The influence of PTFE used as basic covered electrode binder on weld metal acicular ferrite formation

^*Selected from Soldagem & Inspeção 2014 19(2) 177–189

Abstract

Weld metals obtained from covered electrodes agglomerated with polytetrafluorethylene presented ultra-low diffusible hydrogen content and appreciable quantities of acicular ferrite. This article investigates the polymer influence on its constituent formation. The microstructure produced by consumables containing this component presented acicular ferrite quantities higher than expected in the literature for weld metals with the same carbon, silicon and manganese content. This difference could not be related to welding parameters employed. The residual chemical element evaluation indicated nitrogen as being mainly responsible for the microstructural variances observed. The operational characteristics of classic E7018 and polymer-agglomerated electrodes showed the lesser weld metal nitrogen absorption must be associated with two main factors. The dissolved nitrogen of the metallic drops collected during the polymer-agglomerated electrode welding showed most effective shielding atmosphere. The carbon content of the polymer-agglomerated electrode indicated an atmosphere rich in this element. This is in accordance with a best shielding process hypothesis. The metallic drops’ average size, dissolved nitrogen content as a function of size and voltage oscillograms indicated metallic transfer mode changes.

Keywords:

• Basic covered electrodes
• polymers
• metallic transfer
• nitrogen
• acicular ferrite

Acknowledgements

The authors thank the Laboratory of Robotics, Welding and Simulation (LRSS) of the Federal University of Minas Gerais for the structure required for carrying out the experiments, the company Elbras Eletrodos do Brasil for supplying consumables and ESAB Brasil for carrying out the tests.

Notes

^* Selected from Soldagem & Inspeção 2014 19(2) 177–189