Analysis Of Micro-Mechanical State At Tip Of Stress Corrosion Cracking In Nuclear Structural Materials

The Stress Corrosion Cracking(SCC) of the austenitic stainless steels and nickel-based alloys is one of the main failure in the high temperature environment of nuclear power plants, which is induced by the cooperation of environment, material and mechanics at the tip of SCC. To understand the effect of mechanical factors at the crack tip on SCC growth rate, based on oxide film rupture theory and a hypothesis of the morphology at the tip of SCC, the stress-strain state of the base metal and the oxide film at the tip of SCC of austenitic stainless 304 L is analyzed and discussed by used of a compact tensile specimen and a commercial software ABAQUS. The main research works are performed as follows:(1) The SCC crack tip was simplified into two forms, i.e. wedged crack tip and arc crack tip, and the stress-strain state of the SCC crack tip concerning oxide film and base metal was analyzed. It was found that the blunter the wedged crack tip is, the higher the oxide film crack tip stress is, the lower the base metal crack tip stress is. The maximum stress appears on the oxide film surface before the oxide film ruptures, the maximum strain is on both sides of base metal crack extending direction. The strain on the base metal and the stress on the oxide film may be the main factors that cause the breaking of the oxide film.(2)The effect of material mechanical properties and the crack growth driving force to the stress and strain distribution of crack tip area has been analyzed, the stress intensity factor KI on the oxide film material is more sensitive than that on the base metal material. The yield strength and hardening exponent of base metal have large impact on the crack tip stress, and little impact on the strain, the impact of the base metal Young's modulus is quite opposite.(3) Based on SCC growth rate prediction model, the effect of the different oxide film and base metal material mechanical f properties as well as different crack growth driving force on stress corrosion extend rate has been analyzed. It shows that, besides the crack growth driving force, oxide film and base metal material mechanical properties at SCC crack tip have a large effect on stress corrosion cracking growth rate.