Shaping powder and shaped article

Abstract

The present invention provides: a shaping powder, which is suitable for additive processing for making a powder into a near net shape, and with which it is possible to produce a cold die steel where inclusion of coarse carbides is suppressed even if a diffusion annealing treatment that has been required for ingot making is omitted; and a shaped article which uses this shaping powder.　The shaping powder, which includes, in mass%, 0.1% to 1.6% of C, 0.01% to 0.12% of S, 0.1% to 3.0% of Si, 0.1% to 3.0% of Mn, 7.0% to 13.0% of Cr, one or both of W and Mo in the amount (1 / 2 W + Mo) of 0.5% to 1.7%, less than 0.7% (including 0%) of V, less than 0.3% (including 0%) of Nb, 0.3% to 1.5% of Ni, 0.1% to 1.0% of Cu, and 0.1% to 0.5% of Al, with the balance being composed of Fe and unavoidable impurities; and a shaped article which uses this shaping powder, wherein the maximum particle diameter of carbides is less than 1.0 μm in a cross-section that is parallel to a stacking direction.

Description

Powders for molding and molded objects

[0001] The present invention relates to a powder for molding, for example, for producing cold die steel, and a molded product using the powder.

[0002] Conventionally, SKD11 specified by JIS has been widely used as cold work die steel. This cold work die steel requires various properties such as toughness and machinability, and it is important to control the carbides to an appropriate state in order to obtain these properties. To achieve this, improvements in processes such as hot working and heat treatment, as well as chemical composition design, have been investigated.

[0003] For example, Patent Document 1 proposes a cold die steel that combines suppression of dimensional change and galling resistance by applying ingot making and optimizing the size and dispersion of primary carbides.

[0004] Japanese Patent Application Laid-Open No. 2006-169624

[0005] Patent Document 1 is a useful technology in that it can provide tool performance with good dimensional suppression and galling resistance. The cold die steel disclosed in Patent Document 1 is subjected to a diffusion annealing treatment, even for the relatively small ingots described in the examples, in order to control the size of primary carbides formed during solidification. For ingots used industrially, a long diffusion annealing treatment is required after casting, which is thought to require a large number of steps for processing. In particular, the heat treatment known as the diffusion annealing treatment leads to the problem of increased costs due to the increased number of manufacturing steps.

[0006] The object of the present invention is to provide a molding powder that is suitable for additive processing to turn powder into a near-net shape, and that can be used to produce cold die steel with reduced coarse carbide content even when the diffusion annealing treatment required for ingot making is omitted, and a molded product made using the same.

[0007] In order to solve the above-mentioned problems, the present invention is configured as follows: The powder for molding of the present invention has a composition containing, in mass%, 0.1 to 1.6% C, 0.01 to 0.12% S, 0.1 to 3.0% Si, 0.1 to 3.0% Mn, 7.0 to 13.0% Cr, 0.5 to 1.7% of one or both of Mo and W (1 / 2W+Mo), less than 0.7% V (including 0%), less than 0.3% Nb (including 0%), 0.3 to 1.5% Ni, 0.1 to 1.0% Cu, 0.1 to 0.5% Al, with the balance being Fe and unavoidable impurities.

[0008] The powder for molding of the present invention preferably has less than one carbide having a maximum length of 0.1 μm or more in the cross section of the powder.

[0009] The shaped article of the present invention contains, by mass%, 0.1 to 1.6% C, 0.01 to 0.12% S, 0.1 to 3.0% Si, 0.1 to 3.0% Mn, 7.0 to 13.0% Cr, 0.5 to 1.7% of one or both of W and Mo (1 / 2W+Mo), less than 0.7% (inclusive of 0%) V, less than 0.3% (inclusive of 0%) Nb, 0.3 to 1.5% Ni, 0.1 to 1.0% Cu, 0.1 to 0.5% Al, and the remainder being Fe and unavoidable impurities, and the maximum grain size of carbides in a cross section parallel to the lamination direction is less than 1.0 μm.

