Microstructures and mechanical properties of additively manufactured T91 steel and T91/316H bimetallic components by laser powder bed fusion

Precise deposition of multiple materials by additive manufacturing (AM) has considerable potential for controlling the properties of materials. In this work, T91 martensitic steel with various process parameters was deposited on 316H steel fabricated by laser powder bed fusion (L-PBF), and the microstructure, mechanical properties, and corresponding defect formation of the T91 material were investigated based on the volumetric energy density (VED). This work studied the interface characteristics and properties of T91/316H bimetallic components with various process parameters to improve the performance of joint between martensitic and austenitic steels by AM. The presented results showed that the tensile strength and uniform elongation (UE) appeared to increase with the VED of the T91 materials. The ultimate tensile strength and UE of the T91 materials significantly decreased when the VED of the T91 materials approached 110 J, which was determined by the dramatic growth in defect number and defect size. Additionally, these bimetallic components obtained favorable tensile properties, exceeding those of the 316H sections, ascribed to solid solution strengthening at the interface. The 316H grains (γ) and the T91 grains (α) near the interface follow the K–S orientation relationship: {111}γ//{110}α, <110>γ//<111>α. The process parameters of the T91 sections obviously affected the tensile strength of these bimetallic components, as well as the molten pool morphology and mechanical properties of the 316H section near the interface.