1、Designation: E340 15Standard Practice forMacroetching Metals and Alloys1This standard is issued under the fixed designation E340; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number in parentheses in
2、dicates 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 U.S. Department of Defense.1. Scope1.1 These procedures describe the methods of macroetchingmetals and alloys to
3、 reveal their macrostructure.1.2 The values stated in inch-pound units are to be regardedas standard. The values given in parentheses are mathematicalconversions to SI units that are provided for information onlyand are not considered standard.1.3 This standard does not purport to address all of the
4、safety concerns, if any, associated with its 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 specificwarning statements, see 6.2, 7.1, 8.1.3, 8.2.1, 8.8.3, 8.1
5、0.1.1,and 8.13.2.2. Referenced Documents2.1 ASTM Standards:2E3 Guide for Preparation of Metallographic SpecimensE381 Method of Macroetch Testing Steel Bars, Billets,Blooms, and Forgings3. Significance and Use3.1 Applications of Macroetching:3.1.1 Macroetching is used to reveal the heterogeneity ofme
6、tals and alloys. Metallographic specimens and chemicalanalyses will provide the necessary detailed information aboutspecific localities but they cannot give data about variationfrom one place to another unless an inordinate number ofspecimens are taken.3.1.2 Macroetching, on the other hand, will pro
7、vide infor-mation on variations in (1) structure, such as grain size, flowlines, columnar structure, dendrites, and so forth; (2) variationsin chemical composition as evidenced by segregation, carbideand ferrite banding, coring, inclusions, and depth of carburiza-tion or decarburization. The informa
8、tion provided about varia-tions in chemical composition is strictly qualitative but thelocation of extremes in segregation will be shown. Chemicalanalyses or other means of determining the chemical compo-sition would have to be performed to determine the extent ofvariation. Macroetching will also sh
9、ow the presence of discon-tinuities and voids, such as seams, laps, porosity, flakes, bursts,extrusion rupture, cracks, and so forth.3.1.3 Other applications of macroetching in the fabricationof metals are the study of weld structure, definition of weldpenetration, dilution of filler metal by base m
10、etals, entrapmentof flux, porosity, and cracks in weld and heat affected zones,and so forth. It is also used in the heat-treating shop todetermine location of hard or soft spots, tong marks, quenchingcracks, case depth in shallow-hardening steels, case depth incarburization of dies, effectiveness of
11、 stop-off coatings incarburization, and so forth. In the machine shop, it can be usedfor the determination of grinding cracks in tools and dies.3.1.4 Macroetching is used extensively for quality control inthe steel industry, to determine the tone of a heat in billets withrespect to inclusions, segre
12、gation, and structure. Forge shops,in addition, use macroetching to reveal flow lines in setting upthe best forging practice, die design, and metal flow. For anexample of the use of macroetching in the steel forgingindustry see Method E381. Forging shops and foundries alsouse macroetching to determi
13、ne the presence of internal faultsand surface defects. The copper industry uses macroetching forcontrol of surface porosity in wire bar. In the aluminumindustry, macroetching is used to evaluate extrusions as well asthe other products such as forgings, sheets, and so forth.Defects such as coring, cr
14、acks, and porthole die welds areidentified.4. Sampling4.1 As in any method of examination, sampling is veryimportant. When macroetching is used to solve a problem, theproblem itself largely dictates the source of the sample as to thelocation on the work piece and the stage of manufacture; forexample
15、, when looking for pipe, the sample should representthe top of the ingot, or when looking for bursts or flakes, thesample should be taken as soon after hot working as possible.1This test method is under the jurisdiction of ASTM Committee E04 onMetallography and is the direct responsibility of Subcom
16、mittee E04.01 on SpecimenPreparation.Current edition approved June 1, 2015. Published July, 2015. Originallyapproved in 1968. Last previous edition approved in 2013 as E340 13. DOI:10.1520/E0340-15.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service
17、at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States14.2 When macroetching is used as an inspection pr
18、ocedure,sampling ought to be done in an early stage of manufacturingso that if the material proves faulty, no wasteful unnecessarywork is done. However, the sample should not be taken soearly that further working can introduce serious defects. In thesteel industry, for example, the sample is usually
