Laser powder bed fusion of ultra-high-strength 420 stainless steel: Microstructure characterization, texture evolution and mechanical properties

In the present research, AISI 420 stainless steel (420SS) samples were fabricated by the laser powder bed fusion (LPBF) process. The microstructure, grain morphology, crystallographic texture, and mechanical properties of the 420SS deposits were evaluated in both as-printed and heat-treated conditions. In the as-printed condition, the melting pool boundaries were formed, and the martensite laths and needles were observed, with 13.3% retained austenite. Most of the grains exhibit {111}//BD and {110}//BD fiber textures. After heat treatment, the melting pool boundaries were dissolved. Then, the tempered martensite phase was formed, and the carbides were precipitated from the martensite matrix. The phase is fully martensitic, and the grains mostly align to {111}//BD and {110}//BD fiber textures. Generally, the tensile strength and yield strength increased after heat treatment; however, it leads to a decrease in elongation. This behavior is associated with carbide precipitation and the elimination of the austenite phase in the heat-treated condition. Nevertheless, the toughness measured in the heat-treated condition was much higher than the as-printed condition, owing to the formation of tempered martensite during heat treatment. The LPBF 420SS in the as-printed condition has mechanical properties superior to than that of the reported values in the literature. Moreover, the mechanical properties of LPBF 420SS in the heat-treated condition were found to be better than the wrought material under the same condition.