A picric acid-based etch test was found to have the greatest potential for the indirect measurement of phosphorus segregation in NiCrMoV steels. Intergranular depth of penetration was directly dependent on grain boundary phosphorus composition. Electrochemical etching in both calcium nitrate and sodium hydroxide solutions revealed some sensitivity to attack, provided that sufficient phosphorus was present at the boundaries. However, no consistent correlation was observed as a function of grain boundary phosphorus segregation. Peliminary electrochemical testing in the picric acid solution showed promise that phosphorus segregation could be correlated to specimen current density (CD) during intergranular attack (IGA). If this is the case, it may be possible to develop a nondestructive field test for grain boundary phosphorus segregation that would indicate a material’s susceptibility to intergranular embrittlement.

Subject
Acids, Materials, Composition, Correlation, Acid attack, Surfaces, Phosphorus, Solutions, Penetration, Heat, Steel, Grain boundary, Electrochemical potential
National Association of Corrosion Engineers
1986
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