Design and development of CaO–SiO<inf>2</inf>–CaF<inf>2</inf> and CaO–SiO<inf>2</inf>–Al<inf>2</inf>O<inf>3</inf> based electrode coatings to weld low alloy ferritic steels for power plant applications

Dissimilar welding of low alloy ferritic steel to martensitic or stainless steels is an essential requirement in modern thermal and nuclear power plants. Shielded metal arc welding (SMAW) is most commonly used to weld dissimilar metals using the flux coated electrodes. Suitable filler wire selection and electrode coating composition play an important role along with the welding parameters on the quality of welded joints. These parameters also affect the mechanical properties of the welded joints. This article deals with design and development of electrode coatings for joining low alloy steels. Electrode coatings were developed using CaO–SiO2–CaF2 and CaO–SiO2–Al2O3 flux systems with the help of mixture design and extreme vertices approach. Twenty one multipass weld beads were made using developed shielded metal arc welding electrodes. Weld chemistry was obtained using spectrometer for all the twenty-one welds. Microstructural and microhardness analysis was performed on all the welded specimens to observe the metallurgical and mechanical behavior of the welds. Multi-response optimization was carried out to obtain optimum flux composition. The effect of individual constituents and their interactions on the weld chemistry, grain size, and microhardness has been investigated.