Papers by Author: Liu Yang

Abstract: The fatigue limit and S-N curve of Q500q bridge steel were obtained by high-cycle fatigue test. The experimental results show that the fatigue limit of the experimental steel is 552.5MPa at room temperature with stress ratio R=0.1.There are some differences from the traditional fatigue fracture of high-cycle fatigue, the experimental steel’s rapid propagation area shows the morphology feature of both plastic fracture and brittle fracture. From analyzing the fatigue facture, the morphology feature of plastic fracture is mainly caused by the high fatigue limit. The little size (2~4μm) of inclusions in the experimental steel and the acicular ferrite’s microstructure feature of sub-lath structure with high-density dislocation reduce the crack initiation. And that’s the main reason why the steel has such high fatigue limit.

Abstract: The high-temperature deformation resistance of X120 pipeline steel was studied under different deformation temperature and different deformation rate through the hot compression test on the Gleeble-3500 thermal/mechanics simulation test machine. The influence of deformation degree, deformation temperature and deformation rate on deformation resistance was thoroughly investigated. The deformation resistance of X120 pipeline steel increased slowly when deformation degree was higher than 0.2. With the increase of deformation temperature, the work-hardening effect was weakened, so the deformation resistance decreased. And the deformation rate had dual influences on the deformation resistance, including the effect of temperature and time. Based on the experiment data, the parameters in the mathematical model were regressed by using SPSS (Statistic Package for Social Science), and the mathematical model of the deformation resistance of X120 pipeline steel was established finally. Through the regression analysis, the model had been proved to have great matching precision.