Synergistic effect of chromium content and intercritical annealing process on corrosion-resistant improvement of Ni-Cr-Mo low alloy

Dual-phase steel is required for engine bolt applications due to its excellent formability without sacrificing ductility. The research aimed to investigate the synergistic effect of chromium content and the intercritical annealing process on the corrosion-resistant of low alloy Ni-Cr-Mo steel. All samples, with Cr additions ranging from 0.5–3%, were intercritical annealed at 760℃ for 30 min before being quenched in water. As a result, the microstructure revealed the ferrite + lath martensite phase with a proportional volume fraction of martensite and ferrite (close 1.25 ratio). Meanwhile, the carbide particle was invisible in the SEM image. Chromium addition has a significant impact on the mechanical and corrosion properties. The martensite phase increased slightly by 2 wt.% Cr, and the hardness increased to 611 BHN, while the elongation decreased by roughly 13.8%. The highest tensile strength (~751 MPa) was obtained by adding 3 wt.% Cr. Conversely, adding chromium reduced the corrosion rate to 11.19 mmpy in the 3.5% NaCl solution.