中锰钢是第3代汽车用先进高强钢，其焊接性能的好坏直接决定了该钢种在汽车行业中的推广和应用。本项目针对我国宝钢集团自主开发的10Mn、7Mn等中锰钢体系，针对其点焊接头性能不佳的实际情况，结合熔核微区凝固过程与焊接接头组织调控，系统研究不同焊接工艺条件下焊接接头的组织变化规律，分析其中心缩松和成分偏析特征。同时针对中锰钢的相变特点，对焊接接头进行组织调控，并利用微区XRD、聚焦离子束FIB微区精细加工及HRTEM分析等手段，研究调控前后接头凝固组织与析出物相的演变特性。结合对接头力学性能的测试结果，揭示中锰钢组织调控与性能改进的内在机制。着重研究马氏体相变诱导晶粒细化及奥氏体稳定化效应，建立点焊接头组织与性能的关联理论模型。该研究有助于阐明中锰钢小熔池凝固条件下的凝固特性与组织调控机制，并改进焊接接头的力学性能。可为中锰钢点焊组织调控机制这一基础科学问题的诠释提供理论依据与研究基础。

The medium manganese steels are the 3rd-generation advanced high strength ones which are possibly extensively applied in automotive industry. Undoubtedly, the weldability of this kind steels directly determines their promotion and application in automobile industry. Based on the 10Mn, 7Mn medium manganese steel systems self-developed by Baosteel group and the fact of their poor weldability, the characteristics including the microstructure evolution, central shrinkage porosity production and composition segregation, will be investigated in this project. The micro-zone solidification process of the nugget and the microstructure modulation is to be involved. Moreover, micro-zone XRD, focused ion beam (FIB) and HRTEM will be employed to comparatively study the solidification microstructure and precipitated phases before and after the microstructure modulation. Combined with the mechanical property test, the intrinsic mechanism between the microstructure modulation and property improvement is anticipated to be revealed. Meanwhile, the martensitic transformation induced grain refinement and austenite stability effect will be focused. These results are helpful to clarify the solidification behavior of the medium manganese steel produced in the spot welding process. As a result, this proposed research will offer theoretical basis and direct experimental evidence for the microstructure modulation and mechanical property improvement of the medium manganese advanced high strength steels.