Document Type	Master's Dissertation
Author	Du Plessis, John
Email	duplessisj@saiw.co.za
URN	etd-05152007-131110
Document Title	Control of diffusible weld metal hydrogen through arc chemistry modifications
Degree	MSc (Metallurgy)
Department	Materials Science and Metallurgical Engineering
Supervisor	Advisor Name Title Prof M du Toit
Keywords	hydrogen basicity flux water vapour shielded metal arc welding
Date	2006-08-28
Availability	unrestricted
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.
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