The kinetics of cavity growth in 20 Cr/25 Ni stainless steel

The development of cavitation during creep has been examined in an unstabilised 20 Cr/25 Ni austenitic stainless steel, using precise density measurements as an indicator of the level of cavitation. The change in density was proportional to the duration of creep to the power of 3.0 increasing to 4 to 5 just before fracture, and this time exponent was not affected by either grain size or irradiation. Metallographic examination showed that wedge-cracks were the predominant mode of cavitation and helium bubble growth in irradiated specimens increased the rate of crack propagation, thus reducing the ductility. A simple model for the growth of triple-point cracks is used to explain the experimentally observed changes in density.