中文摘要：

研究了X70钢在磷酸盐缓冲溶液中的亚稳态与稳态孔蚀的电化学行为特征．发现Cl^-浓度对X70钢在磷酸盐缓冲溶液中的孔蚀保护电位影响不大，而PO4^3-对X70钢有较强的孔蚀抑制作用，增加PO4^3-浓度，能够有效提高X70钢的孔蚀保护电位．提高缓冲溶液的pH值能够抑制X70钢小孔的形核和生长．X70钢亚稳态小孔形核主要受到铝氧夹杂物的影响，且随着电位的升高，电流波动频率先升后降，而峰值电流则趋于增大．X70钢在磷酸盐缓冲溶液中形成的钝化膜在钝化区内阻抗基本不受电位的影响．

英文摘要：

The electrochemical characteristics of pitting corrosion of X70 pipeline steel in phosphate buffer solution were studied in this paper. It is found that the effect of Cl^- ion on pitting protection potential is neglectable and PO4^3- ion strongly inhibits the nucleation of metastable pitting. Impurities and the surface grooves left by polishing result in the nucleation of metastable pitting. With the increase of the potential, the nucleation frequency increases at first and then drops, while peak current increases continually. The impedance of passive film keeps unchanged when X70 pipeline steel is in passive state. However, the impedance shows an obvious decrease when potential is above pitting potential Eb.