Experimental and theoretical study on mechanical properties of mild steel after corrosion

Abstract

Corrosion seriously affects the strength and stability of steel structures and it has attracted extensive attention in engineering. In this study, the accelerated corrosion testing is performed to investigate the influence of corrosion on mechanical properties of mild steel (i.e., Q235 and Q355 steel). A power function for the relation between the corrosion rate and the corrosion time is found, and the corrosion rate of Q355 steel is relative small in the initial stage but it speeds up after exposed at the salt-spray chamber for 2880 h. Q235 and Q355 steel have similar corrosion products, but Q235 steel has flower-like microstructure while Q355 steel shows honey-comb type microstructure. The results show that the yield strength, the ultimate strength, the elongation, the elastic modulus, and the fracture strain of Q235 steel decrease linearly as the corrosion rate increases. The elongation and the elastic modulus of Q355 steel decrease obviously as the corrosion rate increase, but the effect of corrosion on the yield strength and the ultimate strength of Q355 steel is not obvious. Existing experimental results of material properties for corroded Q235 steel are also collected. More accurate models are developed for estimating mechanical properties (i.e. the yield strength, the ultimate strength, the elongation, the elastic modulus, and the fracture strain) of mild steel. Constitutive models modified from the Hollomon's model are proposed to predict the stress-strain curves of corroded Q235 and Q355 steel, and they are more accurate than existing models.