Study of short crack growth behaviour in single and multiphase steels using rotating bending machine

The characteristics of short fatigue crack growth in 0.003 and 0.47% carbon steels have been studied using a recently developed technique [Ray KK, Narasaiah N, Sivakumar R. Studies on small fatigue crack growth behaviour of a plain carbon steel using a new specimen configuration. Mater Sci Eng A, 2004; 372(1–2): 81–90.[1]]. The influence of microstructure on the fatigue threshold values at the transition of short to long cracks has been examined. The estimated critical crack lengths at the above transitions are found to be dependent on the nature of the short cracks; but the highest fatigue threshold values obtained from the short crack growth experiments on different specimens are found to be independent of the nature of the short cracks. The interaction of short cracks with microstructure indicates that a growing crack has an affinity to traverse through ferrite–pearlite interfaces in multiphase (0.47%C) and ferrite–ferrite interfaces in predominantly single-phase (0.003%C) steels. The short crack threshold values appear to increase with pearlite content of the ferrite–pearlite steels.