The strengthening of an fe-v-c low-alloy steel by carbide precipitation during continuous cooling from the austenitic condition

A simple Fe-1 V-0.2C low-alloy steel has been cooled from the austenitic condition at rates between 0.1 and 500°C per min. Dilatometry, and optical and electron metallography have shown that the austenite undergoes decomposition in the range 800 to 700°C directly to ferrite containing a nonrandom distribution of vanadium carbide. The carbide precipitates are distributed in sheets, and although a range of intersheet spacings can be measured at each cooling rate, the mean intersheet spacing decreases with increasing cooling rate. The mechanical strength was also shown to increase as the cooling rate increased, but a ductile brittle transition occurred on increasing the cooling rate above approximately 20°C per min. The dispersion strengthening was found to obey an empirical relationship of the form σ_p = k • λ^-1.1, where σ_p is the dispersion strengthening effect of the carbide distribution, and λ is the intersheet spacing. The brittle behavior of the alloy obtained at high cooling rates is thought to be possibly due to the carbide morphology and dispersion resulting from the mechanism of precipitation during the austenite-ferrite transformation.