[0010] In the shaped article of the present invention, the maximum particle size of the carbide is preferably less than 0.5 μm.

[0011] The present invention can provide a powder for molding in which the inclusion of coarse carbides is suppressed, even when the diffusion annealing treatment required for ingot making is omitted, and a molded product using the powder. As a result, even when the present invention is applied to, for example, powder bed fusion or directed energy deposition, coarse carbides are unlikely to be generated, and the diffusion annealing treatment can be omitted. In other words, even with a simple process, a cold die steel with excellent properties can be obtained. Therefore, the present invention is a useful technology for producing cold die steel used in dies for molding automobile-related parts, etc.

[0012] Scanning electron microscope photograph of the powder for molding of Inventive Example 1. Scanning electron microscope photograph of the powder for molding of Inventive Example 2. Scanning electron microscope photograph of the powder for molding of Inventive Example 3. Scanning electron microscope photograph of the molded object of Inventive Example 4. Scanning electron microscope photograph of the molded object of Inventive Example 5. Scanning electron microscope photograph of the molded object of Inventive Example 6. Scanning electron microscope photograph of the molded object of Inventive Example 5. Scanning electron microscope photograph of the molded object of Inventive Example 6.

[0013] The shaping powder of the present invention is used in additive processes that turn powder into a near-net shape, such as powder bed fusion and directed energy deposition. This eliminates the need for hot plastic working, such as blooming and finishing, required in conventional ingot making, thereby contributing to a reduction in the number of processing steps.

[0014] The powder for molding and the molded article of the present invention have the following component composition: Specifically, the powder for molding and the molded article of the present invention contain, in mass%, 0.1 to 1.6% C, 0.01 to 0.12% S, 0.1 to 3.0% Si, 0.1 to 3.0% Mn, 7.0 to 13.0% Cr, 0.5 to 1.7% of one or both of W and Mo (½W + Mo), less than 0.7% (including 0%) V, less than 0.3% (including 0%) Nb, 0.3 to 1.5% Ni, 0.1 to 1.0% Cu, 0.1 to 0.5% Al, and the remainder being Fe and unavoidable impurities.

[0015] The reasons for limiting the range of components applicable to the present invention are explained below. In the following explanation, "mass %" will also be simply expressed as "%." C (carbon) combines with carbide-forming elements such as Cr, W, Mo, V, and Nb to form hard complex carbides, which are effective in improving the wear resistance required for tools. C also has the effect of strengthening the matrix by partially dissolving in the matrix. In this case, by setting the C content to 0.1% or more, the hardness required for tools can be ensured. For the same reasons as above, the C content is preferably 0.4% or more, and more preferably 0.8% or more. On the other hand, by setting the C content to 1.6% or less, the amount of carbides can be prevented from becoming excessive, thereby improving toughness. For the same reasons as above, the C content is preferably 1.3% or less, and more preferably 1.1% or less.

[0016] S (sulfur) is an element useful for improving machinability, and its content should be 0.01% or more. For the same reasons as above, S is preferably 0.03% or more, and more preferably 0.05% or more. On the other hand, excessive S content reduces toughness, so S is set to 0.12% or less. For the same reasons as above, S is preferably 0.09% or less, and more preferably 0.08% or less.

[0017] By limiting the Si content to 3.0% or less, it is possible to suppress a decrease in toughness. Furthermore, for the same reasons as above, the Si content is preferably 2.0% or less. Furthermore, Si is contained at 0.1% or more as a deoxidizer. Furthermore, for the same reasons as above, the Si content is preferably 0.7% or more.

[0018] By limiting Mn to 3.0%, machinability can be improved. For the same reasons as above, Mn is preferably 0.8% or less, more preferably 0.6% or less. To improve hardenability, Mn is set to 0.1% or more. For the same reasons as above, Mn is preferably 0.3% or more, more preferably 0.4% or more.

