Wear-resistant boride-forming ferroalloy for powder bed fusion additive manufacturing

Abstract

This application relates to iron (steel) alloy compositions that can be printed using powder bed fusion additive manufacturing. The combination of printability and various properties is achieved by formulating chemistries specifically for the powder bed fusion process.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to U.S. Provisional Application No. 63 / 042,202, filed on June 22, 2021, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This application relates to iron (steel) alloy compositions that can be printed by powder bed fusion additive manufacturing. Background Art

[0004] In its most prevalent form, additive manufacturing (also known as 3D printing) involves the layer-by-layer deposition of material to “build” or “print” a three-dimensional object. Manufacturing in this way offers several advantages, including the production of complex geometries, reduced production time, rapid innovation, elimination of inventory, and savings on material costs.

[0005] In tooling, specifically, conformal cooling channels are an example of complex geometries that are impossible or cost-prohibitive to manufacture through subtractive manufacturing. Conformal cooling channels are internal channels that closely follow the shape and orientation of the exterior surface, through which fluid is pumped for maximum thermal management. Conformal cooling channels can extend tool life and reduce part cycle time (i.e., the time required to produce a part from a tool), both of which can reduce costs. Summary of the Invention

[0006] In at least one embodiment, a method for constructing a metal part layer by layer is provided. Particles of an iron-based alloy are provided. The iron-based alloy has 9.0 to 16.0 wt% Cr; 5.0 wt% or less Ni; 3.0 wt% or less Mo; 3.0 wt% or less Mn; 0.1 to 0.30 wt% C; and 1.0 wt% or less B. One or more elements selected from Cu, W, or V are also present. When Cu is present, the amount of Cu is up to 2.5 wt%; when W is present, the amount of W is up to 7.5 wt%; and when V is present, the amount of V is up to 3.5 wt%. The balance of the iron-based alloy comprises Fe. The formed metal part is formed at least in part by powder bed fusion, which includes melting the particles into a molten state, and cooling and forming one or more solidified layers of the iron-based alloy, the iron-based alloy comprising a martensitic matrix and one or more of Cr-boride, W-boride when W is present, or V-boride when V is present. The formed part has an HRC hardness of H1 and a wear resistance of W1 (mass loss in grams measured by ASTM G65-16e1 procedure A). The formed part is heat treated, wherein the heat treated part exhibits a second value of HRC hardness (H2) and wear resistance (W2), wherein W2 <W1。

[0007] In another embodiment, the formed part has a tensile strength of at least 1000 MPa, a yield strength of at least 700 MPa, an elongation of at least 0.25%, and a hardness (HRC) of at least 40.

[0008] In another embodiment, after heat treating, the metal part has an elongation of at least 5.0%, an HRC hardness of at least 50, and a wear resistance (mass loss in grams as measured by ASTM G65-16e1 Procedure A) of less than or equal to 1.90.

[0009] In another embodiment, the heat treatment comprises heating at a temperature of 900° C. to 1200° C. for 0.5 to 8.0 hours.

[0010] In another embodiment, when Cu is present, the amount of Cu is 0.15 wt% to 0.30 wt%; when W is present, the amount of W is 0.1 wt% to 5.5 wt%; and when V is present, the amount of V is 0.1 wt% to 2.25 wt%.

[0011] In another embodiment, the alloy after heat treatment comprises a Cr-rich boride phase.

[0012] In another embodiment, the alloy comprises 0.1 wt. % to 5.5 wt. % W, and the alloy after heat treatment comprises a W-rich boride phase.

[0013] In another embodiment, the alloy comprises 0.1 wt. % to 2.25 wt. % V, and the alloy after heat treatment comprises a V-rich boride phase.

[0014] In another embodiment, the alloy has 9.0 wt% to 19.0 wt% Cr; up to 3.0 wt% Ni; 0.2 wt% to 0.8 wt% Mo; 0.75 wt% to 3.0 wt% Mn; 0.1 wt% to 0.25 wt% C;

[0015] In another embodiment, in the alloy, when Cu is present, the amount of Cu is at most 0.8 wt %; when W is present, the amount of W is at most 5.5 wt %; and when V is present, the amount of V is at most 2.5 wt %.

