1、Designation: E340 00 (Reapproved 2006)E340 13Standard Test Method 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
2、. 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. Scope1.1 These test procedures describe the methods of macr
3、oetching metals and alloys to reveal their macrostructure.1.2 The values stated in inch-pound units are to be regarded as the standard. The SI equivalents of inch-pound units may beapproximate.standard. The values given in parentheses are mathematical conversions to SI units that are provided for in
4、formationonly and are not considered standard.1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety and health practices and determine the applicability of regula
5、torylimitations prior to use. For specific warning 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 Standards:2E3 Guide for Preparation of Metallographic SpecimensE381 Method of Macroetch Testing Steel Bars, Billets, Blooms, and Forgings3. Significa
6、nce and Use3.1 Applications of Macroetching:3.1.1 Macroetching is used to reveal the heterogeneity of metals and alloys. Metallographic specimens and chemical analyseswill provide the necessary detailed information about specific localities but they cannot give data about variation from one placeto
7、another unless an inordinate number of specimens are taken.3.1.2 Macroetching, on the other hand, will provide information on variations in (1) structure, such as grain size, flow lines,columnar structure, dendrites, etc.; (2) variations in chemical composition as evidenced by segregation, carbide a
8、nd ferrite banding,coring, inclusions, and depth of carburization or decarburization. The information provided about variations in chemicalcomposition is strictly qualitative but the location of extremes in segregation will be shown. Chemical analyses or other means ofdetermining the chemical compos
9、ition would have to be performed to determine the extent of variation. Macroetching will alsoshow the presence of discontinuities and voids, such as seams, laps, porosity, flakes, bursts, extrusion rupture, cracks, etc.3.1.3 Other applications of macroetching in the fabrication of metals are the stu
10、dy of weld structure, definition of weldpenetration, dilution of filler metal by base metals, entrapment of flux, porosity, and cracks in weld and heat affected zones, etc.It is also used in the heat-treating shop to determine location of hard or soft spots, tong marks, quenching cracks, case depth
11、inshallow-hardening steels, case depth in carburization of dies, effectiveness of stop-off coatings in carburization, etc. In the machineshop, it can be used for the determination of grinding cracks in tools and dies.3.1.4 Macroetching is used extensively for quality control in the steel industry, t
12、o determine the tone of a heat in billets withrespect to inclusions, segregation, and structure. Forge shops, in addition, use macroetching to reveal flow lines in setting up thebest forging practice, die design, and metal flow. For an example of the use of macroetching in the steel forging industry
13、 seeMethod E381. Forging shops and foundries also use macroetching to determine the presence of internal faults and surface defects.The copper industry uses macroetching for control of surface porosity in wire bar. In the aluminum industry, macroetching is usedto evaluate extrusions as well as the o
14、ther products such as forgings, sheets, etc. Defects such as coring, cracks, and porthole diewelds are identified.1 This test method is under the jurisdiction ofASTM Committee E04 on Metallography and is the direct responsibility of Subcommittee E04.01 on Specimen Preparation.Current edition approve
15、d Oct. 1, 2006June 1, 2013. Published October 2006October 2013. Originally approved in 1968. Last previous edition approved in 20002006 asE340 001.(2006). DOI: 10.1520/E0340-00R06.10.1520/E0340-13.2 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at
16、 serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous vers
17、ion. Becauseit may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the official document.Copyright ASTM Internation
18、al, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States14. Sampling4.1 As in any method of examination, sampling is very important. When macroetching is used to solve a problem, the problemitself largely dictates the source of the sample as to the location on the work
19、 piece and the stage of manufacture; for example, whenlooking for pipe, the sample should represent the top of the ingot, or when looking for bursts or flakes, the sample should be takenas soon after hot working as possible.4.2 When macroetching is used as an inspection procedure, sampling ought to
