Microstructure and fatigue behavior of a laser additive manufactured 12CrNi2 low alloy steel

In this research, 12CrNi2 low alloy steel was successfully prepared by laser melting deposition (LMD). The mechanisms driving high cycle fatigue fracture of the as-built LMD 12CrNi2 low alloy steel were investigated and a concurrent process-microstructure-property relationship was established through microstructural analysis. The results showed that the crystal structures of the as-built LMD 12CrNi2 steel mainly consisted of the ferrite and a small amount of Cr23C6 carbides. No preferred texture was observed as a result of the complicated heat flux direction during fabrication. Based on the examination of the fracture surface, fatigue cracks of the as-built LMD 12CrNi2 steel initiated from subsurface defects for all the cases. Crack propagation zones showed a mixed mode of transgranular and intergranular fracture in a brittle manner, whereas the final fracture zones displayed dimples typical of ductile fracture. The kernel average misorientation (KAM) map indicated that the strain localization predominantly occurred at the grain boundaries and slightly appeared at the interior of the ferrite grains. Schmid factor distribution results implied that fatigue cracks originated from grains with {123}< 111 > slip system due to the prior activation of {123}< 111 > slip system.