Fatigue crack propagation behavior of multiphase microstructure in a quenched and partitioned medium-carbon bainitic steel |
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| Authors: | Qiangguo Li Yanan Zhang Hong Luo |
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| Affiliation: | 1. Failure Mechanics & Engineering Disaster Prevention Key Laboratory of Sichuan Province, Sichuan University, Chengdu, China;2. School of Materials Engineering, Xi'an Aeronautical University, Xi'an, 710077 China;3. Material Corrosion and Protection Key Laboratory of Sichuan province, Zigong, 643002 China |
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| Abstract: | A medium-carbon steel was treated by the bainitic isothermal transformation plus quenching and partitioning (B-QP) process to obtain bainite/martensite/retained austenite multiphase microstructure, and its fatigue crack propagation (FCP) behavior was evaluated in contrast with BAT (bainite austempering) sample with fully bainite microstructure. Results show that B-QP sample exhibits a lower FCP rate and higher fatigue threshold ΔKth (12.6 MPa·m1/2). Moreover, the FCP path of B-QP sample displays a strongly tortuosity and more crack branching due to more filmy retained austenite (7.2%) and higher percentage of high angle misoriented boundaries (68%). The larger crack tortuosity and the secondary cracks as result of crack branching are primarily responsible for the lower FCP rate of B-QP sample. In addition, the FCP rate curve of B-QP sample shows a pronounced small plateauing at the near-threshold zone, which can be ascribed to the mechanical twinning that occurred in the filmy retained austenite. |
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| Keywords: | bainitic steel fatigue crack propagation mechanical twinning multiphase microstructure retained austenite |
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