GOALI: Deformation Microscopy of Retained Austenite Transformation in TRIP Steels

非技术摘要：现代交通工具的效率严重影响到个人和国家的繁荣、国家能源独立、城市污染水平(以及相关的健康)和气候变化。决定这种效率的一个关键因素是车辆的重量。虽然许多正在进行的努力旨在将轻质材料(如铝、镁和碳复合材料)引入汽车结构，但到目前为止，主要成分仍然是相对较重的钢。因此，该项目专注于替代轻量化战略，即开发具有更好成形性的先进高强度钢；这将使更少的金属能够提供相同的结构和安全性能。新出现的显微技术与模拟相结合，揭示了现代高强度钢的组织和性能之间的关系。由此产生的洞察力导致了更深层次的理解和改进的模型，这是所谓的第三代钢铁的萌芽所必需的，以及车辆重量和效率的阶梯变化。这一研究项目不仅为在学术/工业混合环境中指导研究生和本科生提供了一个环境(通过与通用汽车的密切合作)，而且通过一个外展计划正在改善高中教育。当地高中的老师在暑假的几个月里花时间在这个项目上，同时得到帮助，为他们的班级开发新的和相关的课程组成部分。技术摘要：已经对TRIP(相变诱导塑性)钢进行了许多研究。然而，关于奥氏体化学成分和显微组织对其向马氏体转变的影响，目前还没有系统的资料。这些知识对于设计残余奥氏体织构、形态和体积分数至关重要，以便使低合金TRIP钢获得更高的强度、成形性和抗断裂性能，以实现所需的汽车结构性能。建议的残余奥氏体和马氏体识别技术(基于新兴的电子背散射衍射技术)，以及细观位错表征，与微观数字图像相关(DIC)相结合，提供了一种新的“形变显微镜”能力。所得到的框架允许评估位错和硬相界之间的相互作用，同时也精确地捕捉到各种残余奥氏体岛转变的应变。通过了解显微组织和成形性之间的基本联系，可以建立奥氏体向马氏体相变和相关变形现象的细观模型。

NON-TECHNICAL SUMMARY:The efficiency of modern vehicles critically affects individual and national prosperity, national energy independence, city pollution levels (and related health) and climate change. A key element in deciding this efficiency is vehicle weight. While many ongoing efforts aim at introducing lightweight materials (such as aluminum, magnesium and carbon composites) into automotive structures, the dominant constituent, by far, is still relatively heavy steel. Hence this project focuses on the alternative light-weighting strategy of developing advanced high strength steels with improved formability; this will allow less metal to provide the same structural and safety performance. New and emerging microscopy techniques are combined with simulation to reveal the relationships between microstructure and properties of modern high-strength steels. The resulting insights lead to the deeper levels of understanding and improved models that are required for the nascence of so-called third-generation steels and a step-change in vehicle weight and efficiency. Not only does this research project provide an environment for mentoring graduate and undergraduate students in a mixed academic / industrial setting (via a strong collaboration with General Motors), but high school education is being improved via an outreach program. Teachers from local high schools spend time on the project during the summer months while receiving help in developing new and relevant curriculum components for their classes.TECHNICAL SUMMARY:Many studies have been carried out on TRIP (Transformation Induced Plasticity) steels. However, there is still no systematic information concerning the influence of austenite chemistry and microstructure on the resulting transformation to martensite. Such knowledge is critical to the design of texture, morphology and volume fraction of retained austenite in order to enable low-alloy TRIP steels to achieve enhanced strength, formability, and fracture resistance necessary to achieve the desired automotive structure performance. Proposed retained-austenite and martensite identification technologies (based upon emerging electron-backscatter diffraction techniques), along with meso-scale dislocation characterization, are combined with micro-digital image correlation (DIC) to provide a new 'Deformation Microscopy' capability. The resultant framework allows for the assessment of interactions between dislocations and hard phase boundaries, while also precisely capturing the strains at which the various retained austenite islands transform. Knowledge of the fundamental links between microstructure and formability enables the formulation of a meso-scale model for transformation of austenite to martensite, and related deformation phenomena.