Abstract
Corrosion properties of Mn steel, Cr–Mo steel and 316L stainless steel and effects of surface treatments including Cr or Ni coating, nitriding and oxynitriding on the corrosion resistance of steels were examined in halogen acid gas and solutions. Corrosion behaviours were evaluated by the potentiodynamic polarisation tests in 0·001M HF, HCl and HBr solutions and the exposure test in HBr gas with 1·13 ppm H2O for 24 h. The surface morphology of the tested samples was examined by optical microscope and SEM and the composition of the corrosion product was analysed by EDS after exposure of the tested alloys to HBr gas. The corrosion resistance of Mn steel and Cr–Mo steel were very poor but was considerably improved by Cr or Ni coating. Oxynitriding also reduced the corrosion rate while nitriding was not effective. However the corrosion resistance of steels with Cr, Ni plating or oxynitriding was still much inferior to electropolished 316L stainless steel, which was practically not damaged by corrosion tests in aqueous solutions nor in gas.
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