Grain boundary segregation in austenitic stainless steels and its effect on intergranular corrosion and stress corrosion cracking |
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Authors: | C L Briant P L Andresen |
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Affiliation: | (1) Corporate Research and Development Center, General Electric Company, P.O. Box 8, 12301 Schenectady, NY |
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Abstract: | This paper reports a study of grain boundary segregation, intergranular corrosion, and intergranular stress corrosion cracking
in austenitic stainless steels. The results show that phosphorus, nitrogen, and sulfur all segregate to grain boundaries in
these materials and that they can affect one another's segregation through site compctition. In particular, the results demonstrate
that phosphorus segregation can be lowered by the presence of nitrogen and sulfur in the steel. Also, if manganese is present
in the steel, sulfur segregation will be greatly decreased as a result of formation of manganese sulfides. Phosphorus, sulfur,
and nitrogen will not initiate intergranular corrosion in the modified Strauss test, although if corrosion is initiated by
chromium depletion, these elements might enhance the corrosion process. Phosphorus segregation does enhance corrosion in the
Huey test, even in steels that have not undergone grain boundary chromium depletion, although there does not appear to be
a precise correlation between the depth of corrosion penetration and phosphorus segregation. Intergranular stress corrosion
cracking in 288 °C water at a pH of 2.5 and electrochemical potential of OVSHE can occur in these steels even in the absence of chromium depletion if sulfur is present on the grain boundaries. Phosphorus
segregation appears to have very little effect. |
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