Microstructure evolution and hot deformation behavior of 25Cr–6Mn–3Ni–1Mo–3W–0.1C–0.34N lean duplex stainless steel

Abstract

Hot deformation characteristics of a 25Cr–6Mn–3Ni–1Mo–3W lean duplex stainless steel containing high C and N contents were elucidated. Hot compression tests were performed at temperatures of 600–1100 °C and strain rates of 0.01–10 s−1. Using the stress–strain curves from the hot compression tests, processing maps were established based on the dynamic material model. The hot working domains for the temperature range of 700–900 °C were found to be unstable, regardless of the strain rate. Transmission electron microscopy and electron backscatter diffraction analyses revealed that cracking occurred along the ferrite (α)/austenite (γ) phase boundaries during hot deformation in this unstable hot working regime, where coarse Cr23C6 carbide precipitated along the α/γ interphase. To further understand the hot deformation behavior, hot tension tests were carried out, which indicated that a ductility dip occurred at 700–900 °C due to the interphase precipitation of Cr23C6 carbide; this result was in accordance with the hot compression tests. Finally, the change in the precipitation behavior of Cr23C6 carbide upon deformation temperature and its effect on the hot workability were discussed through a time–temperature-precipitation diagram of Cr23C6 carbide.