Hot work tool steel powder for additive manufacturing and hot work tool steel additively manufactured product

Abstract

The present application provides a hot work tool steel powder for additive manufacturing, which can be used to additively manufacture a hot work tool steel product with excellent crack resistance. The hot work tool steel powder for additive manufacturing and the hot work tool steel product for additive manufacturing each contains, in mass %, 0.10%≦C≦0.24%, 0.01%≦Si≦0.50%, 0.01%≦Mn≦0.19%, 3.6%≦Cr≦4.4%, one or both of Mo and W based on the relationship (Mo+1 / 2W): 2.0%≦(Mo+1 / 2W)≦3.4%, 0.2%≦V≦0.9%, the remainder being Fe and unavoidable impurities, and satisfies formula (1): C+Si / 30+(Mn+Cr) / 20+(Mo+1 / 2W) / 15+V / 10≦0.63.

Description

Technical Field

[0001] This invention relates to a hot work tool steel powder for laminated forming and a laminated product of hot work tool steel. Background Technology

[0002] For hot work tool steels such as hot forging dies or die casting dies, high-temperature strength, toughness, and wear resistance are required because they come into contact with the workpiece at high temperatures. In the past, to meet these requirements, SKD61 or improved versions of SKD61, which are Japanese Industrial Standards (JIS) steels, were used in hot work tool steels.

[0003] Furthermore, recently, stacking has garnered significant attention as a method for easily forming metal products (parts) with complex shapes at near-net-shape. Stacking is also commonly referred to as additive manufacturing (ADM) in 3D printing. Types of stacking include powder spraying, where metal powder is melted by irradiating it with a heat source while being stacked; and powder bed stacking, where metal powder spread on a platform is repeatedly melted and solidified by irradiating it with a heat source. Stacking allows for the production of metal products with complex shapes by significantly reducing traditional machining processes, thus enabling the use of difficult-to-machine metal materials. Moreover, difficult-to-machine metal materials are often specifically designed for high strength, allowing for the production of metal products with complex shapes and long lifespans.

[0004] Furthermore, a method for using hot work tool steel as a metallic material to produce laminated shaped articles through the aforementioned lamination forming method has been proposed. For example, Patent Document 1 discloses a laminated hot work tool characterized by having the following composition by mass: C: 0.3%–0.5%, Si: less than 2.0%, Mn: less than 1.5%, P: less than 0.05%, S: less than 0.05%, Cr: 3.0%–6.0%, one or both of Mo and W based on the relationship (Mo+1 / 2W): 0.5%–3.5%, V: 0.1%–1.5%, Ni: 0%–1.0%, Co: 0%–1.0%, Nb: 0%–0.3%, with the remainder being Fe and impurities, and having an area of ​​1 μm in a cross-section parallel to the lamination direction. 2 The area ratio of the above defects is less than 0.6%.

[0005] Patent document 2 discloses a steel powder designed to balance high thermal conductivity and high corrosion resistance, characterized by the following composition (by mass%): 0.10≦C<0.25, 0.005≦Si≦0.600, 2.00≦Cr≦6.00, -0.0125×[Cr]+0.125≦Mn≦-0.100×[Cr]+1.800 Equation (a) (where [Cr] in equation (a) represents the mass percentage of Cr), 0.01≦Mo≦1.80, -0.00447×[Mo]+0.010≦V≦-0.1117×[Mo]+0.901 Formula (b) (where [Mo] in Formula (b) represents the mass percentage of Mo), 0.0002≦N≦0.3000, with the remainder being Fe and unavoidable impurities.

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: International Publication No. 2019 / 220917

[0009] Patent Document 2: Japanese Patent Application Publication No. 2016-145407 Summary of the Invention

[0010] The problem that the invention aims to solve

[0011] As mentioned above, several types of steel for lamination forming have been proposed. However, depending on the type of lamination forming machine, lamination forming conditions, and lamination forming dimensions, cracks may sometimes occur during lamination forming. For example, in large lamination forming molds or lamination forming molds with complex cavities, there are stress concentration areas (recesses). Because the stress in these areas is particularly concentrated, they are very prone to cracking, thus requiring further improvement in crack resistance.

[0012] Therefore, the object of the present invention is to provide a hot work tool steel powder for laminated forming, which can produce hot work tool steel laminated forming articles with improved crack resistance during laminated forming.

