Simulation of Evolution of Dual-Phase Microstructure
Dual-phase steels, developed in the 1970’s, found until now wide applications related to their optimum combination of strength and ductility, in particular as flat semi-products used for further shaping by deep drawing and cold forming operations. Actually the need appears to manufacture long semi-products of dual-phase steels for further processing by cold forging, in order to obtain high-strength final products, like e.g. fasteners, without additional heat-treatment. An additional aim has been to explore the possibility of achieving from the same chemical compositions dedicated properties for particular applications. In this work a thermo-mechanical route was developed of modifying an originally bainitic-martensitic low-alloy steel to achieve a dual-phase microstructure. For this purpose physical simulation was used on Gleeble 3800 thermal-mechanical simulator, programmed to affect austenite in its dynamic recrystallisation range followed by separation of microstructures in the two-phase austenite-ferrite range. Observation of relaxation was used to monitor advancement of transformation / recrystallisation in subsequent stages of the processing. In the simulated hot-warm rolling process it appeared possible to convert the original bainitic microstructure, having prior austenite grain size ~15μm and the martensite-bainite laths of usual length throughout these grains, to the dual-phase microstructure containing well-recrystallised ferrite of an average grain size 1*1.5μm and fine second-phase islands of less than 1.0μm diameter. SEM and TEM analysis have been applied to describe details of the resulting microstructures.
T. Chandra, N. Wanderka, W. Reimers , M. Ionescu
S. T. Mandziej et al., "Simulation of Evolution of Dual-Phase Microstructure", Materials Science Forum, Vols. 638-642, pp. 2652-2657, 2010