Influ?ancia do uso de PTFE como aglomerante em eletrodos revestidos b??sicos sobre a forma?§?￡o de ferrita acicular no metal de solda

摘要

Weld metals obtained from covered electrodes agglomerated with polytetrafluorethylene (PTFE) presented ultra low diffusible hydrogen content and appreciate quantities of acicular ferrite. This paper investigated the polymer influence on its constituent formation. The microstructure produced by consumables containing this component presented acicular ferrite quantities higher than expected on the literature for weld metals with same carbon, silicon and manganese content. This difference could not be related to welding parameters employed. The residual chemical elements evaluation indicated nitrogen as the main responsible by the microstructural variances observed. The operational characteristics of classic E7018 and polymer agglomerated electrodes showed the less weld metal nitrogen absorption must be associated to 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 polymer agglomerated electrode indicated an atmosphere rich on its 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.