Environment-assisted cracking of 21/4Cr-1Mo steel in fused sodium hydroxide at 623 K, 1 atm-I. Electrochemistry in relation to stress corrosion cracking

The electrochemistry of fused sodium hydroxide has been reviewed, demonstrating the importance of its acid-base properties. The latter are reflected in the electrochemistry of iron which forms relatively insoluble oxide and ferrate in acidic conditions, but highly soluble ferrate in basic conditions. 21/4Cr-1Mo steel was shown to behave similarly to iron, passivating only in acidic melts. Major shifts were observed in the free-corrosion potential, brought about by changes in the water and/or oxygen concentrations in the melt, which are of likely significance to the stress corrosion behaviour of the material. (author)