1、Designation: A 561 71 (Reapproved 2004)Standard Practice forMacroetch Testing of Tool Steel Bars1This standard is issued under the fixed designation A 561; 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 (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 This practice for macroetch testing has been found
3、to bea useful and reliable method for evaluating the quality of toolsteel bars. It is used as a quality control and inspection test toreveal by deep acid etching the macrostructure in specimenscut from bars and to show the presence of such conditions aspipe, cracks, porosity, segregation, or foreign
4、 material. Theetched surface is generally examined visually, but magnifica-tion up to about 103 is occasionally employed.2. Referenced Documents2.1 ASTM Adjuncts:Twelve Photomacrographs23. Apparatus3.1 Etching ContainersMacroetching may be performedin a vessel of borosilicate glass, porcelain, corro
5、sion-resistantmetals, or some other acid-resisting material.4. Reagent4.1 Etching ReagentA solution of equal volumes of con-centrated hydrochloric acid (HCl, sp gr 1.19) and water iscommonly used for macroetching tool steels. This solutionmust be used under a ventilating hood because HCl is volatile
6、and the fumes are corrosive and irritating, although nontoxic.The solution may be reused within limits. With use, theconcentration of dissolved iron and other metals increases andthe acidity of the solution decreases retarding the etchingaction. Spent solution shall be replaced with fresh solution,
7、notreplenished with concentrated acid.5. Sampling5.1 The selection of specimens for macroetch testing mustbe done with care for interpretations to be of value.5.1.1 Specimens are usually cut from hot-rolled annealedbars, but may be cut from machined or ground bars if the barsare to be finish machine
8、d or ground.5.1.2 The specimen should be located at a sufficient distancefrom the end of the bar to avoid end effects.5.1.3 For ease in handling, use specimens14 to12 in. (6.35to 12.7 mm) thick.5.1.4 Cut specimens to expose a transverse section of thebar; however, the test is occasionally performed
9、on a longitu-dinal section.5.1.5 Specimens may be taken from one or both ends of abar. Each bar may be sampled, or a few typical specimens maybe tested as representative of a large number of bars.6. Specimen Preparation6.1 In all cutting and grinding operations on the specimen,care must be excercise
10、d to avoid heating the surface to anexcessively high temperature. Specimens are cut from bars bysawing, machining, abrasive wheel cutting, or other means.Cutting should be controlled to prevent smearing the cut faceand masking the structure.6.1.1 The “as-cut” surface of a specimen may be sufficientl
11、ysmooth to reveal the defects for which the examination isconducted. No additional surface preparation may then benecessary.6.1.2 Additional surface preparation may be required toremove cutting marks and to allow details to be revealed byetching. In such circumstances, machining, grinding, or pol-is
12、hing may be necessary. Generally, the degree of surfacesmoothness required is greater the finer the detail that must beresolved. When the action of the etchant is drastic, a coarsersurface finish may be used.6.1.3 The surface must be free of adhering grease and oil.There should be no scale or oxide
13、on the surface which will beexamined after etching.7. Procedure7.1 Temperature for MacroetchingEtching characteristicsare influenced markedly by the temperature of the etchant.Thus, the reagent temperature should be controlled for macro-etching if comparative results are desired. Tool steels are1Thi
14、s practice is under the jurisdiction of ASTM Committee A01 on Steel,Stainless Steel and Related Alloys and is the direct responsibility of SubcommitteeA01.29 on Tool Steel.Current edition approved September 1, 2004. Published January 2005. Originallyapproved in 1966. Last previous edition approved i
15、n 1999 as A 561 71 (1999).2Available from ASTM International Headquarters. Request AdjunctADJA0561.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.generally macroetched at about 160F (71C). At this tempera-ture, the etching reaction
16、is vigorous and solution lossesthrough evaporation are not excessive. The solution may beheated on a gas or electric hot plate, by an acid-proofimmersion heater, or by steam.7.2 Etching TimeThe etching time should be sufficientlylong to completely reveal the structure in the specimen, yetshould not
