The evolution of dislocation structures was investigated by means of transmission electron microscopy in Fe-Si alloys with 0, 0.5 and 1.0wt%Si during a cyclic bending test in conjunction with fatigue crack behavior. The addition of Si increased the fatigue strength. In steel without Si the cell structure develops, whereas in steel with 1%Si the vein structure evolves, which was considered to lead to the increased fatigue strength. The cell structure in 0%Si steel was postulated to be caused by the easy cross slip of dislocations, whereas the vein structure in the steels with Si was inferred to be caused by the difficulty in cross slip presumably due to the decrease in stacking fault energy. Furthermore, the steel containing Si showed a dislocation-free zone along grain boundaries. A transgranular fracture takes place in 0%Si steel, while in 1%Si steel many intergranular cracks were observed just beneath the top surface, which was thought to be caused by the fact that a) strains were dispersed within grains owing to the vein structure and b) micro-cracks were initiated and propagated along a dislocation-free zone.

Evolution of Dislocation Structure and Fatigue Crack Behavior in Fe-Si Alloys During Cyclic Bending Test. K.Ushioda, S.Goto, Y.Komatsu, A.Hoshino, S.Takebayashi: Journal of Physics - Conference Series, 2010, 240[1], 012041