[0019] Cr combines with C to form carbides, improving wear resistance and hardenability. For this reason, the Cr content is set to 7.0% or more. This allows the amount of carbide formed to be optimized, improving wear resistance and hardenability. For the same reasons as above, the Cr content is preferably 8.0% or more. On the other hand, by setting the Cr content to 13.0% or less, the formation of coarse carbides can be suppressed and toughness can be improved. For the same reasons as above, the Cr content is preferably 11.0% or less, more preferably 10.0% or less, and even more preferably 9.0% or less.

[0020] W (tungsten) and Mo combine with C to form carbides and dissolve in the matrix, increasing heat treatment hardness and improving wear resistance. By increasing the content of one or both of W and Mo to 0.5% or more (1 / 2W + Mo), the Ms point can be raised and the residual austenite after quenching can be reduced, contributing to improved hardness. For the same reasons as above, (1 / 2W + Mo) is preferably 0.8% or more, more preferably 1.0% or more. By increasing the content of one or both of W and Mo to 1.7% or less (1 / 2W + Mo), deterioration of machinability and toughness can be suppressed. For the same reasons as above, (1 / 2W + Mo) is preferably 1.5% or less, more preferably 1.2% or less.

[0021] Vanadium (V) can be added to improve hardenability. However, since V is an element that impairs machinability, its content is limited to less than 0.7%.

[0022] Nb is an element that works to make the distribution of carbides in the structure uniform and reduce dimensional change during heat treatment. On the other hand, if the amount of MX compounds formed by Nb is too large, there is a risk of reducing machinability, so the content of Nb is preferably 0.3% or less.

[0023] Ni combines with Al to form an intermetallic compound, which simultaneously achieves secondary hardening through precipitation and suppresses dimensional change. Here, if Ni is less than 0.3%, this effect is difficult to obtain. On the other hand, if Ni exceeds 1.5%, it increases the solid solubility limit of C in Fe, hindering workability in the annealed state. For this reason, Ni is set to 0.3 to 1.5%.

[0024] Cu allows the precipitation of Ni-Al intermetallic compounds near the secondary hardening temperature of cold work tool steel, as the Cu metal phase begins to precipitate at temperatures above 480°C and acts as a precipitation nucleus for intermetallic compounds. On the other hand, adding a large amount of Cu can cause red shortness. For this reason, the Cu content is set to 0.1 to 1.0.

[0025] Al combines with Ni to form intermetallic compounds, which are responsible for secondary hardening through precipitation. However, if the Al content is less than 0.1%, this effect is difficult to obtain. On the other hand, if the Al content exceeds 0.5%, the formation of delta ferrite becomes significant. For this reason, the Al content is set to 0.1 to 0.5%. The remainder of the shaping powder and shaped product of the present invention is Fe and unavoidable impurities.

[0026] Depending on the heat input conditions during molding, the carbides contained in the molding powder may not melt and remain in the molded product. Furthermore, if the carbides contained in the molding powder are finer, the carbides in the molded product tend to be finer, which can improve galling resistance. Therefore, it is preferable that the molding powder of the present invention has less than one carbide having a maximum length of 0.1 μm or more in the cross section of the powder.

[0027] The powder for shaping of the present invention can be produced by, for example, gas atomization, water atomization, disk atomization, plasma atomization, rotating electrode atomization, etc. Among these production methods, gas atomization allows scrap metal, raw metal raw materials, etc. to be used as the melting raw material, and enables production at a lower cost than plasma atomization and rotating electrode atomization, which require the preparation of raw materials with the desired composition and shape in advance. For this reason, gas atomization is preferred as a production method for the powder for shaping of the present invention.

[0028] In the gas atomization method, raw materials prepared to have a desired composition are heated to or above their melting points by high-frequency induction heating, and then the molten metal flows out through small holes. An inert gas such as argon gas or nitrogen gas is sprayed onto the molten metal to finely pulverize it, and the molten metal is rapidly cooled and solidified to obtain powder. In the present invention, nitrogen gas can also be used to more finely control the size of carbides that crystallize in the powder structure.

