Evaluation of Initial Degradation in Stress Corrosion Cracking by Magnetic Methods
高屋 茂 Shigeru TAKAYA 鈴木 隆之 Takayuki SUZUKI 松本 善博 Yoshihiro MATSUMOTO 出町 和之 Kazuyuki DEMACHI 上坂 充 Mitsuru UESAKA
Electron Backscatter Pattern Technique Evaluation of Degradation Flux Gate Sensor Magnetic Force Microscope Magnetic Method Martensitic Transformation Sensitization Stress Corrosion Cracking
Two magnetic methods are proposed for the evaluation of initial degradations of type 304 stainless steel in stress corrosion cracking (SCC). The first one is the measurement of the distribution of chromium depletion by means of a magnetic force microscope (MEM). MEM observations are performed for some samples sensitized in various conditions, and the obtained results coincide with the expected ones from the chromium behavior. Moreover, the phase distributions in the solution-annealed and sensitized states are observed by electron backscatter pattern technique. The observation results show that the phase transformation from the austenite phase to the martensite phase occurred along grain boundaries where the chromium was depleted. The second one is the detection of initial SCC cracks by measurement of magnetic flux densities. In-situ measurement of magnetic flux density during the SCC test and MEM observation reveal the relation of initial SCC cracks and magnetic properties.