Abstract: Effects of tempering temperature, time and inclusion on microstructure and mechanical properties of 150 KSI 30CrNi2MoV steel for deep wells were studied by means of optical microscope, scanning electron microscope, ASPEX scanning analyzer, tensile test and impact test. The results show that after quenching at 860 ℃ and tempering at 590-610 ℃ for 60 min, the yield strength of the 30CrNi2MoV steel decreases from 1152 MPa to 1058 MPa with the increase of tempering temperature, the tensile strength decreases from 1239 MPa to 1135 MPa, the elongation increases from 17% to 19%, the percentage reduction of area increases from 56% to 61%, and the normal temperature minimum impact absorbed energy increases from 80 J to 99 J. When tempered at 600 ℃ for 60-240 min, the precipitates inside the grains increase with the increase of tempering time. When tempered at 600 ℃ for 60 min, with the inclusion index decreases from 12.8 to 1.1, the mean impact absorbed energy of the tested steel increases from 57 J to 95 J.

Key words: 30CrNi2MoV steel for deep wells, tempering process, microstructure, mechanical properties, inclusions