Effects of vanadium and titanium on mechanical properties of low carbon as cast microalloyed steels

Tensile, hardness and room temperature Charpy V notch impact tests were conducted to evaluate the variations in the mechanical properties of a low carbon cast steel containing vanadium and combinations of vanadium and titanium in the as cast condition. Tensile and hardness test results indicated that good combinations of strength and ductility can be achieved by microalloying additions. The effect of titanium on the yield strength and hardness, however, strongly depended on Ti/N ratio. Ti in hyperstoichiometric amounts increased the yield strength and hardness whereas in hypostoichiometric amounts, it did not have a considerable effect on those properties. Scanning electron microscopy and optical microscopy studies revealed that coarse TiN particles were responsible for this behaviour. On the other hand, microalloying additions significantly decreased the room temperature impact energy and led to the dominance of cleavage facets on the fracture surfaces. Although coarse TiN particles were identified to act as cleavage nucleation sites in the Ti bearing heats, no distinct microstructural feature could be identified as cleavage initiators in the microstructure of the alloy containing only vanadium.