基于铸辗复合成形的马氏体不锈钢晶粒细化与性能调控机理研究

The composite cast-rolling forming technology as a new technology for rolling large ring parts keeps gaining attention. At present, the shape controlling technology of this process tends to be perfect, while the performance controlling technology still exists technical bottleneck, where its grain refinement mechanism and performance controlling scheme are needed to be solved. This project takes a kind of the domestic special steel (0Cr11Ni2MoVNb martensite stainless steel) disk as an example. Considering the uneven effects of the pre-rolling grains, the fine grain reinforcement theory during the hot rolling recrystallization process and the phase transition reinforcement theory that martensite phase transition can promote high-density nanometer phase precipitation through heat treatment will be used to improve the overall performance. Through both numerical simulation and experiments (hot compression experiment and heat treatment), the nano-phases, grain refinement of hot rolling and heat treatment regulation scheme will be systematically investigated. Based on the grain size of cylinder specimens measured by the hot compression experiment under various deformation parameters of strain rates and temperatures, the grain growth model and recrystallization models under different temperatures and residence times will be established; Coupling the microscopic model that considers the material model under thero-physical properties parameters, grain models (the grain growth model and recrystallization models) and crystal plasticity finite element simulation, the focuses on the evolution rules of grain size and crystallization behaviors during the hot rolling process from ring to disk will be deeply studied, thus to realize the quantitative prediction of grain size; The specimens after hot compression experiment will be treated separately under heat treatment, and the microstructure, alloy phase and grain size under will be analyzed; Combining with the corresponding mechanical properties measured, the performance optimization approach and controlling scheme were obtained by comparison of these measurement of these specimens. This promising project will provide a theoretical support for the performance controlling and industrial manufacturing of these difficult-to-deformation and large non-rectangular section workpieces.

铸坯热辗扩复合成形工艺已成为一种制造大型复杂件的新工艺并不断得到关注，目前该工艺的控形技术趋于完善而控性技术仍存在瓶颈，其热变形晶粒细化和热处理性能调控机理亟待解决。以一种特殊用钢（0Cr11Ni2MoVNb马氏体不锈钢）盘件为例，考虑辗前晶粒的不均匀影响，利用热变形再结晶的细晶强化理论和热处理马氏体相变促进高密度纳米相析出的相变强化理论来提高性能。采用模拟与实验相结合以研究其纳米相、细化晶粒及热处理。根据不同参数下热压缩实验所测得的晶粒尺寸大小，建立不同温度和时间下的晶粒长大模型和再结晶模型；耦合含热物性参数的材料模型、晶粒模型和晶体塑性有限元，重点研究热辗扩再结晶过程中晶粒尺寸演变规律，实现对晶粒尺寸的定量预测；分析热压缩试样在热处理实验下的组织、合金相及晶粒尺寸，结合力学性能测试结果，比较得出性能优化途径及调控方案。本研究可为难变形大型非矩形截面件的性能控制及工业化制造提供理论支撑。

X6CrNiMoVNb11-2钢（国内牌号06Cr11Ni2MoVNb钢或0Cr11Ni2MoVNb），类似于俄罗斯牌号ЭП609钢，是一种高强马氏体不锈钢，具有较好的淬透性，用于制造我国研制的重型燃气轮机涡轮盘。通过缩比实验研究了涡轮盘的热变形成形工艺参数、流变行为及热处理后的力学性能。首先，通过热模拟压缩试验，研究了X6CrNiMoVNb11-2钢盘件在成形温度为950℃~1160℃，应变速率为0.01s-1~10s-1条件下的流变应力与应变速率、变形温度之间的关系。同时，建立了热压缩本构模型，得到不同变形程度时变形激活能等值线图，分析了温度、应变速率和应变对变形激活能的影响，为有限元模拟提供了基础。此外，构建了热加工图，获得了热变形最佳工艺参数，即：变形温度1000℃~1100℃，应变速率0.01s-1~0.1s-1。在盘件铸轧控形基础上，通过热物性参数计算、热处理实验、金相分析、性能测试等手段对调质处理中马氏体相变过程进行组织与性能调控，得到不同回火工艺下的回火硬度方程。研究发现了回火中分散在层状马氏体中的M23C6碳化物和回火过形成的高密度共晶纳米晶沉淀相（Ni3Mo和Ni3Nb），同时提高强度与韧性，揭示了热处理相变强化机理。与此同时，研究了热变形微观组织演变及调质工艺对力学性能的影响。研究表明：调质处理中油淬回火空冷后的马氏体组织细小均匀，随着回火温度从550℃升至650℃时，抗拉强度降低，延伸率增大；回火650℃保温1.5h后的晶粒尺寸比较于2h更加均匀细小；采用淬火油冷比淬火空冷得到马氏体组织晶粒更细小；淬火后拉伸断口形貌为大量微裂纹、韧窝以及第二相粒子，断裂优先于第二相粒子处，使塑性下降；回火后断口颈缩明显，放射区占比大，纤维区占比小，呈韧性断裂特征。最佳热处理工艺参数为：1040℃淬火油冷，650℃回火空冷，最终平均硬度为313HV，伸长率为17.9%，断面收缩率为52%，冲击韧性为65J，满足了零件性能指标和使用要求。最终，确立了较完整的涡轮盘铸辗轧制成形工艺优化方案及轧后最佳热处理工艺参数，同时完善了热变形细晶强化、热处理工艺优化和相变强化的相关理论，该研究可为航空类马氏体不锈钢盘件制造与应用一体化的研发提供理论依据。