Understanding main factors controlling high cycle fatigue crack initiation and propagation of high strength maraging stainless steels with Ti addition

摘要

The microstructure and high cycle fatigue (HCF) property of maraging stainless steels with Ti addition have been systematically studied. The two steels showed similar hardening responses in the aging process, which should be attributed to their identical microstructure characters, typical lath martensite immerged with dispersive precipitates Ni_3Ti and R phase. It is proposed that the HCF crack initiation mechanism depends on the value of normalized applied stress (NAS). At high NAS level (slip band control region), the yield strength dominated by nano-size precipitates is the main factor controlling the HCF lifetime. At low NAS level (inclusion control region), the distance between TiN inclusion and the specimen surface is the main factor controlling the HCF lifetime. TiN inclusion could sharply increase the fatigue crack growth rate. It is found that TiN inclusion acted as the nucleation site of microcrack at front of main crack tip, thus deteriorated the crack propagation resistance of the maraging stainless steel.