Stress Corrosion Crack Growth Mechanism on SUS316L Stainless Steel

The stress corrosion cracking (SCC) of stainless steel is one of the biggest problems for maintaining atomic power and chemical plants. However the mechanism has not been solved because of difficulty in observing hydrogen movement. In order to solve this problem, the author has developed a new SCC test method that enables the super Kelvin force microscope (SKFM) and the Kelvin force microscope (KFM) observations. By using this test method, the crack tip deformation and surface potential distribution on SUS316L stainless steels were observed by SKFM and KFM. The existence of hydrogen-induced martensite was examined by the magnetic force microscope (MFM) observations. The results showed that a less noble potential region existed near the crack tip. MFM and KFM observation showed hydrogeninduced martensite existed at the less noble potential region. Repeated SKFM observations revealed that the crack is formed by the movement of hydrogen-induced martensite.