Temperature-Dependent Plasticity and Fracture Properties of Modern BCC Steels

For some modern steels with a body-centered cubic (bcc) crystal structure, it is observed that both tensile strength and ductility are significantly improved with decreasing temperature, which motivates the exploration of the cryogenic formability and fracture properties of these materials. The temperature-dependent plasticity and fracture phenomena of a modern bainitic steels with the bcc structure have been investigated by performing a comprehensive experimental program and finite element simulations, covering a broad range of loading conditions. Uniaxial tensile tests have been performed at different temperatures along three loading directions. Tensile tests using flat specimens with various geometries, including shear, central hole and notched dog bone, have been performed along the rolling direction at room temperature and –196 ℃. An advanced non-associated constitutive plasticity model is used to describe the temperature-dependent strength and hardening properties of the material. The local critical stress and strain variables extracted from finite element simulations of different fracture tests have been used to calibrate a unified fracture criterion, which considers the stress state dependence. The effects of temperature on the plasticity and stress state dependent fracture behavior of the modern bcc steels have been quantitatively determined.