Abstract 2.25Cr-1Mo-0.25 V steel has been widely used to manufacture hydro-processing equipment operating under harsh environments for its good creep performance. Warm bending, a common fabricating process of 2.25Cr-1Mo-0.25 V steel ring shells, inevitably changes the creep property of 2.25Cr-1Mo-0.25 V steel, but its detailed effect still remains obscure. In this work, we experimentally investigated the impact of warm bending on the microstructure and creep behavior of 2.25Cr-1Mo-0.25 V steel. First, a series of creep rupture tests were carried out at 482 °C and 350 MPa, in which test materials were extracted from an actually fabricated ring shell and its raw plate. Thereafter, the microstructures of test materials were semi-quantitatively analyzed by various characterization techniques, such as electron backscatter diffraction (EBSD) and three-dimensional high-resolution X-ray computed tomography (3D μ-XCT). Finally, warm forming induced microstructural degradation as well as their implication for creep was discussed in detail. Creep rupture tests showed that warm bending leads to a significant decrease in creep lifetime at the surface region of virgin plate but a slight decline at the central region of virgin plate. An inhomogeneous creep resistance distribution was thereby revealed along the thickness direction of the ring shell, which could not be completely eliminated by subsequent tempering at 705 °C for 8 h. Moreover, microstructural observations demonstrated that warm deformation leads to multiple microstructural deterioration, including carbide coarsening, ferrite matrix softening, void defect increasing, etc. Their combined action appears to accelerate the creep fracture behavior of 2.25Cr-1Mo-0.25 V steel. This work will contribute to the long-term safety and integrity assessment of 2.25Cr-1Mo-0.25 V steel structures.Graphical abstract
展开▼
