Ferrite transformation from Fe-0.3N Austenite

Ferrite transformation behavior of Fe-0.3 mass%N binary alloy was studied in the temperature range between 500°C and 750°C. By isothermal holding in the α + γ two phase region, two morphologies of Allotoriomorphic ferrite (AF) and Widmanstetten ferrite (WF) formed from the prior γ grain boundary. On the other hand, in the case of isothermal holding at 500°C, nitride-free bainitic ferrite (BF) was formed at the beginning, and changed to bainite accompanied with γ' precipitation in further holding. The retained γ was obtained by decreasing the transformation temperature in the two phase region, and maximum volume fraction of 9% was obtained at 600°C. AF had near K-S OR with one side of the adjacent prior γ and grew into the grain without K-S OR. On the other hand, WF and BF had near K-S relationship with the matrix. Both WF and BF had significantly higher energy dissipation than AF, and the energy dissipation of AF is due to interfacial friction. On the other hand, the strain energy associated with the transformation was dominant in WF.