Effect of Morphology for Novel Bainite/Martensite Dual-Phase High Strength Steel on Its Hydrogen Embrittlement Susceptibility

The susceptibility to hydrogen embrittlement of bainite/martensite dual-phase high strength steel with different morphologies obtained by the conventional and thermo-mechanical heat treatments has been investigated by means of electrolytic hydrogen charging.The results showed that the finer the microstructure,the lower the sensitivity of steel to hydrogen embrittlement.The fractographic analysis suggested that the fracture mode of the hydrogencharged specimens is of a mixture of quasicleavage and dimple for both treating processes.The quasicleavage facet of the thermomechanical treated specimen is smaller than that of the conventional heated one,which is probably the reason for reducing the susceptibility to hydrogen embrittlement.Fracture metallographic observations showed that the crack propagates preferentially along bainite/martensite laths boundary,and suggested that the fracture mode is of predominantly lath boundary separation.