Abstract
Complementary analytical transmission electron microscopy (TEM) and transmission Kikuchi diffraction (TKD) were used to study the influence of temperature on the crack growth rate (CGR) in SUS316 stainless steels. An Arrhenius-type temperature dependence of the CGR has been observed between 250 °C and 320 °C. However, stress corrosion cracking (SCC) CGRs were found to decrease between 320 °C and 360 °C, which cannot be explained in terms of a single operating mechanism. High-resolution characterization has produced direct evidence that the SCC CGR in SUS316 is subjected to, at least, two rate-controlling processes: thermally activated diffusion and mechanical response to external stress and internal strain. While diffusion of metallic and non-metallic species at the crack flanks are enhanced at higher temperatures (350 °C and 360 °C), mechanical response-based mechanisms appear to dominate at lower temperatures (320 °C and 340 °C). Higher strain concentrations and dislocation densities around the crack tip were found at low temperature, potentially leading to accelerated crack growth and a peak in the CGR at ∼320 °C. It is suggested that phenomena occurring near the crack tip can be potentially very different at high and low temperatures.
Highlights
Generally known for their excellent corrosion resistance, reactor grade stainless steels such as SUS316 are susceptible to environmental degradation when exposed to a corrosive environment under the influence of stress
This work comprises a study of the influence of the stress corrosion cracking (SCC) test temperature on the crack growth rate (CGR) in SUS316 stainless steel exposed to pressurized water reactor (PWR) primary water
It can be observed that the total crack length and number of crack tips increases steadily with decreasing SCC test temperature
Summary
Generally known for their excellent corrosion resistance, reactor grade stainless steels such as SUS316 are susceptible to environmental degradation when exposed to a corrosive environment under the influence of stress. In the past decades, owing to thorough research and experiments, a considerable number of factors that influence the rate of SCC crack propagation have been identified. These factors include, amongst others, preexisting cold work level in the material, water chemistry, material composition, electrochemical potential and SCC test temperature [1,2,3,4,5,6,7,8,9,10]. This work comprises a study of the influence of the SCC test temperature on the crack growth rate (CGR) in SUS316 stainless steel exposed to pressurized water reactor (PWR) primary water. The CGR appeared to be affected by other mechanical quantities such as the material's yield strength and the stress intensity factor
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