수퍼 2상 스테인리스강의 피로균열 진전시 발생하는 음향방출신호 특성에 미치는 σ상 석출의 영향 = Effect of σ Phase Precipitation on Fatigue Crack Propagation and AE Signals in Super Duplex Stainless Steels

다국어 초록 (Multilingual Abstract)

The fatigue crack propagation induced by σ phase precipitation of super duplex stainless steels aged at 600℃ was evaluated and the time-frequency analysis according to acoustic emission was conducted. The fracture mechanism by σ phase precipitation can be found from the time-frequency analysis of acoustic emission signals. As a result of aging at 600℃, the dispersed structure showed faster precipitation rate of σ phase than fibrous structure. The time-frequency analysis of acoustic emission signals obtained during the fatigue test revealed that, the specimens with non-precipitated σ phase induced a dominant frequency of 200∼300 ㎑ without any correlation with crack length. As the fatigue crack propagates (stage Ⅱ_c mode), the frequency range was in a high frequency range above 400 ㎑ in addition to frequency range of 200∼300 ㎑. On the other hand, the frequency range in the specimens with σ phase precipitated was not only 200∼300 ㎑ but also 400 ㎑ because of the fracture mechanism emanating high energy such as dimple fracture and separation of inclusion.