[0013] Technical means to solve the problem

[0014] The present invention was made in view of the aforementioned issues.

[0015] That is, one embodiment of the present invention is a hot work tool steel powder for layered forming, which contains, by mass%, 0.10%≦C≦0.24%, 0.01%≦Si≦0.50%, 0.01%≦Mn≦0.19%, 3.6%≦Cr≦4.4%, and one or both of Mo and W based on the relationship (Mo+1 / 2W): 2.0%≦(Mo+1 / 2W)≦3.4%, 0.2%≦V≦0.9%, with the remainder being Fe and unavoidable impurities, and satisfies formula (1): C+Si / 30+(Mn+Cr) / 20+(Mo+1 / 2W) / 15+V / 10≦0.63 (the element symbols in formula (1) represent the content (mass%) of the element).

[0016] In addition, another embodiment of the present invention is a hot work tool steel laminated product containing, by mass%, 0.10%≦C≦0.24%, 0.01%≦Si≦0.50%, 0.01%≦Mn≦0.19%, 3.6%≦Cr≦4.4%, and one or both of Mo and W based on the relationship (Mo+1 / 2W): 2.0%≦(Mo+1 / 2W)≦3.4%, 0.2%≦V≦0.9%, with the remainder being Fe and unavoidable impurities, and satisfying formula (1): C+Si / 30+(Mn+Cr) / 20+(Mo+1 / 2W) / 15+V / 10≦0.63.

[0017] The effects of the invention

[0018] This invention provides hot work tool steel powder for lamination forming, which can be used to form hot work tool steel laminates with particularly excellent crack resistance during lamination forming. Attached Figure Description

[0019] [ Figure 1 [ ] is a schematic diagram of a crack evaluation test piece used to evaluate the shape cracking properties.

[0020] [ Figure 2 [This is a graph showing the tempering temperature and hardness of hot-working tool steel laminated products according to an example of the present invention.]

[0021] [ Figure 3 [This is a graph showing the mechanical properties of the present invention at room temperature ((a) 0.2% endurance, (b) tensile strength, (c) elongation, (d) drawing).

[0022] [ Figure 4 [This is a graph showing the mechanical properties of the present invention at high temperatures ((a) 0.2% endurance, (b) tensile strength, (c) elongation, (d) drawing).

[0023] [ Figure 5 [ ] is a graph showing the Charpy impact values ​​of the present invention at room temperature.

[0024] [ Figure 6 [ ] is a graph showing the thermal conductivity of an example of the present invention. Detailed Implementation

[0025] The present invention has the following composition: comprising 0.10%≦C≦0.24%, 0.01%≦Si≦0.50%, 0.01%≦Mn≦0.19%, 3.6%≦Cr≦4.4%, and one or both of Mo and W based on the relationship (Mo+1 / 2W): 2.0%≦(Mo+1 / 2W)≦3.4%, 0.2%≦V≦0.9%, with the remainder being Fe and unavoidable impurities. First, the rationale for limiting the composition of the hot work tool steel powder for laminated forming (hereinafter also referred to as laminated forming powder, metal powder) as specified in the present invention will be described. Furthermore, unless otherwise specified, "%" indicates "mass %". Additionally, laminated forming is sometimes simply referred to as "forming".

[0026] C: 0.10% ≤ C ≤ 0.24%

[0027] Carbon (C) is a fundamental element in hot-work tool steel, partly dissolved in the matrix to impart strength and partly forming carbides to improve wear resistance or sintering resistance. Additionally, when C and Cr, which are interstitial atoms dissolved in the matrix, are added together, it is expected to contribute to the I (interstitial atom) - S (substitutional atom) effect (acting as drag resistance of solute atoms, contributing to the high strength of hot-work tools). It also improves hardenability. If C is too low, ferrite phase mainly forms during solidification. Since the dominant phase is ferrite up to room temperature, quenching required for rapid cooling from the austenite phase is impossible. If the dominant phase from solidification to room temperature is ferrite, the thermal contraction due to martensitic phase transformation cannot be mitigated, thus increasing the risk of fracture. However, if C is high, hardness increases while toughness decreases, contributing to increased fracturing during forming. In this invention, in order to improve crack resistance while maintaining hardness suitable for mold use, the hardness is set to 0.10% ≤ C ≤ 0.24%. Preferably, the lower limit of C is 0.13%, more preferably 0.15% or more, and even more preferably 0.16% or more or 0.17% or more. Furthermore, preferably, the upper limit of C is 0.23%, more preferably 0.22% or less.

