The observation of dislocation morphology in front of fatigue crack tips of as-rolled 2205 duplex stainless steel at various propagation rates

The purpose of this work is to investigate the dislocation structure in front of crack tips of a duplex (ferrite–austenite) steel at various crack propagating rates, and to investigate the influence of the dislocation structure on the threshold stress intensity. The experimental results show that the result in difference of threshold stress intensity factors for as-rolled 2205 duplex (ferrite–austenite) stainless steel along different crack directions is very slight, which is because the influence of grain boundary is greater than that of grain orientation for small grains. In front of crack tips, no dislocation cells were observed. Instead, persistent Lüder bands embedded in a highly dense dislocation matrix were found, and the dislocation density increased with the increase of the crack propagation rates. Nucleation of fine CrN/CrC particles from many small amorphous domains, which evolved from a very high-density dislocation in the matrix, were also observed along the crack path close to the crack surface.