Innovative Approaches in Physical Simulation and Modeling for Optimal Design and Processing of Advanced High Strength Steels

Abstract

Innovative approaches are necessitated through meticulous physical simulation and modeling for the evaluation and optimal design of the thermomechanically controlled processing (TMCP) of advanced high strength steels (AHSS). While microalloying of dual-phase (DP), the transformation induced plasticity (TRIP) steels have opened up new possibilities to achieve enhanced mechanical properties, proper contemplation of instantaneous strain hardening capability holds the key for optimized process design. Another example that merits mention is the estimation of real-time phase fractions as a function of heating rate and holding in the intercritical annealing of multiphase steels for optimized processing. In the case of direct quenching, a better understanding of the effect of composition on the phase transformation temperatures and hardenability is inevitably necessary for the manufacturing of low carbon bainitic/martensitic steels. Based on an ambitious experimental plan, new regression models have been developed for the start of bainite and martensite transformation temperature and also for the hardenability, as the standard approach to predict the hardenability using the method given in ASTM A255 standard was not very accurate for boron-containing steels. A novel processing route of developing submicron-grained microstructures by reversion annealing of cold-rolled metastable austenitic stainless steels has been investigated leading to the possibilities of excellent strength-ductility combinations. Literature data on the restoration behavior of twinning induced plasticity (TWIP) steels is scarce and proprietary and, hence, fresh efforts have been made to understand the static recrystallization behavior using physical simulation and modeling. Examples of some of the models and activities being pursued at the University of Oulu have been outlined in this article.

Keywords:

• Bainitic/Martensitic steels
• CCT diagram
• CP steels
• Direct quenching
• DP steels
• Hardenability
• Metastable austenitic stainless steels
• Recrystallisation
• Reversion annealing
• TRIP steels
• TWIP steels

ACKNOWLEDGMENTS

The authors wish to express their gratitude to Finnish Funding Agency for Technology and Innovation (Tekes), Research Fund for Coal and Steel (RFCS), Rautaruukki Oyj, and Outokumpu Oy for providing financial support through different projects in the course of these long-term research activities.