Investigation of the influence of hot rolling parameters on CK45 microstructures

Optimization of Ferritic-pearlitic steel properties is one of the most important aims of the researchers in this study branch due to increasing use of these steels in industry applications.Therefore, improving their final microstructure is necessary to enhance the level of the mechanical properties. On the other hand, employing some manufacturing methods such as rolling can improve the microstructure and the mechanical properties in turn. In this research, the hot rolling operation and quenching in two different environments was carried out on CK45 steel. The samples were rolled in different temperatures and different rotational speeds of work-rolls under the same reduction percentage. They were then quickly cooled down in room atmosphere and cold water and the final microstructure was examined using of optical microscope. The results show that in hot rolling process, over 850○C temperatures, the microstructure is always in the form of martensite phase after rolling and cooling in cold water and the microstructure gets smaller even with increasing the temperatures. About the samples which are cooled in room atmosphere and with increasing the temperature, there is enough time for growth and forming continuous background of ferrite phase’s in the sample, so the samples return to their before rolling state. However, in low temperatures and high speeds, because of high strain rate, material has not enough time for retrieving and forming ferrite phase and the ferrite phase is formed only in rolling direction.