Microstructure and mechanical properties of laser solid formed 30Cr-Mn-Si-Ni-2A ultra-high-strength steel

Microstructure and mechanical properties of laser solid formed 30Cr-Mn-Si-Ni-2A steel are investigated. The deposits consist of epitaxial columnar grains, equiaxed grains or direction changed dendrites can be observed in the bulk specimens. The microstructure at the bottom of deposits is mainly composed of tempered martensite; the middle to top zone of the deposits are characterised by martensite and bainite. With the increasing of deposition height, the volume fraction of bainite increases, the size of martensite laths increases but its volume fraction decreases. The microhardness shows a decrease from the bottom zone to the middle-upper zone, and then a significant increase at the top of the deposits. Anisotropic and unevenly distributed tensile properties are observed for the deposits. Samples after heat treatment demonstrate tensile strength of 1720 MPa and elongation rate of 8.7%.