오스테나이트 초저온 탱크의 용입 특성에따른 열영향부의 기계적 성질 변화 분석 = A Study on Changes of Mechanical Properties of Heat Affected Zone According to the Percolation Characteristics of Austenite Ultra-low Temperature Tank

다국어 초록 (Multilingual Abstract)

Austenitic stainless steel SUS304L is widely used in LNG tanks and cryogenic pressure vessels for its toughness and corrosion resistance, but welding and repeated gouging–rewelding introduce accumulated thermal cycles in the HAZ that promote grain coarsening, sensitization, hardness variation, and degradation of mechanical and corrosion performance. This study examines the effects of penetration characteristics and repeated thermal cycles on SUS304L welded joints through tensile, bending, and impact tests, hardness profiling across BM–HAZ–WM, ASTM E112 grain-size measurements, and intergranular corrosion evaluations using ASTM A262 Practices A and E. Repetitive thermal cycles intensified HAZ microstructural alteration, expanded Cr-depleted zones, increased grain coarsening, and produced irregular hardness distributions, resulting in reduced mechanical integrity and corrosion resistance. These findings provide fundamental data for establishing appropriate welding procedures and ensuring structural reliability in LNG and cryogenic pressure-vessel fabrication.