Kinetics Analysis of Thermally Activated Elementary Processes in Stress Corrosion Cracking Crack Growth

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In order to clarify the thermal activated element processes involved in stress corrosion cracking of structural materials in light water reactor environments, steady state crack growth rates were measured and the apparent activation energies were evaluated. The observed apparent activation energies are analyzed based on multiple rate-determining processes involved in stress corrosion crack growth. Several types o f temperature-dependence for crack growth rates of austenitic alloys and their weld metals are classified. Different ways of defining and measuring apparent activation energy are discussed. For the crack growth of Ni-based alloys and their weld metals in simulated pressurized water reactor environments, the apparent activation energy is relatively high and close to those for normal oxidation processes. The crack growth rates of sensitized 304 stainless steels in oxygenated high temperature pure water environments increased monotonically with temperature. On the other hand, a p … More eak in crack growth rate versus temperature was observed in high temperature water containing chemical additions or impurities. The apparent activation energy depends on testing conditions. The stress corrosion cracking growth rates for strain-hardened low-carbon stainless steels in pure water increase monotonically with temperature in the range 200-288°C, which show that crack growth is mainly controlled by thermally-activated processes. The apparent activation energies are different in different temperature ranges, and could be related to the effects of temperature on multiple-element processes that are involved in the crack-tip oxidation kinetics. Time-lag crack growth periods after increasing or decreasing the temperature were observed in all the tested specimens. The effects of temperature, applied loading and material strength on apparent activation energy are analyzed by taking into consideration the effects of temperature on the multiple element processes involved in the crack tip oxidation kinetics. Less