Comparative Research on Fatigue Performance of High-Strength Bainitic Steel with or without Corrosion

High-strength bainitic steels have acquired a promising place among steels due to their wide applications in engineering structures. It is, therefore, worthwhile to investigate their fatigue performance in different environments. When fatigue is atmospheric, lattice strength of weaker zones including granular bainite, phase boundary and MA constituents determines the nucleation life of fatigue. The deflected microstructural short cracks enhance the early propagation life of fatigue. In lath bainite, fine ferrite laths, high-density dislocations within the grains, small grain size and high proportion of HAGBs inhibit the crack growth process to improve propagation life of fatigue. The fracture reveals transgranular mode for propagation of fatigue. The pre-corrosion strategy is adopted before investigating corrosion fatigue process, so that there is an adequate corrosion effect on samples. The pre-corrosion time is determined to be 3 days through the analysis of electrochemical parameters, viz. corrosion potential and current. For overall fatigue life, corrosion grooves have significant deterioration effect. The transgranular and intergranular features are observed in fracture at initial stage of crack growth. Only transgranular features are found at middle and final stages.