Experimental and Numerical Study of Micromechanical Damage Induced by MnS-based Inclusions

The study is focused on the characterization of three microalloyed 38MnSiV6 steel variants in terms of microstructure, mechanical properties, and crack initiation. Conventional steel was used as reference material, while the two other variants with reduced sulfur content and Bi or Se addition were prepared. To determine the influence of the non-metallic inclusions present in the rolled round bars; hardness, tensile, impact toughness, and fatigue properties were examined longitudinally and transversally to the rolling direction. To describe the local strain and deformation around the inclusions during the microtensile tests, scanning electron microscope monitoring was adopted. Finite element analysis was applied to model strain/stress localization around inclusions during the microtensile tests. Modeling was performed in two solutions stages involving a macro-model (microtensile sample) and micro-model (inclusions). The comparison of the numerical analysis with the microstructural observations during microtensile tests showed a good agreement. The MnS and MnSeS inclusions were responsible for the intensive strain localization and subsequent crack initiation, while the Bi-MnS inclusions were not involved in this process.