Enhancing Cryogenic Strength of Austenitic Stainless Steels through Thermo-Mechanical Controlled Processing and Nitrogen Alloying

Austenitic stainless steels are strong candidates for cryogenic applications such as liquid hydrogen storage (20 K) and nuclear fusion technology (4 K) but suffer from low yield strength. In this study, austenitic stainless steels with varying nitrogen contents were evaluated. TMCP-processed and solution-annealed plates were manufactured using a pilot-scale rolling mill, and their microstructures were characterised. Tensile tests were performed from room temperature down to-180°C to assess the cryogenic yield strength of the plates. At all temperatures TMCP significantly increased the yield strength e.g. by a factor of 2 at room temperature, with the effect being mainly due to substantial dislocation hardening. The thermally activated component of yield strength depended mainly on nitrogen content via dislocation-nitrogen interactions, which was found to be much weaker in TMCP plates. Solution annealed plates therefore presented remarkable yield strength at cryogenic temperatures for the highest nitrogen level investigated.