超超临界锅炉用关键材料的制备加工与服役条件下组织演变及性能研究

The development of ultra-supercritical power plants becomes necessary in countries around the world under the high pressure of enhancing thermal efficient, saving energy, and improve environment. Such fast development put forward a high request on the materials’ quality and their service safety for high-parameter boilers. However, microstructure stability and grain boundary embrittlement have become one of critical issues. The present project investigate on the grain boundary embrittlement mechanism and techniques for improving microstructure stability based on two typical materials used for 600 ˚C and 700 ˚C ultra-supercritical boilers. Based on the idea of grain boundary engineering and the manufacturing process of the ultra-supercritical boiler materials in Shanxi Taigang Stainless Steel Co., LTD., the evolution of the microstructure and the grain boundary character distribution during manufacturing process will be studied, and the relationship between the density of coincident site lattice and grain boundary character distribution would be explored. The role of grain boundary character distribution during the microstructure evolution and intergranular precipitation under service condition will be revealed. And the optimum parameter range both for alloy composition controlling and for manufacturing process could thus be achieved. It is hoped that this project would further deepen the understandings about the microstructure aging and performance degradation, as well as extend our understanding about grain boundary engineering and the related strengthening and toughening mechanism. This project can also increase the innovation ability of materials processing, promote the development of the Shanxi coal-based low carbon industry, and promote the regional development of science & technology and the talent construction.

发展超超临界机组是世界各国火力发电提高效率、节约能源、改善环境的必然趋势，这对高参数锅炉材料品质和服役安全性提出了更高要求。长期服役条件下组织稳定性及晶界脆性是超超临界锅炉关键材料已呈现的突出问题。为此，本项目以600℃等级和700℃等级超超临界锅炉典型材料为对象，研究晶界脆性产生机理及改善组织稳定性的技术方法。基于晶界工程思想，结合太钢在超超临界锅炉关键材料的制备流程，研究在制备加工过程中组织和晶界特征分布的变化规律，阐明重合位置点阵密度和晶界特征分布与性能之间的关系，揭示晶界特征分布对服役条件下组织演变、晶界相析出行为的作用机制，提出优化的合金成分和制备工艺控制范围。研究成果将深化对超超临界关键材料在服役过程中组织老化和性能衰退规律的理解，拓展有关合金晶界工程及强韧化机理的认识，增强关键材料国产化制备加工技术的创新能力，推进山西省煤基低碳行业的发展，促进区域科技发展和人才队伍建设。

发展超超临界机组是世界各国火力发电提高效率、节约能源、改善环境的必然趋势。本项目以600℃等级HR3C钢和700℃等级740H合金为对象，系统研究了其在服役条件下的组织与性能演变，服役脆性产生的原因，分析了成分配比和形变+热处理制备工艺对服役过程析出相及性能的影响规律。在服役条件下的组织及性能演变方面，项目明确了HR3C中NbCrN相、MX相，740H中γ’相的弥散析出和稳定存在有效保证了服役条件下的高温强度，而M23C6在晶界的网链状连续析出是服役沿晶脆性的重要原因；项目进一步验证了在HR3C钢中σ相析出并阐明了σ相析出动力学以及影响规律，为长期服役中σ相析出以及脆性加剧现象提出预警；项目发现740H合金在高温服役变形后期晶界迁移及CZ/PFZ区的形成，阐明其本质为相邻晶粒晶界附近的应变梯度诱导晶界迁移以降低局部应变能。在超超临界锅炉用关键材料制备加工与组织性能关系方面，项目构建了HR3C钢和740H合金热变形本构方程和热加工图，基于第一性原理并结合结构单元模型和原子密度径向分布函数，揭示了碳化物易于在晶界析出的原理及与晶界类型的匹配关系，提出适当冷变形/固溶处理工艺可以降低20-50°晶界的比例，促使碳化物在晶界的不连续析出；项目构建了HR3C钢的团簇成分式:[Cr-(Fe10Ni2)](Cr4Ni2)=(Fe53.02Cr24.68Ni22.29 wt.%)，提出通过控制Nb、Ta与C元素的匹配及精纯化制备来改良HR3C钢，有效抑制粗大M23C6和脆性σ相沿晶界析出与聚集，以提高冲击韧性；项目研究结果表明晶粒定向分布可以有效提升冲击韧性，成分均匀化处理的细晶HR3C钢相比粗晶粒钢，可延缓σ相析出，具有更好的冲击韧性。项目成果深化了对超超临界关键材料在服役过程中组织老化和性能衰退规律的理解，推进了山西省煤基低碳行业的发展，促进了区域科技发展和人才队伍建设。