Precipitation and mechanical properties of UNS 2205 duplex steel subjected to hydrostatic extrusion after heat treatment

The aim of this study was to analyze the impact of severe plastic deformation on 1.4462 duplex stainless steel (UNS 2205) subjected to hydrostatic extrusion (HE) and subsequent heat treatment at selected temperatures. The tests were conducted on a material deformed with a total strain of ε = 3.8 after annealing in the temperature range of 400-800 °C. The characterization was carried out using transmission electron microscopy (TEM), optical microscopy, Vickers hardness and tensile testing. The results showed that the strength of the steel was a function of strain aging, grain growth and phase transformation. The highest Ultimate Tensile Strength measured in the experiment was nearly 2.1 GPa compared with 1.7 GPa for the cold-deformed material. The changes in the austenite and ferrite phases after annealing were different, resulting in a peculiar microstructure with a mix of very small and fragmented γ and σ phases and recrystallized α grains. This resulted in an increase in its strength and a bimodal structure. Overall the research has described in detail the interactions that are present in high alloy steel during the heat treatment process.