Abstract：In this paper, 304L stainless steel was fabricated by laser powder bed fusion (LPBF) technology using gas atomized powder as raw material. The effects of laser volumetric energy density on the microstructure of the alloy were investigated by X-ray diffratometer, backscattered electron diffratometer, scanning electron microscope, and transmission electron microscope, and the optimal process window was determined. Stainless steels with printing angles of 0°, 45°, and 90° were fabricated using this process parameter to study the influence of forming angle on the microstructure and mechanical properties of stainless steel. The results show that LPBF 304L stainless steel is mainly composed of austenite and a small amount of ferrite. When the laser volumetric energy density is 93.7 J/mm3, the stainless steel has the least pores and other defects, the lowest porosity, and the highest hardness. The tensile strength, yield strength, and elongation of stainless steel with a printing angle of 0° are (722.6±2.5) MPa, (580.3±1.5) MPa, and (58.6±2.3)%, respectively. The tensile strength, yield strength, and elongation of stainless steel with a printing angle of 45° are (714.3±2.5) MPa, (572.0±2.6) MPa, and (49.2±2.8)%, respectively. The tensile strength, yield strength, and elongation of stainless steel with a printing angle of 90° are (629.0±2.0) MPa, 527.7±3.1) MPa, and (67.4±3.5)%, respectively. Stainless steel with a printing angle of 0° shows finer grains, a higher proportion of low-angle grain boundaries, and a larger dislocation density, which helps to improve the material strength. Two kinds of subgrain structures, cellular subgrains and columnar subgrains, exist in LPBF 304L stainless steel. The differences in grain morphology, grain orientation, dislocation density, and subgrain structure are the reasons for the anisotropic mechanical properties of LPBF 304L stainless steel.
[1] ZHANG H Z, LI C Y, YAO G, et al.Investigation of surface quality, microstructure, deformation mechanism, and fatigue performance of additively manufactured 304L stainless steel using grinding[J]. International Journal of Fatigue, 2022, 160: 106838. [2] 朱溪, 袁铁锤, 王敏卜, 等. 选区激光熔化增材制造高强度Al-Mg-Sc-Zr合金的微观组织与力学性能[J]. 粉末冶金材料科学与工程, 2022, 27(2): 205-214. ZHU Xi, YUNA Tiechui, WANG Minbu, et al.Microstructure and mechanical properties of Al-Mg-Sc-Zr alloy prepared by selective laser melting[J]. Materials Science and Engineering of Powder Metallurgy, 2022, 27(2): 205-214. [3] WILSON-HEID A E, WANG Z Q, MCCORNAC B, et al. Quantitative relationship between anisotropic strain to failure and grain morphology in additively manufactured Ti-6Al-4V[J]. Materials Science and Engineering A, 2017, 706: 287-294. [4] ZHU Z G, LI W L, NGUYEN Q B, et al.Enhanced strength-ductility synergy and transformation-induced plasticity of the selective laser melting fabricated 304L stainless steel[J]. Additive Manufacturing, 2020, 35: 101300. [5] PAN T, ZHANG X C, FLOOD A, et al.Effect of processing parameters and build orientation on microstructure and performance of AISI stainless steel 304L made with selective laser melting under different strain rates[J]. Materials Science and Engineering A, 2022, 835: 142686. [6] WANG Z Q, PALMER T A, BEESE A M.Effect of processing parameters on microstructure and tensile properties of austenitic stainless steel 304L made by directed energy deposition additive manufacturing[J]. Acta Materialia, 2016, 110: 226-235. [7] GUAN K, WANG Z M, GAO M, et al.Effects of processing parameters on tensile properties of selective laser melted 304 stainless steel[J]. Materials & Design, 2013, 50: 581-586. [8] VILARO T, COLIN C, BARTOUT J D.As-fabricated and heat-treated microstructures of the Ti-6Al-4V alloy processed by selective laser melting[J]. Metallurgical and Materials Transactions A, 2011, 42(10): 3190-3199. [9] WEN S F, LI S, WEI Q S, et al.Effect of molten pool boundaries on the mechanical properties of selective laser melting parts[J]. Journal of Materials Processing Technology, 2014, 214(11): 2660-2667. [10] DIXIT S, LIU S Y, SMITH P M, et al.Effects of scan rotation angle and build orientation on mechanical anisotropy in additive manufacturing 316L stainless steel[J]. Journal of Manufacturing Processes, 2024, 129: 