617B合金管材制备过程对组织影响及控制

发布时间：2018-05-14 04:46

  本文选题：镍基高温合金 + 热挤压　； 参考：《北京科技大学》2017年博士论文

【摘要】：镍基高温合金管材因其优异的性能,在石油化工、能源等民用领域的用量逐渐增加。因为管材需要在严苛的环境下长期安全服役,所以对管材质量提出了更高的要求。但镍基高温合金管材的生产流程较长、组织控制困难,如何生产组织稳定的优质镍基高温合金管材成为一大难题。因此,对镍基高温合金管材生产过程组织控制规律和机理的研究为提高管材质量具有重要的理论和工程应用意义。本研究以617B合金管材生产流程为主线,对生产过程中的组织控制问题展开研究。通过对均匀化程度与动态再结晶之间关联性的研究,提出了低温均匀化的设计思路,利用低温均匀化处理后合金中残余的枝晶为动态再结晶提供形核点,使得动态再结晶增加的同时控制了晶粒度的长大。通过等温热模拟压缩实验,得到了热变形参数对617B合金动态再结晶过程的影响规律。采用多种组织观察手段对其动态再结晶机制进行了研究,证明了617B合金以非连续动态再结晶机制为主、连续动态再结晶机制为辅的形核机制：阐明了高应变速率促进动态再结晶的本质是存储能升高、位错密度和孪晶的增加使形核作用更为强烈,弥补了高速率变形导致的动态再结晶时间不足。因此也就明确了绝热温升并非高速率变形时动态再结晶被促进的唯一因素。基于实验数据分析绘制了617B合金的热加工图,实现了热变形参数与组织演变规律之间的半定量表征；同时建立了617B合金的动态再结晶和晶粒长大模型,将组织演变模型与DEFORM-2D有限元模拟软件相结合,实现了挤压工况对挤压参数和组织演变过程的准确预测。在给定荒管晶粒尺寸要求和设备承载能力条件下,可提供617B管材热挤压的优化工艺范围。对热挤压后的荒管进行固溶和冷轧退火研究,得到了617B合金主要工艺参数：荒管固溶制度1190--1210℃/1 h,冷轧中间退火制度1200℃/30～60 min。长期时效实验结果表明,740H合金在720℃时效至10000 h时无有害相析出,但MC碳化物在时效200 h时即开始发生元素的再分配,成为其他相演变过程中合金元素的“源泉”,而617B合金在720℃时效至5000 h左右时有μ相析出：通过组织观察和定量的相分析,构建了近服役条件下主要析出相之间的元素再分配规律。总之,本文对617B合金管材制备过程中的均匀化、热挤压、冷轧退火等关键环节的组织演变过程进行了系统性的研究和深入的理论分析,对管材制备过程中的组织演变和控制原则提供了实验和理论指导依据。
[Abstract]:Because of its excellent properties, nickel-based superalloy pipes have been used in petrochemical, energy and other civil fields. Because the pipe needs to serve in strict environment for a long time, the quality of the pipe is required to be higher. However, the production process of nickel-based superalloy pipe is long and the structure control is difficult. How to produce high-quality nickel-base superalloy pipe with stable microstructure becomes a big problem. Therefore, the study of microstructure control law and mechanism in the production process of nickel-base superalloy pipes has important theoretical and engineering application significance for improving pipe quality. The main line of this study is 617B alloy pipe production process. Based on the study of the relationship between homogenization degree and dynamic recrystallization, the design idea of low temperature homogenization is put forward. The residual dendrites in the alloy after low temperature homogenization treatment provide nucleation point for dynamic recrystallization. The dynamic recrystallization increases and the grain size growth is controlled. The effect of thermal deformation parameters on the dynamic recrystallization process of 617B alloy was obtained by isothermal thermal simulation compression experiment. The dynamic recrystallization mechanism of 617B alloy was studied by various means of microstructure observation. It was proved that the main mechanism of dynamic recrystallization of 617B alloy was discontinuous dynamic recrystallization. Nucleation mechanism supplemented by continuous dynamic recrystallization mechanism: the essence of high strain rate promoting dynamic recrystallization is the increase of storage energy, and the increase of dislocation density and twin makes nucleation more intense. It makes up for the shortage of dynamic recrystallization time caused by high rate deformation. Therefore, it is clear that adiabatic temperature rise is not the only factor to promote dynamic recrystallization during high rate deformation. Based on the analysis of experimental data, the hot working diagram of 617B alloy has been drawn, and the semi-quantitative characterization between the thermal deformation parameters and the microstructure evolution law has been realized, and the dynamic recrystallization and grain growth model of 617B alloy has also been established. By combining the microstructure evolution model with the DEFORM-2D finite element simulation software, the accurate prediction of extrusion parameters and microstructure evolution process under extrusion conditions is realized. Under the condition of grain size requirement and equipment carrying capacity, the optimum technological range of hot extrusion for 617B pipe can be provided. The solid solution and cold rolling annealing of the hot extruded tube were studied. The main technological parameters of 617B alloy were obtained: the solution system of the waste tube was 1190--1210 鈩，

本文编号：1886416