Fracture Mechanism of Steel Q370 under Strong Corrosion Based on Surface Morphology

Abstract

A comprehensive investigation, including experimental research, finite-element analysis, and theoretical derivation, was thoroughly carried out on the steel Q370 under strong corrosion to study its fracture mechanism further. Twenty-seven steel specimens were corroded by 36% industrial hydrochloric acid for 0, 1, 2, 4, 8, 12, 24, 48, and 72 h. In particular, a three-dimensional (3D) noncontact laser scanner measured the size of pits and roughness of the steel surface. To sum up, on the condition that the corrosion time has leaped, the section loss rate mushroomed nonlinearly. An inflection point in the curve of section loss rate occurs at 12 h, and then the growth in section loss rate keeps steady. Moreover, three-dimensional roughness parameters Sa, Sq, and Sp from 3D scanning have a linear increase, and both Ssk and Sv have a nonlinear increase; notwithstanding, Sku has a nonlinear reduction. This finding means growth of surface roughness in corroded specimens. Furthermore, considering the increase in the number of pits and the cross-section reduction, the specimen shows an obvious upward trend in fracture parameters. In this study, the cavitation growth and stress-modified critical strain models were modified to establish a strong corrosion fracture model of steel Q370, including von Mises stress, hydrostatic stress, equivalent plastic strain, and corrosion time. The fracture displacement errors with the comparison of test and finite-element values are within 7%, indicating that the fracture model can precisely simulate the fracture of steel Q370 after strong corrosion. This research can present a reference for the engineering application and subsequent investigation of steel Q370 that suffered strong corrosion.