Abstract: Precision reducers are widely applied in industrial robots nowadays to meet the requirements of high accuracy, heavy load and high reliability. Severe wear damage is prone to occur in gear friction pairs of precision reducers under extreme working conditions, such as heavy load, low speed and boundary lubrication. To improve the tribological performance of the GCr15 (ball)-20CrMo (disk) friction pair in precision reducer, three different friction pairs, GCr15-20CrMo with carburizing and twice quenching (FP1), GCr15-20CrMo with nitrocarburizing (FP2) and GCr15-20CrMo with high concentration nitrocarburizing (FP3) were prepared. The high temperature (100 ℃) and heavy load (maximum Hertzian contact pressure 4 GPa) tribological experiments were conducted by the UMT-5 testing machine, followed by the high temperature and high speed(maximum sliding velocity 562 mm/s) tribological experiments. The wear resistance performance of the three heat treatment technologies was evaluated based on the micro-hardness, friction coefficient, microstructure morphology, element distribution, wear scar dimensions and wear rate of the friction pairs. The hardness results demonstrated that carburizing and twice quenching heat treatment technology could induce the highest hardness for 20CrMo. While the 20CrMo disk after nitrocarburizing exhibited the lowest hardness value in the three friction pairs. The results of heavy load tribological experiments showed that abrasive wear was the main reason for failure of the friction pairs. Under the condition of low speed (50 mm/s) and nominal speed (300 mm/s), the friction coefficient of the three friction pairs was almost not influenced by variations of the heat treatment technologies. The white light morphology results revealed that FP2 and FP3 had deeper furrows on the 20CrMo disk, leading to higher wear rate values(183.61 μm³/(N·m) and 252.04 μm³/(N·m) at low speed, 19.21 μm³/(N·m) and 33.93 μm³/(N·m) at nominal speed). The wear rate of FP1 was relatively 94.47 μm³/(N·m) and 10.46 μm³/(N·m) at low speed and nominal speed. In addition, the EDS analysis on the worn area of the three friction pairs indicated that tribo-film was generated on the worn area attributed to the presence of P element. Notably, the P element content on the worn area of FP1 (0.62%) was higher than that of FP2 (0.35%) and FP3 (0.39) at the relatively lower speed. It could be concluded that the wear resistance of 20CrMo steel had been improved using carburizing and twice quenching technology. In case of the heavy-load and high-speed condition, the P element content on the worn area of FP3 reached 0.53%, which was the highest in the three friction pairs. The wear rate of 20CrMo disk for FP1, FP2 and FP3 were relatively 79.11 μm³/(N·m), 42.33 μm³/(N·m) and 34.45 μm³/(N·m). High concentration nitrocarburizing technology was beneficial for enhancing the tribological performance of 20CrMo steel. These findings further demonstrates that the wear resistance performance of the 20CrMo steel was better with higher P element content in the tribo-film. The results of high speed indicated that there were no furrows observed on the wear scar of the three friction pairs under nominal load condition comparing with that under heavy load condition. FP1 presented the best wear resistance with the wear rate value of 9.22 μm³/(N·m), lower than the wear rate of FP2 23.40 μm³/(N·m) and FP3 23.56 μm³/(N·m). This was due to the highest surface hardness of 20CrMo disk processed by carburizing and twice quenching. This study provided a significant theoretical reference for the improving of tribological performance and longevity of life for the gear friction pairs in precision reducers.