[0016] In at least one embodiment, a method of constructing a metal component layer by layer includes providing particles of an iron-based alloy comprising 9.0 to 16.0 wt% Cr; 2.0 to 3.0 wt% Ni; 0.2 to 0.8 wt% Mo; 0.75 to 3.0 wt% Mn; 0.1 to 0.25 wt% C; 0.25 to 0.25 wt% B; and one or more elements selected from Cu, W, or V, wherein when Cu is present, the amount of Cu is up to 0.3 wt%, when W is present, the amount of W is up to 5.5 wt%, and when V is present, the amount of V is up to 2.25 wt%. The balance of the iron-based alloy comprises Fe. A formed metal part is formed at least in part by powder bed fusion, comprising melting particles into a molten state, and cooling and forming one or more solidified layers of an iron-based alloy, the solidified layers comprising a martensitic matrix and one or more Cr-borides, W-borides when W is present, or V-borides when V is present. The part has an HRC hardness (H1) and a wear resistance (W1) (mass loss in grams measured by ASTM G65-16e1, Procedure A) in the formed condition, and heat treating the part, wherein the part exhibits second values of HRC hardness (H2) and wear resistance (W2) as follows: H2 = H1 + / - 10 and W2 <W1。 BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 Shows the calculated Scheil solidification curve for alloy A1.

[0018] Figure 2 Shows the Scheil solidification curve calculated for alloy A3.

[0019] Figure 3 Shows the Scheil solidification curve calculated for alloy A4.

[0020] Figure 4 The calculated martensite start temperature and the carbon content of the austenite formed during solidification for Alloy A1 are shown.

[0021] Figure 5 The calculated martensite start temperature and the carbon content of the austenite formed during solidification for Alloy A3 are shown.

[0022] Figure 6 The calculated martensite start temperature and the carbon content of the austenite formed during solidification for Alloy A4 are shown.

[0023] Figure 7 Figure 4 shows the X-ray diffraction results of the PBF printed rod of alloy Al.

[0024] Figure 8 Represents the microstructure of the as-formed alloy A1.

[0025] Figure 9 Represents the microstructure of the as-formed alloy A3.

[0026] Figure 10 Represents the microstructure of the as-formed alloy A4.

[0027] Figure 11 shows a micrograph of the as-molded alloy A1.

[0028] Figure 12 shows a micrograph of the as-formed alloy A2.

[0029] Figure 13 shows a micrograph of the as-formed alloy A3.

[0030] Figure 14 shows a micrograph of the as-formed alloy A4.

[0031] Figure 15 Shows the calculated equilibrium phase diagram of alloy A1.

[0032] Figure 16 Shows the calculated equilibrium phase diagram of alloy A3.

[0033] Figure 17 Represents the calculated equilibrium phase diagram of alloy A4.

[0034] Figure 18 Represents the microstructure of the PBF printed bar of alloy A1 after heat treatment with an aging step at 1100 °C for 2 h.

[0035] Figure 19 Represents the microstructure of the PBF printed bar of Alloy A1 after heat treatment with an aging step at 1100 °C for 4 h.

[0036] Figure 20 Represents the microstructure of the PBF printed bar of Alloy A1 after heat treatment with an aging step at 1100 °C for 8 h.

[0037] Figure 21 Represents the microstructure of the PBF printed bar of alloy A3 after heat treatment with an aging step at 1100 °C for 2 h.

[0038] Figure 22 Represents the microstructure of the PBF printed bar of alloy A3 after heat treatment with an aging step at 1100 °C for 8 h.

[0039] Figure 23 Represents the microstructure of the PBF printed bar of alloy A4 after heat treatment with an aging step at 1100 °C for 8 h. DETAILED DESCRIPTION

[0040] As required, detailed embodiments of the present invention are disclosed herein; however, it should be understood that the disclosed embodiments are merely exemplary of the present invention, which can be embodied in many different forms. The drawings are not necessarily to scale; certain features may be exaggerated or minimized to show details of particular components. Therefore, the specific structural and functional details disclosed herein should not be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to employ the present invention in various ways.

[0041] There are various metal additive manufacturing methods. Additive manufacturing can be used to create tools used in industrial manufacturing processes such as metal die casting, injection molding, hot stamping, and compression molding. One additive manufacturing method used for tooling is laser powder bed fusion (L-PBF, or simply "PBF"). PBF can produce nearly 100% dense workpieces with properties similar to or better than their wrought counterparts, while achieving dimensional tolerances, near-net shape, and surface finish that require minimal post-printing finishing. Furthermore, the size of PBF-printed workpieces is limited only by the size of the equipment. Other common metal additive manufacturing methods, such as binder jetting or direct energy deposition (DED), have limitations in one or more areas. For example, binder jetting typically achieves a maximum density of less than 99%, and size is limited by the need to remove binder trapped in the part during the printing process. In DED, tolerances and surface finish require post-printing finishing. Beyond tooling, other specialty parts requiring high performance and reliability, such as those for aerospace and biomedical applications, also prefer PBF for similar reasons.

[0042] One disadvantage of PBF compared to other methods for tooling is the availability of printable tool steels. Conventional forged tool steels that provide the necessary properties (including hardness and wear resistance) cannot be printed efficiently or economically via PBF without cracking. H13, one of the most commonly used tool steels, requires relatively slow printing (typically 9 cm 3 / h or less) or preheating the powder bed to 300°C or higher to avoid cracking. Implementing any of these options will increase printing time, thereby increasing costs, while the latter will also jeopardize quality and consistency. Even so, these strategies are not guaranteed to prevent cracking when printing large parts.

