Mechanical properties of as cast microalloyed steels containing V, Nb and Ti

Tensile, hardness and room temperature Charpy V notch impact tests were used to evaluate the variations in the mechanical properties of a low carbon cast steel containing combinations of vanadium, niobium and titanium in the as cast condition. Tensile and hardness test results indicate that good combinations of strength and ductility can be achieved by microalloying additions. Based on the TEM studies, random and interphase fine scale microalloy precipitates play a major role in the strengthening of the microalloyed heats. However, the presence of titanium leads to some reduction in the strength of the microalloyed heat. Coarse TiN particles can be responsible for this behaviour. On the other hand, microalloying additions significantly decrease the impact energy and lead to the dominance of cleavage facets on the fracture surfaces. It seems that heterogeneous nucleation of microalloy carbonitrides on dislocations along with coarse ferrite grains and pearlite colonies has triggered the brittle fracture in the microalloyed heats.