材料期刊网

选择Ni-Cu-P和Cr-Cu-P两类典型的耐海水腐蚀钢, 在pH=10的3%(质量分数)NaCl溶液中进行极化实验, 比较了钢的点蚀诱发敏感性; 在3%海盐水中进行间浸挂片实验, 评价了钢的点蚀扩展速度; 利用OM, 电子探针(EPMA), SEM和XRD分析钢中夹杂物、腐蚀形貌和锈层的特征. 结果表明, Cr-Cu-P钢中的点蚀诱发敏感性要低于Ni-Cu-P, 且脱氧程度的差异不会影响到两类钢的耐点蚀性能. 挂片实验结果表明, 两类耐海水腐蚀钢的平均腐蚀速率接近, 但Cr-Cu-P钢的点蚀扩展速率明显大于Ni-Cu-P钢. 在酸化的蚀坑内, Ni提高基体的电位, 而Cr则降低基体的电位.锈层分析结果表明, 两类钢的内锈层组成均主要为Fe₃O₄, α-FeOOH和少量的非晶化合物, 但Cr-Cu-P钢表面的锈层比Ni-Cu-P钢更致密.

Ni–Cu–P and Cr–Cu–P steels are well known as sea water resistance steels, but the effects of alloying elements in steels on corrosion resistance are still not clear. Generally, Cr and Ni are important alloying elements for corrosion resistance but their roles in resisting pitting corrosion still need investigating. In order to understand the effects of Cr and Ni on rust layers and resistance against pitting corrosion, Ni–Cu–P and Cr–Cu–P steels were smelted in vacuum induction melting furnace and examined in the laboratory. Pitting susceptibility of two sea water resistance steels was compared by means of potentiodynamic polarization tests in 3% (mass fraction) NaCl solution. In order to evaluate the pitting propagation of steels, the simulating occluded corrosion cell tests and indoor interval hanging plate tests were performed in artificial sea water and 3% sea salt solution, respectively. The composition of inclusions, corrosive feature and characteristic of rust layer were studied by OM, electron probe micro–analyzer (EPMA), SEM and XRD. The results indicate that Ni–Cu–P steels exhibit stronger pitting susceptibility than Cr–Cu–P steels, and pitting susceptibility of two kinds of steels is not influenced by deoxidizing degrees. The results also suggest that pitting propagation rate of Cr–Cu–P steels is obviously greater than that of Ni–Cu–P steels. In acidified pits, alloying element Ni helps to enhance thermodynamic stability of matrix and improve potential of matrix. However, addition of alloying element Cr tends to lower the potential of matrix in pits. The results of rust layer analysis indicate that the compositions of inner rust layer are Fe₃O₄, α–FeOOH and a small amount of amorphous oxides. However, the rust layer of Cr–Cu–P steels is much more compact than that of Ni–Cu–P steels. It can be observed by SEM and EPMA that Cr in Cr–Cu–P steels is enriched in inner rust layer close to the matrix, while Ni is not found enrichment in inner rust layer of Ni–Cu–P steels.