Kinetic study on the coarsening behaviour of equilibrium phases in Nb alloyed ferritic stainless steels at 700 °C

Nb alloyed ferritic stainless steel is an attractive material to be used in automobile exhaust systems. Recently, in some published experimental work it was reported that coarsening rate of Laves phase (Fe2Nb) can be higher than NbC in Nb alloyed ferritic stainless steels during aging at 700 °C. This observation was attributed to the fact that NbC has a more coherent interface with ferrite than has Laves phase. We explore this conclusion and find that the real reason for the smaller coarsening rate of NbC is the incredibly low solubility of carbon in ferrite.