EBSD Study of the Microstructural Evolution during Hot Compression Testing of a Superduplex Steel

Abstract

Superduplex steels exhibit a microstructure of approximately equivalent fractions of austenite and δ-ferrite. This structure combines a higher strength than austenitic steels with a higher toughness than ferritic steels and an excellent corrosion resistance. Superduplex steels can be processed by different routes such as casting, extrusion, rolling or forging and are applied in the chemical industry, oil production or paper manufacturing. It is well known that the two phases exhibit a different dynamic restoration behavior due to their differences in the stacking fault energy. The austenite grains are more likely to undergo discontinuous dynamic recrystallization while the δ-ferrite grains tend to strong dynamic recovery. Modern large area electron back scatter diffraction (EBSD) scans are a powerful technique to study the microstructural evolution of the individual phases during hot-forming of duplex steels. However, detailed EBSD studies explaining the flow behavior, influence of grain orientation and grain size modification during hot forming have not been carried out yet. In the present investigation specimens of a S32750 superduplex steel were deformed in uniaxial compression with strain rates between 0.01 and 1 [s-1] to a true strain of 1 at temperatures between 1000 and 1300°C. The microstructures of the as-deformed specimens were examined by large area EBSD scans with particular attention to the characteristics of the individual phases as for example grain size and stored energy of the austenite grains or subgrain size and grain boundary character of the ferrite grains. The differences due to deformation temperature and strain rate are discussed.