Investigation of the impacts of heat treatment processes on corrosion resistance of certain boron steel

The aim of this study is to investigate the effect of austenitizing and tempering temperature on the corrosion resistance of 27MnCrB5, 30MnB5 and 34MnB5 boron steels. The experiment specimens were austenitized at 850 ° C, 900 ° C and 950 ° C. The specimens were immersed in water at approximately 25 °C. After the hardening, the specimens were tempered at 150 ° C, 300 ° C and 450 ° C for 30 minutes. In this study, after the heat treatment, hardness distribution profıle, average ferrite grain size, microstructure changes, corrosion characteristics and mechanical properties of the specimens were investigated. It was determined that austenitization and tempering temperatures were important in terms of corrosion rates. As a result of the corrosion experiments, it was found that the changing C ratio in the boron steels affected the corrosion rate and the increasing C ratio increased the corrosion rate. A weak correlation was found between the average ferrite grain size and corrosion rate under the heat treatment conditions in experiment. As a result of tensile experiments, it was determined that the increase in hardening and tempering temperature caused a decrease in tensile and yield stres values. The highest tensile, yield, and break stress values were obtained in the tempering process at 150 °C followed by tempering operations at 300 °C and 450 °C, respectively. The effect of the tempering temperature on tensile, yield and break stress was determined to be more effective than the effect of austenitizing temperature. The effect of tempering temperature on the ultimate tensile strength is greater than on the yield strength. Keywords: Boron steels, heat treatment, corrosion resistance, mechanical properties, hardening, Tafel extrapolation, ferrite grain size.