Journal of Materials Engineering and Performance ( IF 2.3 ) Pub Date : 2020-01-02 , DOI: 10.1007/s11665-019-04531-z Juliane Ribeiro da Cruz , Rodnei Bertazzoli
The susceptibility of API-X70 friction stir weld zones to corrosion in a Na2SO4 acid medium is successfully investigated using an innovative microcell setup. Microstructures were characterized by optical and electron microscopy, Vickers microhardness mapping and linear potential scan voltammetry, at micro- and macroscales. Potential galvanic couples between the weld zones were identified. The most anodic zone was base metal, which, with a banded microstructure of ferrite and perlite, developed a potential difference of up to 45 mV in comparison with the adjacent heat-affected zone. Friction stir welding promoted solute redistribution and the formation of martensite/retained austenite constituent, which contributed to reduced galvanic corrosion between ferrite and cementite. The thermo-mechanically affected zone was the most cathodic region, composed of acicular ferrite, coarse bainite and martensite/retained austenite constituent. Polarization resistance progressively increased, and corrosion current density progressively decreased, from base metal toward stir zone. In addition to the reduction in galvanic corrosion, a more uniform distribution of corrosion products in the stir zone also accounted for this behavior.
中文翻译:
使用新型微孔设置表征API X-70钢的摩擦搅拌焊接区内的腐蚀
API-X70摩擦搅拌焊区在Na 2 SO 4中对腐蚀的敏感性使用创新的微池装置成功研究了酸性介质。通过光学和电子显微镜,维氏显微硬度测绘和线性电位扫描伏安法在微观和宏观尺度上对微观结构进行了表征。确定了焊接区域之间的潜在电偶。阳极最多的区域是贱金属,与相邻的热影响区域相比,贱金属具有带状铁素体和珍珠岩的微带状结构,电位差高达45 mV。搅拌摩擦焊接促进了溶质的重新分布和马氏体/残余奥氏体成分的形成,从而有助于减少铁素体与渗碳体之间的电偶腐蚀。受热机械影响的区域是最阴极的区域,由针状铁素体组成,粗贝氏体和马氏体/残余奥氏体成分。从贱金属到搅拌区,耐极化性逐渐提高,腐蚀电流密度逐渐降低。除了减少电偶腐蚀之外,在搅拌区中腐蚀产物的更均匀分布也说明了这种现象。