Improvement of mechanical properties of Cr-Ni-Mo-Cu-Ti stainless steel with addition of vanadium

The effect of vanadium M addition on the mechanical properties of a Cr-Ni-Mo-Cu-Ti stainless steel was studied and its influence on microstructural changes was also investigated. Results indicate that the structure of the solution-treated specimens mainly comprises of austenite-martensite, and adding V leads to the formation of a considerable amount of ferrite. Under this condition, austenite phase is not mechanically stable, and transforms to martensite by plastic deformation. The addition of 0.5%-1.0% (in mass percent) of V increases the hardness and the strength of the 80% cold rolled and aged steel, without any effect on ductility. Improvement in mechanical properties is presumably attributed to the formation of a small amount of ferrite in the primary structure, and the formation of certain precipitates is accelerated by the addition of V during aging. By contrast, excessive V decreases the strength and ductility simultaneously. This is due to the strong effect of ferrite formation compared to the beneficial effect of precipitation. The loss of ductility caused by adding higher amount of V is due to the formation of ferrite phases which in turn are suitable nucleation sites for crack propagation.