AP1000核电主管道316LN奥氏体不锈钢热变形过程的组织演变模拟

发布时间：2018-05-21 07:47

本文选题：核电主管道 + 热锻　；参考：《北京科技大学》2015年博士论文

【摘要】：超低碳控氮316LN奥氏体不锈钢,因其具有良好的加工性能、较好的力学性能和耐晶间应力腐蚀性能,在第三代压水堆AP1000核电站中作为一回路主管道材料,是核一级关键装备材料。然而,AP1000主管道设计由二代、二代加的不锈钢分段铸件焊接改为不锈钢整体锻造,制造难度堪称目前世界核电主管道之最。主管道冷段与热段作为超大型锻件,其工艺要同时满足成形与组织控制的目标,其中晶粒度控制是重点。因而,对316LN奥氏体不锈钢在热变形过程中的微观组织演变行为进行较系统的研究,对晶粒变化规律进行模拟,掌握工艺-组织关系规律,可预测实际锻造过程中的晶粒变化,并且为主管道制备工艺的优化提供依据,对微观组织调控技术的发展有着重要的意义。本文采用Gleeble热模拟实验和物理冶金模型计算相结合的方法,系统研究了316LN在锻造过程中的晶粒演变规律以及组织模拟技术。在Gleeble3500热力模拟试验机上,采用单道次轴向热压缩实验研究了316LN不锈钢的高温流变行为,用以模拟其高温锻造过程。基于实验数据,引入Zener-Hollomon参数,建立了Arrhenius型唯象本构方程,用以描述316LN奥氏体不锈钢热变形过程中应变速率、形变温度与应力应变关系。在此基础上,获得了316LN动态再结晶晶粒尺寸演变的经验公式,可以预测一定工艺条件下的锻造组织的晶粒度。通过对热模拟试样高温淬火后显微组织的研究分析,观察了不同形变参数下样品的微观组织,结果表明在关键性的最后一火次锻造时,在316LN奥氏体不锈钢的锻造工艺条件允许的情况下,应尽可能使用较大的压下量,使其充分发生动态再结晶,以获得细化的奥氏体组织。锻造温度在1273K-1423K之间,应变速率在0.1s-1数量级,可以获得完全动态再结晶组织,晶粒尺寸在10μm～15μm范围,远小于AP1000核电主管道所要求的二级晶粒度的尺寸。本文还探讨了316LN奥氏体不锈钢的形变、动态回复、动态再结晶的相互作用,研究了动态再结晶的形核机制,为建立基于物理冶金原理的模型提供了理论依据。由于Arrhenius型唯象型本构方程作为经验模型,普适度欠佳,为了更好地预测316LN奥氏体不锈钢的晶粒变化,建立了以物理冶金原理为基础,综合化学成分、形变和再结晶微观组织演变的热变形奥氏体再结晶模型。模型包括关键的计算模块包括位错密度模块、形核模块、再结晶和析出模块,以及工艺输入模块,常量模块及合金成分输入模块等辅助部分。通过对模型参数的调整,预测316LN奥氏体不锈钢热锻在不同形变条件下的流变应力行为和再结晶行为,并将模拟所得的晶粒尺寸结果与Gleeble热模拟试验所得的晶粒尺寸结果进行对比,两者吻合较好,从而验证了所建微观组织模型的可靠性。此外,利用该物理冶金模型还对具有碳氮化物析出的含Nb微合金钢的热变形行为进行了预测,通过输入不同钢的成分、本征常量以及变形工艺,进行调试,同Gleeble热模拟试验的结果进行对比验证,模拟结果与实验值符合较好,表明该模型可以运用于不同的钢种,具有较好的普适性。
[Abstract]:The ultra - low carbon nitrogen - controlled 316LN austenitic stainless steel is a key equipment material at the nuclear level because of its good processing performance , good mechanical property and intergranular stress corrosion resistance . However , the design of the main pipeline in the third generation PWR AP1000 nuclear power plant is the primary key equipment material . However , the design of the main pipeline in the third generation PWR AP1000 nuclear power plant is the primary key equipment material . However , the main pipeline cooling section and the hot section of the 316LN austenitic stainless steel are used as the super - large forgings . The grain size control is the key point . Therefore , it is important for the development of the microstructure control technology to provide the basis for the optimization of the preparation process of 316LN austenitic stainless steel .

In this paper , Gleeble heat simulation experiment and physical metallurgy model are used to calculate the grain evolution law and tissue simulation technology of 316LN in forging process .

The high temperature rheological behavior of 316LN stainless steel is studied by single - pass axial thermal compression test on Gleeble 3500 thermal simulation testing machine . Based on the experimental data , the Zener - Holden parameter is introduced to describe the relationship between strain rate , deformation temperature and stress strain in 316LN austenitic stainless steel thermal deformation process . Based on the experimental data , the empirical formula of the size evolution of 316LN dynamic recrystallization grain is obtained , and the grain size of forged tissue under certain process conditions can be predicted .

The microstructure of specimens under different deformation parameters is studied by the study of microstructure of hot - simulated specimens after high temperature quenching . The results show that , under the condition that the forging process conditions of 316LN austenitic stainless steel are permitted under the condition of forging process conditions of 316LN austenitic stainless steel , it is possible to obtain complete dynamic recrystallization structure with grain size of 10 渭m ~ 15 渭m , which is far less than the secondary grain size required by AP1000 nuclear power main pipeline . The nucleation mechanism of dynamic recrystallization is studied , which provides the theoretical basis for the establishment of the model based on the principle of physical metallurgy .

The model includes dislocation density module , nucleation module , recrystallization and precipitation module , process input module , constant module and alloy component input module . The model includes the key calculation module including dislocation density module , nucleation module , recrystallization and precipitation module , process input module , constant module and alloy component input module .

In addition , the thermal deformation behavior of Nb - containing microalloy steel with carbon nitride precipitation is predicted by using the physical metallurgy model . By inputting the composition , the intrinsic constant and the deformation process of different steels , the simulation results are compared with the results of the Gleeble thermal simulation test , and the simulation results are in good agreement with the experimental values , indicating that the model can be applied to different steel types , and has good universality .
【学位授予单位】：北京科技大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TG142.71

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