19、 taken afteringot breakdown and after most chances of bursts or flakesoccurring have passed. Billets or blooms going into small sizesare sampled after initial breakdown. Material going intoforging billets or die blocks is sampled near finish size.Sampling may be done systematically or on a random ba
20、sis.4.3 Samples may be cold cut from the source by anyconvenient fashion; saws and abrasive cutoff wheels areparticularly effective. The use of torch cutting or hot cuttingshould be used only when necessary to cut a sample from alarge piece. The sample then is sectioned well away from thehot-cut sur
21、face. An example of permissible use of torch cuttingis the excising of a piece from a large plate and then cutting asample for macroetching 4 to 5 in. (102 to 127 mm) away fromthe torch-cut edge.4.4 Some common methods of sampling, listed by source,are as follows:4.5 Billets, Blooms, and Hot-Rolled
22、ProductsDisks areusually cut from these products near the end. Samples cut tooclose to the end, however, may have false structures because offish-tailing. Disks from large blooms are sometimes cut intosmaller pieces for ease in handling.4.5.1 Forgings and ExtrusionsDisks cut transverse to thelong di
23、mension will show flakes, bursts, and so forth. Forgingsmay also be cut parallel to the long dimension to show flowlines. In complicated forgings, some thought will have to begiven to the proper method of cutting so as to show flow lines.Macroetching of an unprepared specimen will show surfacedefect
24、s such as shuts, flats, seams, and so forth. In extrusions,coring and coarse grain are more commonly found in the backend of the extrusion.4.5.2 Sheets and PlatesA sufficiently large sample shouldbe taken when looking for surface defects. An ideal lengthwould be the circumference of the last roll, b
25、ut this may beinconveniently long. Several samples totaling some givenfraction of the circumference can be used; however, there isalways a chance then that a defect arising from faulty rollswould not be detected. When seeking information onlaminations, a transverse section is used. In many cases,how
26、ever, to reduce the size of the specimen, only a section outof the center of the plate may be taken.4.5.3 WeldmentsA disk cut perpendicular to the directionof welding will show weld penetration, heat affected zone,structure, and so forth. Careful preparation is usually rewardedwith highly detailed s
27、tructures giving a large amount ofinformation. Welds involving dissimilar metals will produceproblems in etching. The best method is to etch the leastcorrosion-resistant portion first and the more resistant portionafterwards. Occasionally an intermediary etchant may berequired. The boundaries betwee
28、n etched and unetched portionwill give an idea of weld penetration and dilution.4.5.4 CastingsCut the specimen to display the defect orfeature being sought.4.5.5 Machined and Ground PartsWhen looking forgrinding cracks, and so forth, the surface itself is used as asample. Because the machined or gro
29、und part is often thefinished part, it may be undesirable to immerse the part in acid.In this case, other methods such as dye penetrant methods maybe more desirable.5. Preparation5.1 Sample preparation need not be elaborate. Any methodof presenting a smooth surface with a minimum amount of coldwork
30、will be satisfactory. Disks may be faced on a lathe or ashaper. The usual procedure is to take a roughing cut, then afinish cut. This will generate a smooth surface and remove coldwork from prior operations. Sharp tools are necessary toproduce a good specimen. Grinding is usually conducted in thesam
31、e manner, using free-cutting wheels and light finishingcuts. When fine detail is required, the specimen should beground down through the series of metallographic papers (seeGuide E3). Where necessary, details are given in the tabulationof procedures.5.2 After surface preparation, the sample is clean
32、ed care-fully with suitable solvents. Any grease, oil, or other residuewill produce uneven attack. Once cleaned, care should be takennot to touch the sample surface or contaminate it in any way.6. Solutions6.1 The solutions used for macroetching are given in thetables listed under each alloy. In mos
33、t cases a good grade ofreagent should be used but need not be chemically pure or ofanalytical quality. The so-called technical grades are usuallysatisfactory. The solution should be clean and clear, free ofsuspended particles, scum, and so forth.6.2 Caution must be observed in mixing. Many of theetc
34、hants are strong acids. In all cases, the various chemicalsshould be added slowly to the water or solvent while stirring.In the cases where hydrofluoric acid is used, the solutionshould be mixed and used in polyethylene vessels.(WarningHydrofluoric acid must not be allowed to contactthe skin since i
