Microstructure and mechanical property of 12CrNi2 high strength steel fabricated by laser additive manufacturing technology

Abstract

12CrNi2 high strength steel thin wall with few defects was fabricated by laser additive manufacturing technology. The microstructure of as-built sample was studied using optical microscopy (OM), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Additionally, the mechanical property was also investigated by microhardness tests. It was found that the microstructure of the as-built sample mainly consists of columnar dendrites aligned in building direction because of the fast directional cooling during LAM. Cellular grains, and equiaxial dendrites are also observed in different regions of the as-built sample due to heat accumulation effect. Furthermore, many types of microstructure, such as tempered martensite, M-A constituent, retained austenite, lower and upper bainitic ferrite, are appeared in the as-built sample resulting from complex heat history and wide temperature range during LAM process. The maximum and minimum microhardness (499 HV0.2 and 272 HV0.2) occur in the top and bottom region respectively, while microhardness of the middle region with value of 452 HV0.2 just slightly reduces compared to the top section of as-built sample.