[0028] Si: 0.01% ≤ Si ≤ 0.50%

[0029] Si can be used as a deoxidizer to adjust the composition of molten steel. Since it is difficult to achieve a completely additive-free production process, and the closer to zero additive content is to zero, the higher the manufacturing cost, the lower the content is set to 0.01% or more. The preferred lower limit is 0.03%, more preferably 0.05% or more. On the other hand, excessive amounts can lead to the formation of ferrite in the tempered microstructure, therefore the upper limit is set to 0.50% or less. The preferred upper limit is 0.30% or less, more preferably 0.20% or less and 0.15% or less.

[0030] Mn: 0.01% ≤ Mn ≤ 0.19%

[0031] Mn has the effects of improving hardenability, suppressing the formation of ferrite in the microstructure after tempering, and obtaining appropriate hardness after quenching and tempering. To achieve these effects, the lower limit of Mn is set to 0.01%. A preferred lower limit is 0.02%, more preferably 0.03% or more, even more preferably 0.04% or more, and particularly preferably 0.05% or more. On the other hand, excessive Mn will increase the viscosity of the matrix and reduce the machinability of the material. Therefore, the upper limit is set to 0.19%. A preferred upper limit is 0.18%, more preferably 0.17% or less, or 0.15% or less.

[0032] Cr: 3.6% ≤ Cr ≤ 4.4%

[0033] Cr is a fundamental element in hot-work tool steel that improves hardenability, forms carbides, strengthens the matrix, and enhances wear resistance and toughness. However, excessive amounts can lead to a decrease in hardenability or high-temperature strength. Therefore, the Cr content is set at 3.6% ≤ Cr ≤ 4.4%. A lower limit for Cr is preferably 3.7%, more preferably 3.8% or more. Furthermore, an upper limit for Cr is preferably 4.3%, more preferably 4.2% or less.

[0034] Based on the relationship between (Mo + 1 / 2W), one or both of Mo and W are given: (Mo + 1 / 2W): 2.0% ≤ (Mo + 1 / 2W) ≤ 3.4%

[0035] Mo and W can be contained individually or in combination to impart strength, increase softening resistance, or improve high-temperature strength by precipitating or agglomerating fine carbides through tempering. Furthermore, in this invention, to improve crack resistance and reduce C, a slightly higher content of Mo and W is expected to supplement strength. For this content, since the atomic weight of W is approximately twice that of Mo, it can be specified using the Mo equivalent defined by the formula (Mo + 1 / 2 W) (of course, either one or both can be contained). Moreover, to obtain the aforementioned effect, the content is 2.0% or more based on the value of the formula (Mo + 1 / 2 W). A more preferred upper limit is 2.1%, and even more preferably 2.2% or more. However, excessive Mo or W may lead to a decrease in machinability or toughness, resulting in a decrease in crack resistance. Additionally, since the ease of melting at high melting points increases, a large content is not preferred from a manufacturing perspective. Therefore, the content is set to 3.4% or less based on the value of the formula (Mo + 1 / 2 W). The preferred upper limit is 3.0%, more preferably 2.8% or less, and even more preferably 2.6% or less or 2.5% or less. Here, since W is a more expensive element than Mo, it is preferable to contain Mo alone when cost reduction is a priority.

[0036] V: 0.2% ≤ V ≤ 0.9%

[0037] Vanadium (V) has the effect of strengthening the matrix or improving wear resistance and tempering softening resistance by forming vanadium carbides. Furthermore, when the laminated material formed in the lamination process is heated to the quenching temperature and "quenched," the vanadium carbides also act as "pinning particles" to suppress the coarsening of austenite grains during quenching heating, contributing to improved toughness. However, due to V's high carbide-forming ability, if there is too much V, all carbon (C) will become vanadium carbides, and other carbides may not be formed. Hot work tool steel is established by the presence of multiple carbides, so it is not ideal for the carbides to be only vanadium carbides. Therefore, the content is set to 0.2% ≤ V ≤ 0.9%. The preferred lower limit is 0.25%, more preferably 0.30% or more, and even more preferably 0.35% or more. Furthermore, the preferred upper limit is 0.80%, more preferably 0.60% or less, and even more preferably 0.50% or less and 0.45% or less.

