Etching Method for Determining Susceptibility to Intergranular Attack in Ferritic Stainless Steels

An etching test has been developed for determining the susceptibility of stainless steels to intergranular corrosion after either heat treatment or welding. For Types 430, 430 Ti, 430 Nb, 434, 444, and 446 ferritic stainless steels, the test consists of etching a polished sample for five minutes in a boiling 60% (by volume) sulfuric acid plus 120 g/liter copper sulfate solution. The same test method can also be applied to Types 304 and 316 austenitic stainless steels. However, for Type 316 stainless steel, a ten minute etch in a boiling 50% (by volume) sulfuric acid plus 120 g/liter copper sulfate solution instead of the above test condition should be utilized. This test is to be used in the same manner as the oxalic acid etch test (ASTM A262-A) for stainless steels, but gives superior results for ferritic alloys and requires less equipment.