A number in parentheses indicates the year of last reapproval. A superscript epsilon? This standard has been approved for use by agencies of the Department of Defense. Current edition approved April 1, Published April Originally approved in
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A number in parentheses indicates the year of last reapproval. A superscript epsilon? This standard has been approved for use by agencies of the Department of Defense.
Current edition approved April 1, Published April Originally approved in Last previous edition approved in as A — 02a DOI: All stainless grades listed in the accompanying table may be evaluated in these combinations of screening and corrosion tests, except those specimens of molybdenum-bearing grades for example , L, , and L , which represent steel intended for use in nitric acid environments.
The inch-pound equivalents are in parentheses and may be approximate. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
ASTM International. No further reproductions authorized. These lists may contain grades of steels in addition to those given in the rectangles. In such cases, the acid corrosion test is applicable, but not the oxalic acid etch test. NOTE 2—The oxalic acid etch test may be applied to the grades of stainless steels listed in the rectangles when used in connection with the test indicated by the arrow. D Must be tested in nitric acid test when destined for service in nitric acid.
E To date, no data have been published on the effect of sigma phase on corrosion of AISI in this test. Referenced Documents 2. Scope 3. This may be used in connection with other evaluation tests to provide a rapid method for identifying those specimens that are certain to be 3 For referenced ASTM standards, visit the ASTM website, www. Such specimens have low corrosion rates in the various hot acid tests, requiring from 4 to h of exposure.
These specimens are identi? Specimens having acceptable etch structures need not be subjected to the hot acid test. Specimens having nonacceptable etch structures must be tested in the speci? ACI Grade No. A — 10 to the oxalic acid etch test. Apparatus 4.
NOTE 1—The variable resistance and the ammeter are placed in the circuit to measure and control the current on the specimen to be etched. Preparation of Test Specimens 5.
Shearing cold works adjacent metal and affects the response to subsequent sensitization. Microscopical examination of an etch made on a specimen containing sheared edges, should be made on metal unaffected by shearing. A convenient specimen size is 25 by 25 mm 1 by 1 in. Therefore, the preferred sample is a cross section including the surface to be exposed in service.
Only such surface? For very heavy sections, specimens should be machined to represent the appropriate surface while maintaining reasonable specimen size for convenient testing. Ordinarily, removal of more material than necessary will have little in? However, in the special case of surface carburization sometimes encountered, for instance, in tubing or castings when lubricants or binders containing carbonaceous materials are employed it may be possible by heavy grinding or machining to completely remove the carburized surface.
Such treatment of test specimens is not permissible, except in tests undertaken to demonstrate such effects.
Specimens containing welds should include base plate, weld heat-affected zone, and weld metal. Scale should be removed from the area to be etched by grinding to an or grit? This polishing operation can be carried out in a relatively short time since all large scratches need not be removed.
Whenever practical, a polished area of 1 cm2 or more is desirable. If any cross-sectional dimension is less than 1 cm, a minimum length of 1 cm should be polished. When the available length is less than 1 cm, a full cross section should be used. To obtain the correct current density: 5. Gas, which is rapidly evolved at the electrodes with some entrainment of oxalic acid, is poisonous and irritating to mucous membranes.
This increases the resistance of the etching cell. When this occurs, the? One may be cooled in tap water while the other is used for etching. The rate of heating depends on the total current ammeter reading passing through the cell. Therefore, the area etched should be kept as small as possible while at the same time meeting the requirements of desirable minimum area to be etched.
A — 10 6. Steps between austenite matrix and ferrite pools. Deep interconnected ditches. Of importance only when nitric acid test is used. In cases that appear to be dual structures, more extensive examination is required to determine if there are any grains completely encircled. If an encircled grain is found, the steel should be evaluated as a ditch structure.
Areas near surfaces should be examined for evidence of surface carburization. However, any susceptibility to intergranular attack is readily detected by pronounced ditches. If these pits are sharp and so deep that they appear black Fig.
Therefore, even though the grain boundaries all have step structures, specimens having as much or more end grain pitting than that shown in Fig. Such sharp, deep pits should not be confused with the shallow pits shown in Fig.
A — 10 FIG. Steps between austenite matrix and ferrite pools To differentiate between the types of pits, use a magni? The pits which now appear completely black are end grain pits. Deep interconnected ditches 7. Use of Etch Structure Classi?
Important characteristics of each of these tests are described below. It does not detect susceptibility associated This or a greater concentration of end grain pits at using standard etching conditions indicates that the specimen must be tested when screening is for nitric acid test.
It does not detect susceptibility to end grain attack, which is also found only in certain nitric acid environments. The latter may be formed in molybdenum-bearing and in stabilized grades of austenitic stainless steels and may or may not be visible in the microstructure.
This test also reveals susceptibility to end grain attack in all grades of stainless steels. It does not detect susceptibility to intergranular attack associated with sigma phase or end-grain corrosion, both of which have been observed to date only in certain nitric acid environments. It does not detect susceptibility to attack associated with sigma phase. Scope 8. The presence or absence of intergranular attack in this test is not necessarily a measure of the performance of the material in other corrosive environments.
The test does not provide a basis for predicting resistance to forms of corrosion other than intergranular, such as general corrosion, pitting, or stress-corrosion cracking. NOTE 3—See Practice A for information on the most appropriate of the several test methods available for the evaluation of speci? It may also be used to check the effectiveness of stabilizing columbium or titanium additions and of reductions in carbon content in preventing susceptibility to rapid intergranular attack.
It may be applied to wrought products including tubes , castings, and weld metal. The length of time of heating used for this sensitizing treatment determines the maximum permissible corrosion rate for such grades in the ferric sulfate-sulfuric acid test. Rapid Screening Test 9. Preparation, etching, and the classi?
The use of etch structure evaluations in connection with the ferric sulfate-sulfuric acid test is speci? Such specimens are acceptable without testing in the ferric sulfatesulfuric acid test. All specimens having nonacceptable etch structures must be tested in the ferric sulfate-sulfuric acid test.
Apparatus Ditch, Ditch, Ditch, Ditch, 8. It does not detect susceptibility to intergranular attack associated with sigma phase in wrought austenitic stainless steels containing molybdenum, such as Types , L, , and L. The ferric sulfate-sulfuric acid test will detect intergranular corrosion associated with sigma phase in the cast stainless steels CF-3M and CF-8M.
NOTE 4—To detect susceptibility to intergranular attack associated with sigma phase in austenitic stainless steels containing molybdenum, the nitric acid test, Practice C, should be used. A — 10 NOTE 6—No substitutions for this equipment may be used. The cold-? Place the test? Add the acid slowly to the water in the Erlenmeyer? NOTE 7—Loss of vapor results in concentration of the acid.
Overall length: about mm 13 in.
Intergranular Corrosion Testing: An Overview of ASTM A262
The Oxalic Acid test is only used to ensure that no corrosion exists; samples are labeled either "Acceptable" or "Suspect". A different ASTM A test method must be used to quantify the level of corrosion or to disqualify a material for use. The Oxalic Acid test is also only applicable to corrosion associated with chromium carbide precipitates and is only useful for specific material grades. Please refer to the specification for more details. The level of corrosion is determined by mass loss. The samples are weighed at each interval to determine mass loss and degree of susceptibility to intergranular attack. This method is preferable for chromium depletions and corrosion in intermetallic phases.