Effect of Nb-V addition on the mechanical behaviour and structural stability of ultrafine grained steels

A study is presented on microstructural evolution and mechanical behaviour of three ultrafine grained steels produced by severe plastic deformation. Two Nb-V microalloyed steel grades differing only in their Nb content and a C-Mn steel were extensively refined at 773 K by caliber rolling to a reduction of section of the order of 98%. Grain stability and evolution of mechanical properties during annealing at 873 K were then investigated. It was demonstrated that tailored annealing treatments lead to a modification of the tensile behaviour of the ultrafine steels, with a more satisfactory combination of strength and uniform elongation. Nb-V microalloying contributed to increasing the stability of the grain structure and allowed achieving slightly improved properties with respect to the C-Mn grade.