On the Effect of γ-phase transformation kinetics upon microstructure response of Cold Heading Quality Steel

Cold heading quality CHQ steel is a versatile form over other steels as they are used non-heat treated; their strengthening mechanism is achieved through cold heading operations. Metal is therefore stretched without applying any source of heat, metal flow during the cold heading operation must depend on grains flow which increases the mechanical properties such as strength, resistance to indentation and toughness. It is therefore necessary to form the isotropic grains before applying cold heading operation may increase the properties. Gamma phase formation during the heat treatment is crucial factor for cold operation. An effort is made in this research work to study and find out the Austenite nucleation and growth morphology of commercial CHQ steel through continuous heating experiments by utilizing lead-bath up-quenching technique at differentaustenizing temperature ranges. High class Optical Microscope Olympus GX51, scanning electron microscopy techniques have been utilized to reveal and interpret the microstructure and it was found that At the 740°C, the microstructure shows the lack of homogeneity in the structure hence cold-head-ability of CHQ steel is anisotropic but at the high temperature in austenite domain at 60sec the resultant austenite is highly homogenous due to high volume fraction of austenite has been formed then the cold-head-ability properties of CHQ steel turned to be isotropic. Keywords: Up-quenching, cold heading steel, gamma transformation, heating rate etc.