The Mechanism of Modification Influence on Non-Metallic Inclusions in the Weld Metal of High-Strength Low-Alloy Steels

An analysis of the effect of modification by dispersed particles of various compounds on the distribution, composition, and morphology of non-metallic inclusions and phase precipitates in the weld metal of low-alloy high-strength steel has been conducted. It has been established that modification with dispersed TiN or Al<sub>2</sub>O<sub>3</sub> particles leads to the enlargement of non-metallic inclusions in the weld metal. It has been shown that some modifier particles of SiC or TiC dissolve in the liquid metal pool and precipitate as separate new phase inclusions on or near the surface of non-metallic inclusions, which overall results in changes in the composition and morphology of non-metallic inclusions in the weld metal. In the case of using ZrO<sub>2</sub> or TiO<sub>2</sub> modifiers, small 20-60 nm dispersed non-metallic inclusions are formed, enhancing the modification effect. During the analysis, no primary particles of modifiers were detected, but separate phase separations were detected, which may indicate the complete dissolution of particles in a liquid metal bath of some types of SiC, TiC separations and their subsequent separation from a supersaturated solid solution upon cooling welded joint. In cases where zirconium oxides ZrO2 or TiO<sub>2</sub> were used as modifying compounds, the size reduction of refractory oxides inoculated into the welding bath to nanosize (30...70 nm, the size of which can be compared to the size of the tip of the dendrite growing from the liquid metal of the weld pool during the crystallization process, increases the efficiency of the modification.