AbstractThe effect of a 0·05 wt-%Nb addition on the austenite decomposition in a Fe–0·2C–10Cr (wt-%) steel has been studied. Addition of Nb substantially retards the transformation kinetics and also changes the resulting microstructure. In the Nb free steel the transformed microstructure consisted of a ferrite–(Cr,Fe)23C6aggregate over the whole temperature range studied. In the Nb steel this aggregate also formed initially, but carbide free ferrite eventually grew in the later stages of the reaction. These microstructural differences are consistent with the significantly different Avrami plots obtained for each steel.MST/1640