0033] Carbon (0.25-0.45%) Carbon should be present in a minimum content of 0.25%, preferably at least 0.26, 0.27, 0.28, 0.29, 0.30, 0.31, 0.32, 0.33, or 0.34%. The upper limit for carbon is 0.45%, which can be set to 0.44, 0.43, 0.42, 0.41, 0.40, 0.39, 0.38, 0.37, 0.36, or 0.35%. Preferred ranges are 0.30-0.38% and 0.33-0.37%. In any case, the amount of carbon in the steel is M 23 The amount of primary carbides of type C6, M7C3, and M6C should be controlled to be limited, and preferably, the steel does not contain such primary carbides.

[0034] Silicon (0.10-1.5%) Silicon contributes to deoxidation and solid solution strengthening. Si exists in the steel in a dissolved form. Therefore, Si is limited to 1.5%. The upper limits can be 1.4%, 1.3%, 1.1%, 1.0%, 0.8%, 0.50%, 0.28%, 0.26%, 0.25%, 0.24%, and 0.22%.

[0035] Manganese (0.2-1.0%) Manganese contributes to improving the hardenability of steel and, together with sulfur, forms manganese sulfides, which contribute to improved machinability. Therefore, manganese should be present in a minimum of 0.2%, preferably 0.3, 0.35, 0.4, 0.45, or 0.5%. When the sulfur content is high, manganese prevents red brittleness of steel. The steel should contain a maximum of 1.0%, preferably a maximum of 0.9, 0.8, 0.7, 0.6, 0.55, or 0.5%.

[0036] Chromium (2-6%) Chromium should be included at least 2% to provide sufficient hardenability and high thermal conductivity. Too high a chromium content can lead to the formation of high-temperature ferrite, reducing hot workability. The lower limit can be 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4.0, 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8, or 4.9%. The upper limit can be 6.0, 5.8, 5.6, 5.5, 5.4, 5.2, or 5.1%. If the thermal conductivity is high, the upper limit can be further reduced to 3%, preferably 2.9%.

[0037] Molybdenum (1-3%) Mo is known to have a very favorable effect on hardenability. Molybdenum is essential for obtaining a good secondary hardening reaction. The minimum content is 1%, and can be set to 1.5, 2.0, 2.1, 2.2, 2.25, or 2.3%. Molybdenum is both a strong carbide-forming element and a strong ferrite-forming element. Therefore, the maximum molybdenum content is 3.0%. Preferably, Mo is limited to 2.9, 2.8, 2.7, 2.6, 2.5, 2.4, or 2.35%.

[0038] Vanadium (0.4-1.0%) Vanadium forms V(N,C) type primary precipitate carbides and carbonitrides uniformly dispersed in the steel matrix. The upper limit can be set to 0.9, 0.8, 0.7, 0.6, 0.58, 0.56, or 0.55%. The lower limit can be set to 0.42, 0.44, 0.46, 0.48, 0.50, or 0.52%.

[0039] Aluminum (0.001-0.06%) Aluminum is used in combination with Si and Mn for deoxidation. To ensure good deoxidation, the lower limit is set to 0.001, 0.003, 0.005, or 0.007%. The upper limit is restricted to 0.06% to avoid precipitation of undesirable phases such as AlN. The upper limit may also be 0.05, 0.04, 0.03, 0.02, or 0.015%.

[0040] Nitrogen (≤0.12%) To reduce the amount of hard phase in the substrate, particularly V(C,N), nitrogen is limited to 0.12%. The upper limit can be set to 0.12%, 0.10%, 0.07%, 0.05%, 0.04%, 0.03%, 0.02%, 0.015%, or 0.010%.

[0041] Nickel (≤1) Nickel may be present in steel up to a maximum of 1%. Nickel imparts good hardenability and toughness to steel. However, due to its cost, the nickel content in steel should be limited. Therefore, the upper limit may be set at 0.8%, 0.5%, or 0.3%. However, nickel is not usually added intentionally.

[0042] Copper (≦1.0%) Cu is an optional element that contributes to improving the hardness and corrosion resistance of steel. When used, the preferred range is 0.02 to 1%. However, it is impossible to extract copper from steel once it has been added. Therefore, handling the scrap becomes very difficult. For this reason, copper is not usually added intentionally. The upper limit of the impurity content can be set to 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, 0.2, or 0.1%.

[0043] Cobalt (≤1%) Co is an optional element. Because Co increases the solid-state temperature, it provides an opportunity to increase the hardening temperature, which is 15-30°C higher than without Co. Therefore, more carbides can be dissolved during austenitization, improving hardenability. Co also increases the Ms temperature. However, large amounts of Co can reduce toughness and wear resistance. The maximum amount is 1. However, intentional addition of Co is not performed for practical reasons such as scrap processing. The upper limit for impurity content can be set at 0.3%, 0.2%, or 0.1%.

