凝固亚稳经济型高铝多相轻质钢的组织调控与形变机制

Light-weight steels are obtained by adding light element to steels, which improve the mechanical properties and simultaneously reduce its density. High strength light-weight steels not only meet the requirements about energy saving, emission reduction, and safety of automotive, but also expend its applications to aerospace field, which have recently attracted growing attentions. This aim of this work is to attempt to produced complex multiphase high strength light-weight steels by near rapid solidification and make a breakthrough for the lowest density limit of medium and low Mn multiphase light-weight steels prepared by traditional method. This work will explore the solidification structure evolution and control measures of complex multiphase high properties engineering materials prepared by near rapid solidification, and expand the application field of a novel production method whose distinguishing features are energy-saving, environment-friendly, low cost, and high efficient. Due to serious crack-sensitivity of light-weight steels with medium and low Mn, content of Al element added can’t be over 6%, and the density can’t reduce to a desired level. Therefore, this work will examine the structure formation and control of medium and low Mn light-weight steels prepared by near rapid solidification, analyze the relationship between structures and properties, and study the partition of constitution phase and precipitation of κ-carbide under the heating treatment. At last this work will well know about the lowest limit of density of economical high strength light-weight steels, and propose the composition design and structure control of economical high strength light-weight steels. This work gives an important step to explore manufacture complex multiphase high strength light-weight steels by near rapid solidification technology. An energy-saving, environment-friendly industrial technology of near rapid solidification, i.e. twin roll thin strip continuous casting, is its industrial applications. So it has a great value in solving the social problems about energy resource and environment.

轻质钢是通过添加轻元素提高钢铁材料性能同时降低其密度，满足汽车工业节能、环保的发展需求，并扩展在航空、航天领域中应用。项目以突破传统工艺中经济型多相轻质钢密度降低极限为目标，尝试利用亚快速凝固简化轧制和热处理工序直接制备复杂多相高性能轻质钢，探索四元多相合金高性能工程材料的亚快速凝固组织演变规律及调控机制，拓展通过凝固过程调控直接制备复杂多相高性能结构工程材料这一节能、环保、经济、高效新方法的应用广度。重点研究中低锰高铝多相轻质钢的亚快速凝固组织演变、影响因素及机制，构建其微观组织和力学性能的关联特性及形变机制，探讨后续热处理中其亚稳组织的稳定性、元素配分、碳化物析出和组织演化机制，获得经济型多相高强轻质钢的成分设计和组织调控原则。以铸轧高效融合的薄带连铸工业化亚快速凝固技术为应用背景，探索复杂多相高性能结构工程材料的高效制备新工艺，在解决资源、能源和环境问题方面具有重要的社会价值。

本项目以突破传统方法制备的中低锰轻质钢密度降低极限为目标，尝试利用亚快速凝固技术制备传统方法难于制备的低密度钢铁工程材料。主要研究工作包括：系统研究了Al、Mn和C等元素对(2-16)wt.％Mn中低锰轻质钢Fe-Mn-Al-C四元合金体系亚快速凝固组织组成相和κ-碳化物的影响规律；在此基础上，精细表征了8-16％Mn高铝轻质钢亚快速凝固薄板的物相和κ-碳化物的形貌、尺寸、分布等微观组织、力学性能及变形机制。结果显示：亚快速凝固可以有效抑制高铝较低锰的Fe-Mn-Al-C体系中粗大或板条状的κ-碳化物析出，形成铁素体或铁素体+奥氏体为主要相的组织，且组织均匀细小；Mn元素对高铝较低锰的Fe-Mn-Al-C亚快速凝固薄板中奥氏体含量影响不大，但由于对堆垛层错能和溶质元素的固溶度有较大影响，因此可调控合金薄板的强度和塑性；C元素含量增加可明显提高薄板中奥氏体含量，但C含量达到1.2wt.%后容易在晶界富集和析出碳化物颗粒，可能降低甚至恶化塑性。适当温度热处理可促使亚快速凝固薄板中纳米κ-碳化物和有序相B2的析出，同时降低其热应力、位错密度和元素固溶量，可提高强度而不恶化塑性。利用Pandat 热力学软件系统计算了中低锰Fe-Mn-Al-C 四元合金平衡相图，结合Procast软件对实验制备薄板凝固过程冷速的数值分析结果，理论分析了中低锰轻质钢亚快速凝固组织演变的规律和调控机制，揭示了四元多相复杂的轻质钢亚快速凝固组织演变规律及调控机制，获得经济型多相高强轻质钢的成分设计和组织调控原则。以铸轧高效融合的薄带连铸工业化亚快速凝固技术为应用背景，探索复杂多相高性能轻质钢的高效制备新工艺，在解决资源、能源和环境问题方面具有重要的社会价值。