Mechanism of SCC on SUS310S Stainless Steel

The author have 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 device, the crack tip deformation and surface potential distribution were observed on SUS310S stainless steel by SKFM and KFM. At the same time, the distribution of hydrogen was examined by the Ag decoration method with the EDX image mapping analysis combined. Moreover, the existence of hydrogen-induced martensite was examined by the magnetic force microscope (MFM) observations. The results showed that the less noble potential region existed at whole crack and Ag precipitated at less noble potential region in most cases. The MFM and KFM observation showed hydrogen-induced martensite existed at the less noble potential part. SCC is caused by the formation of hydrogen-induced martensite ahead of the crack tip.