Microstructure and Mechanical Properties of As-Deposited and Heat-Treated 18Ni (350) Maraging Steel Fabricated by Gas Metal Arc-Based Wire and Arc Additive Manufacturing

Additive manufacturing has been a promising method for the production of 18Ni maraging steel, which is characterized by excellent mechanical properties. There are only few available studies on wire and arc additive manufacturing of this steel. In this paper, 18Ni (350) maraging steel thin-wall parts were fabricated by gas metal arc-based wire and arc additive manufacturing (GMA-based WAAM). The aim of this study was to reveal the microstructure and mechanical properties of the as-deposited parts and investigate the effects of the heat treatment process. The microstructure of the deposited part was principally martensite with long columnar grains, accompanied by a small amount of austenite. The average hardness of the as-deposited part was 467 ± 60 HV. The tensile strengths (UTS and YS) along the building direction were 1481 and 1221 MPa, respectively, and the elongation was 4.8%, which were all larger than those along the deposition direction. After solution treatment, the austenite content, hardness, and tensile strengths of the as-deposited samples decreased, while the elongation increased slightly. After aging treatment, the austenite content and hardness of the solution-treated samples increased, but the UTS and elongation were not improved, indicating that the heat treatment for preparing 18Ni as-deposited samples with excellent mechanical properties requires further investigation.