20、be done in an early stage of manufacturing sothat if the material proves faulty, no wasteful unnecessary work is done. However, the sample should not be taken so early thatfurther working can introduce serious defects. In the steel industry, for example, the sample is usually taken after ingot break
21、downand after most chances of bursts or flakes occurring have passed. Billets or blooms going into small sizes are sampled after initialbreakdown. Material going into forging billets or die blocks is sampled near finish size. Sampling may be done systematically oron a random basis.4.3 Samples may be
22、 cold cut from the source by any convenient fashion; saws and abrasive cutoff wheels are particularlyeffective.The use of torch cutting or hot cutting should be used only when necessary to cut a sample from a large piece.The samplethen is sectioned well away from the hot-cut surface.An example of pe
23、rmissible use of torch cutting is the excising of a piece froma large plate and then cutting a sample for macroetching 4 to 5 in. (102 to 127 mm) away from the torch-cut edge.4.4 Some common methods of sampling, listed by source, are as follows:4.5 Billets, Blooms, and Hot-Rolled ProductsDisks are u
24、sually cut from these products near the end. Samples cut too closeto the end, however, may have false structures because of fish-tailing. Disks from large blooms are sometimes cut into smallerpieces for ease in handling.4.5.1 Forgings and ExtrusionsDisks cut transverse to the long dimension will sho
25、w flakes, bursts, etc. Forgings may also becut parallel to the long dimension to show flow lines. In complicated forgings, some thought will have to be given to the propermethod of cutting so as to show flow lines. Macroetching of an unprepared specimen will show surface defects such as shuts, flats
26、,seams, etc. In extrusions, coring and coarse grain are more commonly found in the back end of the extrusion.4.5.2 Sheets and PlatesA sufficiently large sample should be taken when looking for surface defects. An ideal length wouldbe the circumference of the last roll, but this may be inconveniently
27、 long. Several samples totaling some given fraction of thecircumference can be used; however, there is always a chance then that a defect arising from faulty rolls would not be detected.When seeking information on laminations, a transverse section is used. In many cases, however, to reduce the size
28、of the specimen,only a section out of the center of the plate may be taken.4.5.3 WeldmentsAdisk cut perpendicular to the direction of welding will show weld penetration, heat affected zone, structure,etc. Careful preparation is usually rewarded with highly detailed structures giving a large amount o
29、f information. Welds involvingdissimilar metals will produce problems in etching. The best method is to etch the least corrosion-resistant portion first and themore resistant portion afterwards. Occasionally an intermediary etchant may be required. The boundaries between etched andunetched portion w
30、ill give an idea of weld penetration and dilution.4.5.4 CastingsCut the specimen to display the defect or feature being sought.4.5.5 Machined and Ground PartsWhen looking for grinding cracks, etc., the surface itself is used as a sample. Because themachined or ground part is often the finished part,
31、 it may be undesirable to immerse the part in acid. In this case, other methodssuch as dye penetrant methods may be more desirable.5. Preparation5.1 Sample preparation need not be elaborate.Any method of presenting a smooth surface with a minimum amount of cold workwill be satisfactory. Disks may be
32、 faced on a lathe or a shaper. The usual procedure is to take a roughing cut, then a finish cut.This will generate a smooth surface and remove cold work from prior operations. Sharp tools are necessary to produce a goodspecimen. Grinding is usually conducted in the same manner, using free-cutting wh
33、eels and light finishing cuts. When fine detailis required, the specimen should be ground down through the series of metallographic papers (see Methods E3). Where necessary,details are given in the tabulation of procedures.5.2 After surface preparation, the sample is cleaned carefully with suitable
34、solvents. Any grease, oil, or other residue willproduce uneven attack. Once cleaned, care should be taken not to touch the sample surface or contaminate it in any way.6. Solutions6.1 The solutions used for macroetching are given in the tables listed under each alloy. In most cases a good grade of re
