Corrosion resistance of refractory metals in high-temperature water

The high-temperature water corrosion resistance of refractory transition metals of group IVa, Va and VIa was studied. Corrosion tests were conducted for 17 kinds of tungsten, 12 kinds of molybdenum and other 9 kinds of metals in flowing water with a dissolved oxygen content of 400 ppb and pH 6–7 at 180, 260 and 320 °C for 200 h. It is shown that the corrosion rate of W and Mo depends strongly on temperature and material. W and Mo are not corroded severely at 180 °C, the corrosion rates are 0.001–0.047 mm/y for W and 0.022–0.029 mm/y for Mo. The heavy alloys are corroded severely at 260 °C, the corrosion rates are 0.141–0.214 mm/y. At 320 °C, significant corrosion attack occurs depending on the materials. CrN coated W shows excellent corrosion resistance, the rate is as low as ≃0.004 mm/y. W–Re and Mo–Re alloys are corroded severely, with a maximum rate of 1.656 mm/y for W–2%Re and 0.405 mm/y for Mo–17.7%Re. Mo shows a considerably higher corrosion resistance than W. All group IVa and Va metals except Nb, as well as Cr, Re and SUS316 at 320 °C show better resistance than Mo.