Load-displacement Curves, Specimen Heating, and Strain-induced Martensitic Transformation of Austenitic Stainless Steels at Cryogenic Temperatures

We performed tensile tests at low temperatures from room temperature to 4 K for SUS 304L and SUS 316L in order to obtain basic data on the mechanical properties of materials to be used in a liquid hydrogen tank service. First we studied tensile curves and specimen heating during tensile testing from 70 K to 4 K, and then evaluated the ferrite contents of those alloys during tensile deformation from room temperature to 4 K. For both SUS 304L and SUS 316L, tensile strength showed a small peak around 10 K, and specimen heating decreased above 30 K as the environment temperature increased. Below 77 K, there was almost no clear influence of testing temperature on strain-induced martensitic transformation. However, for SUS 304L, the amount of ferrite content increased as the temperature decreased down to 233 K, and increased only slightly below 233 K. For SUS 316L, it increased as the temperature decreased down to 4 K, and increased steeply after 60% plastic strain above 243 K.