332 小型パンチ試験によるオーステナイト系ステンレス鋼溶接熱影響部の極低温破壊特性評価(OS1-6 熱影響部と配管の健全性評価)(OS1 高強度材・表面改質材の疲労と破壊) 332 Evaluation of Cryogenic Fracture Properties of the Heat Affected Zone in an Austenitic Stainless Steel Weldment by Small Punch Testing

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. A finite element analysis was also 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. The heat affected zone with high Vickers hardness at room temperature shows lower fracture toughness, compared to other regions.