Precipitation characteristics and tensile properties of high-nitrogen chromium-manganese steel fabricated by wire and arc additive manufacturing with isothermal post-heat treatment

Wire and arc additive manufacturing (WAAM) technology is a promising method for fabricating high-performance protective materials and structural parts from high-nitrogen steel (HNS). However, owing to the complicated thermal fields generated by the process, it may produce some undesirable precipi-tates, such as the intermetallic a phase or chromate nitrides, especially when the fabricated part is large. This study focused on the precipitation features of WAAM-produced high-nitrogen Cr-Mn steel contain-ing 0.7 wt% nitrogen. When the isothermal post-heat treatment was conducted at approximately 900 degrees C, the a phase dominated the original inter-dendritic ferrite (Inter-F) region. And, there were some sec-ondary austenite precipitates (y2) along with a small amount of Cr2N. The oxide inclusions (especially the MnO particles) provided excellent nucleation sites for the a phase in the Inter-F region or at the Inter-F and y matrix interface due to the high interface energy and lattice matching index. Further, when aging above 1000 degrees C, no a phase was found, and the decomposition of the Inter-F to y matrix was dom-inated by element diffusion. With the precipitation of the a phase, a typical brittle fracture was observed in the samples aged at low temperatures of 800 degrees C and 900 degrees C.(c) 2022 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).