低温材料の研究 ＩＩ ＳＵＳ３０４，３１６ステンレス鋼溶接部の極低温における機械的性質と加工による強磁性化

Abstract

SUS 304 and 316 austenitic stainless steel plates were welded by filler wires of Y308 and Y316 using TIG method, and the strength and the toughness of the weldments were evaluated at cryogenic temperatures (77K and 4.2K). The change in magnetic properties due to the strain-induced martensite (α′) were also examined.The yield strength of 304 (parent metals and weld metals) are greater than those of 316 at room temperature, but at 77K and 4.2K, the yield strength of 316 overcomes those of 304. The elongation of both weld metals are smaller than those of their parent metals at room temperature, but become equal to those of their parent metals at 77K and 4.2K.The tensile tests of the notched specimens of weld metals show that the notch yield strength ratios of 304/Y308 and 316/Y316 weld metals keep 2.4 and 1.9 at 4.2K respectively, and both fracture modes correspond to the ductile manner, although the notch sensitivities decrease with decreasing temperature.The relations of the volume pct of γ, e′ and α′ to the amount of strain at 77K and 4.2K were obtained. The amount of martensite (α′) formed in the fractured specimens at 4.2K were 95% for 304/Y308 weld metal and 70% for 316/Y316 weld metal. An austenitic phase of 316/Y316 weld metal is more stable than that of 304/Y308 weld metal.It was found that the weld metals showed similar mechanical and magnetic properties to their parent metals at 77K and 4.2K because of the dominant effect of strain-induced martensitic transformation on those properties.