1、Designation: E 340 00 (Reapproved 2006)Standard Test Method forMacroetching Metals and Alloys1This standard is issued under the fixed designation E 340; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A n
2、umber in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) 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. Scope1.1 These test procedures describe the methods of macro-et
3、ching metals and alloys to reveal their macrostructure.1.2 The values stated in inch-pound units are to be regardedas the standard. The SI equivalents of inch-pound units may beapproximate.1.3 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is
4、 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, 8.10.1.1,and 8.13.2.2. Referenced Documents2.1 ASTM Standa
5、rds:2E3 Guide for Preparation of Metallographic SpecimensE 381 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 ofmetals and alloys. Metallographic specimens and chemical
6、analyses 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 provide infor-mation on variations in (1) structure, such
7、 as grain size, flowlines, columnar structure, dendrites, etc.; (2) variations inchemical composition as evidenced by segregation, carbideand ferrite banding, coring, inclusions, and depth of carburiza-tion or decarburization. The information provided about varia-tions in chemical composition is str
8、ictly 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 show the presence of discon-tinuities and voids, such as seams,
9、laps, porosity, flakes, bursts,extrusion rupture, cracks, etc.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 metals, entrapmentof flux, porosity, and cracks in weld and heat affecte
10、d zones,etc. It is also used in the heat-treating shop to determinelocation of hard or soft spots, tong marks, quenching cracks,case depth in shallow-hardening steels, case depth in carbur-ization of dies, effectiveness of stop-off coatings in carburiza-tion, etc. In the machine shop, it can be used
11、 for thedetermination 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, segregation, and structure. Forge shops,in addition, use macroetching to reveal flow lines
12、 in setting upthe best forging practice, die design, and metal flow. For anexample of the use of macroetching in the steel forgingindustry see Method E 381. Forging shops and foundries alsouse macroetching to determine the presence of internal faultsand surface defects. The copper industry uses macr
13、oetching 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, etc. Defects such ascoring, cracks, and porthole die welds are identified.4. Sampling4.1 As in any method of examination, s
14、ampling 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, when looking for pipe, the sample should representthe top of the ingot, or when looking fo
15、r bursts or flakes, thesample should be taken as soon after hot working as possible.4.2 When macroetching is used as an inspection procedure,sampling ought to be done in an early stage of manufacturingso that if the material proves faulty, no wasteful unnecessary1This test method is under the jurisd
16、iction of ASTM Committee E04 onMetallography and is the direct responsibility of Subcommittee E04.01 on SpecimenPreparation.Current edition approved Oct. 1, 2006. Published October 2006. Originallyapproved in 1968. Last previous edition approved in 2000 as E 340 00e1.2For referenced ASTM standards,
17、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.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 1942
18、8-2959, United States.work 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 taken afteringot breakdown and after most chances of bursts or flakesoccurring have passed. Billets or bloo
19、ms 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 basis.4.3 Samples may be cold cut from the source by anyconvenient fashion; saws and abrasive cutoff wheels ar
20、eparticularly 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 surface. An example of permissible use of torch cuttingis the excising of a piece from a large plate and then c
21、utting 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 ProductsDisks areusually cut from these products near the end. Samples cut tooclose to the end, however, may
22、 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 dimension will show flakes, bursts, etc. Forgings may alsobe cut parallel to the long dimension to show flow l
23、ines. Incomplicated forgings, some thought will have to be given tothe proper method of cutting so as to show flow lines.Macroetching of an unprepared specimen will show surfacedefects such as shuts, flats, seams, etc. In extrusions, coringand coarse grain are more commonly found in the back end oft
24、he 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, but this may beinconveniently long. Several samples totaling some givenfraction of the circumference can be used; however, ther
25、e isalways a chance then that a defect arising from faulty rollswould not be detected. When seeking information on lamina-tions, a transverse section is used. In many cases, however, toreduce the size of the specimen, only a section out of the centerof the plate may be taken.4.5.3 WeldmentsA disk cu
26、t perpendicular to the directionof welding will show weld penetration, heat affected zone,structure, etc. Careful preparation is usually rewarded withhighly detailed structures giving a large amount of information.Welds involving dissimilar metals will produce problems inetching. The best method is
27、to etch the least corrosion-resistantportion first and the more resistant portion afterwards. Occa-sionally an intermediary etchant may be required. The bound-aries between etched and unetched portion will give an idea ofweld penetration and dilution.4.5.4 CastingsCut the specimen to display the def
28、ect orfeature being sought.4.5.5 Machined and Ground PartsWhen looking forgrinding cracks, etc., the surface itself is used as a sample.Because the machined or ground part is often the finished part,it may be undesirable to immerse the part in acid. In this case,other methods such as dye penetrant m
