An investigation was made of the dislocation structure ahead of crack tips in a duplex (ferrite-austenite) steel, at various crack-propagation rates, and the influence of the dislocation structure upon the threshold stress intensity was studied. The experimental results showed that the difference in threshold stress intensity factors for as-rolled 2205 duplex (ferrite–austenite) stainless steel along various crack directions was very slight. This was because the effect of the grain boundary was greater than that of the grain orientation, for small grains. No dislocation cells were observed ahead of crack tips. Instead, persistent Lüder bands which were embedded in a very dense dislocation matrix were found, and the dislocation density increased with increasing crack propagation rate.

The Observation of Dislocation Morphology in Front of Fatigue Crack Tips of As-Rolled 2205 Duplex Stainless Steel at Various Propagation Rates. H.L.Huang, N.J.Ho: Materials Science and Engineering A, 2002, 334[1-2], 134-40