A stainless steel alloy and additive manufacturing method thereof

Abstract

The present invention relates to a stainless steel alloy and an additive manufacturing method thereof, wherein the mass percentage range of the element composition of the stainless steel alloy is: Cr 13.8-18.3%, Ni 29.5-33.0%, Ti 4.5-5.8%, Al 1.8-2.8%, C≤0.10%, O≤500ppm, Fe is the balance, and the additive manufacturing method comprises the following steps: S1: preparing Fe-Cr-Ni-Ti-Al stainless steel alloy powder by gas atomization after taking each metal raw material according to the design ratio and preparing it into a stainless steel ingot; S2: preparing an alloy block by laser powder bed fusion technology; S3: performing aging treatment on the alloy block. Compared with the prior art, the present invention can obtain a new precipitation hardened austenitic stainless steel with excellent mechanical properties, with a yield strength of up to 1168-1470MPa, an ultimate tensile strength of up to 1471-1694MPa, and a uniform elongation of 7.5-11.6%.

Description

Technical Field

[0001] The present invention relates to the technical field of additive manufacturing alloy materials, and in particular to a stainless steel alloy and an additive manufacturing molding method thereof. Background Art

[0002] With the development of manufacturing level, the advanced manufacturing industry has continuously improved the performance and manufacturability of parts. Laser-powder bed fusion (LPBF) additive manufacturing technology has the characteristics of high design freedom, fast preparation and molding speed, and short industrial chain, and has unique advantages in the preparation of complex structural parts. Additively manufactured austenitic stainless steel (e.g., 316, 304 series stainless steel) printing state usually has higher mechanical properties than traditional materials (yield strength can be significantly improved to (~400-600MPa) without too much loss of ductility). Therefore, the additive manufacturing process and mechanical property evaluation of such alloys have become a research hotspot in the industry, but stainless steel products prepared by relying on the traditional alloy composition range are difficult to meet the application scenarios that require higher strength. Breaking through the traditional austenitic stainless steel composition range and developing new stainless steel materials suitable for additive manufacturing processes based on the characteristics of additive manufacturing processes can further improve the mechanical properties of such alloys, thereby further broadening the application range of austenitic stainless steel. However, there are still few studies on the design of new stainless steel powder composition, additive manufacturing process and its mechanical property evaluation, and the additive manufacturing and development of stainless steel are still mostly aimed at traditional alloys. For example, Chinese patent CN 113263173 A and Chinese patent CN 114700499 A respectively announced a high-strength hydrogen embrittlement-resistant additive manufacturing austenitic stainless steel and a nitrogen-controlled stainless steel additive preparation process, but the mechanical properties of their materials still fall within the range of traditional additive austenitic stainless steel. Summary of the invention

[0003] The purpose of the present invention is to provide a stainless steel alloy and an additive manufacturing method thereof, which have excellent mechanical properties.

[0004] The object of the present invention can be achieved by the following technical scheme: a stainless steel alloy, wherein the mass percentage range of the element composition of the stainless steel alloy is: Cr 13.8-18.3%, Ni 29.5-33.0%, Ti 4.5-5.8%, Al 1.8-2.8%, C≤0.10%, O≤500ppm, and Fe is the balance.

[0005] An additive manufacturing method for the above-mentioned stainless steel alloy comprises the following steps:

[0006] S1: preparing Fe-Cr-Ni-Ti-Al stainless steel alloy powder by mixing various metal raw materials according to the designed proportion (Cr 13.8-18.3%, Ni 29.5-33.0%, Ti 4.5-5.8%, Al 1.8-2.8%, C≤0.10%, O≤500ppm, Fe as the balance) into stainless steel ingots and then using gas atomization method to prepare Fe-Cr-Ni-Ti-Al stainless steel alloy powder;

[0007] S2: Fe-Cr-Ni-Ti-Al stainless steel alloy powder is prepared into alloy blocks using laser powder bed fusion technology;

[0008] S3: performing aging treatment on the alloy block.

[0009] Preferably, in step S1, a stainless steel ingot is prepared in a vacuum melting furnace, and the atomization method is to use argon gas atomization in a low oxygen environment (<500ppm).

[0010] Preferably, the Fe-Cr-Ni-Ti-Al stainless steel alloy powder in step S1 has a particle size range of 15-150 μm and a sphericity of ≥0.85 to ensure powder fluidity.

[0011] Further preferably, the particle size range of the Fe-Cr-Ni-Ti-Al stainless steel alloy powder in step S1 is 15-56 μm.

[0012] Preferably, the laser powder bed fusion technology in step S2 is performed using an EOS290M laser powder bed fusion printer.

[0013] Preferably, in the laser powder bed fusion technology described in step S2, the laser head power is 114-264W, the scanning speed is 323-1847mm / s, the layer spacing is 0.03mm, the scanning spacing is 0.1mm, and the laser deposition body energy density range is 48-118J / mm 3 The scanning strategy is 67° layer-by-layer cross scanning.

