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Determination of resistance to intergranular corrosion of stainless steels- Part 2
Ferritic, austenitic and ferritic-austenitic (duplex) stainless steels- Corrosion test in media containing sulfuric acid
This part of ISO 3651 specifies methods for the determination of the resistance to intergranular corrosion of ferritic, austenitic and ferritic-austenitic (duplex) stainless steels in media containing sulfuric acid. It also specifies the purposes which may be assigned to the test. The test methods included are:
---Method A: the 16%sulfuric acid/copper sulfate test (Monypenny Strauss test);
---Method B: the 35% sulfuric acid/copper sulfate test;
---Method C: the 40% sulfuric acid/ferric sulfate test
The methods are applicable to stainless steels supplied in the form of cast, rolled or forged products and tubes and intended for use in a mildly oxidizing acid medium(for example, sulfuric acid, phosphoric acid)
This verification applies only to low carbon steels(C≤0.03%)and stabilized steels specified for resistance to intergranular corrosion. The metal is inspected after having undergone a heat treatment for sensitization which can be a heat treatment or welding for sensitization.
In order to verify the intrinsic resistance to intergranular corrosion, it is necessary to carry out a heat treatment for sensitization for stabilized steels and steels with low carbon content.
The sensitization heat treatment can be:
--T1: Heating the specimen at 700℃±10℃ for 30 minutes followed by water cooling;
--T2: Hearing the specimen at 650℃±10℃ for 10 minutes followed by water cooling.
The above defined treatments only apply to austenitic and duplex steels.
The bent test piece shall be examined under low magnification about (10×)，in order to detect cracking.
Cracking that originates at the edge of the specimen should be disregarded. The appearance of deformation lines, wrinkles, or “orange peel” on the surface, without accompanying cracking or fissures, should also be disregarded.