Effect of tempering process on the mechanical properties and corrosion resistance of E690 marine steel

To accurately replicate actual production and save production costs, this study examines the influence of the tempering process on the structure, mechanical properties, and corrosion resistance of E690 marine steel. Various techniques were employed to evaluate its properties, behavior, and performance, including metallurgical microscopy, scanning electron microscopy, transmission electron microscopy, electron backscatter diffraction, impact experiments, tensile tests, and electrochemical corrosion tests. The results indicate that as the tempering temperature increases, the tempering degree of the tempered martensite structure improves, the martensite strip coarsens, the size of the precipitated carbide increases, and the proportion of large-angle grain boundaries decreases. Consequently, the tensile strength and yield strength initially increase and then decrease, while the impact toughness and elongation gradually improve. At a tempering temperature of 600 °C, the steel exhibits the best overall mechanical properties, with a tensile strength of 729 MPa, yield strength of 649 MPa, and elongation of 18%. Furthermore, at a tempering temperature of 550 °C, the test steel shows an optimal corrosion resistance, with a corrosion rate of 0.03233 mm y⁻¹ and an open-circuit potential of −0.36 V.