調質高張力鋼潜弧溶接熱影響部の切欠靱性と溶接軟化に関する研究(第3報)

Abstract

Experimental studies were made on the effect of alloying elements on the notch toughness of singlepass submerged-arc weld bond and weld softening in heat-affected zone welded with comparatively large heat input, employing 2 mm V notch Charpy impact test and small size tensile test of a systematically prepared 80 kg/mm2 high tensile steel plate.Notch toughness of weld bond diminished with the increase of heat input.Alloying elements which reduce notch toughness of weld bond are carbon, nitrogen, boron and large quantity of titanium. Reducing the carbon content to less than 0.10% improves the notch toughness of weld bond greatly.Alloying elements which improve the notch toughness of weld bond are nickel, silicon and small quantity of vanadium.Increasing aluminium decreases the notch toughness of weld bond, but the results are quite contrary to those of duplicated weld heat-affected zone.Manganese, chromium and molybdenum have slight influences on notch toughness of weld bond, presumably because of bainitic structure in weld bond.Niobium up to 0.05% also has little effect on the notch toughness of weld bond.Alloying elements which reduce weld softening are carbon, niobium, vanadium, chromium, molybdenum, nitrogen, aluminium, phosphorus and adequate quantity of silicon. Tensile strength of softened heat-affected zone is generally improved with the addition of secondary hardening elements.Microstructures of weld bond were upper bainitic and no primary ferrite was found, but a complete lower bainitic structure was hard to obtain in weld bond with highly hardenable steels tested.