17、be so long as to develop artifacts such as etch pitsor to obscure or obliterate the structure. Generally, etchingtimes under 10 min or over 40 min are avoided with tool steels.The time of etching is best adjusted by trial to develop thedegree of etching desired. Where recovery of temperature ofthe s
18、olution is slow after immersion of cold specimens,reproducibility is enhanced by preheating the specimens in hotwater prior to immersing in the etchant.7.3 Macroetching Technique:7.3.1 After preparation as described above, clean the speci-men of dirt and grease with a solvent, if necessary. Then pla
19、cedirectly into the etching solution already heated to the propertemperature, or preheat in water as in 7.2 and then transfer tothe hot etching bath. The purpose of preheating the specimen isto obtain better control of the etching conditions where closereproducibility of degree of development is des
20、ired. Thespecimen must be completely immersed.7.3.2 Moderate agitation (stirring) of the solution duringmacroetching promotes uniform development by eliminatingtemperature and composition gradients. Provision for agitatingthe etchant may be desirable where the volume of solution isrelatively small.7
21、.3.3 At the end of the etching period, remove the specimenfrom the hot acid and rinse immediately in a stream of water.Flush off the sludge which forms on the surfaces of thespecimen during etching with the aid of a stiff brush. Then drythe specimen with alcohol, a clean air blast, or live steam.7.3
22、.4 After drying, protect the etched surface from rustingby an application of oil, grease, glycerine, or transparentlacquer.8. Interpretation of Results8.1 Examine the etched surface visually or at up to 103magnification to determine its structure. Note the presence,absence, and severity of the follo
23、wing conditions:8.1.1 Internal:8.1.1.1 Pipe,8.1.1.2 Bursts,8.1.1.3 Carbide (see Note 1) or alloy segregation,8.1.1.4 Concentrations of nonmetallic inclusions,8.1.1.5 Porosity, and8.1.1.6 Internal cracks or thermal flakes.NOTE 1Carbide segregation is better determined by examination of apolished surf
24、ace after etching in 4 % nital solution.8.1.2 Surface and Subsurface:8.1.2.1 Seams, laps, cracks, etc.,8.1.2.2 Ingot corner segregation or cracks, and8.1.2.3 Pinholes,8.1.3 Miscellaneous:8.1.3.1 Entrapped metallic or nonmetallic material, and8.1.3.2 Ingot pattern (dendritic segregation, columnar gra
25、instructure, etc.).8.2 Twelve photomacrographs provide a numerical rating ofseverity levels of porosity (8.1.1.5) and ingot pattern (8.1.3.2)that may be present in tool steel bars.8.2.1 These conditions identified in general as porosity andingot pattern are described as follows:8.2.1.1 Center Porosi
26、tyA center concentration of minutevoids related to etched out carbides, or nonmetallic inclusions,etc.8.2.1.2 Ring Ingot PatternOne or more concentric ringscharacterized by differential etching associated with a minorgradient in chemical composition or ingot solidification.8.2.2 Ratings for the cond
27、itions can be determined bycomparing macroetched disks with these photographs.8.2.3 The photographs are not intended as standards foracceptance or rejection. The numerical identity listed with eachfigure only refers to a degree of severity. The extent that eachcondition is permissible for a given ap
28、plication should bestated by the tool steel specification covering the application oras negotiated between the supplier and purchaser.ASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standa
29、rd are expressly advised that determination of the validity of any such patent rights, and the riskof infringement of such rights, are entirely their own responsibility.This standard is subject to revision at any time by the responsible technical committee and must be reviewed every five years andif
30、 not revised, either reapproved or withdrawn. Your comments are invited either for revision of this standard or for additional standardsand should be addressed to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of theresponsible technical committee, whi
31、ch you may attend. If you feel that your comments have not received a fair hearing you shouldmake your views known to the ASTM Committee on Standards, at the address shown below.This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,United States. Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the aboveaddress or at 610-832-9585 (phone), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org).A 561 71 (2004)2
