Technical Reports

Fatigue Crack Growth and Fracture Behavior of Bainitic Rail Steels

  • 01
  • Sep
  • 2011
AUTHOR: Heshmat A. Aglan
OFFICE: RPD
REPORT NUMBER: DOT/FRA/ORD-11/17
SUBJECT: Track, Tracks & Structures, Track/Train Interactions
KEYWORDS: bainitic; pearlitic; manganese rail steels; microstructure-mechanical property relationship; hardness; fracture toughness; fatigue crack growth
ABSTRACT: The microstructure–mechanical properties relationships, fracture toughness, fatigue crack growth and fracture surface morphology of J6 bainitic, manganese, and pearlitic rail steels were studied. Microstructure–mechanical properties correlation of the three rail steels under consideration revealed that the bainitic rail steel has the highest mechanical properties as compared with austenitic manganese steel (AMS) and pearlitic rail steels. AMS shows very few signs of being work hardened or toughened, which usually increases the mechanical properties of the material. In pearlite, the microstructure has more detailed features that contribute to its mechanical properties. The bainitic steel has more alloying elements that when mixed, create so many dislocations that the dislocations cannot move against each other. This is where bainitic steel derives its strength. Fracture toughness analysis (KIc) of the three rail steels, namely bainitic, manganese and pearlitic was performed. A valid KIc was determined for the pearlitic and bainitic steels based on the American Society of Testing and Materials (ASTM) E399 criteria. It was found that the pearlitic steel had an average KIc of 41 MPa √m and the bainitic steel had an average value of 52 MPa √m. The manganese steel displayed elastic–plastic behavior, with a dominant plastic component. This invalidated the criteria of standard ASTM E399 and therefore a KIc could not be calculated. An approximate value for the energy release rate (680 kJ/m2 ), based on ASTM standard E1820-01, was calculated instead for the manganese steel.

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