Abstract: Effect of different quenching temperature, and holding time, tempering temperature and tempering time on the microstructure of 26CrMoVNbRE steel was studied. The results show that the microstructure is mainly composed of tempered sorbite after quenched at 870-900 ℃ and tempered at high temperatures, and the primary austenite grains are fine and uniform. The yield strength of the specimens quenched at 870 ℃ for 40 min is similar to that of quenched at 900 ℃ for 30 min. The former has good comprehensive mechanical properties, and the latter is more favorable to field high efficiency heat treatment. Mechanical properties of the BT110TS oil casing tubes made of the steel can meet technical requirements when quenched at 900 ℃ for 30 min and tempered at 720 ℃ for 60 min. The precipitates were observed by means of SEM and EDAS under different tempering temperatures. The results show that the second phase precipitates in the experimental steel are composite phases formed by M₂C type molybdenum carbide and M₃C type chromium carbide. With the decrease of tempering temperature, the precipitates distributed on the grain boundary increase, which is not conducive to low temperature impact properties and stress corrosion resistance.

Key words: 26CrMoVNbRE steel, quenching and tempering process, microstructure and properties, fracture morphology, precipitates