Speaker
Description
Modern bainitic steel is one very promising steel concept contributing to actual, international sustainability development goals reducing carbon emissions during production but also during application, as they combine low material costs (i.e. low alloying element content) and comparatively efficient production processes with enhanced mechanical properties such as strength and ductility in the final product. Their outstanding mechanical properties are based on a composite-like microstructure consisting of a soft phase, i.e. retained austenite and a hard phase, i.e. bainitic ferrite with potentially cementite precipitates. Whereas strength is mainly controlled by the bainitic phase, ductility is mainly affected by retained austenite’s phase fraction and mechanical stability against transformation to martensite during mechanical loading. Both parameters are a function of carbon content in retained austenite. Therefore, to predict and subsequently control the competing mechanisms of cementite precipitation in bainitic ferrite and carbon enrichment in austenite is decisive for the optimization of bainite’s ductility. To this end, thermo-kinetic simulations are carried out using MatCalc 1D cell simulations in order to investigate the influence of the chemical composition and local microstructure size (i.e. thickness of bainitic ferrite and retained austenite) on the maximum carbon concentration of retained austenite. Additionally, electron backscatter diffraction and transmission electron microscopy measurements are conducted for the determination of the thickness distribution of bainitic ferrite and retained austenite. Atom probe tomography measurements of the retained austenite carbon concentration validated the MatCalc 1D cell simulations. Finally, design criteria for chemical composition and microstructure size distributions of bainitic ferrite and retained austenite are derived for an optimized stability of retained austenite and ductility of bainitic steels.
| Speaker Country | Austria |
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