Microstructure, Mechanical Properties, and Surface Integrity of Austenitic-Martensitic Stainless Steel Functionally Graded Materials Prepared by Laser Additive Manufacturing

This study used laser additive manufacturing technology to fabricate austenitic–martensitic stainless steel functionally graded materials (ASS-MSS FGM). The microstructure and mechanical properties of ASS-MSS FGM were characterized, and the surface integrity after milling experiments of the ASS-MSS FGM was analyzed. The microstructure of the ASS-MSS FGM exhibited a dense subgrain structure with diverse subgrain types and no fixed growth direction. The microhardness of the ASS-MSS FGM increased from 283 HV to 530 HV due to the increased proportion of the martensitic phase. The ASS-MSS FGM tensile specimens fractured in the austenitic stainless steel region. The tensile strength is 896 MPa, which is increased by 121 MPa compared to ASS. The fracture elongation is 18%, which is increased by 140% compared to MSS. The milling experiments revealed that the degree of work hardening decreased by 8.1% along the building direction of the ASS-MSS FGM. Compared with the austenitic and martensitic layers, the degree and depth of work hardening of the gradient layer were in the transitional zone between them. The microstructure of ASS-MSS FGM after the milling mainly exhibited three deformation phenomena: grain squeezed deformation, grain broken dislodgement, and grain sheared fracture.