[0029] The molding powder of the present invention preferably has a 50% particle size (hereinafter referred to as "D50") of the cumulative particle size distribution based on volume of 10 to 250 μm. By setting the D50 of the molding powder of the present invention to 250 μm or less, it is possible to ensure a rapid solidification rate and a rapid cooling rate after solidification, and to suppress the formation of carbides with a maximum length of 0.1 μm or more within the powder structure. Furthermore, by setting the D50 of the molding powder of the present invention to 10 μm or more, it becomes less susceptible to the effects of atmospheric moisture, etc., and good fluidity can be ensured. The cumulative particle size distribution of the molding powder of the present invention is expressed as a cumulative volumetric particle size distribution, and the D50 is expressed as a measurement value measured by the laser diffraction scattering method specified in JIS Z 8825.

[0030] The shaping powder of the present invention may have its particle size adjusted by mesh sieving or airflow classification to suit the shaping method in which it is used. For shaping powders used in powder bed fusion using a laser beam, the powder is melted by the laser beam, which serves as the heat source, while coarse powder that is difficult to melt must be removed to minimize the area of ​​thermal influence. Furthermore, highly adhesive fine powder must also be removed to obtain optimal fluidity for ensuring powder spreadability. Therefore, when using the shaping powder of the present invention in powder bed fusion, it is preferable to adjust the D50 to the range of 10 to 53 μm.

[0031] Furthermore, metal powders used in directed energy deposition using a laser beam must be free of coarse particles that are difficult to melt in order to be melted by the laser beam, which serves as the heat source. Furthermore, fine particles must also be removed to prevent dust from scattering when the powder is supplied to the heat source and to ensure fluidity that allows the powder to be easily transported. Therefore, when applying the powder for modeling of the present invention to directed energy deposition, it is preferable to adjust the D50 to the range of 53 to 106 μm. Furthermore, when using an electron beam or plasma as the heat source, it is possible to use coarser metal particles for modeling, so it is preferable to adjust the D50 to the range of 75 to 250 μm.

[0032] To obtain a shaped object using the above-described shaping powder of the present invention, for example, powder sintering, additive manufacturing, or thermal spraying can be applied. For powder sintering, atmospheric sintering or pressure sintering can be applied. For additive manufacturing, the above-described powder bed fusion or directed energy deposition can be applied. For thermal spraying, gas thermal spraying or electric thermal spraying can be applied. Of these, directed energy deposition is preferred for obtaining the shaped object of the present invention. The shaped object of the present invention has a maximum carbide grain size of less than 1.0 μm in a cross section parallel to the layering direction. Compared to ingot-making methods such as ingot casting and continuous casting, the shaped object of the present invention has a much faster cooling rate in the solidification process, resulting in fine primary carbides. For the same reasons as above, the shaped object according to the embodiment of the present invention preferably has a maximum carbide grain size of less than 0.5 μm, more preferably less than 0.1 μm. Furthermore, the shaped article of the present invention is useful in that the primary carbides can be decomposed by heat treatment such as annealing and quenching even if the above-mentioned diffusion annealing treatment is omitted.

[0033] After preparing each metal raw material so as to have the composition shown in Table 1, the raw materials were charged into a high-frequency induction melting furnace and melted. The molten metal was then pulverized with argon gas at a gas pressure of 3.0 MPa to obtain an atomized powder.

[0034] The obtained molding powders were analyzed for C (carbon) by infrared absorption spectroscopy, and for elements other than C listed in Table 1 by ICP emission spectroscopy. Table 1 shows that the analytical values ​​of each element in the molding powders of the present invention are within the ranges specified in the present invention, and it was confirmed that these molding powders can exhibit sufficient properties as cold die steel after molding.

[0035] To observe the microstructure of the molding powders of the present invention, aggregates of each powder were embedded in a thermosetting resin so that the powders were aligned on a roughly uniform surface, following the general procedure for preparing samples for microscopic observation. The samples were then buffed and polished to prepare the samples. These samples were then corroded with nital, and their cross-sectional structures were observed using a JEOL Ltd. JSM-6610 scanning electron microscope to obtain secondary electron images. The results are shown in Figures 1 to 3.

