Effects of prestrain on fracture toughness and fatigue-crack growth of line pipe steels

Crack-tip-opening displacement (CTOD) and fatigue-crack growth tests were conducted for several line pipe steels with uniaxial tensile or compressive prestrain, epsilon (pr). Critical CTOD decreased with increasing /epsilon (pr)/. The reduction of critical CTOD due to prestrain was dependent on the ductile-brittle transition temperature of the steels without prestrain. A few percent of epsilon (pr) induced the ductile-brittle transition for the steels with a higher transition temperature. The compressive epsilon (pr) had larger effects on both reduction of critical CTOD and strain induced ductile-brittle transition than the tensile epsilon (pr). Only the high compressive epsilon (pr) accelerated both fatigue crack initiation and growth, and no obvious effect of the tensile epsilon (pr) on the fatigue properties was observed.