Generating duplex microstructures by nitriding; nitriding of iron based Fe–Mn alloy

Nitriding of Fe–2 at-%Mn alloy at 650°C employing a nitriding potential of 0·05 atm− 1/2 resulted in a highly complex microstructural development as a function of depth below the specimen surface: a surface adjacent layer exhibiting an austenite–martensite duplex microstructure, followed by an intermediate region showing a ferrite–austenite duplex microstructure, and at even larger depths a region where an austenite layer covers the grain boundaries of the ferrite matrix grains. Development of this complex microstructure is attributed to the strong austenite stabilising effects of Mn and N. This work demonstrates the power of a relatively simple nitriding treatment to realise a highly complex microstructure known to be associated with strongly enhanced mechanical properties.