[0043] Steels that can be printed by PBF, such as 316L, M300, and 17-4PH, either lack the hardness, wear resistance, or both for many tooling applications. For example, M300 can have a relatively high hardness, but its wear resistance is nominally half that of H13. In addition, steels such as M300 and 17-4PH are relatively soft after printing and require post-printing aging heat treatment to increase hardness, which increases manufacturing time and cost.

[0044] The disclosure herein addresses the need for alloy compositions that can be used to print tools and specialty parts via PBF that have a combination of relatively high hardness, strength, elongation, and wear resistance.

[0045] The present disclosure describes ferroalloy compositions that are printable via a powder bed fusion (PBF) process and that have a combination of relatively high hardness and wear resistance in both the "as-formed" and "heat-treated" states. Printability, in this context, refers to the ability to additively manufacture or 3D print parts, preferably without defects such as cracks or porosity. The "as-formed" state is defined as the state produced by a PBF printer in which the stated mechanical properties are achieved. The as-formed state is expected to include heating to relieve stresses that may be present in the as-formed part. The combination of printability and properties is achieved by formulating chemistries specifically for the powder bed fusion process.

[0046] As described above, the alloy comprises 9.0 to 16.0 wt% Cr, 2.0 to 3.0 wt% Ni, 0.2 to 0.8 wt% Mo, 0.75 to 3.0 wt% Mn, 0.1 to 0.25 wt% C, and 0.25 to 0.75 wt% B. The alloy may include one or more elements selected from Cu, W, or V, wherein when Cu is present in the alloy, the amount of Cu is up to 0.3 wt% or less; when W is present in the alloy, the amount of W is up to 5.5 wt%; and when V is present in the alloy, the amount of V is up to 2.25 wt%. Thus, the layer-by-layer construction of the alloy provides for the formation of a martensitic matrix comprising one or more of Cr-borides, W-borides when W is present, or V-borides when V is present. It should be noted that reference to the presence of a martensitic matrix for the listed borides does not exclude the presence of some retained austenite / ferrite, which may also be present in the printed alloy parts.

[0047] Thus, the alloy composition may comprise 9.0 to 16.0 wt% Cr, 2.0 to 3.0 wt% Ni, 0.15 to 0.30 wt% Cu, 0.2 to 0.8 wt% Mo, 0.75 to 3.0 wt% Mn, 0.1 to 0.25 wt% C, and 0.25 to 0.75 wt% B. The balance is Fe. The alloy comprises Cr-borides in a martensitic matrix. Furthermore, upon heat treatment of the formed alloy component, Cr-rich borides may be formed, meaning that the predominant species of metallic element in the boride present is Cr. As an example, for the boride M2B_CB discussed further herein, the predominant metallic element in this boride will be Cr.

[0048] Thus, the alloy composition may comprise 9 to 16 wt% Cr, 2.0 to 3.0 wt% Ni, 0.2 to 0.8 wt% Mo, 0.75 to 3.0 wt% Mn, 0.1 to 0.25 wt% C, 0.25 to 0.75 wt% B, and 0.1 to 5.5 wt% W. The balance is Fe. The alloy comprises W-borides in a martensitic matrix. Furthermore, upon heat treatment of the formed alloy component, W-rich borides may now be formed, meaning that the predominant species characteristic of the metallic element in the boride present is W. As an example, for the boride M2B_C16 discussed further herein, the predominant metallic element in this boride will be W.

[0049] Thus, the alloy composition may comprise 9 to 16 wt% Cr, 2.0 to 3.0 wt% Ni, 0.2 to 0.8 wt% Mo, 0.75 to 3.0 wt% Mn, 0.1 to 0.25 wt% C, 0.25 to 0.75 wt% B, and 0.1 to 2.25 wt% V. The balance is Fe. The alloy comprises V-borides in a martensitic matrix. Furthermore, upon heat treatment of the formed alloy component, V-rich borides may now be formed, meaning that the predominant species characteristic of the metallic element in the boride present is V. As an example, for the boride MB_B33 discussed further herein, the predominant metallic element in this boride will be V.

[0050] With respect to the alloy compositions herein, it should be noted that they may contain incidental impurities. Such incidental impurities may include impurities present in a given commercial reagent element that is selected for use in preparing the alloy composition. The incidental impurities may also originate from the powder production process, such as nitrogen from gas atomization. Thus, the level of such incidental impurities may range up to, but not including, 0.1% by weight, and any may, for example, include nitrogen or some other residual element, again present at a level up to, but not including, 0.1% by weight.

