Simulation of Carbo-Nitride Precipitation in the Multi-Phase Microstructure of Micro-Alloyed Transformation-Induced Plasticity Steel

Abstract

During the thermo-mechanical treatment of low-carbon transformation-induced plasticity (TRIP) steel, precipitation of micro-alloying carbo-nitrides occurs in a complex microstructure consisting of various phases and mixtures of these, such as austenite, ferrite, pearlite, bainite, and/or martensite. In addition, the precipitation process is commonly stimulated and accelerated by plastic deformation that is induced by hot and warm rolling. In the present contribution, a method is suggested, which allows for a thermokinetics-based simulation of the amount as well as the type and distribution of secondary precipitates depending on the local chemical and crystal environment of the polymorph microstructure. As basis of this study serves the thermokinetic software package MatCalc, it is used to simulate the evolution of precipitates during the entire steel processing route. According to the present simulation results, the distribution of C among individual precipitation domains, i.e., phases, is the most important factor governing the precipitate evolution in the system. In addition, the simulations show that niobium carbide (NbC) and vanadium carbide (VC) precipitates differ in their nucleation and growth behavior during the thermo-mechanical treatment. While NbC nucleates mainly during the hot rolling process in a purely austenitic matrix, VC predominantly forms at lower temperatures in ferrite.