长期热暴露和高温持久过程中低活化马氏体钢的微观组织演变机制研究

The blanket materials for fusion require very high performance, which long term working in elevated temperature, strong magnetic field and neutron irradiation environment.Reduced Activation Ferritic/Martensitic steels (RAFM) are considered as the primary candidate blanket structural materials for fusion reactor, because of their low irradiation swelling rate, low thermal expansion coefficient, good thermal conductivity, excellent mechanical properties and well-rounded technology basic. Up to now, a large number of researches on RAFM have been done, including alloy composition, heat treatment process, microstructure and mechanical properties before and after irradiation, welding properties, corrosion resistance, and so on. Whereas, some research work is limited, concerning the microstructure evolution mechanism of RAFM during the long term service at elevated temperature.So, the high temperature structure stability of RAFM can not be correctely evaluated. In this project, China Low Activation Martensitic steels (CLAM), which is a kind of RAFM developed by Chinese, will be investigated. The microstructure evolution of CLAM will be researched during long term thermal exposure and endurance testing (up to 30000 h) rang from 500 to 650℃ by means of modern analytical techniques.Some results can be obtained, including alloy elements distribution, pricipitates and martensite laths changing law, building the mathematical and physical models of microstructure evolution as well as evaluating the microstructure stability of CLAM accurately.The results are very important to CLAM for improving properties and engineering application.

聚变反应堆的包层长期工作在高温、强磁场和中子辐照的环境下，对材料的要求极高。低活化铁素体/马氏体钢因其具有较低的辐照肿胀率和热膨胀系数，较高的热导率，优异的力学性能以及相对成熟的技术基础，被普遍认为是聚变反应堆包层的首选结构材料。到目前为止，针对合金成分、热处理工艺、辐照前后的显微组织与力学性能、焊接性能、耐蚀性能等方面已经开展了大量研究工作。关于高温长期服役过程中显微组织演变机制方面的研究非常有限，无法对材料的高温组织稳定性进行正确评价。本课题将以中国自主开发的RAFM钢-CLAM钢为研究对象，采用现代材料分析技术研究CLAM钢在500-650℃范围内长期（30000h）热暴露和持久过程中显微组织的变化规律，掌握CLAM钢中合金元素分布、析出物及马氏体板条等亚结构的演变规律，建立显微组织演变的数理模型，正确评价CLAM钢的组织稳定性，为CLAM钢的性能改进和工程应用提供理论指导。

低活化钢是当前公认的最有希望用于聚变反应堆第一壁的结构材料，在长期高温和应力作用下显微组织和力学性能的稳定性是决定这种材料能否最终得到应用的关键影响因素。为了正确评价低活化马氏体钢在长期高温和应力服役环境下的使用寿命和安全性。本项目以中国低活化马氏体（CLAM）钢为研究对象，系统研究了CLAM钢在高温（500~650℃）长期（长达30000h）热暴露过程中显微组织和力学性能的变化规律，以及高温蠕变变形行为。结果显示，随着热暴露的进行，原奥氏体晶粒尺寸没有明显长大，马氏体板条尺寸不断长大，析出物的总体数量和尺寸均发生了一定变化，M23C6型碳化物尺寸和数量增加，MX型碳化物尺寸和数量均没有明显变化，Laves相集中在550~600℃析出，并且随着热暴露的进行尺寸缓慢长大。在热暴露5000h以内，力学性能变化显著，经过10000h热暴露后，力学性能变化曲线趋于平缓，直到经过30000h的热暴露，力学性能也没有发生显著的变化。建立了蠕变寿命的预测模型，能够比较准确的预测CLAM的服役寿命，明确了CLAM钢在长期高温和应力作用显微组织的演变机制，研究结果对CLAM钢的工程应用和性能改进能够提供一定的理论指导。