The flux oxygen potential and the deoxidizers content in the flux influence on low-alloy steels the microstructure modification welds metal was investigated. It was established that flux basicity, changing the deoxidation alloying system effects on weld metal structure forming processes and contributes to achieving the low-alloy steels welds highest strength and plasticity levels. It was shown that the welding flux oxygen potential reducing contributes to reducing the inclusions size formed in the weld metal. The use of fluxes with a higher basicity index in welding contributes to an increase the refractory inclusions content in the primary austenite grains. An increase the dispersed inclusions content in the primary austenite grains is accompanied by an acicular ferrite content increase in the weld metal structure and an increase in the weld metal resistance to brittle fracture.