利用凝固亚稳增强析出纳米碳化物制备高强高模量轻质汽车钢

For the energy crisis and environmental deterioration, the weight reduction of automobiles would be a natural direction to increase fuel efficiency and decrease CO2 emission. For the safety and stiffness of automobiles, gauge reduction will not be sustainable. The high specific strength/modulus materials would be the better selection for automobiles’ component. The Fe-Mn-Al-C light-weight steels with low density and high strength have attracted increasing attentions. But the expanding of the lattice parameter caused by high Al elements makes these light-weight steels clearly reduce in the elastic modulus. This detrimental effect would restrict their applications to automobiles in future. Based on the distinguishing feature that a large number of nano-carbides could precipitate from the Fe-Mn-Al-C light-weight steels, aim of this project is to improve the elastic modulus of light-weight steels by using the precipitated nano-carbides. In this project, expanding the solid solubility limit of near-rapid solidification will be used to enhance the nano-carbide precipitation, addition of Cr element is to improve the modulus of matrix and reinforced carbide particles, and TiC precipitated by microalloying method will be used to compound reinforce. These measures mentioned above will be made to develop a new generation of automobile steels those have the following characteristics such as low density, high specific strength/ modulus, and good ductility. Based on the twin roll thin strip continuous casting, an industry near-rapid solidification technology, this project will examine the relationship between the microstructures and mechanical properties of the light-weight steels solidified under near-rapid solidification conditions, and explore novel high-efficiency production process of advanced high strength steels. Study of this project would be very useful for energy-saving and emission-reduction.

轻量化是汽车节能、减排的关键，高比强度、高比模量材料是未来汽车轻量化的必然选择。正在研究的低密度、高强塑性Fe-Mn-Al-C系轻质钢，因Al元素的大量添加使其晶格点阵扩张、弹性模量明显降低，严重削弱了其低密度和高比强度的优势，制约其发展应用。基于Fe-Mn-Al-C系轻质钢可大量析出纳米κ-碳化物的特点及申请人前期研究发现，项目提出利用该轻质钢的纳米碳化物提高其模量，通过亚快速凝固扩大固溶极限增强析出、添加Cr元素改善基体和碳化物的模量、微合金化析出TiC纳米颗粒复合增强等措施，探索低密度、高强塑性和高模量的新一代高强汽车钢的设计基础。结合薄带连铸亚快速凝固的工业化应用平台，阐释亚快速凝固、时效处理时组织和纳米κ-碳化物的控制规律，揭示轻质钢组织、纳米碳化物特征和力学性能的关联与调控机制。项目选题有社会意义，材料研发思路有鲜明特色和创新性，探索高强汽车钢高效制备新工艺方面有显著的前瞻性。

项目针对低密度、高强塑性Fe-Mn-Al-C轻质钢弹性模量低的缺陷，基于其固态下可大量析出碳化物的特点，探索了利用亚快速凝固扩大固溶极限增强纳米级κ-碳化物的析出量、同时研究了Cr、Ti等元素对其碳化物析出以及性能的影响。研究发现：亚快速凝固下中高锰Fe-Mn-Al-C轻质钢的组织细小均匀，组成相主要是γ-奥氏体和δ-铁素体，没有明显的粗大碳化物析出，铸态条件下铁素体中存在少量纳米有序相和奥氏体中有纳米κ-碳化物。合适的热处理可大幅度提高奥氏体中纳米尺寸κ-碳化物析出，从而提高轻质钢的强度和模量，不会严重恶化塑性。1％Ti添加后由于纳米TiC颗粒的析出可以明显提高其热处理后弹性模量，但是过量的Ti元素则导致塑性严重恶化。Cr元素添加后可减少其中碳化物的析出，从而降低亚快速凝固薄板的屈服强度，但可显著提高其加工硬化率，从而提高其抗拉强度，热处理后其强度和延伸率显著提高。通过上述亚快速凝固薄板组织、力学性能及其变形行为的系统分析，阐述了中高锰轻质钢亚快速凝固组织与性能关联特征及其作用机制。本研究在探索低密度、高强塑性、高比模量的新一代高性能轻质钢的设计和组织调控方面进行了有意义的研究，以节能、高效的亚快速凝固工业技术--双辊薄带连铸为应用背景，在解决能源危机、环境污染方面具有重要的社会价值。