Heat Treatment Process of Large-section SAE4330V-MOD Alloy Steel Drill Pipes Used in a Gold Mine

Through quenching and tempering the large-section SAE4330V-MOD alloy steel drill pipes used in a gold mine at different temperatures,the heat treatment process of the steel was studied.The results show that by first heating the steel to 650 ℃ and holding for 3 h,then heating to 860 ℃ and holding for 6 h following quenching in less than 70 ℃ water,and finally tempering at 620 ℃ for 6 h,uniform fine tempered sorbite microstructure could be obtained and best match among tensile strength,impact energy and hardness was achieved with various mechanical properties all meeting the technical requirements.If there was small amount of bainite in microstructure of the steel before heat treatment,it would lead the mechanical properties after heat treatment could not meet the requirements.Therefore,original microstructure of the steel should be strictly controlled.