Advanced High Strength Multiphase Steels through a Combined Alloy-Microstructural Design

在接下来的几年里，联邦政府会对美国的汽车车队实施最全面的大修吗？到目前为止，美国的排放和燃油经济性标准。提高燃油经济性的最具吸引力的方法之一是车辆？通过使用先进高强度钢（AHSS），可以找到短期内具有成本效益的减轻重量的解决方案。因此，该奖项的研究目标是设计和制造低合金、低成本的多相钢，其复合组织由超细晶（UFG）铁素体基体与分散的贝氏体和稳定的奥氏体组成。这样的微观结构应该保证高强度以减轻重量，高延展性以允许易于成形，以及高断裂韧性。这些目标将通过合金和显微组织设计的协同结合来实现，包括通过计算和实验方法设计合金成分和热处理计划，以获得最佳本构相的体积分数。并利用包括剧烈应变路径变化和剧烈单纯剪切变形在内的热机械加工技术将晶粒尺寸细化到亚微米到纳米范围，并借助基于新型微观结构的工艺优化建模。如果取得成功，该研究结果将为该领域带来革命性的机遇，从目前昂贵或低延展性和成形性差的hss转向具有高强度-高延展性-良好成形性-低成本组合的ahss；通过创造一个全新的纳米钢家族？这将对未来先进的运输工具、发电设备和武器系统产生重大影响。最终，在这项工作中开发的合金和微观结构设计方法将对提高美国制造业竞争力的整体努力做出重大贡献。研究生和本科生包括少数民族学生将受益于新的课程开发，课堂教学和直接参与研究。K-12学生和高中教师将参与计算/实验研究活动，以提高他们的科学和工程意识，并为他们提供第一手的研究经验。

In the next few years, the Federal government will implement the most comprehensive overhaul of the U. S. vehicle fleet?s emission and fuel economy standards to date. One of most attractive approaches to improved fuel economy is vehicle?s weight reduction for which near-term and cost-effective solutions can be found through the use of Advanced High Strength Steels (AHSS). Thus, the research objective of this award is to design and fabricate low-alloy, low-cost multiphase steels with a composite microstructure consisting of an ultrafine-grained (UFG) ferrite matrix with dispersions of bainite and stabilized austenite. Such microstructure should assure high strength for weight reduction, high ductility to allow easy formability, and high fracture toughness. These goals will be achieved through the synergistic combination of alloy and microstructural design via both computational and experimental approaches including design of alloy compositions and heat treatment schedules for optimal volume fractions of the constitutive phases, and refinement of the grain size to submicron to nano range using thermomechanical processing techniques including severe strain path changes and severe simple shear deformation with the help of a novel microstructure based modeling for process optimization. If successful, the results of this research will provide an opportunity for revolutionizing the field, by moving away from current expensive or low ductility and poor formability HSSs, to AHSSs possessing high strength-high ductility-good formability-low cost combination; and by the creation of an entirely new family of ?nano-steels?, which will have significant impact on future advanced transportation vehicles, power generation equipment, and weapons systems. Ultimately, the methodologies for alloying and microstructural design developed in this work will significantly contribute to the overall effort to increase the competitiveness of U.S. manufacturing. Graduate and undergraduate students including several minority students will benefit through new course developments, classroom instruction and direct involvement in the research. K-12 students and high school teachers will be engaged in the computational/experimental research activities to increase the awareness of science and engineering among them and provide them firsthand research experience.