Abstract: Cr-Ni-Mo heavy-duty gear steel was microalloyed with vanadium and niobium,and the microstructure after quenching and carburizing as well as mechanical properties before and after microalloying were compared.The austenite grains of the test steel are significantly refined after the microalloying process.The impact energy is also increased with the decrease of the austenite grain size.The vanadium/niobium microalloyed steel do not show abnormal coarsening of austenite grains when it was austenitized in the temperature range of carburization for a long time,and the mechanical properties of the carburizing phase are also improved.