核电焊接接头空化水射流冲击表面强化及其缓解应力腐蚀机制

The stainless steel (SS) welded joint of the safe-end in Pressurized Water Reactor (PWR) usually contains ferrite phase. After long-term service at high temperature, the spinodal decomposition and other thermal ageing sensitive microstructures of ferrite phase in the welded joint will be produced. At the same time the welded joint also endures severe corrosion at high temperature water and complex stresses. Therefore, stress corrosion cracking (SCC) of thermal-aged SS welded joint is unavoidable. Cavitation water jet treatment can transform surface microstructure to form compressive stress layer and then reduce SCC sensitivity. It is an effective SCC mitigation technology. Nowadays the effect mechanism of cavitation water jet treatment on the surface microstructure of thermal-aged SS welded joints is still unclear. Further the effect mechanism of thermal-aged ferrite phase and austenite phase transformation and residual stress distribution caused by cavitation water jet treatment on SCC is also unknown. It is necessary to establish the theoretical basis for the mitigation of SCC in the key components. Therefore, the thermal-aged domestic safe-end SS welded joint is studied in this work. The change of surface microstructure of the thermal-aged SS welded joint by cavitation water jet treatment and the effect of cavitation water jet treatment on SCC initiation and expansion behaviours are performed to completely clarify the SCC mitigation mechanism by cavitation water jet treatment in high temperature water. Eventually, a technology based on cavitation water jet treatment helped mitigate SCC behaviour of welded joints after the long-term service is developed.

压水堆核电站一回路安全端不锈钢焊接接头材料通常含有铁素体相。长期在高温环境下服役，铁素体相会发生调幅分解等反应产生热老化敏感组织，同时焊接接头又面临高温高压水苛刻腐蚀且承受复杂应力作用，因此存在应力腐蚀开裂（SCC）失效问题。空化水射流处理可以调控表层组织，形成压应力层，降低SCC敏感性，是一种有效的老化缓解技术。目前空化水射流处理对热老化不锈钢焊接接头表层组织调控机制尚不明确，由空化水射流处理造成的热老化铁素体相和奥氏体组织转变以及表面残余应力分布对SCC影响机制尚需澄清，缺乏核电关键材料及部件服役行为缓解工作的理论依据，因此本项目以热老化国产一回路安全端不锈钢焊接接头为研究对象，开展空化水射流处理对热老化不锈钢焊接接头的表层组织调控研究及其对SCC萌生和扩展行为影响研究，完整阐明空化水射流处理对高温高压水环境SCC影响机制，并以此为基础开发焊接接头长期服役老化行为的缓解技术。

压水堆核电站一回路安全端焊接接头长期在高温高压水环境下服役，存在应力腐蚀开裂（SCC）失效问题。空化水射流冲击表面强化处理可以调控表层组织，形成压应力层，降低SCC敏感性。本项目采用微观分析、空化水射流处理试验及高温高压水环境SCC试验等手段，研究了空化水射流冲击表面强化处理后焊接接头材料表层组织结构特征、表面粗糙度、表层残余应力分布等特征规律，以及空化水射流冲击表面强化处理对焊接接头材料高温高压水环境SCC行为的缓解规律，阐明了空化水射流冲击表面强化处理对高温高压水环境SCC的缓解机制，可为安全端焊接接头SCC行为缓解技术现场应用提供基础。