Effect of Deposition Strategy on Fatigue Behavior of Laser Melting Deposition 12CrNi2 Alloy Steel

In this paper, the 12CrNi2 alloy steel parts were fabricated by laser melting deposition (LMD) using two kinds of deposition strategies, which were single direction scanning(SDS) and cross direction scanning(CDS). The microstructure and fatigue behavior of LMD 12CrNi2 alloy steel samples were investigated. Thy typical microstructure of both deposition strategy were ferrite and can be divided into two zones: remelted zone and non-remelted zone. The non-remelted zone showed typical columnar crystal morphology while the structure of remelted zone was homogenized. Compared with SDS deposition strategy, the microstructure of CDS deposition strategy had shorter columnar grains and finer grains. The relative densities of SDS and CDS deposition strategies were 98.1 and 97.3, respectively, indicating that SDS had lower porosity. The fatigue strength of SDS deposition strategy was higher than that of CDS deposition strategy, which were 320 MPa and 200 MPa. There were more defects in CDS deposition strategy, which accelerated the initiation and propagation of cracks. CDS deposition strategy had longer interlayer interval time, which will reduce the penetration depth of laser, affect the degree of previous layer remelting, and eventually lead to unmelted powder, porosity and other defects in the lap zone.