Phase-field simulation of quenching and partitioning in a polycrystalline Fe-C system under constrained carbon-equilibrium conditionThursday (27.09.2018) 09:45 - 10:00 S1/01 - A01 Part of:
In automobiles, energy efficiency is largely ensured by adopting suitable materials. Therefore, several heat treatment techniques are meticulously devised and precisely employed to engineer materials with perfect combination of mechanical and physical properties. Quenching and Partitioning (Q&P) is one such heat treatment process, developed relatively recently, which increases the toughness and ductility of steels by retaining the desired amount of austenite in the matrix of martensite. In this technique, a conventional quenching cycle is subsequently followed by partitioning, which enables the diffusion of carbon from martensite to the surrounding austenite. This accumulation of carbon in austenite decreases the martensite-start temperature (M_s), ultimately, increasing the stability of the austenite at room temperature.
In the present work, two distinct multiphase multicomponent phase-field models are employed to simulate the phase transformations accompanying the heat treatment cycle of Q&P treatment. The thermodynamically consistent formulation, enables the introduction of CALPHAD based driving forces which, in turn, renders analytically predicted volume fraction of martensite in a polycrystalline system. Furthermore, a unique equilibrium condition, referred to Constrained Carbon Equilibrium (CCE), which characterizes the Q&P technique is incorporated and partitioning of carbon from martensite to austenite is analysed. Under different initial concentrations, and volume fractions of martensite, the kinetics of the partitioning and the consequential temporal change in the volume fraction of the retained austenite are presented. This study provides a theoretical guideline for the optimization of the heat treatment cycle of Q&P processing.