Mechanical Surface Treatment of High-Manganese TWIP/TRIP Steel – Microstructural Stability and Mechanical Properties

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High-Manganese steels showing twinning-induced and transformation induced plasticity (TWIP/TRIP) effect have attracted a lot of attention due to their unique properties. However, from the state-of-the-art it is obvious that knowledge of mechanical properties of TWIP/TRIP steels still is far from in-depth understanding of deformation and degradation mechanisms being related to loading conditions of utmost importance for future applications. From conventional alloys it is well known that especially the detrimental effects of surface condition, sub-surface microstructure and cyclic loading can be a major road-block towards robust application of alloys showing superior performance in laboratory environments, i.e. fully recrystallized and polished conditions tested under uni-axial monotonic loading. Currently, studies focusing on TWIP/TRIP steels available in open literature still do not address this severe issue in-depth. Furthermore, the role of residual stresses and their stability has not been addressed so far. The major working hypothesis of the project applied for is: The concurrent activity and related interaction of three elementary deformation mechanisms, i.e. dislocation slip, twinning and martensitic transformation, lead to an unprecedented stability of residual stresses in TWIP/TRIP steels and, finally, superior fatigue properties of surface treated conditions. As will be detailed in the current proposal, the experimental effort planned by the applicant’s group will close the prevailing gap by analyzing the effects of surface treatments, i.e. shot peening and deep rolling at temperatures ranging from LN2 to 300 °C, on the evolution of residual stress, microstructural stability and cyclic performance of a commercial TWIP/TRIP steel. Experimental techniques employed will allow for in-depth analyses of the elementary mechanisms being active in surface treated TWIP/TRIP steel under thermal and mechanical loading and, thus, provide for data not being available in literature so far.