Development and Performance of Ochre (Anhyd. Fe2O3) Added CaO-CaF2-TiO2-SiO2 Fluxes for Welding Electrode

Novel CaO-CaF2-TiO2-SiO2-coated electrodes with a mining waste, red ochre (anhyd. Fe2O3), to replace commercial ferro-alloy powder have been developed. Addition of mining waste to electrode-coating composition is an attempt to make the process environmentally sustainable. The developed flux coatings have been applied on austenitic 309L stainless steel core wire. The welding electrodes have been tested to fabricate a dissimilar weld between API X70 pipeline steel and super-duplex stainless steel 2507. Performance assessment of electrodes included weld microstructure, microhardness, and wear resistance. The weld solidification occurs in primary-ferrite mode and the microstructure is composed of delta-ferrite in dendritic vermicular morphology with austenite occupying interdendritic spaces. The acidic oxide SiO2 in the coating composition and corresponding silica in the weld fusion zone have increased the hardness and improved wear resistance. The reduction of Fe2O3 by Cr and Mn lowers alloying element concentration in the weld due to formation of chromium and manganese oxides. Welds made with commercial electrode has hardness of 231 +/- 4 Hv which is marginally higher than 224 +/- 3Hv and 219 +/- 3Hv of the laboratory-developed electrode-made welds. Scheil's solidification analysis identifies no precipitation of deleterious phase occurred. Sliding wear for pins extracted from the three welds indicate very low wear occurring in the mixed-mode mechanisms of adhesive, abrasive, and fatigue wear, with material being removed by plowing.

Automated summary

Novel CaO-CaF2-TiO2-SiO2-coated electrodes using mining waste red ochre have been developed to replace commercial ferro-alloy powder, aiming to promote environmental sustainability. These electrodes demonstrated improved weld microstructure, microhardness, and wear resistance when used to weld dissimilar metals. The addition of SiO2 in the coating composition enhanced hardness and wear resistance, while the reduction of Fe2O3 lowered alloying element concentration in the weld.