Bainite in silicon steels: new composition–property approach Part 2

Abstract

AbstractAbstractResearch discussed in Part 1 of this study indicated that the properties of microstructures based on bainitic ferrite and carbon enriched retained austenite can be optimized by ensuring that the austenite exhibits both mechanical and thermal stability. These conditions were quantitatively described in terms of a criterion comprising the volume fraction of bainitic ferrite and other terms deduced experimentally. This paper reports the testing and further development of this criterion: the volume fraction of bainitic ferrite (and hence the carbon content of the residual austenite) can be thermodynamically estimated from a knowledge of the steel composition and the isothermal transformation temperature only. Using thermodynamics, it was predicted that two steel compositions in particular should yield even better properties than have been obtained previously. Therefore, these steels were prepared and tested, and the impact properties at very high strength levels were shown to be much improved.