1Cr18Ni9Ti不锈钢球头表面腐蚀原因分析

1Cr18Ni9Ti不锈钢球头在焊接后经酸洗,表面存在粗糙的腐蚀凹坑.通过采用S-3700N扫描电子显微镜、能谱分析仪、金相显微镜等对表面粗糙的腐蚀凹坑进行成因分析.结果表明:球头在焊接过程中产生了局部敏化现象,球头的晶粒组织细于与之配合的外套螺母组织,使得球头的耐腐蚀性低于外套螺母,在酸洗去氧化皮的过程中,外套螺母与球头的焊缝区、接管嘴的焊缝区之间形成缝隙,酸洗液中的正负离子移动受到了阻滞,导致缝隙处发生严重腐蚀,最终表现为球头表面的点状腐蚀形貌.定期更换酸洗槽液,降低Cl^-浓度,以及在酸洗过程中活动零件,可以减少该类腐蚀的产生.

Causes for Surface Corrosion of 1 Cr18 Ni9 Ti Stainless Steel Globe

Corrosion pits were found at the surface of a 1Cr18Ni9Ti stainless globe after acid pickling. The causes for the corrosion pits were analyzed by using scanning electron microscopy(SEM), energy dispersive spectrum(EDS), and metallographic microscopy. The results show that the globe became locally sensitized in the welding process. The grain size of the globe was smaller than that of the out nut, and consequently, the corrosion resistance of the globe was weaker than that of the out nut. In the acid pickling process, the gaps formed between the out nut and the globe weld zone as well as between the out nut and the mouth weld zone. The moving of positive and negative ions in the pickling solution was blocked, causing serious corrosion in the gaps. As a result, pitting corrosion was present at the surface of the globe. Periodic replacement of the pickling bath, reducing Cl ion concentration, and moving parts in the pickling process can reduce the generation of such corrosion.