Simulation of phase transformation by analysis of first derivative of dilatation using Avrami equation during continuous cooling in low carbon steels

Abstract

The phase transformation during continuous cooling in low carbon steel has been widely measured by dilatometer using the lever rule. However, the concept of lever rule has several limitations. In low carbon steels, it is observed that overlapped transformation region of multi-phase and inflection point of small amount of low temperature phase is hardly differentiated. First derivatives of LVDT during continuous cooling could be better way to identify the inflection point and transformation region of phases (especially low temperature phase). Furthermore, first derivative of LVDT could be expressed as the lattice parameter and phase fraction due to temperature. Therefore, phase transformation behavior is simulated by the analysis of first derivative of LVDT using Avrami equation from experimental LVDT. As a result, the start, finish temperature and the amount of each phase are determined. The method is also confirmed by OM and SEM.