Abstract

This study assessed how austempering heat treatment affected the microstructure and corrosion behaviour of low-carbon steel (AISI 1018). The steel samples were prepared and austenitized at 830 °C for 90 min, followed by isothermal transformation at a quenching temperature of 300 oC in a NaNO3 salt bath for an additional 50 min, and air cooling to room temperature. 0.5 M HCl and 0.5 M NaOH aqueous solutions were used to test the resulting samples for corrosion using the corrosion weight loss approach. A scanning electron microscope (SEM) was applied for the microstructure analyses. The microstructure tests revealed a transformative shift from pearlite to bainite phase, with minor fractions of unrelieved martensite. In the acidic and basic media, the austempered AISI 1018 steel displayed lower corrosion weight loss compared to the as-received sample. The microstructural modifications prove to be instrumental in diminishing the number of active corrosion sites, thereby fostering the stability of the passive film formation on the austempered AISI 1018 steel surface to enhance resistance to corrosion. Furthermore, the study highlights a distinct trend wherein the rate of chemical deterioration in the acidic medium surpasses that in the basic medium. The research underscores the pivotal role of microstructural engineering in material design strategies, emphasizing the potential for tailored microstructures to optimize corrosion resistance in acidic and basic conditions.

Key words: corrosion, AISI 1018 steel, austempering, heat treatment, microstructure