| Perforation is a critical technique which is used in the filed of oil prospecting, it is also a way to raise the recovery efficiency of well.Perforating gun is a tool which used for fixing the direction of perforation and protecting during the perforation operation, therefor, the reuirment of sizes, surface quantity and mechanical properties are very important.In this paper,a new type of steel 27 CrMo has been designed according to the actual needs.The micro-alloy element is added in designed steel like Cr-Mo lowcarbon steel such as V and ect. Through strictly controlling in the process of parameters,such as smelting and refining,the content of each element meets the requirements of design completely. According to the actual situation, rolling process has been designed and the tube blank has been rolled to Φ 134.3mm ×9.51 mm pipe.The phase transition point was determined by using different thermal analyzers.The heating temperature is 880 ℃ ~ 960 ℃ and the heating time is 40 mins or 70 mins,followed by water quenching.820 ℃ ~ 860 ℃ was choosen as the Inter-critical quenching temperature, preservation water was heated after 40 mins. Quenching heating temperature is among 520 ℃ ~ 620 ℃, heat preservation time is 80 min, air cooling.The micro-structure,phase composition and fracture surface of different processes were analyzed by optical microscope and scanning electron microscope, and the fracture inclusions were characterized by eds. Through the hardness, tensile and impact test, the mechanical properties of the steel were measured, and the influence factors of mechanical properties were studied.The experimental steel was heated to nine temperatures from 700 ℃ to 940 ℃,and the balance was studied.The organization of the experimental steel is granular bainite, and the organization of the experimental steel is martensite after quenching completely.The grain size is higher than the level of 9.With the increasing of quenching temperature and holding time,the organization of the tissue was significantly getting thicker,The organization was more sensitive to the heating temperature.After tempering,the microstructure is tempered. The fracture morphology of the impact is tough.With the increasing of the tempering temperature,the number of dimple are increased,and the The inclusion of CaO,Al2O3 and SiO2 in the surface of the fracture is a complex inclusion.The organization is ferrite,martensite and austenite after subcritical quenching,and the grain size can reach to the level of 10.With the increasing of temperature of quenching, the ferrite content is decreased gradually.After tempering,the organization is ferrite、 tempered sorbite,and the retained austenite.The original organization of the quenching state is different from the annealing state and tempered state.The ferrite is massive block after subcritical quenching which is reserved to tempering organization. When the original microstructure is quenched and tempered, the formation of austenite is the fastest. The experimental steel was heated to different temperatures and the equilibrium microstructure was all composed of pearlite and ferrite. With the increasing of heating temperature,,the proportion of pearlite increases gradually.Mechanical performance results show that with the increasing of tempering temperature,whether the completely quenched or the temperature quenching,the toughness of the steel is enhanced and the strength is reduced, the best comprehensive performance was achieved at 560 ℃.Compared with the two best performance groups,the result showed that: the temperature under the condition without reducing strength after quenching significantly improved the toughness of the material, finally 840 ℃ quenching heat preservation 40 mins was chosen the quenched and tempered condition as the original organization, water quenching,then through 560 ℃ tempering heat preservation after 80 mins air cooling is the best heat treatment process.The yield strength is up to 913 MPa, transversed impact energy is 91.3 J,48.5 HRC hardness.The grain size is 10.15,meeting the need of the perforating gun. |
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