Influence of force amplitude on microstructures evolution, fatigue behavior, and ratcheting failure mechanism of 1Cr18Ni10Ti pressure pipe

•Increasing proportion of LAGBs deteriorates low-cycle fatigue behavior of 1Cr18Ni10Ti sample.•Revealing effect of dislocation movements mechanism on cyclic softening behavior.•Activated slip system in ferrite and dislocation accumulation induced fatigue crack initiation in ratcheting-fatigue failure.•Fatigue fracture of pressure pipe experienced progressive ovalization and wall thickness reduction in low-cycle fatigue regime. This paper investigates the effect of force amplitude on microstructures, fatigue behavior, and ratcheting-fatigue fracture mechanism of 1Cr18Ni10Ti pipe. Fatigue tests of non-standardized shape of pressure pipe were conducted. Microstructures were characterized by OM, SEM, and EBSD techniques. Experimental results indicated that the sample under a high-force amplitude contains a higher proportion of LAGBs, causing more prone to fracture. Cyclic softening was triggered by dislocation movements, indicating the dominant deformation mechanism of ratcheting-fatigue sample. More activated system and accumulation of dislocation density inside ferrite grains induced crack initiation. Pipe shows obvious ovalization with plastic deformation response in low-cycle fatigue fracture mode.