Microstructure evolution of 316L stainless steel during laser rapid forming

The solidification behavior and the morphological evolution of 316L stainless steel during laser rapid forming (LRF) were investigated. It was found that, the LRF sample is completely consisted of columnar γ austenitic dendrites which grew epitaxially from the substrate, and have the (100) direction approximately parallel to the deposition direction, but in a thin layer at the top of the LRF sample the dendrites grew along the laser scanning direction. Band-like structures between deposited layers existed in the sample, which don't effect the growth continuity of the columnar dendrites. The solidification pattern and phase selection were predicted by the microstructure selection models based on the maximum interface temperature criterion. The formation of the band-like structure and the epitaxial growth characteristic are also explained by the criteria for planar interface instability and dendritic growth theory and the columnar to equiaxed transition model.