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Alloy design of medium Mn steels based on computational thermodynamics, kinetics and multi-objective optimization

Thursday (27.09.2018)
16:45 - 17:00 S1/01 - A3
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Medium Mn TRIP steels, have received considerable attention in the past years as potential candidates for the 3rd generation of Advanced High Strength Steels. In the present study, the Fe-C-Mn-Ni-Al system, in the region of Medium Mn steels, is examined by applying computational alloy thermodynamics and kinetics, coupled with constraint multi-objective optimization techniques, to identify a short list of compositions and intercritical annealing parameters that result in an optimal combination of quantity and stability of retained austenite. Al is added to allow for increased annealing temperatures and reduced cementite precipitation during cooling, whereas a small amount of Ni is allowed, in an attempt to reduce the Mn required to stabilize the retained austenite. The method is divided in two stages, the first is concerned with thermodynamic calculations that aim to find optimal compositions and annealing temperatures, whereas the second stage involves kinetic calculations to demine the optimal heat treatment time for the specified alloys. During the first stage, Thermocalc is used to explore a large region of the Fe-C-Mn-Ni-Al composition space, to calculate the phase fractions and their composition at thermodynamic equilibrium as a function of annealing temperature. Next specific constraints that define a Process Window are applied and a short list of Pareto Optimal solutions is identified through a multi-objective optimization procedure. The selected alloys maximize the retained austenite fraction and the annealing temperature while minimizing the Ms temperature and the total alloying content. At the second stage kinetic calculations are performed with Dictra, to determine the austenite fraction as well as the concentration profiles as a function of the heat treatment time. The optimal intercritical annealing time is then found by solving an additional constraint multi-objective optimization problem in the domain of time. The method could be used to accelerate the alloy design process by reducing experimental effort required to develop a novel alloy.

Speaker:
Ph.D. John Aristeidakis
University of Thessaly
Additional Authors:
  • Prof. Dr. Gregory Haidemenopoulos
    University of Thessaly
  • Prof. Dr. Gregory Haidemenopoulos
    Khalifa University of Science and Technology