Hot ductility of medium carbon steel with vanadium

Hot ductility of medium carbon steel containing 0.52wt% of carbon and 0.11wt% of vanadium was investigated using a hot tensile test performed up to fracture. The hot ductility was evaluated by measuring the reduction of area of the fractured specimens, which were strained at a variety of test temperatures in a range of 600–1100°C at a strain rate of 2×10−3/s. The hot ductility was excellent in a temperature range of 950–1100°C, followed by a decrease of the hot ductility below 950°C. The hot ductility continued to drop as the temperature was lowered to 600°C. The loss of hot ductility in a temperature range of 800–950°C, which is above the Ae3 temperature, was due to V(C,N) precipitation at austenite grain boundaries. The further decline of hot ductility between 700°C and 750°C resulted from the transformation of ferrite films decorating austenite grain boundaries. The hot ductility continued to decrease at 650°C or less, owing to ferrite films and the pearlite matrix, which is harder than ferrite. The pearlite was transformed from austenite due to relatively high carbon content.