29、ethods may be moredesirable.5. Preparation5.1 Sample preparation need not be elaborate. Any methodof presenting a smooth surface with a minimum amount of coldwork 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 wil
30、l generate a smooth surface and remove coldwork from prior operations. Sharp tools are necessary toproduce a good specimen. Grinding is usually conducted in thesame manner, using free-cutting wheels and light finishingcuts. When fine detail is required, the specimen should beground down through the
31、series of metallographic papers (seeMethods E3). Where necessary, details are given in thetabulation of procedures.5.2 After surface preparation, the sample is cleaned care-fully with suitable solvents. Any grease, oil, or other residuewill produce uneven attack. Once cleaned, care should be takenno
32、t 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 most cases a good grade ofreagent should be used but need not be chemically pure or ofanalytical quality. The so-called technical grades a
33、re usuallysatisfactory. The solution should be clean and clear, free ofsuspended particles, scum, etc.6.2 Caution must be observed in mixing. Many of theetchants are strong acids. In all cases, the various chemicalsshould be added slowly to the water or solvent while stirring.In the cases where hydr
34、ofluoric acid is used, the solutionshould be mixed and used in polyethylene vessels.(WarningHydrofluoric acid should not be allowed to contactthe skin since it can cause painful serious ulcers if not washedoff immediately.)7. Procedure7.1 Many of the solutions are aggressive and may give offirritati
35、ng 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 resistanttray or dish and brought to the operating temperature. Thespecimen or specimens should be placed in a tray of stainlesssteel screen or
36、 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 is com-pleted, remove the specimens from the dish taking great carenot to touch the etched surface. When desmutting is required,dip the specimen into
37、 a second solution. After rinsing thespecimen with hot water, blow dry with clean compressed air.7.2 In the case of large specimens, such as ingot sections,swabbing may be the only practical method of macroetching.Saturate a large wad of cotton held in stainless steel or nickeltongs with the etchant
38、 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 swabE 340 00 (2006)2saturated with solution and frequently sweep over the surfaceof the specimen to renew the solution. When the structure hasbeen sui
39、tably 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 specimen drywith compressed air. Details of the procedure not discussedhere are covered in the sections for the various metals and t
40、heiralloys.7.3 The times given in individual tabulations are onlyintended as guides. In fact, the progress of etching should beclosely watched and etching stopped when the preferredstructural details have been revealed. Specimens should beetched to develop structure. Generally, a light etch is bette
41、rthan a heavy etch; overetching can often lead to misinterpre-tation. The actual time to develop a structure properly may bequite different from the one suggested.8. Specific Preparation Procedures and RecommendedSolutions8.1 Aluminum:8.1.1 The specimens can be cut using common cutting tools,hack sa
42、ws, band saws, shears, abrasive cutoff wheels, etc. Allthese methods will cause cold work at the surface and willgenerate heat. The temperature 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
43、surface should be removed by ma-chining the surface. Again sharp tools and copious lubricationare required. If fine detail is required, the machined surfaceshould be ground using silicon carbide paper lubricated withwater or kerosine.8.1.3 Several of the solutions used in macroetching reactvigorousl
44、y with the metal and can overheat the specimen. Inthese cases the specimen is periodically removed from thesolution, cooled in running water, and reimmersed in theetchant. This procedure is repeated until the desired degree ofetching is obtained.8.1.4 Macroetchants for Aluminum and Aluminum Alloys-(
45、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 areextremely poisonous. (WarningBefore starting any workinvolving beryllium, a review of hazards and plans for han-dling should be made.Anumber of references on b
46、eryllium areavailable. Particular mention may be made of“ Toxicity ofBeryllium” ASD-TR-62-7-667, prepared by the KetteringLaboratory for the Air Force.)8.2.1.1 Generally speaking, beryllium and its alloys havegiven difficulty in obtaining good macroetched specimens.First, beryllium is a rather britt
47、le metal and sectioning can bedifficult. Cut-off wheels with the designation C46FR70 havebeen the most successful. Secondly, beryllium does not grindeasily; hence, specimens should be as small as possible tominimize grinding time. Grinding has been most successfulwith the entire sequence of wet sili
48、con carbide papers.8.2.1.2 The etching of fine grained metal may not always beentirely successful, and further preparation will be required.Rough polishing with 15 m Al2O3suspended in water isperformed on a low-nap cloth. Light pressure and frequentchange of cutting direction produce the best result
49、s. If furtherpolishing is required, 1-m green Cr2O3in tap water onsynthetic suede works best.8.2.2 Macroetchants for Beryllium and Beryllium Alloys(Table 2).8.3 Cobalt and Cobalt Alloys:8.3.1 Many of the cobalt-base high-temperature alloys canbe etched using the same procedures as those for iron- andTABLE 1 Macroetchants for Aluminum and Aluminum AlloysAlloy Composition Procedure CommentsAll NaOHH2O10 g100 mLImmerse sample 5 to 15 min in solution heated to 60to 70C (140 to 160F). Rinse in water, and removesmut in strong HNO3solution. Rinse and repeatetching if necessary.
