Design of a cold-rolled novel advanced high-strength steel: An analysis of microstructural evolution and mechanical properties

Abstract

A novel advanced high-strength steel Fe79.85Cr2.07Ni2.62Si2.68B0.5Mn12C0.23 (wt%) was designed in laboratory scale. Steel microstructures under conditions of cast ingot, cold rolling, annealing and after tensile deformation were characterized by means of scanning electron microscopy, electron backscattered diffraction, X-ray diffraction and transmission electron microscopy. The corresponding mechanical properties were analyzed. Results showed that a high number density of nano-sized boride particles precipitated in austenite matrix, which contributed to grain refinement during annealing and deformation. The M2B boride was confirmed to be of bcc crystal structure and exhibited 11¯2M2B//200γ, 1¯11M2B//011γ orientation relationships with austenite matrix. The differential C–J analysis was used to understand work-hardening behaviors of steel samples subjected to various annealing processes. It was indicated that the tensile deformation was divided into three stages and each stage was associated with a distinct work-hardening exponent n value. A good combination of tensile strength (1260 MPa) and elongation (25%) was achieved as a result of enhanced work hardening behavior concerning mechanisms of dislocation glide, strain-induced martensitic transformation and mechanical twinning.