Validation of a small punch testing technique to characterize the cryogenic fracture properties of austenitic stainless steel welds

Abstract

This study was performed to demonstrate the feasibility of performing liquid helium temperature (4 K) small punch (SP) tests on austenitic stainless steel weld for Large Helical Device (LHD) superconducting magnets. The SP specimens (10×10×0.5 mm) were prepared from the different locations of electron-beam weld in type 316 stainless steel to examine the variation of the fracture properties in the weld and its heat affected zone. Previously proposed correlations for SP and elastic-plastic fracture toughness test methods were applied to predict a SP test-based fracture toughness from equivalent fracture strain. The correlation was also found between the room temperature Vickers hardness of the heat affected zone and its fracture toughness at 4 K. A finite element analysis was performed to convert the experimentally measured load-displacement data into useful engineering information. The maximum strain energy density was calculated and correlated with equivalent fracture strain.