Abstract

The main types of non-metallic inclusions in centrifugal «40H25N20S2» cast steel as well as their effect on the local structure and formation of secondary boundaries and cracks have been discussed. It was found that a higher content of such inclusions causes the reduction of mechanical properties of this steel at the same character of the workpiece macrostructure. It is shown that the inclusions are sources of internal stresses and promote the defect formation (microcracks). Moreover, they cause the local structural changes in austenitic matrix connecting with splitting of interphase inclusion–matrix boundaries and polygonization processes near inclusions promoting the formation of secondary boundaries. Mechanical tests have shown that at the same macrostructure of casting non-metallic inclusions have a significant negative influence on the level of strength and plastic characteristics. In the areas near to its inner surface with a columnar macrostructure the increase of inclusions content in steel has led to reduction of strength by 15…18%, and ductility – by 18...21%.