[0044] Tungsten (≤1%) In principle, due to chemical similarity, molybdenum can be replaced with twice the amount of tungsten. However, tungsten is expensive and complicates the handling of metal scrap. Therefore, the maximum amount is limited to 1%, preferably 0.5%, more preferably 0.3%, and most preferably no intentional addition is made.

[0045] Niobium (≤1%) Niobium is similar to vanadium in that it forms M(N,C) type carbonitrides, and in principle can be used to replace part of vanadium, but this requires twice the amount of niobium. However, Nb makes the M(N,C) shape more angular. The maximum amount is 1%, preferably 0.1%, more preferably 0.05%, and most preferably no intentional addition is made.

[0046] Ti, Zr, and Ta These elements are carbide-forming elements and may be present in the alloy within the scope of this application to alter the composition of the hard phase. However, these elements are not usually added. Therefore, the maximum amount is 0.1%, preferably 0.05%, and most preferably no intentional addition is performed.

[0047] Boron (≤0.1%) B can be used to further increase the hardness of the steel. Its amount is limited to 0.1%, preferably 0.05%, more preferably 0.01%, even more preferably 0.005%, and most preferably ≤0.0035%. When used, the preferred range for the addition of B is 0.001 to 0.004%.

[0048] Impurity elements P, S, and O are the main impurities that adversely affect the mechanical properties of steel. Therefore, P may be limited to 0.03%, preferably 0.01%. S may be limited to 0.003, 0.001, 0.0008, 0.0005, or 0.0001%. O may be limited to 0.015, 0.012, 0.010, or 0.008%. [Examples]

[0049] Example 1 A hot forming tool for a press-hardened tool according to claim 1 was manufactured according to the method described in claim 7. The main body was heat-treated to a hardness of 52 HRC and had the following composition. C 0.36 Si 0.19 Mn 0.46 Cr 5.14 Mo 2.27 V 0.54 Al 0.029 N 0.006

[0050] The average particle size of the pre-alloy powder used was 67 μm, and the tap density was 4.2 g / cm³. 3 The LMD powder had the following composition: C 0.35 Si 0.18 Mn 0.46 Cr 5.09 Mo 2.26 V 0.53 Al 0.008 N 0.01 After preheating the main body to 400°C, pre-alloy powder was deposited to a thickness of 2.4 mm using a conventional LMD process. The thus coated body was tempered twice at a temperature of 540°C (2 × 2 h). Subsequently, the LMD coated surface was milled to a final thickness of 1 mm. The hardness of the machined surface layer was 57 HRC. The amount of retained austenite in the surface layer was found to be below the detection limit of X-ray diffraction. X-ray diffraction measurements were performed according to the standard test method specified in ASTM E975-13. The combination of a body with a hardness of 52 HRC and an outermost surface layer with a hardness of 57 HRC resulted in a hot forming tool with a unique combination of toughness and hardness, making it highly suitable for press hardening of high-strength steels such as AHSS and UHSS.

[0051] Example 2 A hot forming tool for press hardening according to claim 1 was manufactured according to the method described in claim 5. The main body had the following composition (by weight %). C 0.38 Si 0.28 Mn 0.75 Cr 2.6 Mo 2.25 V 0.84 Al 0.021 B 0.0025 N 0.005 The main body was austenitized in a vacuum furnace at 1020°C for 30 minutes and then rapidly cooled with high-pressure gas, resulting in a hardness of 51 HRC. Subsequently, the steel was tempered twice at 645°C, resulting in a hardness of 45 HRC. The thermal conductivity of the steel in the main body was measured at 400°C and 600°C, and was 33 W / mK at both temperatures.

[0052] The average particle size of the LMD pre-alloy powder used was 67 μm, and the tap density was 4.2 g / cm³. 3 The LMD powder had the following composition: C 0.35 Si 0.18 Mn 0.46 Cr 5.09 Mo 2.26 V 0.53 Al 0.008 N 0.01 After preheating the main body to 400°C, pre-alloy powder was deposited to a thickness of 2.4 mm using a conventional LMD process. The thus coated body was tempered twice at a temperature of 540°C (2 × 2 h). Subsequently, the LMD coated surface was milled to a final thickness of 1 mm. The hardness of the machined surface layer was 57 HRC. The amount of retained austenite in the surface layer was found to be below the detection limit of X-ray diffraction. X-ray diffraction measurements were performed according to the standard test method specified in ASTM E975-13. The combination of a body with a hardness of 45 HRC and high thermal conductivity at the operating temperature, and an outermost surface layer with a hardness of 57 HRC, results in a hot forming tool with a unique combination of toughness and hardness, making it highly suitable for press hardening of high-strength steels such as AHSS and UHSS.

