Effects of 0.15 wt% vanadium addition on the microstructure and mechanical properties of a full pearlitic steel isothermally transformed in the range 600-700˚ were investigated.
Microstructural features were characterized by optical and electron microscopy, and mechanical properties were measured by standard tensile, impact, hardness tests using subsize specimens.
Marked increase in the yield strength, ranging 10-25 Kg/㎟ depending on the isothermal transformation temperature, was achieved by the addition of vanadium which accompanied deteriorations in elongation and toughness.
Prior austenite grain size, inter lamellar spacing and colony size of pearlite were significantly reduced by the vanadium addition but a multiple regression analysis on the correlationships between the measured microstructural parameters and the yield strength indicated that the major strengthening increment was due to the precipitation of fine vanadium carbonitride particles in the ferrite of the pearlitic structure.
There were evidence that those precipitates were found to occur by interphase-precipitation mechanism during the austenite-pearlite transformation, the dispersions being finer at lower transformation temperatures which resulted in higher precipitation strengthening.
The results suggested that the structural refinement was the most effective for the improvement of strength-toughness combination in the pearlitic steels which could be achieved by the combined addition of V with other microalloying elements such as Ti and Nb and by accelerated cooling in the commercial continuous cooling processes.