The crack propagation of a 304 stainless steel under repeated load at elevated temperatures was critically examined using specimens of different size to clarify the successful correlating parameter, and the results were discussed in the light of electron fractography. The crack propagation rate at 250 and 500°C where creep is not significant in this material was correlated with the stress intensity range ΔK. At 550 and 650°C where creep is significant, the crack propagation rate was correlated with ΔK at low propagation rate, whereas it correlated with J at high propagation rate and coincided with the rate of creep crack. Cyclic J integral ΔJ appeared to be a somewhat better correlating parameter than ΔK and J in the intermediate rate range.
The fracture surface of specimens tested at 250 and 500°C was fully covered with striations. At 550 and 650°C, striations were predominant at low propagation rate where ΔK was the correlating parameter, and dimples and occasionally intergranular fractures predominantly appeared at high propagation rate where J was the correlating parameter. In the ΔJ correlating region, striations were the predominant feature of fracture surface.
