Effect of Heating Rate on Microstructural Developments in Cold Heading Quality Steel used for Automotive Applications

CHQ (Cold Heading Quality) steels are assumed to be non-heat treatable so strengthened by cold forming which is a quick and mass production makes it low cost manufacturing process. In this study, microstructure and phase transformation in steels is a fundamental aspect of governing the properties. A large number of studies are dedicated on the subject phase transformations owing to availability of several commercial steel grades. Due to several grades of steels commercially available shows differently behavior so it is hard to conclude that phase transformation is universally understood completely. In this study the influence of heating rate on the development of microstructure of CHQ steel has been studied thoroughly by using different heating techniques.For characterization, optical microscope connected with high resolution camera and SEM (Scanning Electron Microscope) was utilized to interpret the microstructural results. In addition, heat treatment methods have been utilized as to vary the microstructure in the steel under experimentation. It was found that heating rate could have major effect on phase transformation of CHQ steel (under study). Rate of heating enhances the austenite development kinetics with respect to dwell time and such austenite has been changed to martensite upon cooling. In addition, heating rate also promotes nucleation sites for the formation of austenite phase of CHQ steel.