Grain Boundary Corrosion of AISI Type 304L Steel in an H₂SO₄/NaCl Environment

In a 5N H₂SO₄-0.1N NaCl solution the intergranular fracture found in an AISI Type 304L steel is not produced by stress corrosion cracking (SCC) but by grain boundary corrosion. A necessary prerequisite for this phenomenon is plastic deformation, but an applied tensile stress state is not needed. The same kind of selective corrosion also occurs at the twin boundaries. When the chloride ion concentration is raised from 0.1N to 0.5N, the selective corrosion of grain and twin boundaries ceases to exist and only shallow grooving of the grain boundaries is observable on the metal surface.