Novel model for accurate calculation of hardenability and continuous cooling transformation

Abstract

The development of an accurate, yet simple, transformation and hardenability model for general use in the heat treatment and steelmaking industries is described. An empirical approach is used, based on both continuous cooling transformation (CCT ) diagrams and hardenability literature. For this purpose, an equation is developed relating hardenability and the critical time requiredfor transformation during continuous cooling. Existing hardenability models and CCT diagrams are analysed to determine a correct mathematical structure for the hardenability multiplication factor equation. The multiplication factor for a fixed weight percentage of an alloying element X isfound to be strongly dependent on carbon content (in wt– %) according to the equation ℳ=(K%Cn)X, where K and n are constantsfor a specific alloying element. Best values of K and nfor the various alloying elements are determined. Very strong interactions (high values of |n) between the carbide forming elements and carbon are reported. The multiplication factors for the carbide forming elements increase exponentially with carbon content. The accuracy of the model proposed is compared with that of existing models, in which a constant carbon effect on ℳ had been assumed, for a wide range of both low and medium carbon steels, and it is shown that significant improvements in accuracy are obtained using the new model. This is attributed to the use of the improved harden ability multiplication factor equation, which reflects the variable influence of carbon content.MST/992