缓冲镍层对轧辊毛化铬镀层耐蚀性的影响

Effect of nickel buffer coating on corrosion resistance of textured chromium coatings applied to rolls

在轧辊用9Cr2Mo钢表面电沉积凸包状毛化铬层,并在毛化铬层与钢基体之间引入缓冲镍层。采用扫描电镜表征了镀铬钢和镀镍/铬钢表面镀层的表面形貌和截面形貌。通过电化学测量和中性盐雾(NSS)试验研究了缓冲镍层的引入对毛化铬镀层腐蚀行为的影响。结果表明,镀镍/铬钢的电化学腐蚀倾向更小。NSS试验后,镀铬钢表面有大量腐蚀产物堆积,其主要成分为FeO和少量铬的氧化物。铬镀层中贯穿性裂纹的存在使得腐蚀介质可以渗透其内部并侵蚀钢基体,产生的腐蚀产物可通过裂纹扩散至镀层表面。相对而言,镀镍/铬钢中生成的腐蚀产物较少,主要为铬的氧化物。由此可见,缓冲镍层的引入通过隔绝腐蚀介质通道,有效抑制了腐蚀产物的形成,进而改善凸包状毛化铬镀层的耐蚀性。

A textured chromium coating with convex hulls at its surface was obtained by electrodeposition on the surface of 9Cr2Mo steel applied to rolls, and a nickel buffer coating was introduced between the textured coating and steel substrate. The surface and cross-sectional morphologies of the Cr-plated steel and Ni/Cr-plated steel were characterized using electron scanning microscope. The effect of the introduction of nickel buffer coating on corrosion behavior of the textured coating was studied by electrochemical measurement and neutral salt spray （NSS） test. It is shown that Ni/Cr-plated steel has a smaller tendency to be corroded. Lots of corrosion products comprised of FeO mainly and a few of chromium oxide were formed on the surface of Cr-plated steel after NSS test. The corrosive medium can corrode the steel substrate due to the existence of penetrating cracks in the chromium coating, which allow the corrosion products to spread onto the surface of coating. In contrast, the Ni/Cr coating has less corrosion products which is mainly consisted of chromium oxide. It can be seen that the introduction of nickel buffer coating effectively inhibits the formation of corrosion products by isolating corrosive media channels, thus improving the corrosion resistance of the textured chromium coatings.