[0051] The layers of the present invention are formed by melting an alloy in powder form, wherein the alloy powder comprises particles having a diameter of from 1.0 micrometers to 150 micrometers. In another embodiment, the powder comprises particles having a diameter of from 10 micrometers to 100 micrometers. In another embodiment, the powder comprises particles having a diameter of from 15 micrometers to 80 micrometers. Such powder form can be provided by gas atomization or water atomization of the above alloy composition. Then, the powder is laid down in a layer having a thickness of from 10 micrometers to 200 micrometers on a build surface. In another embodiment, then the powder is laid down in a layer having a thickness of from 20 micrometers to 100 micrometers on a build surface. In another embodiment, then the powder is laid down in a layer having a thickness of from 30 micrometers to 80 micrometers on a build surface. A high-energy light source, such as a laser or an electron beam, is then used to solidify the melted powder.

[0052] Forming one or more layers in this manner in any orientation or direction results in a formed state of the material volume having the following properties: a hardness of 35 HRC to 56 HRC measured by ASTM E18-20; a wear loss of 2.2 g or less measured by ASTM G65-16el procedure A; a yield strength of at least 700 MPa; a tensile strength of at least 1000 MPa; and an elongation of at least 0.25% measured by ASTM E8M-16ael Moreover, by ASTM E1245-03 optical microscopy measurement, the formed alloy has a porosity of less than or equal to 1.0%.

[0053] The alloy in the formed state is then heat-treated, which heat treatment is designed to affect or improve one or more properties, such as the wear resistance of the component. The heat treatment is also intended to increase the diameter of the borides present in the formed condition. Thus, for a given component having a set of initial properties in the formed condition, namely yield strength YS1, tensile strength TS1, elongation El, HRC hardness H1 and wear resistance W1 (mass loss measured in grams by ASTM G65-16el procedure A), after heat treatment, the component properties exhibit the following second values for yield strength (YS2), tensile strength (TS2), elongation (E2), HRC hardness (H2) and wear resistance (W2): YS2 > YS1, TS2 > TS1, E2 ≥ El, H2 = H1 + / - 10 and W2 < Wl. In addition, E2 is at least 5.0% higher than El and the value of W2 is at least 0.5% lower than W1.

[0054] Heat treatments that affect or improve properties and change the size of borides in the martensitic matrix are equivalent to heating at 900°C to 1200°C for at least 0.5 hours, followed by cooling, such as quenching. Furthermore, heating at 900°C to 1200°C for 0.5 to 9.0 hours, followed by cooling, may be performed. Following this heat treatment, tempering may be performed at 600°C or lower, or in the range of 100°C to 600°C, for a period of 10.0 minutes to 4.0 hours. The heat treatment process described in co-pending application U.S. Application No. 17 / 248,953 is incorporated herein by reference.

[0055] During PBF, a layer of powder having the alloy composition described herein is laid onto a platform or bed, called a substrate. A laser with a relatively small spot size then melts the powder at selected locations corresponding to the shape of the part to be printed. The molten metal cools relatively quickly and is expected to cool within 10 4 ℃ / s to 10 6 A solid, continuous layer forms on top of the substrate or previously printed layer, in the range of 100°C / s. This process repeats until the final part is formed. As the powder layer melts, the underlying printed metal undergoes another cycle of heating and cooling, with the temperature and cooling rate decreasing with distance from the powder layer. The localized nature of the melting, the confined substrate, and the cyclic heating and cooling can generate significant stresses.

[0056] During relatively rapid cooling from the melt, the microstructure of the alloys herein can transform from a primarily liquid austenite to martensite, a relatively hard and relatively brittle phase. The hardness of the martensitic microstructure is ideal for the selected application, and as described above, the alloys herein now contain one or more Cr-borides, W-borides, or V-borides. Notably, without being bound by any theory, it is believed that the presence of such borides provides the improved wear resistance disclosed herein (including after morphology and heat treatment). In this context, it is noteworthy that conventional forged tool steels, such as those used in high-wear applications, typically rely on carbon content not only to form hard martensite, but also to form carbides to enhance wear resistance. However, the transformation from austenite to martensite is associated with a volume change, the magnitude of which increases with increasing carbon content. If the volume of steel undergoing this transformation is confined, as is the case with PBF, stresses can evolve as a function of carbon content. Combined with the thermal stresses mentioned above, cracks can occur in the presence of brittle martensite at relatively high carbide contents.

[0057] Cracks can also occur during the solidification of the melt, a phenomenon known as solidification cracking. The relatively rapid solidification of PBF provides little opportunity for equilibrium conditions to be reached during solidification. Alloying elements undergo significant segregation in the liquid prior to solidification, continuously lowering the solidus temperature of the liquid. As a result, as the stresses increase, liquid or semi-solid regions may exist in the solidifying metal. When the liquid or semi-solid cannot support these stresses, cavitation occurs, leading to cracks. However, these alloying elements cannot be removed because they are required to promote the formation of martensite and carbides in the tool steel.

