Effect of vanadium, niobium, and silicon on the properties of low-pearlite steel

Abstract

1. Small additions of vanadium and niobium either separately or together substantially increase the strength of low-pearlite hot-rolled steel, which is accompanied by an increase of σ0.2/σb and lower ductility. 2. The greatest increase in strength results from additions of about 0.04% Nb and V. With larger amounts of these elements the strength increases at a smaller rate. The highest strength is attained with around 0.04% V and 0.03% Nb. 3. Separate additions of 0.04%V and Nb showed that the effectiveness of Nb in raising the strength of the steel is approximately double that of vanadium, and with 0.11–0.13% Nb the effectiveness is 40–50% higher than that of vanadium. 4. Raising the carbon content from 0.05 to 0.20% in the steel with 0.04% V and 0.03% Nb increases the ultimate strength from 50 to 74 kg/mm2 and the yield strength from 40 to 54.5 kg/mm2; σ0.2/σb decreases from 0.80 to 0.72. Within these limits, carbon shifts the ductile-brittle temperature (T50) of the hot-rolled steel from −50 to +20° and reduces the work of crack propagation ap (with completely ductile fracture) from 10 to 2 kg-m/cm2. 5. Raising the silicon content from 0.02 to 0.44% leads to a substantial increase of the ultimate strength from 41 to 50 kg/mm2, the yield strength from 28 to 36 kg/mm2, and the toughness from 4 to 8 kg-m/cm2 at −40°. 6. The effects of vanadium and niobium on the strength are evidently due to the formation of nitrides (carbonitrides) of these elements with residual nitrogen.