基于双级固溶热处理新工艺的双相不锈钢组织调控及其强化机理研究

To obtain high strength on the basis of maintaining excellent corrosion resistance and toughness through innovative heat treatment processes is one of the key researches in the field of duplex stainless steel. Strengthening the steel materials by microstructure refinement is still the most effective method. In the present study, a novel self-designed single-phase zone + dual-phase zone two-stage solid solution treatment will be performed to widely-used 2205 duplex stainless steel for its shortcoming of coarse and heterogeneous microstructures. By means of optical microscope (OM), laser scanning confocal microscope (LSCM), scanning electron microscope (SEM) equipped with electron backscattered diffraction (EBSD), high resolution transmission electron microscope (HRTEM), electron probe micro-analyzer (EPMA), X-ray diffraction (XRD) and neutron diffraction characterization and mechanical testing, microstructure refinement and macro- and microscopic mechanical behaviors are to be investigated. Morphological evolution of the reformed austenite in duplex stainless steel with the new heat treatment process will be systematically studied, and the refinement mechanism of reformed austenite will be discussed. The interfacial characteristics of δ/γ phases and their change with the evolution of microstructures are to be analyzed. The excitation and slip mechanism of dislocations in δ and γ phases under cold deformation will be examined to clarify the elastic-plastic behavior of two phases. The strengthening mechanism of refined 2205 duplex stainless steel is to be elucidated on a microscale. With this project, it is expected to provide theoretical guidance for the development and production of a new generation of high-quality duplex stainless steel. It is of great significance to the development of China's stainless steel industry and the upgrading of duplex stainless steel products.

通过热处理工艺创新，使不锈钢在维持良好耐蚀性和韧性的基础上获得高强度，是目前双相不锈钢领域的重点研究方向之一。通过细化组织来实现强化仍是钢铁材料最为有效的强化手段。为此，本项目拟以量大面广的2205 DSS为对象，针对其组织粗大及不均匀性问题，利用自主设计的单相区+双相区双级固溶处理新工艺，结合OM、LSCM、SEM、EBSD、HRTEM、EPMA以及XRD和中子衍射等表征手段和力学性能测试，开展双相不锈钢的组织细化和宏微观力学行为研究，揭示新工艺下钢中再生奥氏体的形貌演变规律，解析再生奥氏体的细化机制，分析双相组织演变过程中δ/γ的界面特征及其变化规律，考察位错在δ和γ两相中的激发和滑移过程，探讨δ和γ两相的弹塑性力学行为，从微观层面阐明细晶2205 DSS的强化机理。本项目的实施有望为新一代高品质双相不锈钢的研发和生产提供理论指导，对我国不锈钢产业的发展和产品的升级换代具有重要的意义。

随着我国双相不锈钢产品结构的优化，高等级双相不锈钢材的需求量逐渐增加。但钢中存在的微观组织不均匀性问题，对其力学性能、耐腐蚀性能及实际应用造成一定的影响。针对上述问题，本项目以主流钢种2205 DSS为主要研究对象，通过热处理工艺创新和优化，开展了微观组织调控和力学性能表征研究，揭示了钢中细小再生奥氏体的形成机制，解析了组织演变过程中α/γ的界面特征及其变化规律，探究了位错在α和γ两相中的激发和滑移机制，从微观层面阐明了2205 DSS 的强化机理，并提出了进一步提高单相区+双相区双级固溶处理2205 DSS力学性能的优化工艺。.研究结果表明，随着双相区温度的降低，再生奥氏体的形貌发生魏氏→针状→等轴的演变。一定条件下，可以在铁素体基体中获得均匀分布的等轴奥氏体，再生奥氏体与铁素体基体之间保持K-S或N-W取向关系，且两相比例接近1:1。Cr、Ni和Mo合金元素在铁素体和奥氏体两相中的配分行为，是控制再生奥氏体长大的重要因素。双级固溶处理2205DSS在拉伸时，位错在两相中连续滑移，直至在原始铁素体晶界处发生塞积形成应变集中，不同取向的铁素体晶粒作为一个整体发生不同方向上的倾转，造成试样表面的晶粒状橘皮现象，可通过双级固溶处理后增加室温轧制和短时退火工序予以消除。实验钢最佳优化工艺下，屈服强度达722 MPa，抗拉强度达985 MPa，断裂延伸率达42%，强塑积为41,370 MPa•%，比传统固溶处理后的强塑积提高约90%。形变过程中奥氏体首先发生屈服，促使铁素体的晶格应变随着载荷的增加快速增加，应变集中在相界和铁素体亚晶界处，表现出轻微的应力应变分配行为。铁素体发生屈服后，应变从晶界传递至奥氏体和铁素体晶粒内。随应变量增加，位错可在相界处发生塞积，沿相界产生的GNDs密度增加，形成应变梯度，发生异变诱导强化作用。.本项目的研究结果可以为新一代高品质双相不锈钢、超级乃至特超级双相不锈钢的研发和生产提供理论指导，对我国不锈钢产业的发展和产品的升级换代具有重要的意义，在诸多应用领域具有巨大的应用前景。