[0053] industrial applicability The hot forming tool for press hardening of the present invention is particularly useful for press forming of high-strength steel.

Claims

1. A hot forming tool for press hardening, characterized in that the tool comprises a body and a surface layer partially or entirely laser-metal-deposited, wherein the body is made of a tool steel alloy having the following composition in weight percent. C 0.25 - 0.45 Si 0.10 - 1.50 Mn 0.2 - 1.0 Cr 2 - 6 Mo 1 - 3 V 0.4 - 1.0 Al 0.001 - 0.06 N ≤ 0.12 Optionally, it contains one or more of Ni, Cu, Co, W, and Nb in amounts up to 1% each, and optionally, one or more of Zr, Ta, Ti, and B in amounts up to 0.1% each, with the remainder being Fe, excluding impurities. Here, the laser-deposited surface layer has the following composition in weight percent: C 0.27 - 0.40 Si 0.10 - 0.35 Mn 0.2 - 0.8 Cr 4.0 - 6.0 Mo 2.0 - 3.0 V 0.4 - 1.0 Al 0.001 - 0.06 N 0.003 - 0.12 It optionally contains one or more of Ni, Cu, Co, W, and Nb in amounts up to 1% each, and optionally contains one or more of Zr, Ta, Ti, and B in amounts up to 0.1% each, with the remainder being Fe, excluding impurities, and The laser-deposited surface layer has a hardness of 53 to 59 HRC.

2. The hot forming tool for press hardening according to claim 1, wherein the surface layer has a thickness of 0.3 to 29 mm, preferably 1 to 3 mm.

3. The hot forming tool for press hardening according to claim 1 or 2, wherein the laser-metal-deposited surface layer contains 0.8% by volume or less of carbides larger than 1 μm, preferably 0.5% by volume or less of carbides larger than 0.8 μm.

4. A hot forming tool for press hardening according to any of the claims, wherein the composition of the main body satisfies at least one of the following requirements. C 0.27 - 0.40 Si 0.10 - 0.35 Mn 0.2 - 0.8 Cr 4.0 - 6.0 Ni ≤ 0.8 Mo 2.0 - 3.0 V 0.4 - 0.6 Al 0.001 - 0.06 N 0.003 - 0.12, and / or the body has a hardness of 44 to 54 HRC, preferably 51 to 53 HRC.

5. A hot forming tool for press hardening according to any one of claims 1 to 3, wherein the composition of the main body satisfies at least one of the following requirements. C 0.34 - 0.42 Si 0.10 - 0.50 Mn 0.5 - 1.0 Cr 2.3 - 2.9 Mo2.0-2.5 V 0.7 - 1.0 Al 0.001 - 0.06 N ≤ 0.02 B 0.001 - 0.005

6. The hot forming tool for press hardening according to claim 5, wherein the main body has a hardness of 42 to 47 HRC and / or a thermal conductivity of at least 32 W / mK at 600°C.

7. A method for manufacturing a hot forming tool for press hardening according to claim 1, comprising the following steps: A step of providing a body having the composition specified in claim 1, 4, or 5, A step of providing a pre-alloy powder having a particle size of 20 to 150 μm and the following composition in weight percent, C 0.27 - 0.40 Si 0.10 - 0.35 Mn 0.2 - 0.8 Cr 4.0 - 6.0 Mo 2.0 - 3.0 V 0.4 - 1.0 Al 0.001 - 0.06 N 0.003 - 0.12 It optionally contains one or more of Ni, Cu, Co, W, and Nb in amounts up to 1% each, and optionally contains one or more of Zr, Ta, Ti, and B in amounts up to 0.1% each, with the remainder being Fe, excluding impurities. A step of applying the pre-alloy powder to the surface of the main body to a predetermined layer thickness by laser metal deposition, The hot-formed tool thus obtained is tempered twice at a temperature of 500-650°C for at least one hour in order to reduce or remove retained austenite. A process of machining the tempered surface to its final thickness to obtain a hot-formed tool with a surface layer hardness of 53 to 59 HRC.

8. A method for manufacturing a hot forming tool for press hardening according to claim 7, the method further comprising preheating the body to a temperature of 300°C to 500°C before laser metal deposition.

9. A method for manufacturing a hot forming tool for press curing according to claim 7 or 8, wherein the prealloy powder satisfies at least one of the following requirements. D10 ≤ 50 μm D50 70±15μm D90 ≤ 130 μm

10. A method for manufacturing a hot forming tool for press hardening according to any one of claims 7 to 9, characterized in that the thickness of the surface layer as it is deposited is 1 to 30 mm, and the thickness of the surface layer after machining is 0.3 to 29 mm.

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