EFFECTS OF VANADIUM AND NIOBIUM ON THE NUCLEATION KINETICS OF PROEUTECTOID FERRITE AT AUSTENITE GRAIN-BOUNDARIES IN FE-C AND FE-C-MN ALLOYS

Nucleation kinetics of proeutectoid ferrite allotriomorphs at austenit e grain boundaries were measured in Fe-0.1 mass%C and Fe-0.1 mass%C-2 mass%Mn alloys with small amounts of V or Nb. Nb was one or two orders of magnitude more effective than V in reducing the nucleation kinetic s of ferrite compared at the same amount of addition. The segregation of alloying elements to austenite grain boundaries and the formation o f atom clusters with carbon or fine coherent precipitates at ferrite n ucleation sites were considered as possible causes for the observed su ppression of nucleation. However, quantitative agreement with theory o r direct experimental evidence is yet to be obtained for these possibi lities to be deemed operative in the present alloys.