[0038] Remaining components: Fe and unavoidable impurities

[0039] The remaining portion consists of Fe and unavoidable impurities. Examples of unavoidable impurities include P, S, Cu, Al, Ca, Mg, O (oxygen), N (nitrogen), and B (boron), which are preferably present in the lowest possible amounts. However, on the other hand, small amounts may be present due to additional effects such as inclusion morphology control, other mechanical properties, and improved manufacturing efficiency. In this case, a range of Al≦0.04%, Ca≦0.01%, Mg≦0.01%, O≦0.05%, N≦0.05%, and B≦0.05% is sufficient and is the preferred upper limit of the present invention. Furthermore, P and S can be set according to SKD61, a JIS steel grade, for example, P≦0.030% and S≦0.020%.

[0040] In this invention, by achieving an overall balance within the aforementioned compositional range, hot work tool steel laminates with exceptionally high crack resistance during forming can be obtained.

[0041] Formula (1): C+Si / 30+(Mn+Cr) / 20+(Mo+1 / 2W) / 15+V / 10≦0.63

[0042] In this invention, in addition to the specified composition, one of its features is that the left side of the formula (1) is adjusted to 0.63 or less. The left side of the formula (1) is a modified version of Pcm, which is used as a low-temperature crack susceptibility index for welding. In the formula (1), C, Si, Mn, Cr, Cu, Ni, Mo, W, and V represent the content (mass %) of each element. Welding, like laminated structures, is prone to crack formation. In addition, both are molten solidification structures, so it has been found that an index can be applied to suppress cracks in laminated structures and is applied to this invention. Here, another known crack index for welding is the Hot Cracking Susceptibility Index (HCS), which is used as a high-temperature crack index. However, according to previous studies, the cracks in this composition system break off significantly from the surface, which is different from the morphology of high-temperature cracks that are prone to occur at solidification interfaces. Since the forming cracks in this system are visible in areas prone to tensile stress caused by thermal shrinkage, they are generated at low temperatures. Therefore, it is presumed that they are similar to low-temperature cracks in welding. In this invention, Pcm is used as a low-temperature crack index. In this invention, especially in the case of suppressing cracks during laminated forming, the left side of formula (1) is set to 0.63 or less. Preferably, it is 0.62 or less or 0.61 or less.

[0043] Formula (2): 545-330C+2Al-14Cr-13Cu-23Mn-5Mo-4Nb-13Ni-7Si+3Ti+4V≦450

[0044] In this invention, besides the specified composition, formula (2) can be adjusted to 450 or less. Formula (2) is the relationship between the element after removing Co and the Ms point disclosed in the literature (K. Ishida, Journal of alloys and Compounds, Volume 220 Issues 1-2 1995 p126-131). It is expected that if the value of formula (2) is high, the Ms point will be high, and therefore, at high temperatures in the laminated structure, it will transform into martensite, which is brittle at high temperatures, and tends to crack easily due to thermal shrinkage when cooled to room temperature. In addition, it is preferable to adjust formula (2) to 200 or more. It is expected that if the value of formula (2) is too low, the Ms point will be low, and therefore, if it is too low, the martensitic transformation cannot be completed, and austenite remains, resulting in a decrease in strength. The preferred upper limit of formula (2) is 440 or less. More preferably, the content is 430 or less, and even more preferably 420 or less. Furthermore, the preferred lower limit for formula (2) is 240 or more. More preferably, it is 260 or more, and even more preferably 280 or more. In addition, for elements such as Cu and Ti, which are not actively added in this invention, and Al, which may be present as impurity elements in the range of 0.04% or less, it is sufficient to calculate them as zero%.

[0045] The hot work tool steel powder for layered shaping according to the present invention can be manufactured, for example, by gas atomization, water atomization, disc atomization, plasma atomization, or rotating electrode method. The gas atomization method involves heating a molten raw material prepared in a manner that yields the desired composition to above its melting point using high-frequency induction heating. After melting, an inert gas such as argon or nitrogen is injected into the molten metal flowing out through a fine orifice, thereby finely pulverizing the molten metal and rapidly solidifying it to obtain powder. This gas atomization method can use scrap metal or coarse metal raw materials as the molten raw material, and compared to plasma atomization or rotating electrode methods, which require pre-preparation of raw materials with the desired composition and shape, it offers a cost-effective method for obtaining the metal powder for layered shaping according to the present invention.

