Potentiodynamic polarization and electrochemical impedance spectroscopy ( EIS) were used to investigate the corrosion resistance of 904L stainless steel welding joints in concentrated sulfuric acid, and the corrosion mechanisms were analyzed in brief. Ex-perimental results show that there are no significant changes in cathodic polarization curves of the weld zone and the substrate, both of them are hydrogen reduction reaction process while an opposite trend is seen upon the anodic polarization curves. Compared with the substrate, the corrosion potential of the wilding zone decreases while the anode current increases. Welding contributes to the anode re-action. The corrosion of the substrate and the weld zone is mainly controlled by the electrochemical step. Both Nyquist graphs are simi-lar, which are composed of a single capacitive reactance arc, having a time constant. The corrosion resistance of the substrate is superi-or to the weld zone.%采用动电位极化曲线和电化学阻抗谱研究了904L不锈钢基体和焊接区在浓硫酸溶液中的腐蚀行为，并简要分析其腐蚀机理.实验结果表明：焊接区和基材的阴极极化曲线均为氢还原反应过程，而阳极极化曲线则有较大的差异.焊接区相对于基材，其自腐蚀电位降低且阳极电流增大，焊接对阳极反应起促进作用.904L不锈钢基体和焊接区的腐蚀主要由电化学反应步骤控制，两者的Nyquist图特征相似，均由单一的容抗弧构成，有一个时间常数.基体的耐蚀性能优于焊接区.
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