Optimal Bainite Contents for Maximizing Fatigue Cracking Resistance of Bainite/Martensite Dual‐Phase EA4T Steels

Fatigue crack propagation behavior of bainite/martensite dual‐phase EA4T steels with four different volume fractions of bainite ranging from 21% to 70% is investigated. The results indicate that the bainite/martensite dual‐phase steel specimens with the volume fraction of bainite of 49–60% have the higher resistance to fatigue crack growth than the others. The coupled contributions of plasticity‐induced crack closure and crack deflection to the higher fatigue crack growth resistance is estimated. A model related to the plastic zone size and the roughness of the fracture surface is proposed to evaluate the optimal volume fraction of bainite in the dual‐phase steels.