新型Fe-Mn-Al-C系低密度钢的相关系与合金设计研究

This work deals with the Fe-Mn-Al-C based low density, high strength and ductility steel. And the thermodynamic re-optimizing of the Fe-Mn-Al-C-X (X=Si, Cr, Ni, V, Ti and Nb etc.) alloy systems is carried out by means of the CALPHAD technique. The low-density steel is of great importance in the automotive industry, and CALPHAD technique is an advanced method for the design of the multi-component alloys with specific properties. The thermodynamic properties of the alloy systems are analyzed by means of thermodynamic models for the Gibbs energy of the individual phases and a thermodynamic database of the Fe-Mn-Al-C based low-density steel will be setup. Once self-consistent thermodynamic description of a system is obtained, any kind of phase relationship and thermodynamic property of interest, such as phase diagram, the composition and temperature ranges of the matrix phase, precipitates, such as ordering phases B2 and D03, other carbides (cementite, M7C3, M23C6 and M5C, etc.), and the driving forces of phase formation and precipitation etc. The composition and temperature ranges of miscibility gap and spinodal decomposition and precipitation volume of theк-carbide in this alloy system will be studied. A new type low density steel with spinodal decomposition microstructure the will optimized. The results help to define and plan further key experiments, which need to be performed to understand the system comprehensively and to allow further refinement of new low-density steel based on the spinodal decomposition microstructure.

本申请以Fe-Mn-Al-C-X(X=Si、Cr、Ni、V、Ti和Nb等)为主要研究体系，对Fe-Mn-Al-C系低密度钢中的相关系，κ-碳化物、B2和D03等有序相及其它种类碳化物（包括对强塑性能有不利影响的析出相）的晶体结构、相组成和微观组织结构等进行测定和分析；利用CALPHAD方法，构建κ-碳化物的热力学模型，对Fe-Mn-Al-C-X体系中相关三元系进行热力学重新优化，建立更加精确的Fe-Mn-Al-C系低密度钢热力学数据库；在此基础上，研究不同合金元素对各类低密度钢中所有物相的相组成、相析出量和析出驱动力、相转变温度和转变驱动力、固溶体相层错能以及塑性变形机制等的影响；通过元素部分置换，提高к-碳化物与基体相的晶格共格程度、调整溶解度间隙和调幅分解的成分温度范围等，探讨以调幅分解组织为主的Fe-Mn-Al-C系低密度钢的可行性等，为研发新型低密度钢提供坚实的理论依据。

为了应对日益严重的能源危机和环境污染, 基于轻量化的节能、环保、安全、舒适和智能化是当今汽车技术发展的主流，目前实现汽车轻量化主要途径是使用先进高强钢。本研究以Fe-Mn-Al-C-X(X=Si、Cr、Ni、V、Ti和Nb等)为主要研究体系，对Fe-Mn-Al-C系低密度钢中重要合金体系的相关系，相关化合物和有序相的晶体结构和微观组织结构等进行了测定分析，对重要三元合金体系进行了热力学优化，建立了Fe-Mn-Al-C系低密度钢热力学数据库。本工作采用真空非自耗电弧炉熔炼、扩散偶-电子探针微区分析、扫描和透射电镜(SEM/TEM)、背散射扫描电镜(BSE)、X射线衍射(XRD)、能量弥散X射线谱(EDS)和差热分析(DTA/DSC)等技术测定了Al-Co-Ti、Fe-Mo-Nb和Fe-Nb-Zr等15个重要相关合金体系在1173-1373K之间的等温截面和液相面投影图；结合扩散偶确定了金属间化合物Fe23Zr6的稳定性和Fe-Zr体系相图；实验观察和研究了锆铌合金发生调幅分解组织和温度成分范围。根据化合物的晶体结构，统一了各类化合物的热力学模型，利用CALPHAD方法，对Al-Fe-Nb、Fe-Mo-Nb和Ti-V-Zr等26个重要相关合金体系进行了系统的热力学优化或热力学参数评估，建立更加精确的Fe-Mn-Al-C系低密度钢热力学数据库；利用该数据库，分析了Al-Cu-Zr体系中所有金属间化合物在溶体相中的析出驱动力和长大驱动力，得到了所有不变反应类型和相转变序列图；在此基础上，研究了不同合金元素对各类低密度钢中所有物相的相组成、相析出量和析出驱动力、相转变温度和转变驱动力等的影响；通过元素部分置换，调整溶解度间隙和调幅分解的成分温度范围等，探讨以调幅分解组织为主的Fe-Mn-Al-C系低密度钢的可行性等。为研发新型低密度钢提供坚实的理论依据。