[0014] Preferably, a stainless steel substrate is used in step S2 and the substrate is preheated to 75-85° C. before printing. During the printing process, high-purity argon gas is filled and the oxygen content in the chamber is ensured to be less than 0.1% to prevent oxidation of the powder.

[0015] More preferably, a stainless steel substrate is used in step S2 and the substrate is preheated to 80° C. before printing.

[0016] Preferably, step S3 is to perform high temperature short-time aging treatment on the alloy block to precipitate the strengthening phase.

[0017] Further preferably, the aging treatment process includes rapidly cooling after keeping at 500-950°C for a period of time.

[0018] More preferably, after being kept at 600-750° C. for 1-3 hours, the alloy block is quickly placed in water at room temperature for cooling.

[0019] Preferably, the muffle furnace is first heated to a preset temperature, and then the alloy block is placed in it to keep it warm for 2 hours, and then quickly placed in room temperature water to cool.

[0020] Based on the composition of traditional austenitic stainless steel, the present invention increases the Ni content and adds appropriate Ti and Al elements to precipitate dispersed precipitation phases in the austenite lattice matrix, and combines the dislocation cell structure formed by rapid cooling of additive manufacturing to improve the mechanical properties of the material. On this basis, the present invention further explores the additive manufacturing molding method and heat treatment process of the new stainless steel powder.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] 1. The present invention designs a new type of high-strength austenitic stainless steel alloy powder composition, and uses laser powder bed fusion technology to explore the additive manufacturing molding window of this new type of additive manufacturing high-strength stainless steel. The powder has a wide range of effective molding parameters, specifically: laser head energy: 164-264W, powder layer thickness 0.03mm, scanning spacing 0.09mm, and the corresponding laser injection body energy density range is 48-118J / mm 3 The molded material has no obvious pores, high density (≥99.5%), and excellent mechanical properties (the yield strength of the original material is 775MPa, the ultimate tensile strength is 1118MPa, and the uniform elongation is 16.4%).

[0023] 2. The aging heat treatment of the present invention can further improve the strength of the material. After aging, the yield strength of the material can reach 1168-1470MPa, the ultimate tensile strength can reach 1471-1694MPa, and the uniform elongation is 7.5-11.6%.

[0024] 3. The stainless steel alloy produced by the present invention has excellent mechanical properties and can be applied in the field of advanced manufacturing, and can be used to prepare complex structural parts and high-strength parts. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Schematic diagram of metal powder prepared by gas atomization method of the present invention;

[0026] Figure 2 is a particle size distribution diagram of the metal powder prepared by the gas atomization method of the present invention;

[0027] Figure 3 Optical microscope image of the trial sample prepared by the present invention;

[0028] Figure 4 This is a relationship diagram between the process parameters and relative density of the novel additive manufacturing high-strength stainless steel of the present invention;

[0029] Figure 5 This is a scanning electron microscope image of the new additively manufactured high-strength stainless steel of the present invention;

[0030] Figure 6 It is the relationship diagram between aging temperature and Vickers hardness value;

[0031] Figure 7 The tensile properties of the original and aged states are shown in Figure 2. DETAILED DESCRIPTION

[0032] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0033] Example 1

[0034] A stainless steel alloy, whose alloy elements are selected from Cr, Ni, Ti, Al, and Fe, is prepared by smelting to prepare stainless steel ingots, preparing alloy powders by gas atomization, preparing alloy blocks by laser powder bed fusion technology, and high-temperature short-time aging treatment to obtain a new type of precipitation hardening austenitic stainless steel with excellent mechanical properties. The details are as follows:

[0035] S1. Preparation of Fe-Cr-Ni-Ti-Al stainless steel alloy powder

[0036] a. Melting the raw materials in a vacuum melting furnace to prepare stainless steel ingots;

[0037] b. Fe-Cr-Ni-Ti-Al stainless steel alloy powder is prepared by gas atomization method, and the particle size range of the prepared alloy powder is 15-150 μm;

[0038] S2. Preparation of alloy blocks by laser powder bed fusion technology

[0039] a. Screen out the main particle size distribution range of 15-56μm, and the powder particle size characteristic is D 10 =26.8μm, D 50 =38.8μm, D 90 =55.8μm (such as Figure 2 ) of powder suitable for laser powder bed fusion process, and the alloy specimens were prepared by using EOS290M laser powder bed fusion printer;

[0040] b. As shown in Table 1, the range of process parameters for additive manufacturing that can be formed is determined as follows: laser head power is 114-264W, scanning speed is 323-1847mm / s, layer spacing is 0.03mm, scanning spacing is 0.1mm, and laser deposition volume energy density range is 48-118J / mm 3 The scanning strategy was 67° layer-by-layer cross scanning to produce molding samples No. 1 to 32.

