Ageing effects on the lattice strain behaviour of duplex stainless steel

The mechanical properties of duplex stainless steel (DSS) are known to display embrittlement due to ageing effects. Knowledge of the micro behaviour of aged DSS is important for understanding the mechanisms of deformation and failure, but it has proved difficult to obtain due to the complex effects created by the duplex structure. Lattice strain measurements of DSS aged under various conditions of temperature and time have been performed in order to determine the strain behaviour of individual (hkl) planes in the α- and γ-phases using white synchrotron radiation X-rays at SPring-8. It was found that the lattice strain of α-Fe(200) depends strongly on the ageing conditions and that the lattice strain behaviour in the γ-phase is more stable than that in the α-phase. These results suggest that the changes in macro mechanical properties, including yield strength and ultimate strength, which are revealed by standard tensile tests, are solely due to ageing effects in the α-phase. The results further suggest that the lattice strain of α-Fe(200) can be used as an index to evaluate 475 °C ageing effects in DSS.