核级不锈钢焊接区机加工表面激光喷丸的抗应力腐蚀改性机理

In order to meet the requirement of long-life service of components in reliable nuclear reactor subjecting to high-temperature, high-pressure and corrosive water, the laser shock peening modification mechanism against stress corrosion cracking (SCC) and the control methodology of surface integrity for the machined stainless steel nuclear weldments are to be investigated.Firstly, the evolvement of microstructure and mechanical properties of the surface and subsurface due to machining and laser shock peening will be examined concerning structure, process and surface integrity of the stainless steel nuclear weldments. Then, the relationship between resistance to stress corrosion cracking and the surface integrity which is induced from machining and laser shock peening on weldments will be explored respectively by means of experiments and simulation. Followed, the relation model of crack initiation and crack propagation in SCC against surface integrity is to be established, with the consideration of plastic deformation, surface hardening, residual stress, martensitic transformation, grain refinement of machined stainless steel nuclear weldments. Finally, the optimal process plan for stainless steel nuclear weldments with machining and laser shock peening against SCC will be developed based on the relationship among process parameters, surface integrity and SCC behavior. The research will broaden the application of laser shock peening with the progress in fundamental exploration on anti-SCC modification mechanism.

针对核电装备高温高压水腐蚀环境下的使役工况，研究奥氏体不锈钢焊接区机加工表面激光喷丸抗应力腐蚀改性机理与表面完整性控制方法。探索机械加工和激光喷丸对奥氏体不锈钢焊缝表面完整性状态的影响规律，阐明机械加工和激光喷丸过程中不锈钢焊接件表面及亚表面应力应变状态和微观组织结构的演化机理。开展核级不锈钢焊缝机加工表面激光喷丸强化的抗应力腐蚀改性实验与仿真分析，揭示应力腐蚀的裂纹萌生敏感性及裂纹扩展速率与奥氏体不锈钢焊接件塑性变形、表面硬化特征、残余应力状态、马氏体相变、晶粒细化程度的关联关系。基于"加工工艺参数-表面完整性状态-抗应力腐蚀性能"的内在特性，发展核级不锈钢焊接件改性制造的工艺规划方法，掌握核级不锈钢焊接件的抗应力腐蚀控性制造技术，满足同时具有控形和控性要求的核级不锈钢焊接件长寿命高可靠性要求。本项目的研究将丰富不锈钢激光喷丸抗应力腐蚀改性工艺理论，拓展激光冲击强化技术的应用领域。

针对核电装备高温高压水腐蚀环境下的使役工况，研究了奥氏体不锈钢焊接区机加工表面激光喷丸抗应力腐蚀改性机理与表面完整性控制方法。（1）开展了钴基合金Stellite6在316L不锈钢表面的堆焊工艺试验与仿真分析以及机械与抗腐蚀性能研究，揭示了奥氏体不锈钢堆焊工艺参数（焊接电流、试件预热温度、堆焊层间温度和焊后热处理工艺）与其机械及抗腐蚀性能的关联特性。结果表明，焊接电流和层间温度显著影响试件的显微硬度；焊接电流和焊后热处理温度影响试件的抗拉和抗弯强度。该研究成果可以为核主泵水润滑轴承推力盘以及蒸发器等大型容器表面堆焊工艺过程控制提供技术支撑。（2）提出了激光冲击强化对屏蔽套等薄壁件残余应力及扭曲变形的定量影响模型。采用光斑直径约1mm的Nd:YAG脉冲激光，在15ns的脉冲周期中采用12J的脉冲能量，能够在试件两侧表面均产生250MPa的残余压应力而薄壁试件不产生非均匀扭曲变形。该研究成果可以为屏蔽电机主泵薄壁屏蔽套焊缝激光喷丸强化尺寸控制提供理论依据。（3）量化揭示了加工过程中热效应对磨削切向/法向力比和材料去除率的有利影响以及对表面硬度的削弱作用。（4）提出了磨削微裂纹的三维检测与评价方法，采用精密平面磨床逐层磨削以及表面显微观察，获得裂纹在材料表面及深度方向的三维分布，用于不锈钢堆焊件的裂纹分布测量及裂纹控制评价。（5）通过研究激光冲击强化对增材制造材料疲劳性能的影响规律，揭示激光喷丸对焊缝的改性机理：激光喷丸强化工艺能够有效地提高成形零件的显微硬度，产生高幅值大深度的残余应力，同时减小表层气孔的尺寸，降低表层的孔隙率，有效地提高增材制造成形零件的疲劳寿命。