Multiscale examination of deformation and fracture mechanisms of a duplex advanced high strength steel: Effect of testing temperature and of micromechanical interactions between microstructural constituents

Abstract Physical deformation and fracture mechanisms of a duplex high strength, low density steel have been examined, both in individual phases using TEM in-situ tensile tests and in bulk specimens using tensile and impact tests. Deformation in ferrite concentrated into wavy bands. In both ferrite and austenite, strong pinning induced non-continuous motion of dislocations even at low temperature. The stability of austenite against transformation into martensite was varied using either the test temperature or prior low temperature treatment, while keeping the chemistry, processing parameters and microstructural size and morphology constant. It was shown that the brittle-to-ductile transition in this alloy is driven by mechanical interactions between phases, and that cleavage fracture of coarse delta-ferrite is governed by the presence of hard martensite in the fine-grained regions, before or during the mechanical test.