[0058] To overcome these challenges, it is now understood that the compositions herein have been designed to result in the formation of a microstructure consisting of a relatively hard martensitic matrix and a boride-rich second phase or precipitate that replaces and reduces the level of carbides upon which wear resistance enhancement depends. As described above, the compositions are such that upon heat treatment, they contain Cr-rich borides, V-rich borides, or W-rich borides, and carbon at a level of 0.1 wt. % to 0.25 wt. %.

[0059] Parts were printed using a commercially available PBF printer in an inert gas atmosphere (but either argon or nitrogen). The substrate was preheated between room temperature and 300°C, or between room temperature and 250°C. The substrate was preheated between room temperature and 200°C. A steel substrate with a similar coefficient of thermal expansion to the printed alloy is preferred, but other steels and nonferrous alloys are contemplated as possible substrates.

[0060] Printing parameters include laser power, laser speed, hatch spacing, and layer thickness. The laser power is between 100W and 1000W. In another embodiment, the laser power is between 150W and 800W. In yet another embodiment, the laser power is between 200W and 500W. The laser speed is between 100mm / s and 2000mm / s. In another embodiment, the laser speed is between 150mm / s and 1750mm / s. In yet another embodiment, the laser speed is between 200mm / s and 1500mm / s. The hatch spacing may be between 10 microns and 250 microns. In another embodiment, the hatch spacing is between 30 microns and 200 microns. In yet another embodiment, the hatch spacing is between 50 microns and 150 microns. The layer thickness is between 10 microns and 200 microns. In another embodiment, the layer thickness is between 20 microns and 100 microns. In yet another embodiment, the layer thickness is between 30 microns and 80 microns. However, each parameter is not mutually exclusive when it comes to printing parts with minimal defects, and furthermore, these values can change depending on the printer used and evolving printer technology. With this in mind, energy density is often used as a metric and is defined as follows:

[0061]

[0062] Where P is the laser power, h is the hatch spacing, l is the layer thickness, and v is the laser speed. Using this formula, the energy density of the alloy can be 10J / mm 3 Up to 500J / mm 3 In another embodiment, the energy density of the alloy can be 20 J / mm 3 Up to 400J / mm 3 In another embodiment, the energy density of the alloy may be preferably 30 J / mm 3 Up to 300J / mm 3 .

[0063] Volumetric build speed is calculated by multiplying the laser speed, hatch spacing, and layer thickness and is commercially important because it determines the relative cost and usability of parts printed using these alloys. The speed here can be 1cm 3 / h to 50cm 3 / h. In another embodiment, the speed may be 3cm 3 / h to 40cm 3 / h or 5cm 3 / h to 30cm 3 / h.

[0064] Using these parameters and conditions, defects such as porosity and cracks that negatively impact component performance are preferably minimized, which can be important for many applications, including tooling. Components produced from the alloy by PBF may have an average porosity of less than 1.0%. In another embodiment, the average porosity is less than 0.5%. In yet another embodiment, the average porosity is less than 0.3%.

[0065] Table 1 lists four alloy compositions that are present as examples of the present disclosure. These alloys are designed to form a boride phase in the martensitic matrix after printing and / or heat treatment. As described above, the boride phase includes one or more of Cr-boride, V-boride, or W-boride.

[0066] In alloys A1 and A2, the borides are more specifically Cr-rich, while in alloys A3 and A4, V-rich and W-rich borides are preferentially formed over Cr-rich borides by adding up to 2.25 wt. % V or up to 5.5 wt. % W, respectively. The level of Cr present also preferably contributes to the formation of a relatively hard martensite phase in the matrix.

[0067] Table 1

[0068] element A1 A2 A3 A4 Fe margin margin margin margin Cr 14.53 15.5 14.25 9.39 Ni 2.12 2.86 2.62 2.91 Cu 0.27 0.27 Mo 0.23 0.53 0.43 0.78 Si 0.7 0.84 0.5 Mn 0.9 0.81 0.77 2.7 W 5.05 V 2.17 C 0.21 0.14 0.13 0.14 B 0.68 0.31 0.39 0.38

