Mechanical properties of nanostructured 316LVM stainless steel annealed under pressure

In the reported work, the combination of severe plastic deformation (SPD) and annealing under high hydrostatic pressure was used to enhance the ductility whilst maintaining the high mechanical strength possessed by the nanostructured 316LVM stainless steel. The nanostructure was obtained by a multi-step hydrostatic extrusion process to a total true strain of 1.8. This process produced a microstructure consisting of nanotwins and shear bands. The extruded samples were annealed at 700 and 900 °C for 10 min under atmospheric or hydrostatic pressures of 2 or 6 GPa. The resulting microstructures were examined using TEM and FIB techniques. The microstructural observations and X-ray measurements were used to estimate the crystallite sizes. The mechanical properties were determined by microhardness and tensile tests. It was established that annealing under high pressure improved the ductility of the material whilst retaining its high ultimate tensile strength.