Effect of microstructure and test temperature on impact toughness of superduplex stainless steel UNS S32760.

Superduplex stainless steels (SDSSs) are very attractive materials, combining high mechanical properties with improved corrosion resistance. However, these steels present technical limitations because they experience the precipitation of various intermetallic phases occurring in the temperature range of 600-1000°C. The high level of alloying elements, such as Cr and Mo, accelerates the precipitation of intermetallic phases, which are the responsible of embrittlement. In the present study, isothermal heat treatments were performed in the temperature range of 800 to 1000°C, with different ageing times, on an UNS S32760 superduplex stainless steel. The evolution of mechanical properties has been followed by means of Charpy impact tests performed at different temperatures. Total and instantaneous impact energy has been evaluated using an instrumented drop tower equipped with a strain gauge. Microstructural evolution in the material was also carried out. The results of the impact tests evidence the deleterious effect of secondary phases at room temperature, and even more at lower temperatures. A correlation between the impact properties and the different amount of precipitates has been established.