Relationship of Scan Strategy on Microstructure and Residual Stress of Martensitic Stainless Steel SUS420J2 Fabricated by Laser Powder Bed Fusion

In this study, the relationships of the microstructures, the hardness distributions and the residual stress distributions with the laser scanning patterns were systematically investigated for a martensitic stainless steel SUS420J2 fabricated by laser powder bed fusion (AM material). The microstructures of the AM materials were consisted of mainly the needle-shaped α′ phase, with the retained γ phase and the fine cementite particles. There was the Kurdjumov-Sachs relationship between the (011) plane of the α′ phase and the (111) plane of the retained γ phase. The hardness of the AM materials was higher than that of the wrought material which was quenched and tempered. All AM materials had similar hardness since there were no significant differences in their microstructures, even though the scanning patterns were different. It was experimentally shown that the residual stresses of the AM materials can be reduced by changing the laser scanning patterns. Especially, the residual stress value was reduced by 75% using the chessboard-type scanning pattern with the alternating scanning directions and shifting the pattern.