Study on fatigue crack growth behavior of casing-drilling steel N80

An investigation into the fatigue crack growth behavior of N80 steel was carried out for casing-drilling technology. The results show that the effect of stress ratio on the Delta K corresponding to access of the tensile overload region is remarkable, and increasing the stress ratio is found to increase the FCGR at the same Delta K and reduce Delta K of access of the tensile overload region; the transgranular failure machanism is dominant for the N80 steel in the all crack growth stage; the fracture surface roughness decreases as the cracks propagate through threshold region and into Paris region, whereas it increases as the cracks propagate through Paris region and into the tensile overload region; the typical ductile-dimpled fracture mechanism observed on the tensile overload region is similar to the tensile fracture mode, although the orientation of the dimples significantly inclines to fatigue crack growth direction.