The effect of varying the MnO content of the flux used for the submerged arc welding of Navy HY-100 steel

Abstract

Weld metal strength and toughness are determined by its microstructure, which is in turn determined by the concentration of various alloying elements and impurities as well as the welding thermal cycle. This study investigated the effects of systematically varying the manganese oxide content in the flux used for HY-l00 submerged arc welds. A trial addition of cerium oxide was also performed. Specimens were compared using mechanical properties, weld metal chemistry, inclusion chemistry, and microstructural analysis. It was found that cerium oxide addition and the correct amount of manganese oxide resulted in improved toughness. These improved properties were determined to arise from a low proportion of bainite in the fully reaustenitized region of the weld metal HAZ in these multipass welds. In the MnO series welds, the bainite is replaced by a fine low carbon martensite due to the increased weld metal hardenability. In the CeO2 weld it is replaced by acicular ferrite due to the lowering of the austenite grain boundary energy by the cerium. The production of a series of welds with different manganese contents also resulted in the extension of existing theories of weld metal deoxidation. p3.