[0036] It was confirmed that none of the molding powders of the present invention contained coarse carbides with a maximum length of 0.1 μm or more in the cross-sectional structure. This confirmed that when the molding powder of the present invention is used for molding, it is possible to produce cold die steel with a fine carbide distribution without the need for diffusion annealing treatment during the manufacturing process.

[0037]

[0038] Next, additive manufacturing was performed by directed energy deposition using the powders of Invention Examples 1 to 3. Specifically, using a LASERTEC 65 3D manufactured by DMG Mori Seiki Co., Ltd., linear beads were laminated on a carbon steel (S50C) plate by irradiating it with a laser heat source while supplying the molding powders of Invention Examples 1 to 3, thereby producing objects of Invention Examples 4 to 6. Each of the objects obtained above was then quenched at 1030°C and tempered at 500°C.

[0039] The structure of the cross section parallel to the layering direction (cross section in the thickness direction) of the quenched and tempered shaped object obtained above was observed. Specifically, the shaped object was embedded in a thermosetting resin so that the cross section in the thickness direction was exposed, and then the object was buffed to prepare a sample. Then, the sample was etched with nital to prepare an observation specimen. Each of these observation specimens was then observed at a magnification of 5000x using a scanning electron microscope. The results are shown in Figures 4 to 6. Granular carbides, indicated by the arrows, were observed in the scanning electron microscope secondary electron image shown in Figure 4 for the shaped object of Inventive Example 4. The maximum particle size of the granular carbides observed was 0.8 μm. Furthermore, the shaped objects of Inventive Examples 4 to 6 all contained carbides so fine that it was difficult to evaluate the area ratio and equivalent circle diameter for carbide evaluation as specified in Patent Document 1.

[0040] In particular, the maximum particle size of carbides was not clearly observed for the shaped articles of Inventive Examples 5 and 6 when observed using a scanning electron microscope, as shown in Figures 5 and 6. To confirm the carbide dispersion state in more detail, for Inventive Examples 5 and 6, backscattered electron images were taken without etching using a JEOL Ltd. composite beam processing and observation system JIB-4700F to confirm the presence of carbides. The results are shown in Figures 7 and 8. As a result of the observation, in both Inventive Examples 5 and 6, black particles with a maximum particle size exceeding 1 μm were MnS. On the other hand, in both Inventive Examples 5 and 6, only particles with a maximum particle size less than 0.5 μm were observed as carbides. From the above, it was confirmed that the shaped articles of the present invention are cold die steels containing only fine carbides less than 1.0 μm, even when the diffusion annealing treatment required for ingot making is omitted. This confirms that the shaping powder of the present invention is suitable for directed energy deposition.

Claims

1. A powder for molding containing, by mass, C: 0.1-1.6%, S: 0.01-0.12%, Si: 0.1-3.0%, Mn: 0.1-3.0%, Cr: 7.0-13.0%, one or both of W and Mo (1 / 2W+Mo) 0.5-1.7%, V: less than 0.7% (including 0%), Nb: less than 0.3% (including 0%), Ni: 0.3-1.5%, Cu: 0.1-1.0%, Al: 0.1-0.5%, and the remainder being Fe and unavoidable impurities.

2. The powder for molding according to claim 1, wherein the powder has less than one carbide having a maximum length of 0.1 μm or more in its cross section.

3. A shaped object containing, by mass, 0.1-1.6% C, 0.01-0.12% S, 0.1-3.0% Si, 0.1-3.0% Mn, 7.0-13.0% Cr, 0.5-1.7% of one or both of W and Mo (1 / 2W+Mo), less than 0.7% (including 0%), less than 0.3% (including 0%) Nb, 0.3-1.5% Ni, 0.1-1.0% Cu, 0.1-0.5% Al, with the remainder being Fe and unavoidable impurities, and in a cross section parallel to the lamination direction, the maximum grain size of carbides is less than 1.0 μm.

4. The shaped object according to claim 3, wherein the maximum grain size of the carbide is less than 0.5 μm.

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