３０４ステンレス鋼突合せ溶接継手のクリープ破断強さの継手効率

Abstract

The short-time tensile strength and creep-rupture strength of butt welded joints for 304 stainless steel by electron beam welding (EBW), narrow-gap gas tungsten arc welding (GTAW) and submerged arc welding (SAW) were evaluated. Three types of SAW joints, were prepared by using a conventional 308 wire and two modified wires with the addition of Nb and V. Short-time tensile and creep-rupture tests were conducted on 308 weld metal specimens (GL=30mm, Dia.=6mm) and welded joint specimens (GL=100mm, Dia.=10mm) at 500, 550, 600, 650 and 700°C. Little difference in short-time tensile strength was observed among conventional and modified 308 SAW weld metals. On the other hand, the creep-rupture strength of modified 308 weld metals was higher than that of conventional 308 weld metal. However, the creep rupture ductility of the 308 weld metals was not improved by the addition Nb and V.First, the creep-rupture data of the welded joints and the base metal were evaluated by the Larson-Miller parametric method. Then, the stress rupture factor (SRF) of the welded joints for creep-rupture strength were computed, and were compared with that for weldments given in Code Case N-47-28 of ASME Boiler and Pressure Vessel Code. The relationship between the SRF and the time dependent allowable stress Smt was discussed.Generally, the SRF for EBW, GTAW and Modified SAW joints were larger than 1.0, which means overmatching joints. But the SRF of SAW joint with conventional 308 wire decreased with increasing time or temperature, becoming as low as 0.67 in 100000h at 650°C and below the value of CC N-47. Besides, it was shown that the allowable stress Smt of the weldment became lower than that of CC N-47 when the SRF was less than 0.83.