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[References: 4 tit.]

Microstructure of coatings obtained by manual arc welding with commercial electrode MP-3 and experimental electrode modified with carbonitride nanoparticles was studied using scanning tunnel microscopy. It was found that microdispersed additives lead to structure refinement and bianite formation. Using dihedral angle measurements relative energies of ferrite/ferrite and ferrite/cementite grain boundaries were estimated. It was shown that the average relative grain boundary energy for experimental electrode coating is more than two times less than the corresponding value for commercial electrode coating. This phenomenon might be related to the increase of ferrite/cementite boundary portion. The decrease in grain boundary energy is correlated with the impact toughness increase of specimens with experimental electrode coating.