1、Designation: A262 10Standard Practices forDetecting Susceptibility to Intergranular Attack in AusteniticStainless Steels1This standard is issued under the fixed designation A262; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the
2、year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.This standard has been approved for use by agencies of the Department of Defense.1. Scope*1.1 These practices cover the fo
3、llowing five tests:1.1.1 Practice AOxalic Acid Etch Test for Classificationof Etch Structures of Austenitic Stainless Steels (Sections 3 to7, inclusive),1.1.2 Practice BFerric SulfateSulfuric Acid Test forDetecting Susceptibility to Intergranular Attack in AusteniticStainless Steels (Sections 8 to 1
4、4, inclusive),1.1.3 Practice CNitric Acid Test for Detecting Suscepti-bility to Intergranular Attack in Austenitic Stainless Steels(Sections 15 to 21, inclusive),1.1.4 Practice ECopperCopper SulfateSulfuric AcidTest for Detecting Susceptibility to Intergranular Attack inAustenitic Stainless Steels (
5、Sections 22 to 31, inclusive), and1.1.5 Practice FCopperCopper Sulfate50 % SulfuricAcid Test for Detecting Susceptibility to Intergranular Attackin Molybdenum-Bearing Austenitic Stainless Steels (Sections32 to 38, inclusive).1.2 The following factors govern the application of thesepractices:1.2.1 Su
6、sceptibility to intergranular attack associated withthe precipitation of chromium carbides is readily detected in allsix tests.1.2.2 Sigma phase in wrought chromium-nickel-molybdenum steels, which may or may not be visible in themicrostructure, can result in high corrosion rates only in nitricacid.1
7、.2.3 Sigma phase in titanium or columbium stabilizedalloys and cast molybdenum-bearing stainless alloys, whichmay or may not be visible in the microstructure, can result inhigh corrosion rates in both the nitric acid and ferric sulfate-sulfuric acid solutions.1.3 The oxalic acid etch test is a rapid
8、 method of identify-ing, by simple etching, those specimens of certain stainlesssteel grades that are essentially free of susceptibility tointergranular attack associated with chromium carbide precipi-tates. These specimens will have low corrosion rates in certaincorrosion tests and therefore can be
9、 eliminated (screened) fromtesting as “acceptable.”1.4 The ferric sulfatesulfuric acid test, the coppercoppersulfate50 % sulfuric acid test, and the nitric acid test are basedon weight loss determinations and, thus, provide a quantitativemeasure of the relative performance of specimens evaluated. In
10、contrast, the coppercopper sulfate16 % sulfuric acid test isbased on visual examination of bend specimens and, therefore,classifies the specimens only as acceptable or nonacceptable.1.5 In most cases either the 15-h coppercopper sul-fate16 % sulfuric acid test or the 120-h ferric sulfatesulfuricacid
11、 test, combined with the oxalic acid etch test, will providethe required information in the shortest time. All stainlessgrades listed in the accompanying table may be evaluated inthese combinations of screening and corrosion tests, exceptthose specimens of molybdenum-bearing grades (for example316,
12、316L, 317, and 317L), which represent steel intended foruse in nitric acid environments.1.6 The 240-h nitric acid test must be applied to stabilizedand molybdenum-bearing grades intended for service in nitricacid and to all stainless steel grades that might be subject to endgrain corrosion in nitric
13、 acid service.1.7 Only those stainless steel grades are listed in Table 1 forwhich data on the application of the oxalic acid etch test and ontheir performance in various quantitative evaluation tests areavailable.1.8 Extensive test results on various types of stainless steelsevaluated by these prac
14、tices have been published in Ref (1).21.9 The values stated in SI units are to be regarded asstandard. The inch-pound equivalents are in parentheses andmay be approximate.1.10 This standard does not purport to address all of thesafety problems, if any, associated with its use. It is theresponsibilit
15、y of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use. (Specific precau-tionary statements are given in 5.6, 11.1.1, 11.1.9, and 35.1.)1These practices are under the jurisdiction of ASTM Committee
16、A01 on Steel,Stainless Steel and Related Alloys and are the direct responsibility of SubcommitteeA01.14 on Methods of Corrosion Testing.Current edition approved April 1, 2010. Published April 2010. Originallyapproved in 1943. Last previous edition approved in 2008 as A262 02a (2008).DOI: 10.1520/A02
17、62-10.2The boldface numbers in parentheses refer to the list of references found at theend of these practices.1*A Summary of Changes section appears at the end of this standard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.2. Refere
