Heat treatment method for selective laser melting 430 stainless steel formed part and application

Abstract

The invention provides a heat treatment method for a selective laser melting 430 stainless steel formed part, which comprises the following steps: annealing the selective laser melting 430 stainless steel formed part, heating from room temperature to 840-860 DEG C at a heating rate of 10-20 DEG C / min, preserving heat for 30 minutes, and cooling to room temperature to obtain the heat-treated selective laser melting 430 stainless steel formed part. According to the method, the residual thermal stress of the selective laser melting 430 stainless steel in the forming process can be effectively reduced or eliminated, the plasticity of a formed part is improved, the material obtains excellent strength and plasticity matching performance, and the reliability of the part in the service process is ensured.

Description

Technical Field

[0001] The present invention belongs to the technical field of stainless steel heat treatment, and in particular relates to a heat treatment method and application of a selective laser melting 430 stainless steel formed part. Background Art

[0002] 430 stainless steel is an acid-resistant and corrosion-resistant material based on a ferrite matrix, widely used in aerospace, medical, chemical, and machinery manufacturing. Stainless steel can be broadly categorized into martensitic, austenitic, ferritic, and duplex stainless steels based on their chemical composition and microstructure. Ferritic stainless steel is a key stainless steel type, second only to austenitic stainless steel in production volume. Compared to austenitic stainless steel, ferritic stainless steel is more affordable and offers superior processability. It also exhibits excellent corrosion resistance in certain corrosive environments. Therefore, in certain applications, 430 ferritic stainless steel is an ideal alternative to 304 stainless steel, offering a more cost-effective alternative. This material exhibits high strength, high thermal conductivity, low linear expansion coefficient, and excellent corrosion resistance, making it widely used in industries such as automotive, water treatment, construction, power generation, and chemical equipment.

[0003] With the development of industrial technology, traditional processing methods face many difficulties in producing complex structural parts and small, micro-precision devices, such as high processing costs and difficulty meeting precision and performance requirements, which greatly limit the application of 430 stainless steel. The rise of additive manufacturing technology has provided a new solution for the production of fine and complex parts, overcoming the limitations of traditional manufacturing methods. Selective Laser Melting (SLM), as an advanced additive manufacturing technology, can quickly form complex parts, but it is prone to generating a large amount of residual thermal stress and high-density dislocations during the forming process. Although these properties can improve the strength and hardness of the material, they can also reduce the plasticity of the formed part and cause warping, deformation, and cracks in the formed part.

[0004] To improve the mechanical properties of SLM 430 stainless steel parts and eliminate residual thermal stresses, appropriate post-heat treatment processes are necessary. Reducing or eliminating residual thermal stresses while improving the overall performance of the part ensures its reliability during service. This study used SLM 430 stainless steel as the research object. By analyzing the changes in microstructure, mechanical properties, and corrosion resistance at different heat treatment temperatures and comparing them with as-rolled specimens, the optimal post-heat treatment temperature was determined. This study provides a reference for optimizing the post-heat treatment process of SLM 430 stainless steel in practical engineering applications. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to address the deficiencies of the above-mentioned existing technologies and provide a heat treatment method and application for selective laser melting of 430 stainless steel formed parts. This method can solve the residual thermal stress and high-density dislocations caused by the extremely rapid melting-solidification process in the SLM process, thereby ensuring the service safety of selective laser melted 430 stainless steel parts in engineering applications.

[0006] To solve the above technical problems, the present invention adopts a technical solution: a heat treatment method for selective laser melting 430 stainless steel formed parts, the method comprising: The selective laser melted 430 stainless steel formed parts were annealed by heating from room temperature to 840°C to 860°C at a heating rate of 10°C / min to 20°C / min, keeping the temperature for 30 minutes, and cooling to room temperature to obtain the heat-treated selective laser melted 430 stainless steel formed parts.

[0007] After heat treatment, the fusion line trajectory of SLM 430 stainless steel disappears, while the cross-sectional melt path features perpendicular to the printing direction and the columnar crystal features parallel to the printing direction still exist. As the heat treatment temperature increases, it gradually tends to be equiaxed, and the grain orientation is randomly distributed.

[0008] After heat treatment at 840℃~860℃, the residual thermal stress in the original selective laser melted 430 stainless steel formed specimens was eliminated and the dislocation density was significantly reduced.

[0009] Preferably, the preparation method of the selective laser melting 430 stainless steel formed part is: forming the 430 stainless steel formed part by a selective laser melting process, the process parameters are: laser power is 200W, powder thickness is 40μm, substrate material is 316L stainless steel, preheating temperature is 100℃, scanning speed is 600mm / s, scanning line spacing is 0.08mm, spot diameter is 100μm, and the scanning strategy selects "S"-shaped stacking fault rotation of 67°.

