硫化物夹杂对低碳钢孔蚀扩展的影响

EFFECT OF SULFIDE INCLUSIONS ON PROPAGATION OF PITTING IN CARBON STEELS

选择两种具有不同类型硫化物夹杂的碳钢 ,通过模拟蚀孔的闭塞腐蚀电池试验 ,研究了它们在人工海水中的孔蚀扩展行为。结果表明 ,具有Ⅱ类硫化物的钢的零电流电位明显负于具有Ⅰ类硫化物的钢 ;在同样的阴极极化电位下 ,前者的阳极腐蚀电流明显地大于后者。通过显微分析考察了硫化物夹杂对孔蚀扩展过程的影响。结果发现 ,硫化物夹杂处的腐蚀速度明显高于钢基体 ,从而促进了孔蚀的扩展。由于Ⅱ类硫化物的相界面积远大于Ⅰ类硫化物 ,前者对孔蚀扩展的促进作用也明显地大于后者。

Using OCC simulation test, behavior of pitting propagation of two carbon steels for shipbuilding with different sulfide inclusions in synthetic seawater was studied. Test results showed that the zero current potential of the steel with typeⅡ sulfide was more negative than that of the steel with typeⅠsulfide; and at the same cathodic polarization potential , the anodic dissolution current of the former was greater than that of the latter. The effect of sulfide inclusions on the pitting propagation was examined by means of micro-analysis. It was found that the sulfide accelerated propagation of the pit with a higher dissolution speed than that of the steel matrix. Because typeⅡ sulfide was of the thin piece shape and presented in crowds, the dissolution along it could easily spread from one piece to another. TypeⅠsulfide, with the shape similar to potato or cigar, presented in steel bulk separately. Such that, the dissolution around the latter couldn't spread as the former did. In addition, because typeⅡ sulfide had much larger S_v (phase boundary surface ) than typeⅠsulfide, the corrosion propagation of the macro-pit was accelerated much more quickly by the former than by the latter.