Creep crack growth behavior of type 316L steel

The creep crack growth behavior of a 316L type stainless steel was studied at 600°C and 650°C using widely different specimen geometries. A strong emphasis was laid on crack initiation, early crack growth, and slow crack growth rates (a). The applicability of four load parameters, the stress intensity factor, the nominal stress, the reference stress, and the contour integral C^*, was investigated. Finite element calculations were made to compare the experimental load line displacement rates with the calculated values.It is shown that it is possible to correlate time to initiation (T_i) with C^*. The obtained experimental relation is not in full agreement with a theoretical expression derived from models for creeping solids. The reasons for this discrepancy are discussed. Furthermore, it is observed that there is no unique correlation between a and any of the four investigated load parameters, especially at low crack growth rates (a0^?3mm/h). At large crack growth rates (a?10^?2 mm/h) the apparent correlation between a and C^* is essentially due to the fact that the displacement rate is controlled by crack growth and not by the overall creep behavior of the specimens. A simple model based upon the data on crack initiation and the creep ductility exhaustion concept is shown to give results in reasonable agreement with the experiments.