[0010] Preferably, the 430 stainless steel formed part is a cubic block specimen of 100 mm×100 mm×100 mm.

[0011] Preferably, the cooling method is water cooling.

[0012] Preferably, the hardness of the selective laser melted 430 stainless steel formed part after heat treatment is 180HV to 210HV, the yield strength is 540MPa to 560MPa, the tensile strength is 590MPa to 610MPa, the elongation is 32.4% to 35%, the corrosion potential Ecorr is -0.731V to -0.721V, and the corrosion current density Icorr is 2.159×10 -10 A.cm -2 ~2.513×10-10 A.cm -2 .

[0013] The present invention also provides an application of the selective laser melted 430 stainless steel formed parts after the above-mentioned heat treatment method. The selective laser melted 430 stainless steel formed parts after the heat treatment are used to manufacture small precision metal components with complex structures, high dimensional accuracy and harsh service conditions.

[0014] The selective laser melted 430 stainless steel formed part after heat treatment has good comprehensive mechanical properties, corrosion resistance and dimensional stability.

[0015] Compared with the prior art, the present invention has the following advantages: The present invention significantly improves the hardness, yield strength and tensile strength of 430 stainless steel formed parts by precisely controlling the heat treatment process parameters, while also improving the elongation, so that the formed parts have better mechanical properties. After the optimized heat treatment process, the corrosion resistance of the formed parts is effectively improved, the corrosion potential and corrosion current density are reduced, and the formed parts have a longer service life in a corrosive environment. After heat treatment, the grain structure of the formed parts tends to be equiaxed, and the grain orientation is randomly distributed, which significantly improves the microstructure and thus improves the overall performance of the material. Through annealing treatment, the residual stress and dislocation density in the formed parts are significantly reduced, and the mechanical properties and stability of the material are improved. The present invention successfully improved the comprehensive performance of 430 stainless steel formed parts through selective laser melting and optimized heat treatment process, and has significant industrial application value and broad market prospects.

[0016] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 These are the austenite-martensite microstructure diagrams of the cross-section and longitudinal sections of SLM 430 stainless steel at different heat treatment temperatures in Example 1 of the present invention and Comparative Examples 1-2, where (a) and (d) are at 850°C; (b) and (e) are at 950°C; and (c) and (f) are at 1050°C.

[0018] Figure 2 Figures 1 and 2 show tensile fracture morphologies of SLM 430 stainless steel subjected to different heat treatment temperatures in Example 1 and Comparative Examples 1-2 of the present invention, where (a) and (d) are at 850°C; (b) and (e) are at 950°C; and (c) and (f) are at 1050°C. DETAILED DESCRIPTION

[0019] Example 1 The heat treatment method of the selective laser melting 430 stainless steel formed part of this embodiment is as follows: The selective laser melted 430 stainless steel formed parts were annealed by heating from room temperature to 850°C at a heating rate of 15°C / min, keeping the temperature for 30 minutes, and cooling to room temperature to obtain the heat-treated selective laser melted 430 stainless steel formed parts.

[0020] The preparation method of 430 stainless steel formed parts by selective laser melting is as follows: the 430 stainless steel formed parts are formed by selective laser melting process, and the process parameters are as follows: laser power is 200W, powder thickness is 40μm, substrate material is 316L stainless steel, preheating temperature is 100℃, scanning speed is 600mm / s, scanning line spacing is 0.08mm, spot diameter is 100μm, and the scanning strategy selects "S"-shaped stacking fault rotation of 67°.

[0021] The 430 stainless steel formed part is a cubic block specimen with a size of 100 mm × 100 mm × 100 mm.

[0022] The cooling method in this embodiment is water cooling.

[0023] The hardness of the selective laser melted 430 stainless steel formed part after heat treatment is 200HV, the yield strength is 550MPa, the tensile strength is 600MPa, the elongation is 34%, the corrosion potential Ecorr is -0.721V, and the corrosion current density Icorr is 2.159×10 -10 A.cm -2 .

[0024] Microstructure and mechanical properties of samples after heat treatment: After heat treatment in this embodiment, the fusion line trajectory of the SLM 430 stainless steel disappeared, while the cross-sectional melt path features perpendicular to the printing direction and the columnar crystal features parallel to the printing direction still existed. As the heat treatment temperature increased, it gradually tended to be equiaxed, and the grain orientation was randomly distributed.

[0025] After heat treatment at 850℃, the residual thermal stress in the original selective laser melted 430 stainless steel formed specimens was eliminated and the dislocation density was significantly reduced.

