Morphology and Mechanical Properties of Bainitic Steels Deformed in Unrecrystallized Austenite Region

Abstract

Bainite structure in low carbon low alloy steels has played an important role for the practical use of these steels in many constructions[1,2]. By improving the strength and toughness they will be applied to new fields in the future. From the viewpoint of microstructure, it is a packet size that determines the toughness of bainitic steels. Optical micrographs of upper bainite structures exhibit a straight elongated lathlike bainitic ferrite whose growth is determined by austenite grain boundaries. However the application of accelerated cooling after controlled rolling [1,2] makes the microstructures considerably different from those in the conventional quenching and tempering process. Although some of these complicated microstructures have been called Zw[3] , the nature of them has never been clarified. It is very important to define an effective way to refine the bainite structure by the deformation in unrecrystallized austenite region in order to improve the toughness of steel plates. This study focuses upon the effects of deformation on the morphology of bainite structure and mechanical properties in low carbon low alloy bainitic steels.