Niobium-microalloyed steels for automotive applications

This work aims to review the scientific knowledge on the effects of niobium in the steels used in the automotive sector, for car-body applications, by means of an extensive literature survey. Environmental issues lead to increasingly stringent regulation for CO2 emissions; therefore, weight reduction is required for passengers cars. First, the effects of niobium in steels are discussed. Niobium, used as a microalloying element, improves mechanical strenght, allowing a reduction in weight, but it can also enhance formability, energy absorption or fractures resistance. The strenghtening mechanisms through which it acts are mainly two: grain refinement and precipitation. The first, in particular, has the greatest advantages, since it improves both strenght and toughness at the same time. Also of great importance is the contribution of niobium to improve the resistance to hydrogen embrittlement, especially for the steel with the highest strength. Thereafter, the common steel typologies used in the modern vehicles are reviewed, and the effects of niobium in each of these steel classes is discussed.