| Electrochemical methods were employed as nondestructive means of diagnosis of thermal aging embrittlement of cast duplex stainless steels of CF8 and CF8M grade. In polarization experiments conducted in 5wt% CH₃ COOH solution and the mixture of 0.5M H₂SO₄ and 0.01M KSCN, the anodic current density peak increased, with the aging time. SEM observations to investigate what gives rise to the increase of the anodic current density peak, however, indicated that such change was not related to the spinodal decomposition that was known to be the main cause of thermal aging embrittlement. In polarization experiments for CF8 grade specimens conducted in the mixture of 0.05M H₂SO₄ and 0.01M KSCN, two current density peaks, i_(peak1) and i_(peak2_ appeared. i_(peak1) was attributed to preferential dissolution of the ferrite phase and decreased by aging. The decrease of i_(paek1) was caused by the decrease of ferrite dissolution in aged specimens and reflected the degree of spinodal decomposition occurring in the ferrite phase. A correlation was established between the increase of ferrite hardness and Δi_(peak1)/ferrite%. It was suggested that thermal aging embrittlement of duplex stainless steels of CF8 grade could be evaluated nondestructively by electrochemical method. |
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