[0069] Figure 1 、 Figure 2 and Figure 3The Scheil solidification diagrams for alloys A1, A3, and A4, calculated using Thermo-Calc software (Thermo-Calc Software GmbH, Version 2019a, TCFE9: TCS Steel / Iron-Alloy Database, v9), are shown, respectively. The Scheil solidification diagram was used because it best represents the rapid solidification that the powder undergoes as it melts and cools during the PBF printing process. The diagrams and calculations show that austenite forms early in the solidification process, followed by boride formation. The relatively rapid cooling of austenite below the martensite start temperature, Ms, results in the transformation of austenite into martensite. Ms is calculated based on the composition of the austenite phase and is given in Table 1. Figure 4 、 Figure 5 and Figure 6 Alloys Al, A3, and A4 are shown in the accompanying figures, respectively. Since most of the austenite formed in these alloys has a Ms above room temperature, martensite is expected to form. The borides in alloys A1, A3, and A4 are considered to be Cr-rich, V-rich, and W-rich, respectively. Although the chemical properties of these borides evolve during solidification, a representative composition of each boride phase is provided in each figure. That is, the figures identify the boride crystal structure as M2B_CB or M2B_C16 or MB_B33, where M refers to the specific metal element present in weight percentage. "Phase" refers to other possible solid state or crystal structures.

[0070] On an SLM280HL laser PBF printer, preheating to 200°C, bars of each alloy with dimensions of 1 cm × 1 cm × 1 cm, 6.7 cm × 1.4 cm × 1.4 cm, and 7.4 cm × 2.5 cm × 0.6 cm were printed. The laser power, speed, hatch spacing, and layer thickness used for each alloy are shown in Table 2, and the powder size distribution used for each alloy is shown in Table 3.

[0071] Table 2

[0072] Printing parameters A1 A2 A3 A4 Laser power (W) 280 300 300 350 Laser speed (mm / s) 400 1000 1000 1200 Hatch spacing (um) 100 120 100 100 Layer thickness (μm) 40 40 40 40 <![CDATA[Energy density (J / mm 3 )]]> 175 63 75 73 <![CDATA[Construction speed (cm 3 / hr)]]> 5.8 17.3 14.4 17.3

[0073] Table 3

[0074] alloy D10(μm) D50(μm) D90(μm) A1 17.3 28.4 45.5 A2 17.3 27.2 42.5 A3 15.9 24.6 38.1 A4 14.3 22.8 35.5

[0075] Figure 7 X-ray diffraction (XRD) results of bars made from Alloy A1 in Figure 3 show that the microstructure is predominantly martensite, as predicted by the alloy design and Thermo-Calc calculations. Figure 8 、 9The microstructure of these bars, shown in Figures 10 and 11 for alloys Al, A3, and A4, respectively, is dendritic, consistent with the segregation of alloying elements in the liquid during solidification and the formation of borides at the end of solidification. The darker phases decorating the periphery of the dendrites are likely borides, while the interior of the unit cell is martensite.

[0076] All printed rods are preferably crack-free and have a relatively low average porosity, ranging from 0.01% to 1.00%, as measured in accordance with ASTM E1245-03, which involves optical image analysis of micrographs of metallographic cross-sections of the component. More preferably, the component is free of visible cracks over a majority of the component's surface area at a magnification of up to 1000x, for example, 95% or more of the component's surface area. Thus, this includes 96% or more, 97% or more, 98% or more, 99% or more, or 100% of the component's surface area being free of visible cracks at a magnification of up to 1000x. Figure 11 、 12 , 13 and 14 show micrographs of 1 cm × 1 cm × 1 cm bars of the A1, A2, A3 and A4 alloys, respectively, as examples of the typical porosity observed in each alloy.

[0077] Table 4 lists the tensile properties, hardness, and wear mass loss of the shaped alloys listed in Table 1. Bars measuring 6.7 cm × 1.4 cm × 1.4 cm were tensile tested according to ASTM E8-16ael. Bars measuring 1 cm × 1 cm × 1 cm were hardness tested according to ASTM E18-20. Bars measuring 7.4 cm × 2.5 cm × 0.6 cm were wear tested according to ASTM G65-16e1 procedure A. Wear resistance is inversely proportional to mass loss (i.e., higher mass loss indicates lower wear resistance). For comparison, the tensile properties, hardness, and wear mass loss of conventional steels 316L, M300, 7-4PH, and H13 printed on the SLM280HL printer are also provided. Note that to print H13 without severe cracking, the powder bed needs to be preheated to 500°C.

[0078] Table 4

[0079]

[0080] When printed on a substrate or previously cured layer at 200°C, alloys A1, A2, and A4 exhibited higher as-formed hardness than the other alloys (316L, M300, and 17-4PH). Alloys A1 and A4 exhibited the same hardness as as-formed H13 printed at 500°C. Furthermore, alloys A1, A2, A3, and A4 exhibited lower wear mass loss, indicating better wear resistance than 316L and M300. Alloys A1 and A3 exhibited similar wear mass loss to H13, indicating similar wear resistance.