[0041] S3. Heat treatment process control

[0042] a. As shown in Table 2, the No. 4 molded sample was subjected to a high-temperature short-time aging treatment at a temperature of 500-950°C in a muffle furnace (temperature interval of 50°C, insulation for 2h) to precipitate the strengthening phase.

[0043] Performance evaluation:

[0044] (1) The scanning electron microscope image of the alloy powder obtained in step b of step S1 is as follows: Figure 1 As shown, the spheroidization rate of the powder is detected to be greater than 0.9. The alloy composition of the powder is measured using an inductively coupled plasma atomic emission spectrometer (ICP-AES), and the oxygen content in the powder is measured using a gas analyzer, and the alloy composition is measured to be within the required range.

[0045] (2) The density of the molded sample obtained in step b of step S2 is evaluated. The density is measured by metallographic polishing and optical microscopy. The optical microscopy obtained is as follows: Figure 3 As shown, the relationship between the bulk density and volume energy density of the powder is obtained as follows: Figure 4 The relationship between parameters and density is summarized in Table 1

[0046] (3) Taking the No. 4 molded sample as an example, the typical microstructure is measured as follows Figure 5 As shown, the matrix of the material is austenite, and there are printing structures such as dislocation cell structures.

[0047] (4) Hardness evaluation was performed on the original state of molded sample No. 4 and the aged state samples obtained by different isothermal treatments (e.g. Figure 6 and Table 2), and obtain its high strength heat treatment range (600-800°C, hardness of 453-524Hv).

[0048] (5) The original sample and the aged samples after three preferred heat treatment processes (①600℃ / 2h, ②700℃ / 2h and ③750℃ / 2h) were subjected to uniaxial tensile tests parallel to the printing direction, and the tensile performance curves were obtained (such as Figure 7As shown). Among them, the yield strength of the original material is 775MPa, the ultimate tensile strength is 1118MPa, and the uniform elongation is 16.4%; the yield strength of the aged material can reach 1168-1470MPa, the ultimate tensile strength can reach 1471-1694MPa, and the uniform elongation range is 7.5-11.6%.

[0049] Table 1 Additive manufacturing process parameters and relative density of samples

[0050]

[0051]

[0052] Table 2 Trial parameters Vickers hardness of sample No. 4 in original state and after aging

[0053] Aging temperature,℃ <![CDATA[Vickers hardness, Hv 0.2 > RT 331±35 500 366±9 550 393±12 600 455±10 650 494±14 700 523±6 750 524±9 800 453±7 850 357±6 900 297±7 950 287±5

[0054] The above description of the embodiments is to facilitate the understanding and use of the invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the scope of protection of the present invention.

Claims

1. A stainless steel alloy, characterized in that: The mass percentage range of the element composition of the stainless steel alloy is: Cr13.8-18.3%, Ni 29.5-33.0%, Ti 4.5-5.8%, Al 1.8-2.8%, C≤0.10%, O≤500ppm, and Fe is the balance; The additive manufacturing method of the stainless steel alloy comprises the following steps: S1: preparing various metal raw materials according to the designed proportions to form stainless steel ingots, and then preparing Fe-Cr-Ni-Ti-Al stainless steel alloy powder by gas atomization method; S2: Fe-Cr-Ni-Ti-Al stainless steel alloy powder is prepared into alloy blocks using laser powder bed fusion technology; S3: performing aging treatment on the alloy block; The Fe-Cr-Ni-Ti-Al stainless steel alloy powder in step S1 has a particle size range of 15-150 μm and a sphericity of ≥0.

85.

2. The stainless steel alloy according to claim 1, characterized in that Step S1 is to prepare a stainless steel ingot in a vacuum melting furnace, and the atomization method is to use argon gas atomization in a low oxygen environment.

3. The stainless steel alloy according to claim 1, characterized in that The particle size range of the Fe-Cr-Ni-Ti-Al stainless steel alloy powder in step S1 is 15-56 μm.

4. The stainless steel alloy according to claim 1, characterized in that In the laser powder bed fusion technology described in step S2, the laser head power is 114-264W, the scanning speed is 323-1847mm / s, the layer spacing is 0.03mm, the scanning spacing is 0.1mm, and the laser deposition body energy density range is 48-118J / mm 3 The scanning strategy is 67° layer-by-layer cross scanning.

5. The stainless steel alloy according to claim 1, characterized in that In step S2, a stainless steel substrate is used and preheated to 75-85° C. before printing. During the printing process, high-purity argon gas is filled and the oxygen content in the chamber is ensured to be less than 0.1%.

6. The stainless steel alloy according to claim 1, characterized in that Step S3 performs high temperature short time aging treatment on the alloy block to precipitate strengthening phase.

7. The stainless steel alloy according to claim 6, characterized in that The aging treatment process includes keeping the temperature at 500-950° C. for a period of time and then cooling rapidly.

8. The stainless steel alloy according to claim 7, characterized in that After keeping the alloy at 600-750°C for 1-3 hours, quickly put the alloy block into room temperature water to cool it down.

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