調質高張力鋼のユニオンメルト自動溶接に関する研究

Abstract

The welded butt joint carsied out by automatic submerged arc welding is mostly fractured under transverse tension load at "soften part" in heat-affected zone, and the joint efficiency frequently falls lower than 100 percent.This paper is concerned with the investigation on the influence of the heat input energy given by automatic submerged arc welding (UNION MELT) on the strength of joint, the notch toughness of weld metal at center, and the microscopic structures in weld heat-affected zone.From experimental results it is summarized as follows ; When welding heat input energy exceeds 80×103 Joules/cm the joint efficiency falls lower than 100 percent. Using the authors' standard welding procedure, there is no problem on the reducing of welded joint efficiency up to 30 mm plate thickness.On the other hand, the notch toughness of weld metal which is made by various welding conditions is examined by Vee Charpy impact test, and shows the highest level when welding is carried out by the condition of heat input energy (70-80) × 103 Joules/cm.From the microscopic examination, "soften part" are regarded as the refined grain structure made by welding heat, and micro-Vicker's hardness in soften part is measured as 90 percent to the mother metal, Thus the most favorable procedure to selected for submerged welding has been clarified by the above mentioned.In this shipyard the production of superior 2H-steel pressure vessels, penstocks, and steel constructions has been successfully carried out by thus found proper UNION MELT welding procedure.