1、Designation: A763 15Standard Practices forDetecting Susceptibility to Intergranular Attack in FerriticStainless Steels1This standard is issued under the fixed designation A763; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the ye
2、ar 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.1. Scope*1.1 These practices cover the following four tests:1.1.1 Practice WOxalic acid etch test for detecting sus-ceptibil
3、ity to intergranular attack in stabilized ferritic stainlesssteels by classification of the etching structures (see Sections 310).1.1.2 Practice XFerric sulfate-sulfuric acid test for detect-ing susceptibility to intergranular attack in ferritic stainlesssteels (Sections 1116).1.1.3 Practice YCopper
4、-copper sulfate-50 % sulfuric acidtest for detecting susceptibility to intergranular attack in ferriticstainless steels (Sections 1722).1.1.4 Practice ZCopper-copper sulfate-16 % sulfuric acidtest for detecting susceptibility to intergranular attack in ferriticstainless steels (Sections 2329).1.2 Th
5、e following factors govern the application of thesepractices (1-6)2:1.2.1 Practice W, oxalic acid test, is a rapid method ofidentifying, by simple electrolytic etching, those specimens ofcertain ferritic alloys that are not susceptible to intergranularcorrosion associated with chromium carbide preci
6、pitation.Practice W is used as a screening test to avoid the necessity, foracceptable specimens, of more extensive testing required byPractices X, Y, and Z. See Table 1 for a listing of alloys forwhich Practice W is appropriate.1.2.2 Practices X, Y, and Z can be used to detect thesusceptibility of c
7、ertain ferritic alloys to intergranular attackassociated with the precipitation of chromium carbides ornitrides.1.2.3 Practices W, X, Y, and Z can also be used to evaluatethe effect of heat treatment or of fusion welding on suscepti-bility to intergranular corrosion.1.2.4 Table 2 lists the identific
8、ation ferritic stainless steelsfor which data on the application of at least one of the standardpractices is available.1.2.5 Some stabilized ferritic stainless steels may show highrates when tested by Practice X because of metallurgicalfactors not associated with chromium carbide or nitride pre-cipi
9、tation. This possibility must be considered in selecting thetest method. Combinations of alloys and test methods forwhich successful experience is available are shown in Table 1.Application of these standard tests to the other ferritic stainlesssteels will be by specific agreement between producer a
10、nd user.1.3 Depending on the test and alloy, evaluations may beaccomplished by weight loss determination, microscopicalexamination, or bend test (Sections 30 and 31). The choices arelisted in Table 1.1.4 This standard does not purport to address all of thesafety problems, if any, associated with its
11、 use. It is theresponsibility 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. For specific safetyprecautionary statements, see 3.2.5, Section 7, 13.1, and 19.1.2. Referenced Documents2.1 ASTM
12、Standards:3A370 Test Methods and Definitions for Mechanical Testingof Steel Products3. Apparatus3.1 Apparatus for Practice W, Oxalic Acid Etch Test:3.1.1 Source of DCBattery, generator, or rectifier capableof supplying 15 V and 20 A.3.1.2 Ammeter, range 0 to 30 A.3.1.3 Variable Resistance, for contr
13、ol of specimen current.3.1.4 CathodeOne-litre stainless steel beaker or suitablepiece of stainless steel.3.1.5 Electric Clamp, to hold etched specimen.1These practices are under the jurisdiction of ASTM Committee A01 on Steel,Stainless Steel and RelatedAlloys and are the direct responsibility of Sub
14、committeeA01.14 on Methods of Corrosion Testing.Current edition approved March 1, 2015. Published March 2015. Originallyapproved in 1979. Last previous edition approved in 2014 as A763 14. DOI:10.1520/A0763-15.2The boldface numbers in parentheses refer to the list of references appended tothese prac
15、tices.3For referenced ASTM standards, 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.*A Summary of Changes section appears at the end of thi
16、s standardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States13.1.6 Metallurgical Microscope, for examination of etchedstructures at 250 to 500.3.1.7 ElectrodesThe specimen is made the anode and thebeaker or other piece of stainless steel
17、 the cathode.3.1.8 ElectrolyteOxalic acid (H2C2O42H2O) reagentgrade, 10 weight % solution.3.2 Aparatus Common to Practices X, Y, andZSuplementary requirements are noted as required.3.2.1 The apparatus used is shown in Fig. 1.NOTE 1No substitution for this equipment may be used. Thecold-finger type o
18、f condenser with standard Erlenmeyer flasks may not beused.3.2.2 Allihn or Soxhlet Condenser, four-bulb (minimum)with a 45/50 ground-glass joint. Overall length shall be about330 mm (13 in.), with condensing section 241 mm (912 in.).3.2.3 Erlenmeyer Flask, 1-L with a 45/50 ground-glassjoint. The gro
