Investigation On The Cold-deformation Microstructures And Properties Of 2800MPa Grade Maraging Steel

Ultra-high strength maraging steel, possesing ultra-high strength, good toughness,is widely used in aerospace and atomic energy fields.There are hundreds of publications investigating the aging mechanism of maraging steel,but most of them are often confined to research on the peak in the process of aging and overaging stage,not many studies are on the change of organization in the early aging.Strain hardening index of low carbon maraging steel is low and the cold rolling deformation reinforcement before aging is limited. Moreover,the strengthening effect is controversial.Based on the above background, the study of maraging steel aging mechanism plays a significant role in excavating the strong potential of maraging steel further and developing new steel grade.systematic research on the cold change of maraging steel in the aging process is imminent and imperative.In the present study, optimized heat treatment condition of CM400 maraging steel is normalizing at 820℃ for 2h, subsequently cooling in liquid nitrogen for 1h,Then aging at 500 ℃, 4h, maraging steel achieve its peak aging. After above heat treatments, the lath width of martensite is approximately 250 nm, Ni3M(Ti,Al,Mo)particles well disperse in its matrix. Ni3 Mo and Ni3 Ti not precipitate at the same time,Mo prior segregation on phase interfaces.The investigation revealed that when the treatments of solid solution, cryogenic treatment, cold rolling deformation and aging were applied on the CM400 maraging steel, the peaking aging strength can be increased greatly comparing normal heat treatment applied only. Cold rolling deformation reduces the time of peaking aging at the same aging temperature. When increase peaking aging strength through lowering the aging temperatures, the peaking aging duration was extended. Micro hardness increased by 50 HV when dislocations of high density were produced through cold rolling. The contribution of aging on the hardness of cold rolling maraging steel is much lower than steel without deformation. It indicates that there are no relations between hardness and the cold rolling deformation quantity.