Effect of Pre-Straining on High Cycle Fatigue and Fatigue Crack Propagation Behaviors of Complex Phase Steel

Abstract

Pre-straining tends to increase yield/tensile strengths and dislocation density by strain hardening of steel while also, affecting its high cycle fatigue (HCF) and fatigue crack propagation (FCP) behaviors greatly. The HCF and FCP behaviors of complex phase (CP) steel with different levels of pre-straining from 0 to 9% were examined. It was found that the resistance to HCF of CP steel decreased with 5% pre-straining, while it increased with 9% pre-straining, suggesting that such an abnormal HCF behavior of CP steel with different levels of pre-straining could be attributed to the nature of dislocation structure formed during cyclic straining. Based on the detailed micrographic and fractographic analyses, the effect of pre-straining up to 9% on the fatigue behavior of CP steel was discussed.