19、und-glass opening is somewhat over 38 mm(112 in.) wide.3.2.4 Glass Cradles (Note 2), can be supplied by a glassblowing shop. The size of the cradles should be such that theycan pass through the ground-glass joint of the Erlenmeyerflask. They should have three or four holes in them to increasecircula
20、tion of the test solution around the specimen.NOTE 2Other equivalent means of specimen support such as glasshooks or stirrups may also be used.3.2.5 Boiling Chips, must be used to prevent bumping. Ithas been reported that violent boiling resulting in acid spillscan occur. It is important to ensure t
21、hat the concentration ofacid does not become more concentrated and that an adequatenumber of boiling chips (which are resistant to attack by thetest solution) are present.43.2.6 Silicone Grease, is recommended for the ground-glassjoint.4Amphoteric alundum granules, Hengar Granules, from the Hengar C
22、ompany,Philadelphia, PA have been found satisfactory for this purpose.TABLE 1 Methods for Evaluating Ferritic Stainless Steels for Susceptibility to Intergranular CorrosionAlloy Time of Test, hEvaluation CriteriaWeight Loss MicroscopicalExaminationBend TestPRACTICE WOXALIC ACID ETCH TEST439 0.025 NA
23、 AANA18Cr-2Mo 0.025 NA AANAXM27 0.025 NA AANAXM33 0.025 NA AANA26-3-3 0.025 NA AANAPRACTICE XFERRIC SULFATE - SULFURIC ACID TEST430 24 AB,CANA446 72 ACXM27 120 ADACNA29Cr-4Mo 120 NAEACNA29Cr-4Mo-2Ni 120 NA ACNAPRACTICE YCOPPER-COPPER SULFATE - 50% SULFURIC ACID TEST446 96 ACANAXM27 120 ADACNAXM33 12
24、0 ADACNA2633 120 ADACNA29-4C 120 ADACNA29Cr-4Mo 120 NA ACNA29Cr-4Mo-2Ni 120 NA ACNAPRACTICE ZCOPPER-COPPER SULFATE - 16% SULFURIC ACID TEST430 24 NA NA no fissures434 24 NA NA no fissures436 24 NA NA no fissures439 24 NA NA no fissures18Cr-2Mo 24 NA NA no fissuresAPolished surface examined at 250 to
25、 500 with a metallurgical microscope (see 3.1.6). All other microscopical examinations are of the corroded surface under 40binocular examination (see Section 27).BA = Applicable.CPreferred criterion, these criteria are the most sensitive for the particular combination of alloy and test.DWeight loss
26、measurements can be used to detect severely sensitized material, but they are not very sensitive for alloys noted with this superscript and may not detectslight or moderate sensitization.ENA = Not applicable.TABLE 2 Steels for Which Test Results are AvailableUNS Designation Alloy Practice(s)S43000 4
27、30AX, ZS43400 434AZS43600 436AZS43035 439 W, ZS44400 18Cr-2Mo W, ZS44600 446AX, YS44626 XM33 W, YS44627 XM27 W, X, YS44660 2633 W, YS44700 29Cr-4Mo X, YS44735 29-4C YS44800 29Cr-4Mo-2NI X, YATypes 430, 434, 436, and 446 are nonstabilized grades that are generally notused in the as-welded or sensitiz
28、ed condition in other than mildly corrosiveenvironments. In the annealed condition, they are not subject to intergranularcorrosion. For any studies of IGA on Types 430, 434, 436, or 446, the indicated testmethods are suggested.A763 1523.2.7 Electrically Heated Hot Plate, or other device toprovide he
29、at for continuous boiling of the solution.4. Preparation of Test Specimens4.1 The preparation of test specimens is common amongPractices X,Y, and Z.Additional requirements are noted wherenecessary.4.2 A specimen having a total surface area of 5 to 20 cm2isrecommended for Practices X, Y, and Z. As-we
30、lded specimensshould be cut so that no more than 13 mm (12 in.) width ofunaffected base metal is included on either side of the weld andheat-affected zone.4.3 The intent is to test a specimen representing as nearly aspossible the surface of the material as used in service. Onlysuch surface finishing
31、 should be performed as is required toremove foreign material and obtain a standard, uniform finishas specified. For very heavy sections, specimens should beprepared to represent the appropriate surface while maintainingreasonable specimen size for convenience in testing.Ordinarily, removal of more
32、material than necessary will havelittle influence on the test results. However, in the special caseof surface carburization (sometimes encountered, for instance,in tubing when carbonaceous lubricants are employed) it maybe possible by heavy grinding or machining to remove thecarburized layer complet
33、ely. Such treatment of test specimensis not permissible, except in tests undertaken to demonstratesuch surface effects.4.4 Sensitization of Test Specimens:4.4.1 Specimens from material that is going to be used in theas-received condition without additional welding or heat treat-ment may be tested in
34、 the as-received condition without anysensitizing treatment.4.4.2 Specimens from material that is going to be welded orheat treated should be welded or heat treated in as nearly thesame manner as the material will experience in service.4.4.3 The specific sensitizing or welding treatment, or both,sho
