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

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 (1 (1) over bar2)(M2B)< b >//(200)(gamma), [(1) over bar 11](M2B)//[011](gamma) 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.