AbstractThis paper investigated stress flow in weathering steel Q345 after strong acid corrosion. In total, 27 specimens were immersed in 36% industrial hydrochloric acid for 0, 1, 2, 4, 8, 12, 24, 48, and 72 h, respectively. A three-dimensional noncontact laser scanner was used to measure geometric parameters of pits on the surface of the steel. The influence on ductile crack initiation in steel under the pit was investigated through tensile testing and finite-element simulation, which obtained the relationship among depth-diameter ratio, depth ratio, and stress triaxiality. Based on analysis of 65 finite-element models, the equivalent ductile fracture criterion of strong-corrosion steel per corrosion times was proposed. The results showed that the depth-to-diameter ratio of pits increased linearly with pit depth, whereas the depth ratio of pits increased nonlinearly with corrosion time extending. After 24 h of corrosion, the depth ratio of pits in weathering steel Q345 showed an inflection point where the growth rate was relatively slow. When corrosion time reached 72 h, the depth-diameter ratio and depth ratio of the maximum pit was 0.74 and 0.01, respectively. With the development of the depth-to-diameter ratio, the stress triaxiality inside corrosion steel increased; meanwhile, the equivalent plastic fracture strain decreased, which accelerated internal crack initiation. For pits in weathering steel Q345 with a depth-diameter ratio of 0.40–0.80, stress triaxiality increased from 0.56 to 1.23. Finally, the elongation of corrosion steel degraded gradually. By comparing test values, formula values, and finite-element values, fracture strain errors were all less than 5%. These data show that the equivalent ductile fracture criterion can accurately simulate the ductile degradation in weathering steel Q345 after hydrochloric-acid corrosion. The research results can provide a theoretical basis and application reference for strong-corrosion protection ways of weathering steel Q345 after hydrochloric-acid corrosion.