基于轧制短流程工艺贝/马复相超高强钢两相区深冷处理的强韧性改善及其机理研究

Duo to the problems of traditional ultra-high strength steel with high alloy content, hot forged, long process, small batch duplicated production, so the regulation technology of strength and toughness in the two-phase region by rolling deformation was an effective measure to solve this plight. However, Previous research from our team showed that the technical space based on TMCP parameter adjustment to enhance the performance of strength and toughness is fairly tiny. Nevertheless, on-line cryogenic treatment is another effective way to further improve the performance, showing a large potential for industrial applications. While, further studies on the enhancement and mechanism of cryogenic treatment in the two-phase are critical for the application. Firstly, the effect laws of strain induction parameters on the content of α phase, the internal morphology of γ phase and the precipitation of MC will be analyzed by thermodynamics calculation and thermo-mechanical simulation. Moreover, external conditions and internal transformation of enhancement regulation of strain-induced ferrite transformation will be obtained; Furthermore, through thermal simulation experiment, the influence laws of cooling path and its parameters on the microstructure composition will be obtained by controlled cooling method in γ+α two-phase region ; Finally, the on-line deep cryogenic treatment experiment in two-phase region will be utilized to obtain the regulation mechanism of this treatment on phase composition and MC intergranular precipitation. And then enhancement and mechanism of strength and toughness by deep cryogenic treatment in two-phase region based on the short rolling process will be revealed, which provides theoretical guidance for the production and application of the economic ultra-high strength steel.

传统超高强度钢合金含量高、热锻成型、工艺流程长、小批量重复生产，热轧两相区强韧调制技术是解决其困境的一项有效措施。然而，项目组前期研究结果表明，基于TMCP参数调整提升其强韧性能的技术空间已经很小。在线深冷处理是进一步提升强韧性能的一个有效途径，具有较大的工业应用潜力。而深入研究两相区深冷处理的强韧改善方法及其机理，是该方法能否工业应用的关键。本项目拟先采用热力学计算和热-力模拟实验相结合的实验方法，分析应变诱导参数对α相含量、γ相内部形态及MC析出行为的影响，得出应变诱导铁素体相变韧化调控的外部诱发条件和内部转变规律；再通过热模拟试验法，进行γ+α组织的两相区相变控冷实验，得出控冷路径及其参数对相组成的影响规律；最后，采用两相区在线深冷处理实验，得出深冷工艺对相组成和MC晶内析出的调控机理。进而揭示基于轧制短流程工艺两相区深冷处理的强韧性改善机理，为节约型超高强钢生产提供理论指导。

传统超高强度钢存在合金含量高、热锻成型、流程长、小批量重复生产等缺点。热轧后两相区在线深冷处理是突破当前困局的一个新途径。本项目采用热力学计算，热-力模拟和热轧深冷实验相结合的方法，进行了合金成分优化设计和对比分析，得出了与轧制生产工艺温度窗口相吻合的减量化成分体系和Ce微合金作用下超高强钢的组织转变及析出规律。研究了应变诱导铁素体相变韧化调控的外部诱发条件和内部转变规律，计算得出了最佳α取值为0.0086，获得了Z参数方程、热加工方程、临界应变等热轧数学模型。研究了控冷路径及其参数对相组成的影响规律。明晰了塑性加工对连续冷却过程中相变的影响规律，900 ºC未再结晶区变形促进了γ向α转变，抑制了γ向GB转变，提升了γ相稳定性，当冷却速率达到5 ºC/s以上时，其扩散相变机理与静态CCT相变相同。研发了两相区相变强韧控制方法。采用奥氏体和铁素体的两相区等温热处理后直接深冷处理，可在等温过程中制备所需铁素体，液氮深冷却可快速高效制备所需的马氏体组织，同时提升Cr-Mo超高强钢的强度和韧性。研究了在线DCT对相组成和MC晶内析出作用机理。热轧过程中高密度位错的产生以及DCT过程中碳化物的形成共同提高了其综合力学性能。通过两相区轧制后在线DCT处理，{111}<112>滑移系更易于激活并形成高密度位错，可提高超高强度钢的抗拉强度。本项目建立了热轧方式制备2006 MPa以上超高强钢的强韧调控方法，研究结果可为我国节约型热轧超高强钢生产提供技术支撑。