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 chemical behavior of the rust was investigated by the electrochemical chemical impedance spectroscopy (EIS) method after a wet/ dry cyclic corrosion test with chloride ions. The 1.0 mass% tungsten-bearing steel showed high corrosion resistance compared to carbon steel (SM) in the corrosion test. EPMA and XPS showed that tungsten existed as WO4 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 WO4 was stable in the rust, which confirmed the results of the physical analysis. An EIS measurement was taken to find the corrosion reaction resistance (Rt) of the rust. Rt of tungsten-bearing steel was much larger than that of SM. The corrosion of the tungsten-bearing steel was suppressed by the insoluble FeWO4 formed near the base metal restricting the anodic reaction and the WO42- ions in the rust changing the selective permeability to prevent the transport of chloride ions.
ASJC Scopus subject areas
- 化学 (全般)