35、uld be agreed upon between the supplier and the purchaser.4.5 For Practice W, a cross section of the sample includingmaterial at both surfaces and a cross section of any weld and itsheat affected zones should be prepared. If the sample is toothick, multiple specimens should be used. Grind the crosss
36、ection on wet or dry 80- or 120-grit abrasive paper followedby successively finer papers until a number 400 or 3/0 finish isobtained. Avoid excessive heat when dry-grinding.4.6 For Practices X, Y, and Z, all surfaces of the specimenincluding edges should be ground on wet or dry 80- or 120-gritabrasi
37、ve paper. Avoid excessive heat when dry-grinding. Donot use sand- or grit-blasting. All traces of oxide scale formedduring heat treatment must be removed. To avoid scaleentrapment, stamp specimens for identification after heattreatment and grinding.4.7 Degrease and dry the sample using suitable nonc
38、hlori-nated agents.PRACTICE WOXALIC ACID ETCH TEST FORDETECTING SUSCEPTIBILITY TOINTERGRANULAR ATTACK BY CLASSIFICATIONOF MICROSTRUCTURE FOR SCREENING OFCERTAIN FERRITIC STAINLESS STEELS5. Scope5.1 The oxalic acid etch test is intended and may be used forscreening of certain ferritic stainless steel
39、s to precede orpreclude the need for corrosion testing as described in PracticesX, Y, or Z. Specimens with unacceptable microstructuresshould be subjected to Practices X, Y, or Z to better determinetheir susceptibility to intergranular attack. See Table 1 for alisting of alloys for which Practice W
40、is appropriate.6. Etching Conditions6.1 The polished specimens should be etched at 1A/cm2for1.5 min. This may be accomplished with the apparatus pre-scribed in 3.1 by adjusting the variable resistance until theammeter reading in amperes equals the immersed specimenarea in square centimetres. Immersi
41、on of the specimen-holdingclamp in the etching solution should be avoided.7. Etching Precautions7.1 Etching should be carried out under a ventilating hood.Gas evolved at the electrodes with entrained oxalic acid ispoisonous and irritating. The temperature of the etchingsolution, which increases duri
42、ng etching, should be kept below50C by using two beakers of acid, one of which may becooled while the other is in use.FIG. 1 Test ApparatusA763 1538. Rinsing Prior to Examination8.1 Following etching, the specimen should be rinsed in hotwater then acetone or alcohol to avoid oxalic acid crystalliza-
43、tion on the etched surface during forced air-drying.9. Examination9.1 Examine etched specimens on a metallurgical micro-scope at 250 to 500 as appropriate for classification of etchedmicrostructure type as defined in Section 10.10. Classification of Etched Structures10.1 Acceptable structures indica
44、ting resistance to chro-mium carbide-type intergranular attack:10.1.1 Step StructureSteps only between grainsnoditches at grain boundaries (see Fig. 2).10.1.2 Dual StructureSome ditches at grain boundaries inaddition to steps, but no single grain completely surrounded byditches (see Fig. 3).10.2 Una
45、cceptable structures requiring additional testing(Practices X, Y, or Z):10.2.1 Ditch StructureOne or more grains completelysurrounded by ditches (see Fig. 4).PRACTICE XFERRIC SULFATE-SULFURIC ACIDTEST FOR DETECTING SUSCEPTIBILITY TOINTERGRANULAR ATTACK IN FERRITICSTAINLESS STEELS11. Scope11.1 This p
46、ractice describes the procedure for conductingthe boiling ferric sulfate-sulfuric acid test which measures thesusceptibility of ferritic stainless steels to intergranular attack.This test detects susceptibility to intergranular attack associ-ated with the precipitation of chromium carbides and nitri
47、des instabilized and unstabilized ferric stainless steels. It may alsodetect the presence of chi or sigma phase in these steels. Thetest will not differentiate between intergranular attack resultingfrom carbides and that due to intermetallic phases. The ferricsulfate-sulfuric acid solution may also
48、selectively attack tita-nium carbides and nitrides in stabilized steels. The alloys onwhich the test has been successfully applied are shown in Table1.11.2 This test may be used to evaluate the susceptibility ofas-received material to intergranular corrosion caused bychromium carbide or nitride prec
49、ipitation. It may be applied towrought products and weld metal.11.3 This procedure may be used on ferritic stainless steelsafter an appropriate sensitizing heat treatment or weldingprocedure as agreed upon between the supplier and thepurchaser.12. Apparatus12.1 The basic apparatus is described in Section 3. Alsoneeded are:12.1.1 For weight loss determination, an analytical balancecapable of weighing to at least the nearest 0.001 g.12.1.2 For microscopical examination, a microscope withmagnification to at least 40.13. Ferric Sulfate-Sulfuric A
