As-cast mechanical properties of vanadium/niobium microalloyed steels

Tensile and room temperature Charpy V-notch impact tests along with microstructural studies were used to evaluate the variations in the as-cast mechanical properties of low-carbon steels with and without vanadium and niobium. Tensile test results indicate that good combinations of strength and ductility can be achieved by microalloying additions. While the yield strength and UTS increase up to respectively 370–380 and 540–580 MPa in the microalloyed heats, their total elongation range from 20 to 25%. TEM studies revealed that random and interphase fine-scale microalloy precipitates play a major role in the strengthening of the microalloyed heats. On the other hand, microalloying additions significantly decreased the impact energy and led 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 trigger the brittle fracture in the microalloyed heats.