Cryogenic mechanical properties of a novel high-strength and high-ductility steel: Constitutive models and microstructures

This work aims to study the constitutive models and microstructures of a novel high-strength and high-ductility (HSHD) steel under cryogenic temperature. A series of cryogenic tensile tests were conducted using a testing machine equipped with a cryogenic chamber. The results showed that the HSHD steel exhibits an obvious temperature-dependence effect. As the temperature decreased, the yield strength and tensile strength gradually increased, while the uniform elongation increased and then decreased. At a cryogenic temperature of -196 degrees C, the HSHD steel exhibited significantly enhanced mechanical properties. Specifically, the yield strength, tensile strength, and uniform elongation were 1200 MPa, 1620 MPa, and 30 % respectively. Based on the obtained temperature-dependence effect, the classic Ludwigson constitutive model that all parameters were functions related to temperature was developed and its accuracy was verified through numerical analysis. Furthermore, the microstructure of HSHD steel was investigated during the different deformation stages through microstructure characterization techniques. The excellent cryogenic mechanical properties of HSHD steel stem from the synergic effects of high-density dislocations, denser mechanical twins, and Lomer-Cottrell locks as well as their extensive interactions, rarely observed in their siblings deformed at room temperature. Furthermore, the transformationinduced plasticity (TRIP) effect, which is a significant mechanism for plasticity and favors strain hardening, delays the initiation of necking at -196 degrees C. These findings reveal the relationship between mechanical behavior and deformation mechanisms in HSHD steel within the low-temperature regime, providing valuable insights for the design of HSHD steel in cryogenic applications.