Effect of tempering time on the microstructure and corrosion resistance of carbon steel/stainless steel bimetallic composites

Purpose This study aims to investigate the effect of tempering time during heat treatment on the microstructure and corrosion resistance of carbon steel/stainless steel (SS) bimetallic composites. Design/methodology/approach The microstructure of SS surface and the corrosion morphology after double loop electrochemical potentiokinetic reactivation (DL-EPR) testing were observed by optical microscope and scanning electron microscope. X-ray diffraction and electron backscattered diffraction were used to analyze the phase composition and microstructural characteristics of the SS surface. The corrosion resistance of the material was characterized using DL-EPR, electrochemical impedance spectroscopy and potentiodynamic polarization tests. Findings Tempering heat treatment increases the martensite content on the SS surface and leads to severe intergranular corrosion. With prolonged tempering time, the susceptibility to intergranular corrosion increases. After heat treatment, the proportion of low-angle grain boundaries (LAGBs) and geometrically necessary dislocation (GND) density decreases, affecting the material’s corrosion resistance. Originality/value As the tempering time increases, intergranular corrosion susceptibility intensifies, resulting in more severe intergranular corrosion. In addition, the martensite content on the SS surface increases, while the proportion of LAGBs and GND density decreases, leading to a decline in the material’s corrosion resistance.