Effect of overload on creep deformation, crack initiation and growth behaviors of a C(T) specimen for 12Cr steel.

• Crack growth tests under creep and initial overload creep conditions were conducted for 12Cr steel. • The initial overload was found to be suppressed the crack initiation. • The effect of initial overload does not significantly affect the crack growth rate. • The dual value behavior of C* parameter was dominated by crack initiation. 12Cr steel is used as one of the materials for steam turbine rotor. Steam turbine rotor is an important component and high reliability is required. In actual turbine rotor which has central hole, thermal stress induced by inflow of steam is generated at start-up. At this time, an overload greater than the load level during steady-state operation is exerted on the stress concentration area near the central hole. Therefore, it is important to evaluate the effect of overload on the creep crack initiation and growth behavior. In this study, using a C(T) specimen for 12Cr steel used for steam turbine rotor, crack growth tests under creep and initial overload creep conditions were conducted and behaviors of creep deformation, crack initiation and growth were investigated. In addition, these results were evaluated by various fracture mechanics parameters. As a result, it was found that the initial overload suppressed creep deformation and delayed creep crack initiation. Especially, this tendency was more pronounced at the low temperature and high stress condition. However, the initial overload does not significantly affect the creep crack growth rate. [ABSTRACT FROM AUTHOR]