M6C Precipitation in Niobium-Alloyed Ferritic Stainless Steel

N. Fujita, H.K.D.H. Bhadeshia and M. Kikuchi


Niobium is used as an important alloying element in the design of heat-resistant stainless steels for automotive exhaust systems. When in solid solution, the niobium improves both the high-temperature strength and the resistance to thermal fatigue life. However, it also forms coarse Fe3Nb3C carbides during service at elevated temperatures, making it important to understand the kinetics of carbide precipitation and coarsening. In the present work, the kinetics of M6C precipitation in ferrite have been modelled, taking into account the multicomponent nature of the diffusion process while at the same time allowing for capillarity effects. The lack of appropriate thermodynamic data has been dealt with using a solubility product based on new experiments on a 19Cr-O.8Nb mass pct steel.

Metallurgical and Materials Transactions A, Vol. 33A (2002) 3339-3347.

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