The temperature dependence of fatigue crack growth rates of a 351 CF8A cast stainless steel in LWR environment

The fatigue crack growth rates for A 351-CF8A cast stainless steel were determined over a range of temperatures from 930C to 3380C (2000F to 6400F). The waveform was 17 mHz sinusoidal and the load ratio was 0.2. The environment was borated and lithiated water with a dissolved oxygen content of about 1 ppb. The results show an easily measurable (factors of 2 to 5) increase in crack growth rates due to the environment. However, these rates are well within the known band of results for other pressure vessel and piping steels in LWR environments. An extensive fractographic investigation shows fatigue fracture surfaces covered with brittle-appearing features. These features are similar to those found from stress-corrosion cracking specimens of stainless steel, suggesting that there is a distinctive environmental assistance mechanism resulting in the increased growth rates