Effects of Vanadium and Austempering Temperature on Microstructure and Properties of CADI

The effects of vanadium and austempering temperature on the microstructure and mechanical properties of carbidic austempered ductile iron were researched. The results showed that the microstructure of as-cast samples mainly consisted of pearlite, nodular graphite, and carbides, and the amount of carbides increased gradually with the increase of vanadium content (0–0.71 wt%). After austenitizing at 900 °C for 1.5 h and austempering at different temperatures for 1.5 h, the microstructure was mainly composed of acicular ferrite, retained austenite, carbides, and nodular graphite. The x-ray diffraction analysis indicated that the carbides consisted of (Cr, Fe)₃ C and VC. With the increase of V (0–0.71 wt%) at the same austempering temperature, the tensile strength and impact toughness increased initially and then decreased above a critical V concentration, the Rockwell hardness and wear resistance always increased. As the austempering temperature (220–320 °C) increased, the tensile strength increased initially and then decreased after a critical austempering temperature, but the impact toughness increased, the Rockwell hardness and wear resistance decreased.