Ultra-low stress triaxiality ring-roller spinning: microstructure, plastic behavior, and cumulative large deformation mechanism

Spinning is a common processing method for ultra-thin-walled tube. However, it is susceptible to surface ruptures in the deformation zone due to point-by-point contact, which affects the quality of products. In response to this issue, a ring-roller spinning (RRS) process is proposed, where the spinning roller makes tangential inner contact with the tube blank. This expands the triaxial compressive region, reducing ruptures tendency. And the tangential compressive stress is strengthened on the basis on triaxial compression of the conventional spinning (CS) process, which provides shear stress state in deformation zone. This paper conducts a comprehensive investigation into the RRS for thin-walled tubes made of 304 austenitic stainless steel. The study combines theoretical and experimental approaches and employs the finite element method (FEM) to evaluate the stress state within the tangential region. Various characterization methods are applied to examine the microstructural evolution under ultra-low stress triaxiality (ULST). The results confirm that the deformation zone is primarily characterized by tangential pressure under ULST, which significantly influence the metal microstructure, plastic behavior, and cumulative large deformation. This innovative process facilitates the continued deformation of the tubes, even under the saturated conditions of work hardening with the martensitic plasticising behaviour promotes grain refinement to 124 nm, resulting in an increase in the yield strength of the tubes from -1060 MPa to 1550 MPa. Continuous processing of ultra-thin-walled tube with a cumulative thinning rate of 90% was achieved by conducting RRS five-pass spinability experiments.