553 / 2019-01-17 15:01:39

Investigation on residual stresses and microstructure of sanicro25 tube bends

residual stresses；numerical simulation；microstructure；deformation twin；dislocation

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The change of the properties and microstructure of the tube bends occurs due to the work-hardening and Bauschinger effect after cold bending of Sanicro 25 tubes. Additionally, the residual stress exists in the elbow, which makes it more vulnerable to failure during its service. The present study aims to explore the distribution of the circumferential residual stress and the relationship between the residual stress and the microstructure. For the above investigation, the circumferential residual stress was investigated with numerical simulation and experimental measurement through ANSYS Microsoft and X-ray diffraction (XRD). Moreover, the evolution of microstructure was performed by scanning electron microscopy and transmission electron microscopy. Dislocation densities and deformation twin widths, their spacings were determined. The circumferential residual stress of numerical simulation was essentially in agreement with the experimental measurement. Initially, a significant increase of the residual stress was observed from -100 to +100MPa near the external wall. However, the residual stress tended to stability with the increasing of the detection depth. Additionally, the residual stress of the elbow outer arc revealed tensile in the interval of stable, while inter arc showed compressive stress. The evolution of microstructure showed that some grains were curved in the bending deformation. The deformation twins and slip lines were observed in the grain interior. Furthermore, it is suggested that the residual stress is affected by the factors such as deformation twin, deformation martensite and dislocation densities.