Niobium in Microalloyed Structural and Engineering Steels
The use of Niobium as a microalloying element is particularly beneficial in increasing strength and toughness through its ability to control austenite grain size during reheating, and via grain refinement and precipitation hardening after austenite transformation. Steels with lower carbon contents can thus be utilised, further enhancing toughness and weldability.
T. Chandra, K. Tsuzaki, M. Militzer , C. Ravindran
C. Klinkenberg "Niobium in Microalloyed Structural and Engineering Steels", Materials Science Forum, Vols. 539-543, pp. 4261-4266, 2007