Effect of austenitisation temperature on corrosion resistance properties of dual-phase high-carbon steel

Austenitisation is one of the most important factors in heat treatment process of dual-phase high-carbon steel, as it can affect the grain size, production of secondary phase precipitation, size of martensite laths and distribution of the phases. Despite the importance of this heat treatment on mechanical behaviour, its correlation on corrosion behaviour and electrochemical properties of high-carbon steel required in-depth investigation. The aim of this study is to investigate the effect of different austenitising temperatures on microstructure and corrosion behaviour of dual-phase high-carbon steel. Microstructural evolution was observed in situ using ultra-high-temperature laser microscope, and the steels have been characterised further using optical microscope, electron backscatter diffraction, 3D laser scanning confocal microscope, scanning electron microscope and energy energy-dispersive spectroscope and electron probe microanalysis. The powerful electrochemical corrosion test was employed by using Tafel polarisation method to measure its corrosion rate. Results have indicated that higher austenitising temperature increased grain size of retained austenite and martensite, which reduced the grain boundary length, but at the same time increased the size and amount of carbide precipitations. As the main corrosion mechanisms in dual-phase high-carbon steel were pitting corrosion and intergranular corrosion, effect of generated precipitations has overcome grain boundary corrosion caused by influence of size and shape of microstructures and, thus, reduced the corrosion resistance around 9.68% as temperature increased. These findings are crucial for designing new applications from high-carbon steels for mining and automotive industries.