Study on fatigue crack growth behaviour of Q690D high strength steel with corrosion damage

High-performance steel bridges are an important development direction in the field of civil engineering due to their advantages of high load bearing, high durability and efficient construction. However, bridge structures are subjected to long-term corrosive environments when in service, and problems such as corrosion and fatigue damage are difficult to avoid. In this paper, indoor salt spray, dry and wet cyclic accelerated corrosion tests on Q690D high strength steel (HSS) were carried out according to the characteristics of the marine atmospheric region. The fatigue crack growth rate (FCGR) tests and threshold tests were carried out on compact tensile (CT) specimens of two plate thicknesses with different degrees of corrosion damage. And based on the fatigue fracture and surface morphology of corroded CT specimens, the fatigue crack growth (FCG) mechanism of HSS was investigated. The results show that the thickness of the corrosion products deepens with the increase of corrosion time. And the corrosion pits are randomly distributed on the surface of the specimen in clusters, with large and deep pits surrounded by small and shallow pits. The FCGR of Q690D HSS increases significantly with increasing corrosion cycles. The FCGR values at 60 days, 90 days, 120 days and 150 days of corrosion increased by 28.11 %, 35.01 %, 38.87 % and 51.45 % compared with those without corrosion, respectively. And the FCG threshold (FCGT) values decrease approximately linearly with the increase of corrosion damage degree. When the mass loss rate of the specimen increased to 9.195 % and the maximum depth of the corrosion pit was 786 μm, the threshold value was reduced by 31.53 %.