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

Abstract

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, highdensity 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.

Fatigue damage evolution and failure of pre‐corroded aluminum alloy 7075‐T651 under air and corrosion environments

“…On the one hand, the insoluble corrosion product covered the crack propagation zone and blocked the crack tip, as shown in Figures 10–12, and the “crack closure” due to a wedge effect induced by the formation of corrosion product will hinder crack propagation. On the other hand, the corrosive environment can also cause the anodic dissolution of the aluminum alloy at the crack tip, thereby corroding the crack tip into a rounded corner with a certain radius, thereby reducing the shape factor and alleviating the local stress concentration 35 . It was noted that material hydrogen embrittlement is still likely to occur during the crack propagation process.…”

“…On the other hand, the corrosive environment can also cause the anodic dissolution of the aluminum alloy at the crack tip, thereby corroding the crack tip into a rounded corner with a certain radius, thereby reducing the shape factor and alleviating the local stress concentration. 35 It was noted that material hydrogen embrittlement is still likely to occur during the crack propagation process. As shown in Figure 11, mud cracking is also found in the stable propagation zone of the specimen, but its effect does not seem to be obvious, which is related to the corrosive solution concentration.…”

Morphological characteristics and geometric prediction model of pits in complex corrosion environment

“…Therefore, Q represents the corrosion equivalent on the surface of the material with an area of S after a certain t under a certain environmental parameter. The corrosion increases into a steady state stage with t , and i c is stable at this stage, [ 26‐28 ] it is believed that i c does not change with t at this time. i c involved in the following is corresponding to the t = 72 h, so the corrosion equivalent conversion based on Q can be converted into the conversion of i c .…”