ASTM A262 Susceptibility to Intergranular Attack in Steel

What Is ASTM A262?

ASTM A262 tests austenitic stainless steel for susceptibility to attack at grain boundaries. Precipitation of chromium carbides can occur at grain boundaries when the material undergoes welding, slow cooling, or any time spent in a temperature range of 425-815 °C, resulting in a chromium-deficient area that is much more reactive than the rest of the grain. MatX Lab offers all five tests covered in ASTM A262. It contains five separate practices, and your specification names which one applies:
Practice A, oxalic acid etch. An electrolytic etch in 10% oxalic acid, examined at 250x to 500x. The resulting structure classifies as step, dual, or ditch. A step structure usually exempts the material from the longer tests.
Practice B, ferric sulfate and sulfuric acid. A 120-hour boiling exposure, evaluated by mass loss and reported as a corrosion rate.
Practice C, nitric acid. The Huey test. Five consecutive 48-hour periods in boiling 65% nitric acid, with mass loss recorded for each period separately.
Practice E, copper, copper sulfate and 16% sulfuric acid. The Strauss test. A 24-hour boiling exposure followed by a bend, with the bent surface examined at 16x for fissures.
Practice F, copper, copper sulfate and 50% sulfuric acid—a 120-hour exposure for molybdenum-bearing grades, evaluated by mass loss.

Practice A is a screening step rather than an acceptance test on its own. It is fast and cheap, and when the etch shows a clean step structure, it saves you the days that the immersion practices take.

ASTM A262 Scope and Applications

Specimen preparation and solution control decide the outcome. The chemistry in these practices is aggressive, and small departures change the result.

Limitations: Practice A tests and having a ditch structure indicate that you move into a more extended practice rather than a failure. Each practice uses a different mechanism; therefore, materials can succeed in one practice and fail in another, which is why specifications list the specific practice. Sigma phase in molybdenum-bearing and stabilized grades reacts well with the nitric acid used in Practice C. That reaction is not carbide sensitization; hence, any failure in Practice C requires metallography interpretation. Practice E depends on the bend, and bending the sample with the wrong mandrel or viewing it at lower magnification can cause the failure to be missed, since some fissures are too tiny to detect in that case. Cut edges are part of the surface, and failure to prepare them properly can overshadow the mass loss test results.

ASTM A262 Specimen Requirements and Test Conditions

Send material with its heat number, product form, and heat treatment condition. A Practice C rate means one thing on solution-annealed plate and something else entirely on as-welded pipe, and without that history the number floats.
Tell us if the specimen came from a failed part. Where the answer matters legally or commercially, we section for metallography alongside the practice rather than only reporting a rate.

ASTM A262 Test Results and Reporting

Your report names the practice, the exposure conditions, and the result in the form the practice defines. Practice A results appear as the classification with representative micrographs at the examination magnification. Mass loss practices report the corrosion rate along with the individual mass measurements, and Practice C shows each of the five periods separately, since a rate that climbs period to period tells you something a single average would hide. Practice E reports the bend result with images of the examined surface.
Samples provenance sits with every result: heat number, product form, condition, and where in the material the coupon came from. Where we sectioned for metallography, we describe depth and morphology of attack with micrographs.

ASTM A262 FAQs