Cryogenic fracture toughness evaluation for austenitic stainless steels bymeans of unloading compliance method

Most research to date concerning the cryogenic toughness of austenitic stai nless steels has concentrated on the base metal and weld metal in weldments . The most severe problem faced on the conventional austenitic stainless st eel is the thermal aging degradation such as sensitization and carbide indu ced embrittlement. In this paper, we investigate the cryogenic toughness de gradation which can be occurred for austenitic stainless in welding. The te st materials are austenitic stainless JN1, JJ1 and JK2 steels, which are ma terials recently developed for use in nuclear fusion apparatus at cryogenic temperature. The small punch(SP) test was conducted to detect similar isot hermally aging condition with material degradation occurred in service weld ing. The single-specimen unloading compliance method was used to determine toughness degradation caused by thermal aging for austenitic stainless stee ls. In addition, we have investigated size effect on fracture toughness by using 20% side-grooved 0.5TCT specimens.