準安定ラメラ組織を有する鋼の高ΔK領域かつ長いき裂での疲労き裂閉口現象

抄録

Transformation-induced plasticity (TRIP) maraging steel has a high fatigue resistance because of its laminated structure and metastable austenite. In this study, we present the crack length dependence in fatigue crack growth on two types of TRIP-maraging steels with different annealing times. ΔK increasing compact tension tests were carried out on the TRIP-maraging steels. In the case of rotating fatigue bending test (short crack), it is reported that 1h heat-treated TRIP-maraging steel has better fatigue limit than 8h heat-treated TRIP-maraging steel. However, in the case of ΔK increasing compact tension test (long crack), the 1h heat-treated TRIP-maraging steel showed larger fatigue crack growth rates than the 8h heat-treated TRIP-maraging steel. To consider the crack length dependence, we focused on plasticity-induced crack closure (PICC), roughness-induced crack closure (RICC) and transformation-induced crack closure (TICC). The most dominant factor for the crack length dependency for fatigue property is TICC.