碳钢中磷的偏析对坑孔腐蚀的影响

选择五种具有不同冶金特点的碳钢，通过模拟蚀孔的闭塞腐蚀电池试验及室内挂片试验，研究了轧制钢板中磷偏析对坑孔腐蚀扩展的影响。结果表明，磷偏析是形成蚀坑内梯田状腐蚀形态的主要原因；磷偏析及较低的磷含量都加速蚀坑的发展；沿轧向延伸的磷偏析带及夹杂物导致了蚀坑沿平行板面方向的腐蚀扩展速度大于垂直方向的扩展速度。

EFFECT OF PHOSPHORIC SEGREGATION ON THE PITTING IN CARBON STEELS

Using OCC simulative test and indoor exposure test,the effect of phosphoric segregation on pitting propagation of five rolling carbon steels with different metallurgical feature has been studied.The results showed that the phosphoric segregation was the main cause of forming stair-shape corrosion on the wall of pits.Due to smaller corrosion inhibition of lower phosphoric zone in steel and its quicker dissolution,phosphoric segregation and lower phosphorus content accelerated propagation of the pit.The extension of phosphoric segregation and inclusions along the rolling direction resulted in higher dissolving speed in the direction which was parallel to the plate surface than that in the direction which was vertical to.Consequently,the caliber of pits in carbon steels was generally larger than its depth.Exposure conditions had important effect on the action of phosphoric segregation.The effect of phosphoric segregation in alternating immersion with dry and wet was stronger than that in stirring immersion ,and that in quiet immersion was the weakest.The stronger oxygen depolarization (i.e.more positive corrosion potential ) and the formation of typical rust tubercle (i.e.acid active region ) were the favorable conditions which enable phosphoric segregation to act.