論文ID: 17-00353
Effect of grain boundary microstructure, such as the spatial distribution and the connectivity of grain boundaries with different character, on the process of fatigue crack propagation in SUS430 ferritic stainless steel was investigated using the technique combined in-situ observations of crack propagation with EBSD measurements. The ratio of intergranular fracture to the overall fracture path increased with decreasing stress intensity factor range. Particularly, the ratio of intergranular fracture reached about 60 %, when the stress intensity factor range was less than 40 MPa m1/2. Moreover, the larger deflection of crack propagation occurred by the cyclic deformation at the higher stress intensity factor range more than 50 MPa m1/2, depending on the grain boundary microstructure. The intergranular fatigue cracks mainly propagated along random boundaries, and the deflection of intergranular crack path occurred at grain boundary triple junctions, owing to the further propagation along random boundary ahead. Moreover, when the fatigue crack propagation along random boundaries was inhibited by a triple junction composed of low-∑ CSL boundaries, the branching of fatigue crack occurred at a triple junction behind and the crack subsequently propagated along another random boundary. The propagation of fatigue crack was inhibited for a while by crossing low-∑ CSL boundaries and triple junctions. The possible grain boundary microstructure for control of fatigue crack propagation in SUS430 stainless steel was discussed based on the observed results.
