Materials Science and Engineering: A ( IF 4.652 ) Pub Date : 2020-01-17 , DOI: 10.1016/j.msea.2020.138963 Bo Kan; Weijie Wu; Zixuan Yang; Jinxu Li
The uptake and accumulation of hydrogen in materials during a service process is the primary prerequisite of hydrogen embrittlement. However, the actual hydrogen concentration that causes brittle fracture is unknown. In this study, slow strain rate tensile tests combined with finite element simulations (FESs) were used to study the influence of stress variation and initial hydrogen content C0 (0.91, 1.70, 2.90, and 3.41 ppm) on the hydrogen redistribution and fracture behavior of smooth tensile specimens of Q960E steel for the first time. Furthermore, the actual threshold hydrogen content for hydrogen-delayed cracking was also obtained. Results showed that the presence of hydrogen significantly increases the elongation loss but has a minimal effect on strength loss. The occurrence of brittle cracking depends on the duration and the quantity of accumulated hydrogen. Brittle fracture occurs only at low strain rates under low C0 of 0.91 and 1.70 ppm. However, a high strain rate can result in brittle fracture at high C0 of 2.90 and 3.41 ppm. FES and fracture behavior indicate that the critical hydrogen content that causes brittle fracture is 1.8 ppm. If the C0 is less than 1.8 ppm, brittle fracture is also observed at the center of the specimen by stress-induced hydrogen diffusion to achieve this critical value at low strain rate. A logarithmic relationship is observed between C0 and the brittle zone size with a constant strain rate.