Abstract: Heat treatment test of Cr-Mo-V-microalloyed Q125 steel was carried out to study the effect of tempering temperature on its microstructure and properties. The results show that the Q125 steel exhibits good mechanical properties and low temperature impact properties after quenching at 920 ℃ and tempering at 600-615 ℃, which can meet the requirements of API 5CT standard. As the tempering temperature increases from 580 ℃ to 630 ℃, the yield strength and tensile strength decrease, the low-temperature impact absorbed energy increases. At the same time, the diffusion of carbon promoting by temperature increasing, results in that the phase boundary of tempered martensite shift outward gradually, and the lath martensite coarsens from 0.5 μm to 0.7 μm, the small island martensite gradually fuses into the lath martensite, the lath martensite boundary changes from zigzag to flat, the precipitates at the martensitic lath boundary gradually coarsen from 100 nm to 300 nm with the morphologies change from spherical to short rod, and the proportion of fine precipitates in the martensitic lath gradually decreases.

Key words: Q125 steel, tempering temperature, martensite, mechanical properties, precipitate