Effects of microstructural changes,loading conditions and test temperature on toughness of fully pearlitic eutectoid steel used in transportation industry

Abstract

The mode I fracture toughness of fully pearlitic eutectoid steel used in the transportation industry has been investigated at temperatures ranging from −196 to 225°C using bend bar specimens notched and fatigue precracked to contain different root radii. The effects of changes in microstructure on the cleavage fracture stress were determined over a similar range. In addition, the notched and fatigue precracked specimens have been subjected to combined mode I/II fracture under asymmetric three point bend loading at −125°C on different microstructural conditions. Increasing the offset distance between the notch and the loading point produces an increase in the ratio mode II/mode I, a change in the crack deflection angle and a reduction in the total energy of fracture. Significant effects of changes in microstructure, test temperature and notch root radius on the toughness will be presented, followed by the significant effects of changes in microstructure and the ratio mode II/mode I on the fracture load, crack deflection angle and resulting toughness. Fractured specimens were examined both macroscopically and microscopically using stereomicroscope and scanning electron microscopy.

Keywords

PEARLITIC STEEL FRACTURE TOUGHNESS NOTCH ROOT RADIUS LOW TEMPERATURE MIXED MODE LOADING I/II SEM CLEAVAGE FRACTURE STRESS NUCLEATION SITES

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