[0026] Comparative Example 1 The heat treatment method of the selective laser melted 430 stainless steel formed part in this comparative example is the same as that in Example 1, except that the temperature is raised from room temperature to 950° C. during the annealing treatment.

[0027] Comparative Example 2 The heat treatment method of the selective laser melted 430 stainless steel formed part in this comparative example is the same as that in Example 1, except that the temperature is raised from room temperature to 1050° C. during the annealing treatment.

[0028] Figure 1The microstructure of the cross-section and longitudinal section of SLM 430 stainless steel at different heat treatment temperatures is presented. Figure 1 (a) Figure 1 (b) Figure 1 (c) Microstructure of the cross section of SLM 430 stainless steel after heat treatment at 850°C, 950°C, and 1050°C (Example 1, Comparative Examples 1-2), Figure 1 (d) Figure 1 (e) Figure 1 (f) Microstructure of the longitudinal section of SLM 430 stainless steel after heat treatment at 850°C, 950°C, and 1050°C (Example 1, Comparative Examples 1-2). It is observed that the fusion line feature in the longitudinal section completely disappears after heat treatment.

[0029] Figure 2 The tensile fracture morphology at different heat treatment temperatures. Figure 2 (d) Figure 2 (e) 、 2(f) are Figure 2 (a) Figure 2 (b) Figure 2 (c) A partial enlarged view. The main feature of the tensile specimen after heat treatment is a large number of dimples, showing excellent macroscopic plastic fracture behavior, which is a typical plastic fracture feature. However, as the heat treatment temperature increases, the number and diameter of the dimples first increase and then decrease. In addition, Figure 2 (b) Figure 2 (e) 950℃ and Figure 2 (c) Figure 2 (f) The tensile fracture surface of the 1050℃ specimen also has many holes and shows certain cleavage fracture characteristics. Figure 2 (a) Figure 2 (d) After heat treatment at 850°C, the specimen exhibits the best strength-ductility combination. The fracture surface of the tensile specimen is mainly characterized by a large number of dimples, indicating excellent ductile fracture behavior.

[0030] Example 2 The heat treatment method of the selective laser melting 430 stainless steel formed part of this embodiment is as follows: The selective laser melted 430 stainless steel formed part was annealed by heating from room temperature to 840°C at a heating rate of 10°C / min, keeping the temperature for 100 minutes, and cooling to room temperature to obtain the heat-treated selective laser melted 430 stainless steel formed part.

[0031] The preparation method of 430 stainless steel formed parts by selective laser melting is as follows: the 430 stainless steel formed parts are formed by selective laser melting process, and the process parameters are as follows: laser power is 200W, powder thickness is 40μm, substrate material is 316L stainless steel, preheating temperature is 100℃, scanning speed is 600mm / s, scanning line spacing is 0.08mm, spot diameter is 100μm, and the scanning strategy selects "S"-shaped stacking fault rotation of 67°.

[0032] The 430 stainless steel formed part is a cubic block specimen with a size of 100 mm × 100 mm × 100 mm.

[0033] The cooling method in this embodiment is water cooling.

[0034] The hardness of the selective laser melted 430 stainless steel formed part after heat treatment is 210HV, the yield strength is 540MPa, the tensile strength is 590MPa, the elongation is 35%, the corrosion potential Ecorr is -0.728V, and the corrosion current density Icorr is 2.342×10 -10 A.cm -2 .

[0035] After heat treatment, the fusion line trajectory of SLM 430 stainless steel disappears, while the cross-sectional melt path features perpendicular to the printing direction and the columnar crystal features parallel to the printing direction still exist. As the heat treatment temperature increases, it gradually tends to be equiaxed, and the grain orientation is randomly distributed.

[0036] After heat treatment at 840℃, the residual thermal stress in the original selective laser melted 430 stainless steel formed specimen was eliminated and the dislocation density was significantly reduced.

[0037] Example 3 The heat treatment method of the selective laser melting 430 stainless steel formed part of this embodiment is as follows: The selective laser melted 430 stainless steel formed part was annealed by heating from room temperature to 860°C at a heating rate of 20°C / min, keeping the temperature for 30 minutes, and cooling to room temperature to obtain the heat-treated selective laser melted 430 stainless steel formed part.

[0038] The preparation method of 430 stainless steel formed parts by selective laser melting is as follows: the 430 stainless steel formed parts are formed by selective laser melting process, and the process parameters are as follows: laser power is 200W, powder thickness is 40μm, substrate material is 316L stainless steel, preheating temperature is 100℃, scanning speed is 600mm / s, scanning line spacing is 0.08mm, spot diameter is 100μm, and the scanning strategy selects "S"-shaped stacking fault rotation of 67°.

