Research on Pitting Corrosion of Micro-alloyed High Strength Steel Bars

Abstract

ABSTRACT In this study, a series of soaking experiments were conducted in simulated marine environment solution to explore the pitting corrosion behavior induced by four types of inclusions in micro-alloyed steel bars: Al2O3, MnS, Al2O3-(Ti,V,Nb)N and Al2O3-MnS-(Ti,V,Nb)N. In the early stage of corrosion, due to the high-density lattice distortion zone around the MnS and Al2O3 inclusions, along with the fact that these inclusions are not closely connected with the steel matrix, micro-cracks can occur leading to the initial corrosion of MnS in the Cl- environment. The corrosion rate of Al2O3 is the second highest after MnS, and clusters of Al2O3 can further accelerate the corrosion rate. The lattice distortion density around (Ti, V, Nb)N precipitates is significantly lower than that around MnS and Al2O3 inclusions. Additionally, (Ti, V, Nb)N is closely connected with the steel matrix without any micro-voids. Therefore, (Ti, V, Nb)N is not sufficient to induce pitting corrosion of the matrix. The trend of pitting corrosion induced by the four types of inclusions, Al2O3, MnS, Al2O3-(Ti,V,Nb)N, and Al2O3-MnS-(Ti,V,Nb)N, is as follows: MnS > Al2O3> Al2O3-MnS-(Ti,V,Nb)N > Al2O3-(Ti,V,Nb)N.