[0046] The hot work tool steel powder for laminated forming of the present invention preferably has a particle size of 50% of the cumulative particle size distribution based on volume (hereinafter referred to as "D50") of 10 μm to 250 μm. By setting its D50 to below 250 μm, the metal powder for laminated forming of the present invention facilitates powder melting and suppresses the formation of internal defects in laminated forming products.

[0047] Furthermore, the metal powder for lamination of the present invention, by setting its D50 to 10 μm or more, is not easily affected by moisture or other factors in the atmosphere of metal powder processing or lamination, thus ensuring good flowability.

[0048] Furthermore, the cumulative particle size distribution of the shaping powder of the present invention is represented by the cumulative volumetric particle size distribution, and its D50 can be represented by the measured value obtained by the laser diffraction scattering method specified in JIS Z 8825.

[0049] According to the method described above, the D50 of the hot work tool steel powder for layered forming of the present invention can also be adjusted by using sieving and classification with a screen or airflow classification. For example, in the powder bed method, the metal powder is melted by a laser beam as a heat source. On the other hand, in order to minimize the range of heat-affected zone, it is necessary to remove coarse metal powder that is difficult to melt. In addition, in order to obtain optimal flowability to ensure the layability of the metal powder, it is also necessary to remove fine metal powder with high adhesion. Therefore, when applying the metal powder of the present invention to the powder bed method, it is preferable to adjust the D50 to the range of 10 μm to 53 μm. The upper limit of D50 is preferably 40 μm, and the lower limit of D50 is preferably 20 μm. In addition, when applying the powder for layered forming of the present invention to the laser metal deposition method, it is preferable to adjust the D50 to the range of 50 μm to 150 μm.

[0050] By using the manufacturing method described later to laminate the hot work tool steel powder for lamination forming of the present invention, a hot work tool steel laminated product (hereinafter also referred to as a laminated product) can be obtained, which contains, by mass %, 0.10%≦C≦0.24%, 0.01%≦Si≦0.50%, 0.01%≦Mn≦0.19%, 3.6%≦Cr≦4.4%, and one or both of Mo and W based on the relationship (Mo+1 / 2W): 2.0%≦(Mo+1 / 2W)≦3.4%, 0.2%≦V≦0.9%, with the remainder being Fe and unavoidable impurities, and satisfying formula (1): C+Si / 30+(Mn+Cr) / 20+(Mo+1 / 2W) / 15+V / 10+≦0.63. The aforementioned laminated shapes are particularly superior in that they are less prone to cracking (forming cracks) during the laminated shaping process.

[0051] In addition to the aforementioned forming crack characteristics, the hot work tool steel laminated products of the present invention are expected to exhibit excellent mechanical properties. For example, the hot work tool steel laminated products of the present invention preferably have a room temperature (around 20°C) tensile strength of 1000 MPa to 2000 MPa when the tempering hardness is adjusted to 45 Rockwell hardness (HRC) ± 1 HRC. A more preferred lower limit is 1200 MPa, and even more preferred is 1300 MPa, and even more preferred is 1400 MPa. The room temperature 0.2% endurance when the tempering hardness is adjusted to 45 HRC ± 1 HRC is preferably 800 MPa to 2000 MPa. A more preferred lower limit is 800 MPa, and even more preferred is 1000 MPa. The room temperature elongation when the tempering hardness is adjusted to 45 HRC ± 1 HRC is preferably 8% or more. A more preferred lower limit is 10%, and even more preferred is 12%. Furthermore, the room temperature drawing rate when the tempering hardness is adjusted to 45 HRC ± 2 HRC is preferably 30% or more. A more preferred lower limit is 40%, and even more preferably 50%.