[0039] The 430 stainless steel formed part is a cubic block specimen with a size of 100 mm × 100 mm × 100 mm.

[0040] The cooling method in this embodiment is water cooling.

[0041] The hardness of the selective laser melted 430 stainless steel formed part after heat treatment is 180HV, the yield strength is 560MPa, the tensile strength is 610MPa, the elongation is 32.4%, the corrosion potential Ecorr is -0.731V, and the corrosion current density Icorr is 2.513×10 -10 A.cm -2 .

[0042] After heat treatment, the fusion line trajectory of SLM 430 stainless steel disappears, while the cross-sectional melt path features perpendicular to the printing direction and the columnar crystal features parallel to the printing direction still exist. As the heat treatment temperature increases, it gradually tends to be equiaxed, and the grain orientation is randomly distributed.

[0043] After heat treatment at 860℃, the residual thermal stress in the original selective laser melted 430 stainless steel formed specimens was eliminated and the dislocation density was significantly reduced.

[0044] Therefore, after heat treatment at 840°C to 860°C, the present invention can effectively reduce or eliminate residual thermal stress in SLM430 stainless steel during the forming process. Compared to SLM430 before heat treatment, its elongation is increased from 27% to 32.4% to 35%, effectively improving the plasticity of the formed parts, enabling the material to achieve excellent strength-to-plasticity matching, and solving the problems of warping, deformation, and cracking in the formed parts. According to statistics, one-fifth of the specimens before heat treatment showed varying degrees of edge warping and microcracks. However, after optimal heat treatment, the forming stability reached 100%, with no warping or cracking occurring, significantly improving the dimensional accuracy and structural integrity of the formed parts. This ensures the reliability of the parts during service.

[0045] In summary, the heat treatment method of the present invention can effectively improve the microstructure and mechanical properties of SLM 430 stainless steel parts, significantly enhancing their service safety in engineering applications. This method is not only simple to operate but also has significant industrial application value and broad market prospects.

[0046] Selective laser melting of 430 stainless steel after heat treatment is particularly suitable for manufacturing small metal components with complex structures, high dimensional accuracy and harsh service conditions. It is especially suitable for precision structural parts working in high-temperature environments, such as high-temperature sensor housings, micro-combustion system parts, hot end support components and small corrosion-resistant connectors, etc. It has important application potential in aerospace, energy equipment and advanced manufacturing fields.

[0047] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent variation made to the above embodiment based on the essence of the invention technology shall still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A heat treatment method for selective laser melting 430 stainless steel formed parts, characterized in that: The method is: The selective laser melted 430 stainless steel formed parts were annealed by heating from room temperature to 840°C to 860°C at a heating rate of 10°C / min to 20°C / min, keeping the temperature for 30 minutes, and cooling to room temperature to obtain the heat-treated selective laser melted 430 stainless steel formed parts.

2. The heat treatment method for selective laser melting 430 stainless steel formed parts according to claim 1, characterized in that: The preparation method of 430 stainless steel formed parts by selective laser melting is as follows: the 430 stainless steel formed parts are formed by selective laser melting process. The process parameters are as follows: laser power of 200W, powder thickness of 40μm, substrate material of 316L stainless steel, preheating temperature of 100℃, scanning speed of 600mm / s, scanning line spacing of 0.08mm, spot diameter of 100μm, and scanning strategy of "S"-shaped stacking fault rotation of 67°.

3. The heat treatment method for selective laser melting 430 stainless steel formed parts according to claim 2, characterized in that: The 430 stainless steel formed part is a cubic block specimen with a size of 100 mm × 100 mm × 100 mm.

4. The heat treatment method for selective laser melting 430 stainless steel formed parts according to claim 1, characterized in that: The cooling method is water cooling.

5. The heat treatment method for 430 stainless steel selective laser melting parts according to claim 1, characterized in that: The selected laser melted 430 stainless steel formed part after heat treatment has a hardness of 180HV to 210HV, a yield strength of 540MPa to 560MPa, a tensile strength of 590MPa to 610MPa, an elongation of 32.4% to 35%, a corrosion potential Ecorr of -0.731V to -0.721V, and a corrosion current density Icorr of 2.159×10 -10 A.cm -2 ~2.513×10 -10 A.cm -2 .

6. An application of a 430 stainless steel formed part processed by selective laser melting according to the heat treatment method of any one of claims 1 to 5, characterized in that: The heat-treated selective laser-melted 430 stainless steel formed part is used to manufacture small precision metal components with complex structures, high dimensional accuracy and harsh service conditions.

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