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

高锰钢具有孪晶诱发和相变诱发塑性（TWIP/TRIP）效应，由于其独特的性能而引起了人们的广泛关注。然而，从最新技术水平来看，很明显，TTRIP/TRIP钢的机械性能的知识仍然远未深入理解与未来应用最重要的载荷条件相关的变形和退化机制。从常规合金中，众所周知，特别是表面条件、亚表面微观结构和循环载荷的有害影响可能是在实验室环境中显示出上级性能的合金的稳健应用的主要障碍，即在单轴单调载荷下测试的完全再结晶和抛光条件。目前，公开文献中关于TTRIP/TRIP钢的研究仍未深入解决这一严重问题。此外，残余应力及其稳定性的作用迄今尚未得到解决。该项目的主要工作假设是：三个基本变形机制，即位错滑移，孪生和马氏体相变的同时活动和相关的相互作用，导致TTRIP/TRIP钢中前所未有的残余应力稳定性，并最终导致表面处理条件下的上级疲劳性能。如将在本提案中详述的，申请人的小组计划的实验努力将通过分析表面处理（即，在从LN 2至300 °C的温度范围内的喷丸和深滚）对商业TTRIP/TRIP钢的残余应力、微观结构稳定性和循环性能的演变的影响来缩小现有差距。采用的实验技术将允许在热负荷和机械负荷下，在表面处理的TTRIP/TRIP钢中活跃的基本机制的深入分析，因此，提供文献中没有的数据。

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.