Characterization of the Q* parameter for evaluating creep crack growth rate for type 316LN stainless steel

In this study, the Q* parameter was characterized to evaluate the Creep crack growth rate (CCGR) of type 316LN stainless steel. Creep crack growth (CCG) data were obtained by CCG tests under different applied loads at 600A degrees C. An additional CCG test was conducted at 550A degrees C to investigate the possible temperature dependence of the stress intensity factor. An equation using the Q* parameter for evaluating CCGR was proposed, and this parameter was characterized and compared with the typical C* fracture parameter, which is commonly used. The Q* parameter exhibited good linearity of the data, exhibiting no nonlinearity-induced dual value at the early stage. The Q* parameter was suitable for characterizing the CCGR regardless of different applied loads and types of steels. In addition, fracture microstructures near the crack revealed a typical intergranular fracture mode, and this fracture was dominantly propagated along the grain boundary. The cracks were developed by the growth and interlinking of cavities, which were attributed to the precipitates forming along the grain boundary.