低密度、高弹性模量、高强韧性钢的理论与技术基础研究

The present project, for the first time, proposes to fabricate, by conventional steel processing technology, novel steel matrix composites (SMCs) consisting of a strong and ductile steel matrix and a large volume fraction (~15%) of TiB2 particles. During the steel casting process, an appropriate amount of FeTi and FeB alloys are added to achieve a eutectic chemical composition so that eutectic reaction takes place during casting and therefore TiB2 particles can precipitate in the steel matrix. Such SMC possesses simultaneously low density, high Young’s modulus, high strength and good ductility. Compared to powder metallurgy method, producing the SMCs by conventional steel processing can ensure its low production cost and high productivity, enabling its potential industrial applications. It may be anticipated that such SMCs may receive intensive research attentions in the area of automotive steels in the future. The present project intends to investigate two strong and ductile SMCs: (1) a steel matrix consisting of ultrafine-grained ferrite and retained austenite, which can provide excellent TRIP effect and therefore offers high strength and good ductility. (2) an austenitic TWIP steel matrix which can also provide high strength and excellent ductility. Many metallurgical understanding of eutectic reaction, microstructure evolution, deformation behaviour and interface deformation and fracture remain largely unknown, which are the new scientific challenges and therefore the objective of the proposed project. The present project is timely and capable of making a significant contribution to these topics and can provide better understanding on the composition-process-microstructure-property relations, which can provide theoretical foundations for future industrialization of the novel SMCs.

基于钢铁常规工艺，在炼钢过程中加入Ti铁、B铁合金获得钢水中合理Ti、B配比，凝固过程发生共晶反应，在钢铁基体中析出约15％体积分数的TiB2陶瓷颗粒，以获得低密度、高弹性模量、高强度高延性的铁基复合材料。对比目前铁基复合材料所采用的粉末冶金制备方法，该共晶析出方法具有低成本和高效率的优点，适合汽车钢的大规模工业生产。该研究方向已经成为当前汽车用钢发展的新的热点之一，可能引领将来汽车钢技术发展。本项目将研究两种高强高延性铁基复合材料：1）创新提出新型超细板条铁素体+残余奥氏体的基体，其较高分数残余奥氏体的TRIP效应可获得超高强度和高延性的匹配；2）全奥氏体的TWIP钢基体，该基体可以提供类似TWIP钢高强塑积。解决两种材料的共晶反应机理、组织演化规律、加工硬化机理、TiB2与基体界面处变形与断裂机理等关键科学问题，深入理解成分－工艺－组织－性能之间的关系，为工业化生产奠定理论基础。

汽车已成为世界第二大温室气体排放源。为了降低排放量，通过汽车轻量化来达到节能减排的目的是最为直接有效的手段。.近年来，先进高强钢迅速发展，在提高强度的同时，兼具与延性的匹配，其应用能够在保证安全的前提下减薄材料厚度。除了利用高强韧性保证成形的前提下提高强度从而减薄材料厚度实现轻量化外，在此基础上，降低材料密度亦可有效降低构件重量实现轻量化。然而，一方面，由于刚度只与弹性模量和厚度有关，单纯依靠高强韧性来减薄材料的厚度势必导致刚度的下降，因此，材料减薄到一定程度会遇到瓶颈；另一方面，高轻质元素（Al、Mg等）添加虽然降低了材料的密度，但会致使材料弹性模量降低，这将导致构件刚度和碰撞安全性的恶化。因此，低密度、高强韧性钢的发展还需面对保证弹性模量的技术难题和关键科学问题。.TiB2增强钢基复合材料具有高弹性模量、低密度等优良特性，同时利用凝固共晶反应生成钢铁基复合材料的“原位自生”法，非常适合钢铁工业连铸和轧制生成流程的大规模工业化生成，可大大降低制造成本并提高生成效率，可满足汽车工业的需求。因此，设计开发新型的TiB2增强钢基复合材料是解决上述问题的有效途径。.本课题主要针对钢基复合材料所面临的三个主要问题展开：.1. 增强相TiB2尺寸与分布控制；2. 增强相TiB2与基体界面力学关系；3. 高强韧性基体的设计与研究。