[0052] The hot-work tool steel laminate of the present invention preferably has a high-temperature (around 550°C) tensile strength of 600 MPa to 1400 MPa when the tempering hardness is adjusted to 45 HRC ± 1 HRC. A more preferred lower limit is 800 MPa, and even more preferably, 900 MPa. The high-temperature 0.2% endurance when the tempering hardness is adjusted to 45H ± 1RC is preferably 600 MPa to 1200 MPa. A more preferred lower limit is 700 MPa, and even more preferably, 800 MPa. The high-temperature elongation when the tempering hardness is adjusted to 45 HRC ± 1 HRC is preferably 10% or more. A more preferred lower limit is 13%, and even more preferably, 16%. The high-temperature drawing yield when the tempering hardness is adjusted to 45 HRC ± 1 HRC is preferably 30% or more. A more preferred lower limit is 40%, even more preferably, 50%, and even more preferably, 60%.

[0053] Furthermore, the hot work tool steel laminate of the present invention is preferably a 2 mm U-shaped cut with a Charpy impact value of 30 J / cm at room temperature when the tempering hardness is adjusted to 45 HRC±1 HRC. 2 The above. A more preferred lower limit is 50 J / cm. 2 Therefore, the preferred lower limit is 80 J / cm. 2 Furthermore, a more preferred lower limit is 100 J / cm². 2 The preferred lower limit is 150 J / cm³. 2 .

[0054] Furthermore, the hot work tool steel laminate of the present invention preferably has a room temperature thermal conductivity of 10 W / (m·K) or higher when the tempering hardness is adjusted to 45 HRC±1 HRC. More preferably, the lower limit is 15 W / (m·K), further preferably, the lower limit is 20 W / (m·K), and particularly preferably, the lower limit is 25 W / (m·K).

[0055] Next, an example of a manufacturing process for obtaining the laminated articles of the present invention using the hot work tool steel powder for lamination shaping according to the present invention will be described. Furthermore, unless otherwise specified, the manufacturing processes described below are assumed to be the powder bed method.

[0056] In the manufacturing method of the present invention, the steps include spreading the prepared hot work tool steel powder (hereinafter also referred to as "metal powder") for layering shaping into a layer, and forming a solidified layer by successively melting and solidifying the spread metal powder using a scanning heat source having a diameter larger than the D50 of the metal powder. Then, by repeating the steps of spreading the metal powder into a layer and forming the solidified layer, multiple layered solidified layers are formed, and the layered shape of the present invention can be produced. The scanning heat source can be, for example, a laser or an electron beam. Furthermore, by making the diameter of the scanning heat source larger than the D50 of the metal powder, the aggregate of metal powder can be melted uniformly, which is preferable in this respect.

[0057] In the manufacturing method of the present invention, the laser output power when scanning and irradiating the metal powder can be set to 50 W to 400 W, the scanning speed to 200 mm / s to 2000 mm / s, and the scanning interval to 0.02 mm to 0.20 mm. Here, if the layer thickness of each laser scan is too large, heat is difficult to transfer to the entire metal powder during laser irradiation, resulting in insufficient melting of the metal powder and promoting the formation of internal defects. On the other hand, if the layer thickness of each scan is too small, the number of layers required to reach the desired size of the stacked product increases, and the time required for the stacking and forming process increases. Therefore, the layer thickness of each scan is preferably set to 10 μm to 200 μm. A more preferred lower limit for the layer thickness is 20 μm, and a more preferred upper limit is 100 μm. Furthermore, a preheating process may be performed before the lamination forming process. However, since the metal powder of the present invention has particularly improved crack resistance compared with conventional hot work tool steel powder, for example, if the laminated product has few stress concentrations and is small, the preheating before lamination forming can be omitted or the temperature can be lowered.

[0058] In the manufacturing method of the present invention, in order to impart the mechanical properties required for use as a metal product, it is preferable to perform a tempering treatment at a temperature of 500°C to 700°C on the component that maintains the laminated shape (the state after lamination without heat treatment). By tempering, a product of a "laminated hot-working tool" with a specified hardness can be obtained. Moreover, during this period, the laminated object can be adjusted into the shape of a hot-working tool through various machining processes such as cutting or piercing. In this case, to facilitate machining, the laminated object formed in the lamination process can be annealed. Annealing is also expected to have the effect of refining the vanadium carbides in the microstructure of the tempered laminated hot-working tool. Furthermore, finishing machining can be performed after tempering. In addition, depending on the situation, the finishing machining can also be performed on the tempered laminated object together with the finishing machining, thereby finishing the product of a laminated hot-working tool.

