Evaluation of Cryogenic Fracture Characteristics on TIG Weldments of Superconducting Magnets Structural Steel by Small Punch Testing Method

소형펀치 시험법에 의한 초전도 마그넷 구조용강 TIG 용접부의 극저온 파괴특성 평가

In order to evaluate the cryogenic fracture characteristics of structural steels for superconducting magnets of fusion reactor, small punch (SP) testing was performed on austenitic stainless steel (JN1 base metal) and its TIG weldments at 293K, 77K and 4K. The mechanical properties with respect to the extracted location of the weld metal, on the effects of welding heat cycle about base metal near fusion line in TIG weldments were investigated. The mechanical property of the weld metal in TIG weldments depends on distance from welding root, root region of weldments having the lowest mechanical property. The base metal near fusion line showed degradation of mechanical property caused by cyclic heating during the TIG welding. Based on the test results, HAZ was found to be up to 5mm from the fusion line. It is shown that SP testing is a useful tool to evaluate the mechanical properties with respect to the microstructures changes such as HAZ as well as weld metal in TIG weldments at cryogenic temperature.