| 00Ni18Co12Mo5Ti maraging steel is an ultra-low carbon high alloy ultra-high strength steel and strengthened and toughened mainly through precipitating intermetallic precipitation phase from the supersaturated solid solution during the aging process.The maraging steel has not only high strength but also high showed and it also has good plasticity and ductility.But the insufficient is that when the level of strength is up to2400MPa, The fracture toughness(Kic) fell sharply.How to improve the level of strength and toughness of maraging steel has become an important research direction.In this article,Metallographic microscope and scanning electron microscope (SEM) were used to observe the microstructure of the00Ni18Co12Mo5Ti steel under different heat treatment process and the extent of the fine grain strengthening on the strength and toughness was studied;The influence of different solid solution time, solution temperature, aging time and aging temperature on the microstructure and mechanical properties of00Ni18Co12Mo5Ti steel was studied with the Orthogonal test,and this test found out the best heat treatment process to achieve the best mechanical properties; The influence of different cycles and cyclic temperature on the microstructure and mechanical properties of00Ni18Co12Mo5Ti steel was studied using cyclic heat treatment method and the principle of the cyclic heat treatment refining grains was discussed.What’s more,Methods of Solid solution strengthening and aging reinforcement on the mechanical behavior were researched and the strengthening mechanism of steel was discussed.The experimental results showed that the strength and toughness of18Ni maraging steel were the comprehensive action of solid solution time, solution temperature, aging time and aging temperature. Solid solution treatment significantly effected the organization of the steel and also prepared for aging treatment. With the increasing of solution temperature and solution time, the grain size of steel increased,and the solid solution time on the influence of grain size was bigger.High strength and toughness of18Ni maraging steel was mainly obtained through aging treatment,and aging temperature on the influence of strength and toughness was much more significant Compared with aging time.The results showed that through860℃×l0min solution and480℃x4h aging,18Ni maraging steel has the best mechanical properties.Cyclic heat treatment can significantly refine the grain size of steel so that it can Obtain uniform and fine equiaxed crystal.The original austenite grain size can be refined to nearly11level and the strength of Maraging steel can be improved about100MPa after four cycle processing at860℃solution temperature.The study found that though improving circulation processing temperature can refine the grain size of steel to some extent,the effect was not that large.The circulating temperature was higher, the refining effect was less obvious.This paper also discussed the mechanism of solid solution strengthening and aging strengthening.The results showed that the effect of solution strengthening was not big and the structure defect of Austenite on the mechanical properties of maraging steel was more significant.Strong means of18Ni maraging steel were given priority to aging strengthening.The main strengthening phases were Ni3Ti,Ni3Mo and reversal austenite when chose480℃aging temperature,and at this temperature18Ni maraging steel can obtain the best strong toughness. |
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