Abstract
Narrow gap submerged arc welding consumables for V-modified 21/4 Cr-1 Mo steels are developed through the investigation of effects of V and Nb contents in weld metals on tensile strength, toughness and creep rupture strength of weld metals. Tensile and creep rupture strengths of the weld metals increase with increasing V and Nb contents in the weld metals. However excessive Nb addition up to 0.033% deteriorates toughness of the weld metal. The optimum V and Nb contents in the weld metal to satisfy both creep rupture strength and toughness are 0.2-0.3% and 0.02%, respectively. Coarse precipitates contained Cr, Mo, Fe, and V are observed in the conventional weld metal contained 0.07%V with a transmission electron microscopy. On the other hand, fine precipitates which contained Cr, Mo, Fe, V, and Nb are observed in the newly developed weld metal contained 0.29%V and 0.018%Nb besides the coarse ones. Due to these fine precipitates, a newly developed weld metal shows about 10MPa higher creep rupture strength at 755K for 100, 000h than the conventional one and shows excellent resistance to hydrogen attack.
