Modification of the ASTM Standard Ferric Sulfate-Sulfuric Acid Test and Copper-Copper Sulfate-Sulfuric Acid Test for Determining the Degree of Sensitization of Ferritic Stainless Steels

The ASTM standard ferric sulfate-sulfuric acid test (ASTM A262-B) and copper-copper sulfate-sulfuric acid test (ASTM A262-E) have been modified to quantify the degree of sensitization (DOS) of ferritic stainless steel Types 430, 430 Ti, 430 Nb, 434, 444, and 446. The modified ferric sulfate-sulfuric acid test consists of a 24-hour immersion in 600 ml of a boiling solution of 50% (by weight) sulfuric acid plus 40 g of ferric sulfate. The modified copper-copper sulfate-sulfuric acid test consists of a 24-hour immersion in 600 ml of a boiling solution of 50% (by weight) sulfuric acid plus 72 g of copper sulfate. The final corrosion rate of a specimen expressed in units of mm per year (in. per month) is used as the measure of the degree of sensitization. The modified ferric sulfate-sulfuric acid test should not be utilized for stainless steels containing titanium and/or niobium, such as Types 430 Ti, 430 Nb, and 444 stainless steels, since titanium and/or niobium carbonitrides are not stable in this test solution.