Corrosion behavior of low alloy steels containing Cr, Co and W in synthetic potable water

The corrosion behavior of new alloy steels was investigated using potentiodynamic (PD) tests, electrochemical impedance spectroscopy (EIS) and galvanostatic test in synthetic potable water. PD test results showed that all specimens exhibited active corrosion behavior, and corrosion rate tended to decrease as a result of adding alloying elements. The EIS measurements were taken to determine the polarization resistance (RP) of the rust layer. The RP values of the new alloy steel were much larger than that of carbon steel. Furthermore, more alloying elements led to a remarkable increase in the RP values. The chemical state of alloying elements (Cr, Co and W) in the rust layer of new alloy steels was analyzed by electron probe microanalysis (EPMA) and X-ray photoelectron spectroscopy (XPS). EPMA and XPS results showed that alloying elements existed in protective compounds in the rust layer. Corrosion of the new alloy steels was suppressed by insoluble compound formed near the surface.