Properties of Advanced Experimental CMnSiMo Steel Achieved by QP Process

AbstractIn relation to technological development in all branches of industry, the requirements for properties of structural materials and for their various combinations are constantly increasing. For instance, the types of advanced materials are sought which would have low procurement costs and high ultimate tensile strength and yield strength while retaining sufficient levels of elongation and toughness. Normally, ductility of materials declines with increasing strength. In some types of steels, special heat treatment can be used to achieve excellent combination of strength, elongation and toughness when compared to conventional treatment processes. One of such advanced heat treatment techniques is the Q-P (Quenching and Partitioning) process. It consists in austenitizing and rapid quenching of the steel between Ms and Mf temperatures to prevent the martensitic transformation from propagating through the entire volume of the workpiece. The subsequent heating causes tempering of martensite and diffusion of excess carbon from martensite to retained austenite, thereby increasing the stability of the austenite. The aim of the QP process is to produce very fine martensite micro structure with retained austenite between martensite plates. The experiment was performed on high-strength low-alloyed steel containing 0.2% carbon and a higher amount of silicon about 1.5%. Higher silicon content contributes to stabilization of retained austenite by suppressing formation of carbides. This grade of steel is a very cost-effective material thanks to its low amount of alloying elements. The entire group of these low-alloyed steels, if heat treated or thermomechanically treated in a suitable manner, offers a favourable combination of strength, elongation and toughness. Thanks to these properties and a low content of alloying elements (i.e. low price), QP steels are used primarily in the automotive industry. The present paper deals with the relationship between parameters of the Q-P process, the austenitizing temperature, the partial quenching temperature and the tempering temperature, mechanical properties and resulting micro structure of the CMnSiMo experimental steel