Fracture and Fatigue Damage Tolerance of Bainitic and Pearlitic Rail Steels: Research Results
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2006-02-01
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Abstract:The Federal Railroad Administration sponsored a research project to investigate the fracture and fatigue damage tolerance of baintic steels. Low carbon baintic steel shows promising potential, especially in critical components such as frogs and switches. The study examined the microstructure – fracture and fatigue damage tolerance relationships of bainitic rail steel in comparison with pearlitic rail steel. It was found that the bainitic microstructure consists of a mixture of tempered martensite and ferrite associated with intralath carbides. The pearlitic microstructure consists of fine lamellar aggregate of very soft and ductile ferrite and very hard carbide. The J6 bainitic steel studied in the present work has ultimate strength, yield strength and elongation to failure of about 1500MPa, 1100MPa and 13% respectively. These values are higher than those for pearlitic steel as shown in Figure 1. The bainitic steel exhibits a higher rate of crack deceleration in the second stage, as indicated by the lower slope of the fatigue crack propagation kinetics curve in comparison with the pearlitic steel. This attests to the superior fatigue damage tolerance of the bainitic rail steel and provides evidence to support the superior rolling fatigue damage tolerance of the bainitic rail steel reported in the literature.
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