基于薄带连铸的高性能微纳米晶钢非平衡组织调控及其增强增塑机理

中锰钢作为典型的第三代汽车用钢材料，因其优异的强塑性能、较低的合金成本和诱人的轻量化潜力而备受关注。然而，连铸坯偏析裂纹、粗大δ铁素体所致的加工脆性、冷轧板长吕德斯带以及点焊性能差等瓶颈问题严重制约着新钢种的生产实践和商业化应用。双辊薄带连铸通过调整凝固及冷却工艺，可以促进铸态组织均质化和超细化、过饱和固溶体以及非平衡相的保留，在开发新一代汽车钢方面具有独特的优势。本项目以δ-中锰钢为对象，系统研究薄带连铸条件下典型非平衡组织形成与调控的基本理论，探索亚快速凝固、临界区变形与逆相变一体化下碳/锰协同配分的物理本质，通过控制微纳米“双峰/双相”结构、应变配分和奥氏体特性，实现材料塑性变形过程位错滑移和TRIP/TWIP等增强增塑机制的综合调优。本研究旨在全面突破传统流程中锰钢制造的理论框架，为更高性能钢铁材料的开发提供新的基础理论支撑，具有重要的科学意义和实用价值。

Medium manganese steel, as one of third-generation automotive steels, has attracted much attention because of its excellent strength and ductility, low alloy cost and light-weight potential. However, bottleneck problems such as segregation and crack of continuous casting slab, work brittleness caused by coarse δ-ferrite, long Lüders bands in cold-rolled sheets and poor spot weldability severely restrict industrial practice and commercial application. The twin-roll strip casting can obtain ultra-fine grained and homogeneous microstructure and retain more amounts of supersaturated solid solution as well as non-equilibrium phase by controlling rapid solidification and secondary cooling parameters, thereby indicating a distinct advantage in producing the new-generation automotive steel. Based on the medium Mn steel containing δ-ferrite, the formation and control michanism of non-equilibirium microstructure during strip casting will be studied systematically. The physical essence of C/Mn coopertive partitioning under the combined action of sub-rapid solidification, intercritical deforming and reverse transformation will be explored in this project. In addition, the comprehensive optimization of strength-ductility enhancing mechanism including dislocation glide, TRIP and TWIP effects during plastic deformation of materials will be achieved by controlling the bimodal (micro- and nano-) and dual-phase structure, strain partitioning and austenite characteristics. This investigation is aiming at making a breakthrough in the manufacturing theory of conventional medium manganese steel, and proposing a basic theory to develop new super-high performance steels, which has important scientific significance and practical value.