Title page for ETD etd-05152007-131110

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
Advisor Name Title
Prof M du Toit
  • hydrogen
  • basicity
  • flux
  • water vapour
  • shielded metal arc welding
Date 2006-08-28
Availability unrestricted
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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