PRODUCTION OF ULTRA-HIGH STRENGTH WIRE ROD STEELS BY VANADIUM MICROALLOYING

Ultra-high strength high-carbon wire rod steels have been produced usi ng vanadium-microalloying technique instead of the conventional expens ive and environment polluting lead patenting treatment. The strength i ncrement attained in the hot rolled steels due to vanadium additions i s maintained in the cold drawn wire. By using this technique, high ten sile strength levels of 1550-1600 N/mm(2) were attained either by cold drawing of 0.17% V microalloyed high-carbon steel to 45-47% reduction or by cold drawing of 0.20% V microalloyed high-carbon steel to 25-30 % reduction. An equation has been developed to predict the tensile str ength from the chemical composition, cooling rate and reduction of are a due to cold drawing. A combination of vanadium microalloying and acc elerated cooling resulted in additional strength increment due to refi ning of microstructure and increasing the precipitation strengthening component. Inspite of the decrease in the amount of vanadium precipita tes due to the increase in cooling rate, it is suggested that an incre ase in precipitation strengthening due to refining of these precipitat es by accelerated cooling more than offsets the loss of precipitation strengthening due to decreasing the precipitates fraction.