Effect of Microaddition of Vanadium on Superplasticity of CrNiMo Series Forged Steel

The tensile properties at 25,400,600,800℃ and tensiled microstructure evolution of CrNiMo series forged steel with and without vanadium were studied and compared. The effect of vanadium on the superplasticity of the tested steels was analyzed. The results show that with the test temperature rising, the strength decreased and the plasticity increased of the two tested steels. The elongation at 800℃ of the tested steel without vanadium was 71%, while that after the addition of vanadium reached 154%, indicating a superplasticity. The microstructure of the tested steel without vanadium was homogeneous lath martensite, while that with vanadium was mainly martensite+retained austenite+vanadium carbide. Vanadium carbide provided fine grain strengthening and precipitation strengthening. High temperature softening weakened the strengthening effect of vanadium carbide but enhanced its plasticizing effect.