35、agentshould be used but need not be chemically pure or of analytical quality. The so-called technical grades are usually satisfactory. Thesolution should be clean and clear, free of suspended particles, scum, etc.6.2 Caution must be observed in mixing. Many of the etchants are strong acids. In all c
36、ases, the various chemicals should beadded slowly to the water or solvent while stirring. In the cases where hydrofluoric acid is used, the solution should be mixed andused in polyethylene vessels. (WarningHydrofluoric acid shouldmust not be allowed to contact the skin since it can causepainful seri
37、ous ulcers if not washed off immediately.)E340 1327. Procedure7.1 Many of the solutions are aggressive and may give off irritating and corrosive fumes. Etching should be done in awell-ventilated room, preferably under a fume hood. The solution should be mixed and placed in a corrosion resistant tray
38、 or dishand brought to the operating temperature.The specimen or specimens should be placed in a tray of stainless steel screen or on somenon-reactive support. Glass rods often are placed on the bottom of the acid container and the specimens laid directly on the rods.When etching is completed, remov
39、e the specimens from the dish taking great care not to touch the etched surface. Whendesmutting is required, dip the specimen into a second solution. After rinsing the specimen with hot water, blow dry with cleancompressed air.7.2 In the case of large specimens, such as ingot sections, swabbing may
40、be the only practical method of macroetching. Saturatea large wad of cotton held in stainless steel or nickel tongs with the etchant and sweep over the surface of the specimen. An effortshould be made to wet the entire surface as soon as possible. After the initial wetting, keep the swab saturated w
41、ith solution andfrequently sweep over the surface of the specimen to renew the solution. When the structure has been suitably developed, rinsethe specimen, either with a swab saturated with water, or better still, by pouring water over the specimen. After rinsing with hotwater, blow the specimen dry
42、 with compressed air. Details of the procedure not discussed here are covered in the sections for thevarious metals and their alloys.7.3 The times given in individual tabulations are only intended as guides. In fact, the progress of etching should be closelywatched and etching stopped when the prefe
43、rred structural details have been revealed. Specimens should be etched to developstructure. Generally, a light etch is better than a heavy etch; overetching can often lead to misinterpretation. The actual time todevelop a structure properly may be quite different from the one suggested.8. Specific P
44、reparation Procedures and Recommended Solutions8.1 Aluminum:8.1.1 The specimens can be cut using common cutting tools, hack saws, band saws, shears, abrasive cutoff wheels, etc.All thesemethods will cause cold work at the surface and will generate heat. The temperature rise can be enough to cause ch
45、anges instructure. For these reasons sharp tools and generous lubrication are necessary for sectioning.8.1.2 The cold-worked surface should be removed by machining the surface. Again sharp tools and copious lubrication arerequired. If fine detail is required, the machined surface should be ground us
46、ing silicon carbide paper lubricated with water orkerosine.8.1.3 Several of the solutions used in macroetching react vigorously with the metal and can overheat the specimen. In thesecases the specimen is periodically removed from the solution, cooled in running water, and reimmersed in the etchant.
47、Thisprocedure is repeated until the desired degree of etching 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 areextremely poisonous. (WarningB
48、efore starting any work involving beryllium, a review of hazards and plans for handling shouldbe made. A number of references on beryllium are available. Particular mention may be made of“ Toxicity of Beryllium”ASD-TR-62-7-667, prepared by the Kettering Laboratory for the Air Force.)8.2.1.1 Generall
49、y speaking, beryllium and its alloys have given difficulty in obtaining good macroetched specimens. First,beryllium is a rather brittle metal and sectioning can be difficult. Cut-off wheels with the designation C46FR70 have been the mostsuccessful. Secondly, beryllium does not grind easily; hence, specimens should be as small as possible to minimize grinding time.Grinding has been most successful with the entire sequence of wet silicon carbide papers.8.2.1.2 The etching of fine grained metal may not always be entirely successful, and further preparation will be required.
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