硫酸盐还原菌对EH40焊接钢海水腐蚀的影响

目的研究无菌和SRB体系中EH40钢焊接接头的母材区、热影响区和焊缝区腐蚀差异。方法利用金相显微镜观察、失重法、电化学测试、扫描电镜和X射线光电子能谱仪等分析手段。结果焊缝区微观组织由块状铁素体(BLF)和魏氏组织(W)组成;热影响区可再分为粗晶区(CGHAZ)和细晶区(FGHAZ)两个区;母材区主要由BLF、AF和少量珠光体组成。在无菌对照体系中,焊缝区腐蚀速率为0.0026 mm/a,混合区次之,为0.0023 mm/a,母材区最小,为0.0019 mm/a。含SRB体系中,各区的腐蚀速率为:焊缝区(0.0037 mm/a)混合区(0.0034 mm/a)母材区(0.0030 mm/a)。热影响区腐蚀产物形貌粗大,点蚀孔也较大。结论焊缝区比母材区容易腐蚀,由此易造成小阳极大阴极加速腐蚀,热影响区容易发生点蚀。SRB能促进三个区域试样腐蚀加速。

Effects of Sulfate-reducing Bacteria on Marine Corrosion of Weld Joints of EH40

Objective To study differences of corrosion of EH40 weld joints in base metal zone, heat affected zone and weld zone in sterile and SRB systems. Methods The metallurgical microscope observation, weight loss method, electrochemical methods, scanning electron microscopy (SEM) and energy dispersive X ray analysis (EDS) were applied. Results Microstructure of weld zone was composed of block lath ferrite (BLF) and widmanstatten structure (W). The heat affected zone was composed of coarse grain heat affected zone (CGHAZ) and fine grain heat affected zone (FGHAZ); the base metal zone was composed of BLF, acicular ferrite(AF) and some pearlite. Corrosion rate decreased in the order of weld zone (0.0026 mm/a)> mixed zone (0.0023 mm/a)>base metal (0.0019 mm/a) when there was no SRB. When SRB was introduced, corrosion rate decreased in the order of weld zone (0.0037 mm/a)>mixed zone (0.0034 mm/a)>base metal (0.0030 mm/a). Furthermore, localized corrosion attack was observed in the heat affected zone. Conclusion The weld area is easier to corrode than the base material zone, causing accelerated corrosion from small anode and large cathodes. The heat affected zone is likely to suffer from localized corrosion. SRB could accelerate corrosion in the three zones.