Origin of little post-uniform elongation of 304L/310S austenitic stainless steels at extremely low temperatures

To elucidate the mechanism of little post-uniform elongation ( e pu ) in tensile curves of austenitic 304L and 310S stainless steels (SSs) at 4.2 K, tensile tests were performed at 4.2 K with an initial strain rate of 1×10 -3 /s using 304L and 310S SS specimens, showing different strain-induced martensite transformation (SIMT). For the comparison, pure Cu and Cu-35Zn (wt%) α -brass alloy with high thermal conductivity ( κ ) were also examined. Consequently, 304L and 310S SSs exhibited little e pu in their tensile curves, contrary to the curves of pure Cu and Cu-35Zn (wt%) alloy with large e pu values. Pronounced cryogenic serrations appeared in Cu-35Zn (wt%) alloy and 304L and 310S SSs. Tensile result of Cu-35Zn (wt%) alloy and the discrepancy between the temperature ranges of little e pu and cryogenic serrations in SSs suggested that cryogenic serrations and their origin are unrelated to the little e pu . Despite the difference in SIMT behavior between 304L and 310S SSs, both SSs exhibited similarly little e pu at 4.2 K, indicating that SIMT is also not the cause. Instead, rather than heat capacity, low κ values (∼0.25 W/m·K for 304L and ∼0.16 W/m·K for 310S) was proposed as the key factor. After necking, it is considerably difficult for the generated adiabatic heat in the shear band to be dissipated to the adjacent regions. This hinders the redistribution of the local deformation by thermal softening, leading to the immediate fracture without necking and eventually little e pu in the tensile curve.