低密度δ-QP钢δ铁素体晶粒细化机制

As the existing of banded coarse-grain δ ferrite, the high-aluminium low-density δ-QP steel is hard to obtain the tensile strength of 1180MPa and high formability. In this project, we proposed recrystallization and deformation together refine δ ferrite grain by thermo-mechanical controlled rolling of δ-QP steel, achieving fine and homogeneously distribution of δ ferrite. The influence of deformation storage energy on recrystallization refinement of δ ferrite, recrystallization refinement mechanism, stress and strain distribution of δ ferrite and austenite, and the effect of stress and strain distribution on deformation refinement will be studied. The δ-QP steel with yield strength ≥700 MPa, tensile strength ≥1180 MPa and elongation ≥20% will be developed, which could establish theoretic and technical foundation for its industrial application. The research on grain refinement mechanism and microstructure regulation of δ ferrite in this project will not only achieve the development of high strength δ-QP steel, but also has beneficial for the microstructure optimization of other low-density steels with coarse grain δ ferrite, such as δ-TRIP steel, low-density medium-Mn TRIP steel. This research will greatly improve the industrial production feasibility of low-density steel.

δ铁素体晶粒粗大且呈带状分布是高铝低密度δ-QP钢突破1180MPa抗拉强度和获得高成形性的技术瓶颈。本项目提出热轧过程中控制轧制，通过再结晶细晶和形变细晶共同作用实现δ铁素体的晶粒细化和弥散均匀分布。拟解决热轧形变储存能对δ铁素体再结晶行为的影响及其晶粒细化机理、δ铁素体与奥氏体高温轧制变形过程中的应力应变分配及其对δ铁素体的形变细晶行为的影响机理等关键科学问题。实现屈服强度≥700MPa、抗拉强度≥1180MPa、延伸率≥20%低密度δ-QP原型钢开发的目标，为其工业应用奠定理论和技术基础。本项目所提出的δ铁素体晶粒细化机制及其组织调控方法不仅可突破高强度δ-QP钢开发的瓶颈，对δ-TRIP钢、低密度中Mn-TRIP钢等存在粗大δ铁素体问题的高铝低密度钢组织性能调控均具有重要的科学和技术价值，大大提高了低密度钢生产实践的可行性和工业化的潜力。

目前，汽车轻量化对于高强韧低密度钢的需求日益迫切，而粗大的带状δ铁素体的存在限制了高铝低密度钢强度和成形性能的进一步提升。本研究中通过热变形模拟、热轧模拟等手段探索了δ铁素体的组织演变规律，明确了热变形δ铁素体再结晶行为及相应机理，实现了δ-QP钢中δ铁素体的热轧控制轧制晶粒细化。基于δ铁素体晶粒细化研究，成功开发了屈服强度≥700MPa、抗拉强度≥1180MPa、延伸率≥25%的低密度δ-QP原型钢，其力学性能稳定，工艺窗口较宽。此外，深入的研究了δ-QP钢的变形行为及相应微观机制，为高强韧δ-QP钢的开发提供了更多的思路。该研究工作的开展成功突破了高铝低密度钢的强度瓶颈，为δ-QP钢的工业应用奠定了重要的理论与技术基础，大大提高了低密度钢生产实践的可行性和工业化的潜力。