Experiments on static and fatigue behaviour of corroded Q235B and 42CrMo steels: Fid-Bau Portal

Experiments on static and fatigue behaviour of corroded Q235B and 42CrMo steels

Dang, Hengyao / Liang, Anrui / Feng, Ran / Zhang, Jingzhou / Shao, Yongbo / Yam, Michael C.H.

Abstract This paper studies the mechanical properties and low-cycle fatigue behaviour of corroded Q235B and 42CrMo steels. Tensile test and low-cycle fatigue test were conducted on the corroded specimens after the accelerated corrosion process in the 25 °C salt spray, 25 °C dry/wet cycle or 50 °C dry/wet cycle conditions. Based on the accelerated corrosion test, the corrosion rate and ratio of weight loss were calculated and their relationships with the exposure time were described by a time-dependent model. The tensile test results indicate that the 50 °C dry/wet cycle condition caused the most degradation on the strength and ductility of both Q235B and 42CrMo steels. The modified three-stage constitutive model is used to describe the stress-strain curve of specimens under different conditions and the key parameters in the model were obtained by regression analysis on the experimental data. The low-cycle fatigue test results demonstrate that the coupling effect of corrosion environment, such as chloride ion and higher temperature, and applied cyclic load can lead to decrease in the fatigue life of these two metallic materials. Comparisons between the test fatigue life and the design values demonstrate that the current design codes cannot provide accurate fatigue life predictions for the Q235B and 42CrMo steels in the salt spray and dry/wet cycle conditions.

Highlights • 50 °C dry/wet cycle shows the largest corrosion damage on Q235B and 42CrMo steels. • 50 °C dry/wet cycle causes great degradation on the mechanical and low-cycle fatigue behaviour. • Constitutive models for Q235B and 42CrMo steels under different conditions were obtained by regression analysis. • Corrosion pits with stress concentration work as the initiation of fatigue crack. • Existing fatigue curves underestimate fatigue life of corroded Q235B steel and overestimate that of corroded 42CrMo steel.