Study of the interfaces between austenite and ferrite grains in P/M duplex stainless steels

Duplex stainless steels produced by powder metallurgy (PM) can be obtained by two different methods. On one hand, a fully pre-alloyed powder with a duplex designed composition can be used as raw material; on the other hand, by mixing ferritic and austenitic powders into the desired proportion it is possible to achieve the required duplex microstructure. Through this second method, when austenite is <50 wt.%, materials show net duplex microstructures. But when the austenite percentage is higher than ferrite, a diffusion interface appears at grain boundaries, which modifies all the properties. The objective of this work is to characterize this interface in order to identify its nature and predict the behaviour of the duplex stainless steel. For this purpose, a duplex stainless steel has been produced by mixing ferritic–austenitic stainless steel grade powders, compacting at 700 MPa and sintering in vacuum at 1250 °C for 30 min. The mentioned interface has been studied by SEM and light optical microscopy (LOM) and characterized by nanoindentation in order to determine the hardness and Youngʹs modulus of each phase. Testing mechanical properties completes the study.