NaCl溶液腐蚀后304不锈钢的射流空蚀特征

Characteristics of Waterjet Cavitation Erosion of 304 Stainless Steel After Corrosion in NaCl Solution

对采用3%NaCl溶液腐蚀后的304不锈钢试样,借助符合ASTM G134标准的射流空蚀实验装置进行空蚀实验,测量表征试样的质量损失、表面微观组织、表面三维形貌和显微硬度,分析304不锈钢试样的空蚀特征,探究腐蚀时间和空蚀时间对空蚀效果的影响。结果表明,腐蚀时间为24 h的试样,空蚀120 min后即进入空蚀衰减阶段。在空蚀前期,空蚀坑的尺寸小且深度较浅;空蚀后期,试样表面的塑性变形加重,大尺寸空蚀坑增多,晶界处的微裂纹沿晶界扩展,最终空蚀坑之间相互连接导致试样表面出现晶界剥落现象。试样的表面粗糙度随着空蚀时间延长而增大;未经3%NaCl溶液腐蚀时的表面粗糙度最大。空蚀时间为120 min时,腐蚀时间为120 h的试样,其表面塑性变形较腐蚀时间为24 h的试样加剧,且晶界处出现微裂纹。3%NaCl溶液的腐蚀起到延缓空蚀的作用,但延缓程度随着腐蚀时间的延长而减小。

The 304 stainless steel specimens were corroded in 3%NaCl solution, and then cavitation erosion experiments were performed on these specimens using an experimental rig that conformed to the ASTM G134 standard. The effects of both the corrosion time and erosion time on cavitation erosion were analyzed. The cavitation erosion characteristics were described via the mass loss, surface microstructure, three-dimensional surface morphology and microhardness. The results show that for the specimen corroded for 24 h, the stage of cavitation erosion attenuation commences at the cavitation erosion time of 120 min. In the early stage of cavitation erosion, erosion pits manifest small size and depth. In the later stage of cavitation erosion, the plastic deformation is intensified and large erosion pits are abundant. Microcracks expand along grain boundaries. Eventually, the interconnection between erosion pits incurs peeling-off of grain boundaries. The surface roughness increases with the cavitation erosion time. Compared to the corroded specimens, the non-corroded specimen demonstrates higher surface roughness after cavitation erosion. As the corrosion time increases from 24 h to 120 h and the cavitation erosion time is remained at 120 min, the plastic deformation is strengthened and microcracks emerge at grain boundaries. The 3%NaCl solution helps to suppress cavitation erosion. Nevertheless, as the corrosion time increases, the suppression effect attenuates.