Abstract
Cryogenic structural materials are often subjected to cold-forming and heat treatment in the process of construction. The severest heat treatment for cryogenic steels is thought to be sensitization like aging for many hours at 973K to form the superconducting phase. In the present study, therefore, the effects of cold-rolling and sensitization on mechanical properties at cryogenic temperature were investigated for austenitic stainless steels strengthened by nitrogen. By cold-rolling, the yield strength was increased markedly. However, sensitization lowered largely the yield strength of the cold-rolled materials. The Charpy absorbed energy, CVN, and the fracture toughness, KIC (J), were drastically decreased by cold-rolling and/or a sensitization treatment. The decrease in toughness by sensitization treatment was due to the intergranular fracture associated with the precipitation of carbides on grain boundaries.
