Temperature-dependent mechanical properties of an austenitic-ferritic stainless steel studied by in situ tensile loading in a scanning electron microscope (SEM)

In situ tensile tests at various temperatures, ranging from 25 to 750°C, were conducted on an austenitic-ferritic cast duplex stainless steel (CDSS) to investigate both the plastic deformation mechanisms and the effect of temperature on mechanical properties. A continual reduction in the mechanical properties, such as ultimate tensile strength (UTS) and yield strength (0.2% proof stress, σ_0.2), was found as the temperature increased. Fractographic analysis demonstrated that tearing topography surface (TTS) was more likely to occur at elevated temperatures. In situ observations revealed that the plastic deformation occurred within the soft austenite matrix at first and was followed by slip gliding in the ferrite phase as the load increased. Voids tended to form at the ferrite-austenite interphase boundaries or around the inclusions and then merge and propagate in the austenite matrix. The present study also shows that the clustered distribution of the ferrite phase in the matrix can cause crack initiation easily at early stages of deformation.