Microstructure evolution and mechanical behavior of high nitrogen austenitic stainless steel fabricated by wire-arc directed energy deposition under quasi-static and dynamic loading

Abstract

The dynamic mechanical behavior of wire-arc directed energy deposition (DED) high nitrogen steel (HNS) remains underexplored, with limited studies available and unclear underlying mechanisms. However, practical application demands necessitate an investigation into its dynamic mechanical behavior. In order to elucidate the relevant mechanisms during dynamic deformation and enrich the relevant data, this study investigates and compares the microstructure evolution, deformation behavior, and strengthening mechanisms between dynamic and quasi-static deformation. The results show that the microstructure of wire-arc DED HNS consists of austenite and ferrite. The ultimate tensile strength in the X, Y, and Z directions are 948 MPa, 976 MPa, and 891 MPa, respectively, with corresponding elongation of 50.4 %, 39.1 %, and 48.8 %. Under dynamic loading, wire-arc DED HNS exhibits strain rate strengthening effect. The peak stress in the X, Y, and Z directions under 0.3 MPa are 1750 MPa, 1830 MPa, and 1710 MPa, respectively, with corresponding strain of 49.7 %, 43.4 %, and 48.5 %. The high manganese content, the reduction of grain size, and the increase of stacking fault energy during dynamic deformation impede the austenite from undergoing phase transformation during deformation. Dislocation slip and twin deformation are the main deformation mechanisms of HNS. Dislocation slip is more adequate under dynamic loading compared to quasi-static loading. The primary strengthening mechanisms of wire-arc DED HNS are solid solution strengthening and dislocation strengthening. Under dynamic loading, fine grain strengthening and dislocation strengthening are more pronounced compared to quasi-static loading. This study offers reference for subsequent studies at higher strain rate.