Abstract |
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Low carbon baintic steel shows promising
potential, especially in critical components such as frogs and
switches. Microstructural analysis of J6 bainitic rail steel was
performed and compared with the microstructure of premium
pearlitic rail steel. The bainitic microstructure revealed a
mixture of tempered martensite and ferrite associated with
intralath carbides. Typical pearlitic microstructure with a
fine lamellar aggregate of very soft and ductile ferrite
and very hard carbide cementite was observed. The mechanical
properties, plane stress fracture toughness, KIc, and
the fatigue crack growth behavior of the two steels were
evaluated. Test specimens were machined from railheads of each
material using electrical discharge machining (EDM). Rectangular
unnotched and notched specimens were used for the mechanical
properties and fatigue evaluation respectively. 1 ∕ 2T compact
tension specimens were used for the KIc
evaluation according to ASTM E399. The J6 bainitic steel has
ultimate strength, yield strength, and elongation to failure of
about 1500 MPa, 1100 MPa, and 13% respectively. These values are
higher than those for pearlitic steel. It was found that the
average KIc for the bainitic rail steel is 52 MPa
√m, while that of the premium pearlitic steel is
41 MPa √m. Fatigue studies showed that the crack speed
for the bainitic steel is lower than that for the pearlitic steel
over the entire range of the energy release rate. 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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Keywords
bainitic steel, fracture toughness, fatigue, pearlitic steel
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Authors
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