[0059] Furthermore, quenching can be performed before the tempering. Moreover, normalizing can be performed on the laminated object formed in the lamination process, regardless of whether annealing is performed or before or after annealing.

[0060] The tempering temperature varies depending on the target hardness, but is generally around 500℃ to 700℃. Additionally, if quenching is performed before tempering, the quenching temperature is approximately 900℃ to 1100℃. For example, in the case of SKD61, a representative hot work tool steel, the quenching temperature is around 1000℃ to 1030℃, and the tempering temperature is around 550℃ to 650℃.

[0061] Furthermore, the tempering hardness is preferably set to 50 HRC (Rockwell hardness) or less, or 520 Vickers hardness (HV) or less. More preferably, it is 48 HRC or less, or 500 HV or less. Additionally, it is preferably set to 40 HRC or more, or 380 HV or more. More preferably, it is 42 HRC or more, or 400 HV or more. Moreover, in this invention, the hardness can be measured according to the measurement method described in JIS Z2245 "Rockwell Hardness Test - Test Method" or JIS Z 2244-1 "Vickers Hardness Test - Part 1: Test Method", and Rockwell C scale hardness (HRC) or Vickers hardness (HV) can be used.

[0062] Example

[0063] (Example 1)

[0064] After preparing the raw metal materials according to the composition shown in Table 1, they were placed in a high-frequency induction melting furnace and melted. The molten metal was then pulverized using argon gas to obtain gas-atomized powder. The particle size of the obtained atomized powder was adjusted by sieving and airflow classification using a sieve to obtain the laminated molding powders of the present invention and comparative examples with a D50 of 35 μm. For each of the laminated molding metal powders obtained, laminated molded articles were produced using an M290 manufactured by EOS Corporation under the molding conditions shown in Table 2. Table 3 shows the composition of molded articles of Sample No. 3 made from the powder of Sample No. 1 and Sample No. 4 made from the powder of Sample No. 2.

[0065] In addition, Table 4 shows the values ​​of formula (1): C+Si / 30+(Mn+Cr) / 20+(Mo+1 / 2W) / 15+V / 10 for samples No.1 to No.4, and the values ​​of formula (2): 545-330C+2Al-14Cr-13Cu-23Mn-5Mo-4Nb-13Ni-7Si+3Ti+4V.

[0066] [Table 1]

[0067]

[0068] [Table 2]

[0069]

[0070] [Table 3]

[0071]

[0072] [Table 4]

[0073]

[0074] (Example 2)

[0075] To evaluate the fragility of layered artifacts, such as... Figure 1The crack evaluation test pieces shown were shaped. Specifically, the layered shaping powders of Sample No. 1 and Sample No. 2 from Example 1 were layered and shaped under the same shaping conditions as in Example 1, and shaped into Sample No. 5 (composed of Sample No. 3) and Sample No. 6 (composed of Sample No. 4) with the same composition as Sample No. 3 and Sample No. 4. The crack evaluation test pieces were 50 mm long, 10 mm wide, and 16 mm high. A stress concentration section was created in the middle at R8. The stress concentration section was comb-shaped to make it easy to break, and it was assumed that the layered shaping mold had a complex cavity. The crack length of the comb-shaped section was measured after shaping to evaluate the ease of shaping and breaking of the material. The crack lengths of the crack test pieces of Sample No. 5 (Example of the Invention) and Sample No. 6 (Comparative Example) are shown in Table 5. According to Table 5, it can be confirmed that the crack length of the present invention example is shorter than that of the comparative example, and it has better crack resistance in the stacked molding process than the comparative example.

[0076] [Table 5]

[0077]

[0078] Next, the tempering behavior of the present invention examples was confirmed. For laminated articles prepared under the same conditions as sample No. 3 of Example 1, in Figure 2 Tempering heat treatment was performed twice within the temperature range shown, each time for 1 hour, and Rockwell hardness was measured based on JIS Z2245. Figure 1 The graph shows the relationship between various tempering temperatures and hardness. It is confirmed that the present invention can be tempered to a hardness of 40 HRC or higher, which is commonly used in conventional hot work tool steels.

