Effect of tempering time on fatigue crack growth behavior of CLAM steel

Effect of tempering time on fatigue crack behavior of China Low Activation Martensitic (CLAM) steel was studied at room temperature in air. The fatigue crack growth rates subjected to the tempering time range of 90-9000 min were investigated. The results showed that the fatigue crack growth decelerated in the near-threshold region as the tempering time increased. The fatigue crack growth rate after tempering for 9000 min was approximately one-third of that of the specimen tempered for 90 min with ΔK of 14 MPa m0.5. The improved fatigue crack growth resistance could be explained by the influence of variation in microstructure, i.e., martensitic laths and precipitates. This study suggested that the effective driving force for fatigue crack growth was reduced in the near-threshold region by the activated roughness-induced crack closure mechanism as a result of rougher fracture surface caused by coarsened martensitic laths and precipitates.