The microstructure of low carbon microalloyed steel and impact toughness scattering during fracture in ductile-to-brittle transition region

Abstract

The connection between occurrence of remarkable impact toughness scattering in ductile-to-brittle transition region and microstructure features of low carbon microalloyed steel was established by means of multiple impact toughness tests and electron backscatter diffraction microstructure measurements. The phenomenon of local inhomogeneity in ductility of plastic zone was established on the base of different microcracks nature revealed by electron backscatter diffraction. The residual microcracks occur in local embrittled regions of material as a result of cleavage at the early stage of fracture. Pre-strained regions with local ductility variations are fractured by the formation of splittings and by the ductile tearing. Pancaked parent austenite microstructure, various ferritic microstructures and martensite-austenite constituent along with the significant grain size variations can be considered as the sources for the occurrence of remarkable impact toughness scattering in low carbon microalloyed steels during fracture in ductile-to-brittle transition region.