18、nced Documents2.1 ASTM Standards:3A370 Test Methods and Definitions for Mechanical Testingof Steel Products2.2 ISO Standard:4ISO 3651-2 Determination of Resistance to IntergranularCorrosion of Stainless SteelsPart 2: Ferritic, Austenitic,and Ferritic-Austenitic (Duplex) Stainless SteelsCorrosion Tes
19、t in Media Containing Sulfuric AcidPRACTICE AOXALIC ACID ETCH TEST FORCLASSIFICATION OF ETCH STRUCTURES OFAUSTENITIC STAINLESS STEELS (2)3. Scope3.1 The oxalic acid etch test is used for acceptance ofmaterial but not for rejection of material. This may be used inconnection with other evaluation test
20、s to provide a rapidmethod for identifying those specimens that are certain to befree of susceptibility to rapid intergranular attack in these othertests. Such specimens have low corrosion rates in the varioushot acid tests, requiring from 4 to 240 h of exposure. Thesespecimens are identified by mea
21、ns of their etch structures,which are classified according to the following criteria:3.2 The oxalic acid etch test may be used to screenspecimens intended for testing in Practice BFerric Sulfate-Sulfuric Acid Test, Practice CNitric Acid Test, PracticeECopper-Copper Sulfate16 % SulfuricAcid Test, and
22、 Prac-tice FCopper-Copper Sulfate-50 % Sulfuric Acid Test.3.2.1 Each practice contains a table showing which classi-fications of etch structures on a given stainless steel grade areequivalent to acceptable, or possibly nonacceptable perfor-mance in that particular test. Specimens having acceptable e
23、tchstructures need not be subjected to the hot acid test. Specimenshaving nonacceptable etch structures must be tested in thespecified hot acid solution.3.3 The grades of stainless steels and the hot acid tests forwhich the oxalic acid etch test is applicable are listed in Table2.3.4 Extra-low-carbo
24、n grades, and stabilized grades, such as304L, 316L, 317L, 321, and 347, are tested after sensitizingheat treatments at 650 to 675C (1200 to 1250F), which is therange of maximum carbide precipitation. These sensitizingtreatments must be applied before the specimens are submitted3For referenced ASTM s
25、tandards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.4Available from International Organization for Standardization (ISO), 1 rue deVarem
26、b, Case postale 56, CH-1211, Geneva 20, Switzerland, http:/www.iso.ch.TABLE 2 Applicability of Etch TestAISI Grade No. ACI Grade No.Practice BFerric Sulfate-Sulfuric Acid Test 304, 304L, 316, 316L, 317, 317L CF-3, CF-8, CF-3M,CF-8MPractice CNitric Acid Test 304, 304L CF-8, CF-3Practice ECopper-Coppe
27、r Sulfate-16 % Sulfuric Acid Test 201, 202, 301, 304, 304L, 304H, 316, 316L, 316H, 317, 317L, 321, 347 . . .Practice FCopper-Copper Sulfate-50 % Sulfuric Acid Test . . . CF-8M, CF-3MTABLE 1 Application of Evaluation Tests for Detecting Susceptibility to Intergranular Attack in Austenitic Stainless S
28、teelsNOTE 1For each corrosion test, the types of susceptibility to intergranular attack detected are given along with the grades of stainless steels in whichthey may be found. These lists may contain grades of steels in addition to those given in the rectangles. In such cases, the acid corrosion tes
29、t is applicable,but not the oxalic acid etch test.NOTE 2The oxalic acid etch test may be applied to the grades of stainless steels listed in the rectangles when used in connection with the test indicatedby the arrow.OXALIC ACID ETCH TESTAISIA: 304, 304L AISI: 304, 304L, 316, 316L,317, 317LAISI: 201,
30、 202, 301, 304,304L, 304H, 316, 316L,316H, 317, 317L, 321, 347ACI: CF-3M, CF-8M,ACIB: CF-3, CF-8 ACI: CF-3, CF-8, CF-3M,CF-8MNitric Acid TestC(240hinboiling solution)Ferric Sulfate-Sulfuric Acid Test(120 h in boiling solution)Copper-Copper Sulfate-Sulfuric Acid Test (15 hin boiling solution)Copper-C
31、opper Sulfate-50 % Sulfuric AcidTesting Boiling SolutionChromium carbide in: 304,304L, CF-3, CF-8Chromium carbide and sigmaphase in:D316, 316L, 317,317L, 321, 347, CF-3M, CF-8MEnd-grain in: all gradesChromium carbide in: 304,304L, 316, 316L, 317, 317L,CF-3, CF-8Chromium carbide and sigmaphase in: 32
32、1, CF-3M, CF-8MEChromium carbide in: 201,202, 301, 304, 304L, 316,316L, 317, 317L, 321, 347Chromium carbide in: CF-3M,CF-8M, 316TiAAISI: American Iron and Steel Institute designations for austenitic stainless steels.BACI: Alloy Casting Institute designations.CThe nitric acid test may be also applied
33、 to AISI 309, 310, 348, and AISI 410, 430, 446, and ACI CN-7M.DMust be tested in nitric acid test when destined for service in nitric acid.ETo date, no data have been published on the effect of sigma phase on corrosion of AISI 347 in this test.A262 102to the oxalic acid etch test. The most commonly
34、used sensitiz-ing treatment is1hat675C (1250F).4. Apparatus4.1 Source of Direct CurrentBattery, generator, or recti-fier capable of supplying about 15 V and 20 A.4.2 AmmeterRange 0 to 30 A (Note 1).4.3 Variable Resistance (Note 1).4.4 CathodeA cylindrical piece of stainless steel or,preferably, a 1-
