Effect of Ti addition on the toughness improvement of as-rolled microalloyed vanadium steels

Two Ti-V microalloyed medium C steels, with different Ti additions, are analyzed in the as-rolled and normalized conditions. Their toughness values have been determined and an extensive micromechanistic study of brittle fracture behavior has been performed. In the analyzed microstructures, brittle fractures nucleate mainly at the coarse TiN particles. In the case of a higher addition of Ti, a microstructural refinement is observed, but this modification has not been sufficient enough to obtain a significant toughness improvement. In contrast, the microstructural refinement achieved in the normalized conditions gives rise to a completely ductile behavior in both steels at room temperature. These results show that to obtain a significant improvement in toughness with the Ti addition, an extensive and homogeneous microstructural refinement is required. If this condition is not achieved, the coarse TIN particles, precipitated as a consequence of the Ti addition, can lead to the opposite effect.