[0081] The wear resistance of tool steels is generally a function of precipitate size and distribution. The equilibrium phase diagrams for alloys A1, A3, and A4, generated by Thermo-Calc software, are shown in Figure 1. Figure 15 、 Figure 16 and Figure 17 As shown, it is shown that at 1000℃ or above 1000℃, austenite M is formed above room temperature. s , all precipitates except the boride dissolve, providing the opportunity to grow the boride phase within a commercially relevant temperature / time range. As mentioned above, the temperature is in the range of 900°C to 1200°C for 0.5 to 8.0 hours. Austenite has a calculated M of 165°C to 175°C. s , it is therefore expected that after aging at these temperatures the alloy will transform to martensite by quenching, retaining the hard martensitic matrix. Figure 18 、 Figure 19 and Figure 20 The microstructure of Alloy A1 is shown after aging at 1100°C for 2 hours, 4 hours, and 8 hours, followed by gas quenching, freezing at -85°C for 2 hours, and tempering at 175°C for 2 hours. This process is similar to the quenching and tempering commonly used for martensitic tool steels. Figure 8 The dendritic microstructure observed in the as-formed state is no longer present, replaced by a uniform structure consisting of nominally round borides in a martensitic matrix. The diameter of the borides increases with aging time, from 0.1 μm to 1 μm after 2 hours and from 1 μm to 4 μm after 8 hours. It is assumed that the size of these borides can also be controlled by the temperature of the aging step. After the same heat treatment as Alloy A1, the diameter of the borides increases with aging time, from 0.1 μm to 1 μm after 2 hours and from 1 μm to 4 μm after 8 hours. It is assumed that the size of these borides can also be controlled by the temperature of the aging step. After aging time of 2 hours and 8 hours respectively, the diameter of the borides increases with aging time. Figure 21 and Figure 22 Similar microstructural evolution was observed in alloy A3. Figure 23 Shown is the microstructural evolution of alloy A4 after the same heat treatment as alloy A1 and aging time of 8 h.

[0082] Table 5 shows the tensile properties, hardness, and wear mass loss of alloys A1, A2, A3, and A4 after heat treatment. The tensile properties, hardness, and wear mass loss were measured using the same method recorded as the as-formed values in Table 4. All tensile properties and hardness of alloys A1, A2, A3, and A4 were recorded on workpieces that were aged at 1100 °C for 8 hours, then gas quenched, frozen at -85 °C for 2 hours, and tempered at 175 °C for 2 hours. The wear mass loss of alloys A1, A2, A3, and A4 was recorded on workpieces that were aged at 1100 °C for 2 hours, then gas quenched, frozen at -85 °C for 2 hours, and tempered at 175 °C for 2 hours. For comparison, the values of printed and heat-treated M300, 17-4PH, and H13 are also provided. The heat treatments performed on these alloys were selected to maximize hardness. After printing, M300 was aged at 490 °C for 6 hours. After printing, 17-4PH was heat-treated according to the ASTM A564M H900 procedure. H13 was heated at 1050 °C for 0.5 hours, quenched, and tempered at 500 °C for 2 hours. As described above, and as confirmed in Table 5, for a given printed part having a set of initial properties in the as-formed condition, namely yield strength Yl, tensile strength TS1, elongation E1, HRC hardness HI, and wear resistance W1 (mass loss measured by ASTM G65-16e1 procedure A, in grams), after heat treatment, the properties showed a second set of values for yield strength (YS2), tensile strength (TS2), elongation (E2), HRC hardness (H2), and wear resistance (W2). As can be seen from Table 5, the heat-treated parts can be characterized by any one or more of these secondary values observed as follows: YS2 > YS1, TS2 > TS1, E2 ≥ E1, H2 = H1 + / - 10, and W2 < Wl. More preferably, E2 is at least 5.0% greater than E1, and W2 is numerically at least 0.5 lower than W1.

[0083] More specifically, for alloys Al, A2, A3, and A4, the heat treatment increased the yield strength, tensile strength, and elongation while reducing the wear mass loss in the as-formed state (i.e., increasing wear resistance). In particular, after heat treatment, the alloys herein showed an elongation of at least 5.0%, an HRC hardness of at least 50, and a wear resistance (mass loss measured by ASTM G65-16e1 procedure A, in grams) less than or equal to 1.90. The wear mass loss of alloys A1, A2, and A3 was lower than that of all conventional steels. The hardness after heat treatment increased for alloy A3 from the as-formed state but decreased for alloys A1, A2, and A4. Nevertheless, the hardness of all new alloys remained above 50 HRC. Since the size and distribution of precipitates can be controlled by aging time and / or temperature, as Figure 18 、 19As shown in the A1 alloy in Figure 20, it is expected that wear resistance can be tailored to specific applications.

