Fracture behavior of 9% nickel high-strength steel at various temperatures: Part I. Tensile tests

Fracture behavior of a 9% nickel 1000 MPa grade high-strength steel was investigated with tensile tests at various temperatures. Four critical stresses were found, which determined the fracture behaviors at various temperatures. Various fracture behaviors could be classified into three categories: (1) at −196 °C, a longitudinal crack initiated from the center of the necking region and propagated along the tensile direction to the regions close to both ends of the necking, it then changed the orientation and developed into two transverse cracks which propagated into opposite directions on two separated cross-sections. (2) In the range of −30 °C to 20 °C, the fracture surfaces were composed of typical center-fibrous-initiation region, middle shear-radical region and outer shear-lip region. (3) In the range of −150 °C to −60 °C, the middle shear-radiation region showed a very rough pattern with several convex ridges. Fracture mechanisms were analyzed by combining various fracture morphologies with FEM-calculated results of stress and strain.