1. Ando and Krauss [19] proposed that IG cracking in high-carbon steels was caused by cementite formation along PAGBS during quenching. Kar et al. [20] alternatively suggested that large transformation stresses associated with plate-martensite formation produce microcracks within PAGs which are weak due to the presence of undissolved pro-eutectoid cementite, thereby resulting in IG fracture. In this study, all the microstructures had undissolved cementite along PAGBs after the austenitization step, which was potentially responsible for IG fracture during fatigue and overload. Sadananda and Vasudevan proposed that FCG rates depend on two crack tip driving parameters, ?K and K max [13], and that static fracture modes during fatigue crack propagation are K max dependent. At low K max , the crack growth process is fatigue dominated whereas at high K max , the crack growth is fracture dominated [21]. The extent of IG fracture (static failure) increased with increasing ?K (increasing K max ) for all the microstructure conditions (Figure 13 (a)), suggesting that the crack growth process is increasingly fracture dominated;and thus high values of m were observed for the FCG data