Nb添加非調質高張力鋼板に関する研究(第2報)

Abstract

The burst test by application of internal static pressure of a welded steel pipe made of carbon steel and niobium-containing high tension steel plate was carried out to know the initiation properties of brittle fracture of the pipe.The following method was found suitable for initiating a fracturee in the pipe and obtaining the transition temperature from ductile fracture to brittle one of the pipe. The pressure ram was located between two pillars welded vertically at the outer surface of the pipe so as to force the pillars apart when the ram operated statically. The fracture was initiated at the welding toe under pillar.The absorbed energy in Charpy impact test of the high tension steel plate containing niobium, of which the welded pipe was made, was small. But the transition temperature of facture surface in Charpy test of the plate was comparatively low.The pipe about 6 mm thick and about 250 mm in diameter was burst at the temperature down to -70°C.The transition temperature from ductile fracture to brittle one, which was obtained from the burst test of pipe, was comparatively low in spite of the absorbed energy in Charpy test being small.The initiation temperature obtained from the burst test of pipe agreed with the critical temperature, up to which the steel plate could be used without brittle fracture initiation, as calculated from the transition temperature of facture surface in Charpy impact test according to WES (tentative specification of Japan Welding Engineering Society "Evaluation criteria for brittle fracture characteristics of structural steels for low temperature application").