122-133. [11] BAKHTIARIAN M, OMIDVAR H, MASHHURIAZAR A, et al.The effects of SLM process parameters on the relative density and hardness of austenitic stainless steel 316L[J]. Journal of Materials Research and Technology, 2024, 29: 1616-1629. [12] YAKOUT M, ELBESTAWI M A, VELDHUIS S C.Density and mechanical properties in selective laser melting of Invar 36 and stainless steel 316L[J]. Journal of Materials Processing Technology, 2019, 266: 397-420. [13] YANG Z Y, WANG W X, CHEN Y, et al.An experimental and numerical study on the evolution of pores and its effect on the tensile properties of LPBF Invar36 with different energy density[J]. Journal of Materials Research and Technology, 2024, 31: 3064-3078. [14] ABD‐ELGHANY K, BOURELL D L. Property evaluation of 304L stainless steel fabricated by selective laser melting[J]. Rapid Prototyping Journal, 2012, 18(5): 420-428. [15] SABZI H E, MAENG S, LIANG X Z, et al.Controlling crack formation and porosity in laser powder bed fusion: alloy design and process optimisation[J]. Additive Manufacturing, 2020, 34: 101360. [16] CEPEDA-JIMÉNEZ C M, POTENZA F, MAGALINI E, et al. Effect of energy density on the microstructure and texture evolution of Ti-6Al-4V manufactured by laser powder bed fusion[J]. Materials Characterization, 2020, 163: 110238. [17] DUAN H, LIU B, FU A, et al.Segregation enabled outstanding combination of mechanical and corrosion properties in a FeCrNi medium entropy alloy manufactured by selective laser melting[J]. Journal of Materials Science & Technology, 2022, 99: 207-214. [18] TAN C L, ZHOU K S, MA W Y, et al.Microstructural evolution, nanoprecipitation behavior and mechanical properties of selective laser melted high-performance grade 300 maraging steel[J]. Materials & Design, 2017, 134: 23-34. [19] ZHANG H Z, LI C Y, YAO G, et al.Effect of annealing treatment on microstructure evolution and deformation behavior of 304 L stainless steel made by laser powder bed fusion[J]. International Journal of Plasticity, 2022, 155: 103335. [20] LIU W, LIU C S, WANG Y, et al.Tailoring the microstructural and mechanical properties of 316L stainless steel manufactured by laser powder bed fusion[J]. Journal of Materials Research and Technology, 2023, 25: 7389-7405. [21] YUE D Y, LI D M, ZHANG X, et al.Tensile behavior of AlSi10Mg overhanging structures fabricated by laser powder bed fusion: effects of support structures and build orientation[J]. Materials Science and Engineering A, 2023, 880: 145375. [22] GAO H, HUANG Y, NIX W D, et al.Mechanism-based strain gradient plasticity: I. theory[J]. Journal of the Mechanics and Physics of Solids, 1999, 47(6): 1239-1263. [23] ZHANG M K, LI J W, LIAO X, et al.Influence of cycle number on the compression behavior of nonlinear periodically gradient porous structures produced by laser powder bed fusion[J]. Materials & Design, 2022, 223: 111257. [24] JEON J M, PARK J M, YU J H, et al.Effects of microstructure and internal defects on mechanical anisotropy and asymmetry of selective laser-melted 316L austenitic stainless steel[J]. Materials Science and Engineering A, 2019, 763: 138152. [25] LI S H, ZHAO Y K, KUMAR P, et al.Effect of initial dislocation density on the plastic deformation response of 316L stainless steel manufactured by directed energy deposition[J]. Materials Science and Engineering A, 2022, 851: 143591. [26] ZHANG H Z, LI B X, HU J, et al.Experimental investigation on the deformation behavior of an isotropic 304L austenitic steel manufactured by laser powder bed fusion with hot isostatic pressing[J]. Materials Characterization, 2024, 214: 114086. [27] KONG D C, NI X Q, DONG C F, et al.Anisotropy in the microstructure and mechanical property for the bulk and porous 316L stainless steel fabricated via selective laser melting[J]. Materials Letters, 2019, 235: 1-5. [28] QU H Q, LI J, ZHANG F C, et al.Anisotropic cellular structure and texture microstructure of 316L stainless steel fabricated by selective laser melting via rotation scanning strategy[J]. Materials & Design, 2022, 215: 110454. [29] ŠMÍD M, KOUTNÝ D, NEUMANNOVÁ K, et al. Cyclic behaviour and microstructural evolution of metastable austenitic stainless steel 304L produced by laser powder bed fusion[J]. Additive Manufacturing, 2023, 68: 103503.
2025, Vol. 30 