[0084] Table 5

[0085]

[0086] The foregoing description of several methods and embodiments has been presented for illustrative purposes and is not intended to limit the claims to the precise steps and / or forms disclosed.

[0087] Although exemplary embodiments have been described above, it is not intended that these embodiments describe all possible forms of the present invention. On the contrary, the words used in the specification are descriptive rather than restrictive, and it should be understood that various changes can be made without departing from the spirit and scope of the present invention. In addition, the features of various implementation embodiments can be combined to form further embodiments of the present invention.

Claims

1. A method for constructing a metal component layer by layer, comprising: Particles of an iron-based alloy are provided, the iron-based alloy comprising: 9.0 to 16.0 wt% Cr; 2.0 wt% to 3.0 wt% Ni; 3.0 wt% or less of Mo; 3.0 wt% or less of Mn; 0.1 wt% to 0.30 wt% C; 0.25 wt% to 1.0 wt% of B; One or more elements selected from W and V, wherein: When W is present, the amount of W is up to 7.5 wt%; When V is present, the amount of V is up to 3.5 wt%; The balance of the iron-based alloy comprises Fe; and forming a shaped metal part at least in part by powder bed fusion, comprising melting the particles into a molten state, and cooling and forming one or more solidified layers of the iron-based alloy, the iron-based alloy comprising a martensitic matrix and one or more of Cr-boride, W-boride when W is present, or V-boride when V is present, wherein the shaped part has an HRC hardness of H1 and a wear resistance of W1, wherein the wear resistance is mass loss in grams as measured by ASTM G65-16e1 Procedure A; and Heat treating the component, wherein the heat treated component exhibits an HRC hardness of H2 and a wear resistance of W2, wherein W2 <W1。 2. The method according to claim 1, wherein The formed part has a tensile strength of at least 1000 MPa, a yield strength of at least 700 MPa, an elongation of at least 0.25%, and an HRC hardness of at least 40.

3. The method according to claim 1, wherein After heat treatment, the metal component has an elongation of at least 5.0%, an HRC hardness of at least 50, and a wear resistance of less than or equal to 1.90, wherein the wear resistance is mass loss in grams as measured by ASTM G65-16e1 Procedure A.

4. The method according to claim 1, wherein The heat treatment includes heating at a temperature of 900° C. to 1200° C. for 0.5 to 8.0 hours.

5. The method according to claim 1, wherein The iron-based alloy further comprises 0.15 wt% to 0.30 wt% Cu; when W is present, the amount of W is 0.1 wt% to 5.5 wt%; and when V is present, the amount of V is 0.1 wt% to 2.25 wt%.

6. The method of claim 1, wherein The alloy after heat treatment contains Cr-rich boride phase.

7. The method of claim 1, wherein The alloy includes 0.1 wt % to 5.5 wt % W, and the alloy after heat treatment includes a W-rich boride phase.

8. The method of claim 1, wherein The alloy contains 0.1 wt % to 2.25 wt % V, and the alloy after heat treatment contains a V-rich boride phase.

9. The method of claim 1, wherein The alloy comprises: 9.0 to 16.0 wt% Cr; Up to 3.0 wt% Ni; 0.2 wt% to 0.8 wt% Mo; 0.75 wt% to 3.0 wt% Mn; 0.1 wt% to 0.25 wt% C; 0.25 wt% to 0.75 wt% of B.

10. The method of claim 1, wherein The alloy comprises: When Cu is present, the amount of Cu is up to 0.8 wt %; When W is present, the amount of W is up to 5.5 wt%; When V is present, the amount of V is up to 2.5 wt%.

11. A method of constructing a metal component layer by layer, comprising: Particles of an iron-based alloy are provided, the iron-based alloy comprising: 9.0 to 19.0 wt% Cr; 2.0 wt% to 3.0 wt% Ni; 0.2 wt% to 0.8 wt% Mo; 0.75 wt% to 3.0 wt% Mn; 0.1 wt% to 0.25 wt% C; 0.25 wt% to 0.75 wt% of B; One or more elements selected from W and V, wherein: When W is present, the amount of W is up to 5.5 wt%; When V is present, the amount of V is up to 2.25 wt%; The balance of the iron-based alloy comprises Fe; and forming a shaped metal part at least in part by powder bed fusion, comprising melting the particles into a molten state, and cooling and forming one or more solidified layers of an iron-based alloy comprising a martensitic matrix and one or more of a Cr-boride, a W-boride when W is present, or a V-boride when V is present, wherein the shaped part has an HRC hardness of H1 and a wear resistance of W1, wherein the wear resistance is mass loss in grams as measured by ASTM G65-16e1, Procedure A; and heat treating the component, wherein the heat treated component exhibits an HRC hardness of H2 and a wear resistance of W2, wherein: H2 = H1 + / - 10; and W2 <W1。

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