The chemical state of tungsten in the rust of low-alloy steel was analyzed by electroprobe x-ray microanalysis (EPMA) and x-ray photoelectron spectroscopy (XPS), and the electrochemical behavior of the rust was investigated by the electrochemical impedance spectroscopy (EIS) method after a wet/dry cyclic corrosion test with chloride ions. The 1.0 mass percent tungsten-bearing steel showed high corrosion resistance compared to carbon steel (SM) in the corrosion test. EPMA and XPS showed that tungsten existed as WO_4 compounds in the rust of tungsten-bearing steel. An Fe-W binary potential (E)-pH diagram was made to investigate the thermodynamic stability of Fe-W oxides, and this showed that WO_4 was stable in the rust, which confirmed the results of the physical analysis. An EIS measurement was taken to find the corrosion reaction resistance (R_t) of the rust. R of tungsten-bearing steel was much larger than that of SM. The corrosion of the tungsten-bearing steel was suppressed by the insoluble FeWO_4 formed near the base metal restricting the anodic reaction and the WO_4~(2-) ions in the rust changing the selective permeability to prevent the transport of chloride ions.
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