35、qt (0.946-L) stainless steel beaker.4.5 Large Electric ClampTo hold specimen to be etched.4.6 Metallurgical MicroscopeFor examination of etchedmicrostructures at 250 to 500 diameters.4.7 Electrodes of the Etching CellThe specimen to beetched is made the anode, and a stainless steel beaker or a piece
36、of stainless steel as large as the specimen to be etched is madethe cathode.4.8 ElectrolyteOxalic acid, (H2C2O42H2O), reagentgrade, 10 weight % solution.NOTE 1The variable resistance and the ammeter are placed in thecircuit to measure and control the current on the specimen to be etched.5. Preparati
37、on of Test Specimens5.1 CuttingSawing is preferred to shearing, especially onthe extra-low-carbon grades. Shearing cold works adjacentmetal and affects the response to subsequent sensitization.Microscopical examination of an etch made on a specimencontaining sheared edges, should be made on metal un
38、affectedby shearing. A convenient specimen size is 25 by 25 mm (1 by1 in.).5.2 The intent is to test a specimen representing as nearly aspossible the surface of the material as it will be used in service.Therefore, the preferred sample is a cross section including thesurface to be exposed in service
39、. Only such surface finishingshould be performed as is required to remove foreign materialand obtain a standard, uniform finish as described in 5.3. Forvery heavy sections, specimens should be machined to repre-sent the appropriate surface while maintaining reasonablespecimen size for convenient tes
40、ting. Ordinarily, removal ofmore material than necessary will have little influence on thetest results. However, in the special case of surface carburiza-tion (sometimes encountered, for instance, in tubing or castingswhen lubricants or binders containing carbonaceous materialsare employed) it may b
41、e possible by heavy grinding ormachining to completely remove the carburized surface. Suchtreatment of test specimens is not permissible, except in testsundertaken to demonstrate such effects.5.3 PolishingOn all types of materials, cross sectionalsurfaces should be polished for etching and microscop
42、icalexamination. Specimens containing welds should include baseplate, weld heat-affected zone, and weld metal. Scale should beremoved from the area to be etched by grinding to an 80- or120-grit finish on a grinding belt or wheel without excessiveheating and then polishing on successively finer emery
43、 papers,No. 1,12 ,10 ,20 , and30 , or finer. This polishing operationcan be carried out in a relatively short time since all largescratches need not be removed. Whenever practical, a polishedarea of 1 cm2or more is desirable. If any cross-sectionaldimension is less than 1 cm, a minimum length of 1 c
44、m shouldbe polished. When the available length is less than 1 cm, a fullcross section should be used.5.4 Etching SolutionThe solution used for etching isprepared by adding 100 g of reagent grade oxalic acid crystals(H2C2O42H2O) to 900 mL of distilled water and stirring untilall crystals are dissolve
45、d.5.5 Etching ConditionsThe polished specimen should beetched at 1 A/cm2for 1.5 min. To obtain the correct currentdensity:5.5.1 The total immersed area of the specimen to be etchedshould be measured in square centimetres, and5.5.2 The variable resistance should be adjusted until theammeter reading i
46、n amperes is equal to the total immersed areaof the specimen in square centimetres.5.6 Etching Precautions:5.6.1 WarningEtching should be carried out under aventilated hood. Gas, which is rapidly evolved at the electrodeswith some entrainment of oxalic acid, is poisonous andirritating to mucous memb
47、ranes.5.6.2 A yellow-green film is gradually formed on thecathode. This increases the resistance of the etching cell. Whenthis occurs, the film should be removed by rinsing the inside ofthe stainless steel beaker (or the steel used as the cathode) withan acid such as 30 % HNO3.5.6.3 The temperature
48、of the etching solution graduallyincreases during etching. The temperature should be keptbelow 50C by alternating two beakers. One may be cooled intap water while the other is used for etching. The rate ofheating depends on the total current (ammeter reading) passingthrough the cell. Therefore, the
49、area etched should be kept assmall as possible while at the same time meeting the require-ments of desirable minimum area to be etched.5.6.4 Immersion of the clamp holding the specimen in theetching solution should be avoided.5.7 RinsingFollowing etching, the specimen should bethoroughly rinsed in hot water and in acetone or alcohol toavoid crystallization of oxalic acid on the etched surface duringdrying.5.8 On some specimens containing molybdenum (AISI 316,316L, 317, 317L), which are free of chromium carbidesensitization,
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