Research And Optimization On37CrMnMo Heat Treatment Process

37CrMnMo is a medium carbon alloy steel with high hot working character, fine harden ability, tempering stability and high strength and toughness after heat treating,which is widely used in oil drilling tool. Oil drill tool works in a complex condition and undergoes various complex repeated fluctuating stress, so it needs good torsion strength,good impact toughness and other mechanical properties. This thesis studied the effects of heat treatment and deep cryogenic treatment on the structure and mechanical properties of oil drill material 37 CrMnMo.Firstly, it needs obtained the regression equation between quenching temperature,quenching time, tempering temperature, tempering time and mechanical properties by orthogonality, according to the orthogonality and mechanical properties of oil drill tool application, it was concluded that the optimized heat treatment parameters were quenching temperature 890℃, quenching time 50 min, tempering temperature 580℃ and tempering time 60 min. After thermal refining, the structure became tempering sorbite with martensite position,it had smaller grains, homogeneous distribution, compact arrangement and precipitated dispersively fine carbide in the metal matrix. And torsion strength was951.9MPa, impact toughness was 51.0J, macro-hardness was 37.9HRC, tensile strength was 1218.9MPa and yield strength was 1161.1MPa, comparing with mechanical properties of oil drill tool application, it improved a lot.Secondly, the effects of deep cryogenic treatment time and number on the micro-structure and mechanical properties of oil drill material 37 CrMnMo were studied,and compared structure and mechanical properties with thermal refining. It showed that with deep cryogenic treatment time increasing, thick carbides firstly decreased then increased, fine carbides firstly increased then kept the level, when the deep cryogenic treatment time reached to 16 h, thick massive carbides turned into fine ball carbides, the number of fine carbides in homogeneous distribution reached to peak; when the deep cryogenic treatment number reached to three times, the size of grains became finer and more homogeneous, compact arrangement, the number of fine carbides precipitated dispersively in matrix and grain boundaries, thicker carbides intended to formfiner ball carbides and distributed homogeneously. The effects of deep cryogenic treatment time and number on impact toughness were the most significantly, when the time was 4h,the impact toughness was 80 J and increased by 56.9% compared with that of thermal refining, when the number was 3 times, the impact toughness reached to top, it was 88.2J and increased by 72.9% compared with that of thermal refining. The effects of deep cryogenic treatment time and number on torsion strength, macro-hardness, tensile strength and yield strength were not obvious.At last, the deep cryogenic strength mechanism of 37 CrMnMo steel was explored, it could be concluded that super cooling degree can impel retained austenite to transform into martensite. Meanwhile, in the liquid nitrogen temperature, the grains shrank,which impelled fine carbides to precipitate and grains to refine; thicker carbides broke into fine carbides, in the low temperature, the carbon and alloying elements gathered nearby defects, such as dislocation and vacancy, massive fine carbides formed when the liquid nitrogen temperature recovered to the room temperature; some fine carbides disperse,gather and grow in the defects and grain boundaries when the liquid nitrogen temperature go back to room temperature.