35、t can cause painful serious ulcers if not washedoff immediately.)7. Procedure7.1 Many of the solutions are aggressive and may give offirritating and corrosive fumes. Etching should be done in awell-ventilated room, preferably under a fume hood. Thesolution should be mixed and placed in a corrosion r
36、esistanttray or dish and brought to the operating temperature. Thespecimen or specimens should be placed in a tray of stainlesssteel screen or on some non-reactive support. Glass rods oftenare placed on the bottom of the acid container and thespecimens laid directly on the rods. When etching iscompl
37、eted, remove the specimens from the dish taking greatcare not to touch the etched surface. When desmutting isrequired, dip the specimen into a second solution. After rinsingthe specimen with hot water, blow dry with clean compressedair.7.2 In the case of large specimens, such as ingot sections,swabb
38、ing may be the only practical method of macroetching.E340 152Saturate a large wad of cotton held in stainless steel or nickeltongs with the etchant and sweep over the surface of thespecimen.An effort should be made to wet the entire surface assoon as possible. After the initial wetting, keep the swa
39、bsaturated with solution and frequently sweep over the surfaceof the specimen to renew the solution. When the structure hasbeen suitably developed, rinse the specimen, either with a swabsaturated with water, or better still, by pouring water over thespecimen. After rinsing with hot water, blow the s
40、pecimen drywith compressed air. Details of the procedure not discussedhere are covered in the sections for the various metals and theiralloys.7.3 The times and temperatures given in individual tabula-tions are only intended as guides. In fact, the progress ofetching should be closely watched and etc
41、hing stopped whenthe preferred structural details have been revealed. Specimensshould be etched to develop structure. Generally, a light etch isbetter than a heavy etch; overetching can often lead tomisinterpretation. The actual time to develop a structureproperly may be quite different from the one
42、 suggested.8. Specific Preparation Procedures and RecommendedSolutions8.1 Aluminum:8.1.1 The specimens can be cut using common cutting tools,hack saws, band saws, shears, abrasive cutoff wheels, and soforth.All these methods will cause cold work at the surface andwill generate heat. The temperature
43、rise can be enough to causechanges in structure. For these reasons sharp tools and gener-ous lubrication are necessary for sectioning.8.1.2 The cold-worked surface should be removed by ma-chining the surface. Again sharp tools and copious lubricationare required. If fine detail is required, the mach
44、ined surfaceshould be ground using silicon carbide paper lubricated withwater or kerosine.8.1.3 Several of the solutions used in macroetching reactvigorously with the metal and can overheat the specimen. Inthese cases the specimen is periodically removed from thesolution, cooled in running water, an
45、d reimmersed in theetchant. This procedure is repeated until the desired degree ofetching is obtained.8.1.4 Macroetchants for Aluminum and Aluminum Alloys(Table 1).8.2 Beryllium:8.2.1 While beryllium in the massive form is not dangerous,beryllium and its compounds in the finely divided state areextr
46、emely poisonous. (WarningBefore starting any workinvolving beryllium, a review of hazards and plans for han-dling should be made.Anumber of references on beryllium areavailable. Particular mention may be made of “Toxicity ofBeryllium” ASD-TR-62-7-667, prepared by the KetteringLaboratory for the Air
47、Force.)8.2.1.1 Generally speaking, beryllium and its alloys havegiven difficulty in obtaining good macroetched specimens.First, beryllium is a rather brittle metal and sectioning can bedifficult. Cut-off wheels with the designation C46FR70 havebeen the most successful. Secondly, beryllium does not g
48、rindeasily; hence, specimens should be as small as possible tominimize grinding time. Grinding has been most successfulwith the entire sequence of wet silicon carbide papers.8.2.1.2 The etching of fine grained metal may not always beentirely successful, and further preparation will be required.Rough
49、 polishing with 15 m Al2O3suspended in water isperformed on a low-nap cloth. Light pressure and frequentTABLE 1 Macroetchants for Aluminum and Aluminum AlloysAlloy Composition Procedure CommentsAll NaOHH2O10 g100 mLImmerse sample 5 to 15 min in solution heated to 140to 160F (60 to 70C). Rinse in water, and removesmut in strong HNO3solution. Rinse and repeatetching if necessary.Good general-purpose etchant, can beused on almost all aluminum alloys.Does not require fine grinding.3XXX4XXX5XXX6XXXHigh Si castingsHCl (concentrated)HNO3(concentrated)HF (48 %)75 mL25 mL5mLMix fr
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