Hot Corrosion of Some Heat Resisting Alloys by V2O5-Na2SO4-NaCl Mixtures

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Abstract
The accelerated attack in an atmosphere contaminated with vanadate, sulphate, and halide which is often found in alloys for gas turbine or marine diesel has been examined by means of crucible test. Six different materials used for turbine blades or valves were tested in this investigation. Samples partly immersed in mixtures of vanadium pentoxide and sodium sulphate and/or sodium chloride were heated in air at temperatures of 700 and 800°C, and weight losses were determined after descaling. The results obtained are as follows: (1) Mixtures of Na2SO4+0.5-70% NaCl and V2O5+10-40%(Na2SO4+NaCl) were the most corrosive for these materials. (2) At lower temperatures, all alloys were resistant to attack by Na2SO4/NaCl but above about 750°C, they were subject to severe effects. These reactions occurred only in the reducing environments. (3) In the V2O5/Na2SO4 environment, there was a considerable attack for S 590, LCN 155, SUH 3, and SUH 31 at even 700°C. (4) LCN 155 and YA2B were the most corrosion-resistant alloys in the Na2SO4/NaCl environment, but they were subject to some intergranular attack. CRK 22 and YA2B have a comparatively good corrosion resistance in V2O5/Na2SO4mixtures.