Abstract
Electrochemical reaction for a CrMoV rotor steel in 2,4-dinitrobenzoic acid solutions has been investigated to explain a characteristic correlation between the open circuit potential and the embrittlement level of the steel. Despite relatively low pH of the solution (pH < 3), the cathodic reaction was not hydrogen evolution, and the observed limiting current had no linear relation with hydronium ion concentration. From analytical investigations on the reaction product, it was proved that 2,4-dinitrobenzoic acid was reduced to 2-nitro-4-aminobenzaldehyde on the steel surface. It was shown that this reaction was controlled by diffusion of both 2,4-dinitrobenzoic acid (or its dissociated ions) and hydronium ion, and was not influenced by the embrittlement level of the steel. On the other hand, anodic dissolution was largely affected by the embrittlement level and became inactive with embrittlement progress. Microstructural observation showed that the dislocation density for embrittled steel was much lower than that for unembrittled steel. That is, the aging of the steel caused the reduction of dislocation density, concurrently with embrittlement. Thus, it was concluded that the shift in the open circuit potential with the progress in the embrittlement level was caused by the inactivation in the anodic dissolution reaction due to the microstructure change such as dislocation density reduction.
Published Version
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