Empirical Prediction Model of the Incremental Strengthening of Ferrite /Pearlite Steels with Additions of Vanadium and Nitrogen

Several prediction models of V-N strengthening have been published and used over the course of many years of vanadium microalloying experience.The basis and origin of a proven strength model previously distributed is reviewed and explained.Inherent in the prediction accuracy of the model is the assumption of the amount of nitrogen actually available for VN precipitation.Various situations where the amount of nitrogen available can be significantly altered by the presence of other alloy elements,particularly Ti, Nb,and Al are discussed.Of these,the effect of the Al content(and prior processing history) seem to be most widely overlooked when evaluating and predicting the expected strengthening of the VN precipitate in polygonal ferrite.The possible interactions of Al and N that can affect nitrogen availability are reviewed, and the unintended effects of specification Al requirements are explained.