This study investigates the weldability of gas tungsten arc (GTA) on stainless steel (STS) 304 using STS 308L filler and elucidates the cryogenic properties in STS 304 weld. GTA welding were performed with welding current of 90 A, welding velocity of 10.5 cm/min, Ar shielding gas, and in a single-pass. The GTA welding conditions were configured to ensure a full penetrating weld. For full penetration weld metal (WM), a small amount of δ-ferrite formed. Additionally, the WM of STS 304 exhibited larger dendrite packets compared to the grain size of base metal (BM). Therefore, the drop of hardness in WM was more significant compared to BM. The GTA welds had tensile properties that were inferior to BM at 298 K, and the tensile fracture occurred near the centerline of the transverse welds. The cryogenic tensile strength of GTA welds was superior to the room-temperature property due to the significant phase transformation of martensite at 77 K. However, the elongation decreased.

The demand for LNG fueled tank on ship is growing in accordance with the IMO 2020 regulation. The 9% nickel steel has been used for LNG storage tank because this material has higher tensile strength than the other materials in the IGF code. The nickel-based alloy type welding consumable has been applied on 9% nickel steel welding because of good toughness at cryogenic environment and high tensile property. However that welding consumable has disadvantages of high price and poor weldability. In this study, new stainless steel-based flux-cored wire is developed for 9% nickel steel and mechanical properties are satisfied Class requirement. Additionally, fatigue, FCGR and CTOD test had been carried out to verify structure design suitability.

Three different welding wires were used to study the effects of Al content on weld metal toughness and porosity formation in self-shielded arc welding. Weld metal microstructure showed that while wire with 1.3% Al content contains coarse δ-ferrite, wires with less than 0.5% Al content showed no such phase. In addition to the microstructural differences, cleanliness in weld metal was also different among wires. It showed that weld metal toughness was influenced by the δ-ferrite formation, cleanliness and Ni addition. Even though wires with less than 0.5% Al content showed higher weld metal toughness, they showed relatively poor workability, forming porosities in weld bead in lower arc voltages.Key Words : Self-shield arc welding wire, Al content, Weld metal microstructure, Toughness, porosity . 본 연구에서는 500MPa급 SSAW 플 연 구 논 문

Three different welding wires were used to study the effects of Al content on weld metal toughness and porosity formation in self-shielded arc welding. Weld metal microstructure showed that while wire with 1.3% Al content contains coarse δ-ferrite, wires with less than 0.5% Al content showed no such phase. In addition to the microstructural differences, cleanliness in weld metal was also different among wires. It showed that weld metal toughness was influenced by the δ-ferrite formation, cleanliness and Ni addition. Even though wires with less than 0.5% Al content showed higher weld metal toughness, they showed relatively poor workability, forming porosities in weld bead in lower arc voltages.Key Words : Self-shield arc welding wire, Al content, Weld metal microstructure, Toughness, porosity . 본 연구에서는 500MPa급 SSAW 플 연 구 논 문

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