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三峡700MW级大型混流式水轮机转轮由上冠、下环和13-15片叶片组焊而成,重达400余吨,是目前世界上最大的水轮机转轮。上冠、下环和叶片材质均为ZG04Cr13Ni4Mo马氏体不锈钢。ZG0Cr13Ni4Mo马氏体不锈钢具有高强度、高韧性以及良好的焊接性能,其性能与微观组织、化学成分和热处理工艺密切相关。从韩国、日本、欧洲进口的三峡转轮铸件中焊接时有时出现裂纹,分析结果表明该钢中含有大量的δ-铁素体,降低了材料的塑性和韧性。同时,δ-铁素体也会在在腐蚀性的环境中易引起材料的破坏。为了实现水轮机转轮大型铸件的国产化,系统地开展了转轮用ZG04Cr13Ni4Mo马氏体不锈钢的化学成分、显微组织、力学性能、铸造工艺与热处理工艺等关键工艺技术的研究,提出了通过优化化学成分和热处理工艺定量控制ZG04Cr13Ni4Mo马氏体不锈钢中高温δ铁素体和逆变奥氏体两种相,提高了材料的综合性能。在对铸件材料研究的基础上,结合计算机模拟,实现了三峡大型水轮机转轮叶片的近终形制造。水轮机转轮在水电站机组运行中会出现的新问题,如空蚀、腐蚀、磨损、疲劳断裂等。本文讨论了长运行周期大型铸件的前瞻性失效预测所面临的科学问题和挑战。
The Three Gorges 700MW large-scale Francis turbine wheel by the crown, the next ring and 13-15 blade welding unit formed, weighing 400 tons, is the world’s largest turbine runner. The crown, the ring and the blade material are ZG04Cr13Ni4Mo martensitic stainless steel. ZG0Cr13Ni4Mo martensitic stainless steel with high strength, high toughness and good welding performance, its performance and microstructure, chemical composition and heat treatment process are closely related. Cracks sometimes appear in the castings of Three Gorges imported from South Korea, Japan and Europe. The analysis shows that the steel contains a large amount of δ-ferrite, which reduces the plasticity and toughness of the material. At the same time, δ-ferrite can also cause material damage in a corrosive environment. In order to realize localization of large castings of turbine runner, the key technology of ZG04Cr13Ni4Mo martensitic stainless steel for runner, such as chemical composition, microstructure, mechanical properties, casting process and heat treatment process, has been systematically studied. Chemical composition and heat treatment process quantitative control of ZG04Cr13Ni4Mo martensite stainless steel δ ferrite and reverse austenite phase, improve the overall performance of the material. Based on the research of the casting materials and the computer simulation, the near net shape of the turbine blades of the Three Gorges Turbine was realized. Turbine runner in the operation of hydropower units in the new problems that occur, such as cavitation, corrosion, wear, fatigue fracture. This article discusses the scientific issues and challenges facing forward-looking failure prediction of large castings in long run cycles.