Abstract
Effects of Ni content and B addition on the hot workability of austenitic stainless steels containing 4.56.2%Mo for sea water applications have been investigated by hot tensile tests and physical analyses of fractured surfaces. Optimum Ni contents were 22% for 25Cr-4.5Mo steel and 17% for 20Cr-6.2Mo steel respectively, since 34% δ ferrite remaining in the solidification structure was effective to improve the ductility at temperatures between 1000°C and 1150°C. The addition of 0.0020.004% B was also effective in the improvement of hot workability of the steels containing δ ferrite less than 4%. It was clarified by Auger Electron Spectrometer and Ion Micro Analyser that the hot workability was greatly affected by the degree of S segregation at grain boundaries, which could be decreased by the existence of small amount of δ ferrite and the segregation of B at grain boundaries.
