Influence of stress states on cleavage fracture in X70 pipeline steels

Stress state is a primary factor controlling the ductile fracture behavior of steels, which typically represented as combination stress triaxiality and Lode angle parameter. The cleavage properties pipeline steels at low temperatures are usually assessed under plane strain conditions, such using mechanics experiments. In this study, X70 steel liquid nitrogen temperature (?196 °C) characterized over broad range states. A comprehensive experimental program carried out by performing tensile tests various flat specimens different geometries immersed in nitrogen, including shear, central hole, notched dog bone, side grooved strain. Pronounced plasticity occurs prior to final within tested states very temperature. Anisotropy effects considered conducting along rolling, diagonal transverse directions. Finite element simulations corresponding experiments performed an evolving quadratic model extract local variables establish criteria, formulated based on critical values plastic maximum principal stress. investigated material affected triaxiality, parameter loading direction.