Control of diffusible weld metal hydrogen through arc chemistry modifications

Abstract

This project examined the feasibility of using flux modification to reduce the as-deposited hydrogen content of basic-type shielded metal arc welds. Additions of oxidizing ingredients (micaceous iron oxides) to the reference flux formulation lowered the diffusible weld hydrogen content by up to 70%. Increasing amounts of silica caused a slight reduction in hydrogen content, probably as a result of the reaction between SiO2 and CaF2, which produces SiF4 and CaO as reaction products. Flux formulations containing additions of fluorine-containing compounds and calcite displayed lower hydrogen levels, with the diffusible weld metal hydrogen content reaching a minimum with increasing additions. Higher levels caused an increase in the weld hydrogen content. Thermodynamic slag modelling attributes the existence of these minima to a decrease in slag water capacity with an increase in slag fluorine content (at constant basicity), brought about by higher concentrations of fluorine-containing compounds in the flux formulation. The effect of flux additions on the weld mechanical properties and the electrode operating characteristics was not evaluated during the course of this investigation.