[0079] Furthermore, the mechanical properties and thermal conductivity of the present invention were confirmed. For the laminated specimens prepared under the same conditions as Specimen No. 3 of Example 1, tempering heat treatment was performed in the temperature range of 500°C to 650°C to temper the test pieces to 40 HRC ± 1 HRC and 45 HRC ± 1 HRC, followed by tensile testing and a 2 mm U-shaped notch Charpy impact test. Additionally, after tempering the test pieces to 45 HRC ± 1 HRC, thermal conductivity was measured using a laser flash method. Figure 3 The results of the tensile test at room temperature (22°C) are shown below. Figure 4 The results of the high-temperature (550℃) tensile test are shown. Figure 5 The results of the Charpy impact test are shown in the figure. Figure 6 The results of the thermal conductivity measurement are shown in the figure.

[0080] according to Figure 3The laminated articles of this invention, under all the tempering hardness conditions of this invention, have a room temperature tensile strength of 1200 MPa or more, a room temperature 0.2% tensile strength of 1000 MPa or more, a room temperature elongation of 13% or more, and a room temperature draw weight of 60% or more. Furthermore, according to... Figure 4 The laminated articles of the present invention, under all the tempering hardness conditions of the present invention, exhibit a high-temperature tensile strength of 800 MPa or more, a high-temperature 0.2% tensile strength of 600 MPa or more, a high-temperature elongation of 13% or more, and a high-temperature drawability of 50% or more. Furthermore, under a hardness of 45 HRC ± 1 HRC, the laminated articles of the present invention exhibit a room-temperature tensile strength of 1400 MPa or more, a room-temperature 0.2% tensile strength of 1200 MPa or more, a room-temperature elongation of 13% or more, and a room-temperature drawability of 60% or more. Additionally, under a hardness of 45 HRC ± 1 HRC, the laminated articles of the present invention exhibit a high-temperature tensile strength of 900 MPa or more, a high-temperature 0.2% tensile strength of 700 MPa or more, a high-temperature elongation of 16% or more, and a high-temperature drawability of 60% or more.

[0081] according to Figure 5 It was confirmed that the laminated articles of this invention have a Charpy impact value of 60 J / cm² or higher at all tempered hardnesses. At a hardness of 45 HRC ± 1 HRC, the Charpy impact value is also 60 J / cm² or higher, which is a good value. Furthermore, according to... Figure 6 It was confirmed that the laminated product of the present invention has a thermal conductivity of 25 W / (m·K) or higher at room temperature at a hardness of 45 HRC±1 HRC.

[0082] Based on the above, Figures 3-6 It has been confirmed that the laminated articles of the present invention have properties at the same level as hot work tool steel as a smelting material, for example, suitable for hot work tool applications.

[0083] Industrial availability

[0084] The hot work tool steel powder and laminated molded products of the present invention are most preferably used for hot work tool applications such as die casting molds. However, due to the various excellent properties of the laminated molded products of the present invention, they can also be used, for example, for mold repair using powder spraying. In addition, due to the various excellent properties of the laminated molded products of the present invention, they can also be used for molds requiring internal cooling mechanisms, such as plastic molds.

Claims

1. A hot work tool steel powder for laminated forming, comprising, by mass % 0.10%≦C≦0.24%, 0.01%≦Si≦0.50%, 0.01%≦Mn≦0.19%, 3.6%≦Cr≦4.4%, one or both of Mo and W based on the relationship (Mo+1 / 2W): 2.0%≦(Mo+1 / 2W)≦3.4%, 0.2%≦V≦0.9%, with the remainder being Fe and unavoidable impurities, and further satisfying the following formula (1). Formula (1): C+Si / 30+(Mn+Cr) / 20+(Mo+1 / 2W) / 15+V / 10≦0.63 Here, the symbols of each element in equation (1) represent the content (mass%) of the element.

2. A hot work tool steel laminate, comprising, by mass%, 0.10%≦C≦0.24%, 0.01%≦Si≦0.50%, 0.01%≦Mn≦0.19%, 3.6%≦Cr≦4.4%, one or both of Mo and W based on the relationship (Mo+1 / 2W): 2.0%≦(Mo+1 / 2W)≦3.4%, 0.2%≦V≦0.9%, with the remainder being Fe and unavoidable impurities, and further satisfying the following formula (1). Formula (1): C+Si / 30+(Mn+Cr) / 20+(Mo+1 / 2W) / 15+V / 10≦0.63 Here, the symbols of each element in equation (1) represent the content (mass%) of the element.

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