Effect of nonmetallic inclusions morphology on destruction of a perspective high strength corrosion-resistant steel 04Х20Н6Г11М2АФБ

Abstract

Alloying by nitrogen imparts to a steel high strength, viscosity, corrosion resistance and enables to save expensive alloying elements. As a result of theoretical and experimental studies carried out last decades, the problems of composition optimization, plastic deformation and thermomechanical treatment were solved as a whole. The solutions were used at elaboration of new perspective high strength corrosion-resistant steels, in particular, of steel 04 Х 20 Н 6 Г 11 М 2 АФБ . The items of comprehensive hardening of nitrogen-bearing steel of the mentioned composition for plates production were studied quite well. Effect of grain and subgrain metal structure, recrystallization, morphology of secondary phases, their composition and other factors on mechanical and corrosion properties of the steel were studied earlier. However, there are practically no studies dealing with morphology, chemical composition, sulphide and oxide nonmetallic inclusions distribution, evaluation of their influence on deformability and properties of high strength nitrogen-bearing steels, including properties in Z-direction. The aim of this study was revelation of dependence of the steel destruction character at rupture on the type and morphology of nonmetallic inclusions. Study of morphology, chemical composition, sulphide and oxide nonmetallic inclusions distribution density was carried out, as well as evaluation of their influence on properties of hot-rolled sheet, made of experiment high strength steel 04 Х 20 Н 6 Г 11 М 2 АФБ . It was determined, that nonmetallic inclusions of oxides, sulphides and nitrides can locate in a plane, parallel to Z-direction in both ways: evenly and forming stitches, at that one stitch can contain particles of various types. Comparatively low level of plasticity in Z-direction is stipulated both by general contamination of the metal by oxide inclusions and by stitch morphology of accumulation of nonmetallic inclusions of various types. It was shown, that at comparatively low density of nonmetallic inclusions stitches, their length plays the main role in the plasticity decrease in Z direction. In case of many stitch accumulations, the distance between them begins to play the leading role.