1、Designation: B 795 93 (Reapproved 2002)e1Standard Test Method forDetermining the Percentage of Alloyed or Unalloyed IronContamination Present in Powder Forged (P/F) Steel Parts1This standard is issued under the fixed designation B 795; the number immediately following the designation indicates the y
2、ear oforiginal adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.e1NOTETitles of referenced documents were updated and paragraphs
3、 4.3, 6.2, 7.1, and 8.1.2 were revised editorially in June2002.1. Scope1.1 This test method covers a metallographic procedure fordetermining the percentage of alloyed or unalloyed ironcontamination present in powder forged low-alloy steel partsand the percentage of alloyed iron contamination in powd
4、er-forged iron and carbon steel parts.1.2 Property values stated in SI units are the standard.Conversion factors to inch-pound units may be approximate.1.3 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of thi
5、s standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:B 243 Terminology of Powder Metallurgy2E 3 Practice for Preparation of Metallographic Specimens3E 562 Test Method for Det
6、ermining Volume Fraction bySystematic Manual Point Count33. Terminology3.1 DefinitionsDefinitions of powder metallurgy termscan be found in Terminology B 243. Additional descriptiveinformation is available in the Related Material Section of Vol02.05 of the Annual Book of ASTM Standards.3.2 Descripti
7、on of Term Specific to This Standard:3.2.1 cross product contaminationthe unintentional mix-ing of powders with distinct differences in chemical composi-tion.4. Summary of Test Method4.1 A section representing the core region of the part istaken from the powder forged part and prepared for metallo-g
8、raphic examination.4.2 The polished and etched sample is examined micro-scopically at a magnification of 1003 and a systematic pointcount made of features with etching characteristics differentfrom that of the matrix.4.3 The amount of contaminant is reported as a percentageto the nearest 0.1 %.5. Si
9、gnificance and Use5.1 Cross product contamination occurs whenever alloysteel powders are processed in the same equipment as ironpowders.5.2 Unalloyed iron particles, because they may not hardenupon heat treatment, are a potential source of soft spots inlow-alloy steel parts.5.3 Alloyed iron particle
10、s, having higher hardenability thanan iron or carbon steel matrix, are a potential source of hardspots.5.4 Hard or soft spots may cause problems in service ormachining.5.5 The results of the tests may be used to qualify parts forshipment in accordance with guidelines agreed between pur-chaser and ma
11、nufacturer.6. Apparatus6.1 Equipment for the metallographic preparation of testspecimens.6.2 A metallographic microscope permitting observationand measurement at a magnification of 1003.7. Sampling7.1 Take a metallographic specimen from the powder-forged part. The polished surface of the specimen sh
12、ould be notless than that required to superimpose 2500 grid points at amagnification of 1003. Multiple sections are permitted inorder to obtain the necessary area for measurement on smallparts.7.2 The polished surface shall be parallel to the direction offorging, that is, parallel to the direction o
13、f travel of the forging1This specification is under the jurisdiction of ASTM Committee B09 on MetalPowders and Metal Powder Products and is the direct responsibility of Subcom-mittee B09.11 on Near-Full Density Powder Metallurgy Materials.Current edition approved July 15, 1993. Published December 19
14、93. Originallypublished as B 795 88. Last previous edition B 795 88.2Annual Book of ASTM Standards, Vol 02.05.3Annual Book of ASTM Standards, Vol 03.01.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.punch, or as specified in the con
15、tract or purchase order, andshall represent an area away from the surface of the part.8. Procedure8.1 Preparation of Specimens:8.1.1 PolishingIn polishing the specimens, it is highlyimportant that the polished surface be free from artifacts anddebris. It is recommended that the procedures described
16、inPractice E 3 be followed. Automated grinding and polishingprocedures are recommended.8.1.2 EtchingLightly etch the freshly polished specimenwith 2 % nital (2 mL nitric acid, 98 mL ethyl alcohol). Next,etch the polished and lightly etched specimen by immersion ina freshly prepared aqueous solution
17、containing 3 g potassiummetabisulfite and 10 g sodium thiosulfate per 100 mL. Rinsethe specimen in running water, then rinse with low residuealcohol and dry with a blast of dry air.8.1.2.1 The etching time will depend on alloy type, carboncontent, and microstructure. The greater the alloy content, t
18、heslower the etching rate; the greater the carbon content, thefaster the etching rate.8.1.2.2 A good contrast is developed between the matrix andthe contaminant because of a combination of etching andstaining. The areas containing the highest alloy content are theleast affected. Unalloyed iron will
19、become darkened in alow-alloy matrix and low-alloy particles will remain light in aniron or carbon steel matrix. In a low-alloy matrix, contaminantparticles of another low-alloy powder can be distinguishedfrom unalloyed iron contamination because the particles etchdifferently (see Fig. 1 and Fig. 2)
20、.8.2 ExaminationSuperimpose a grid of between 100 and250 systematically placed points upon a 1003 magnifiedimage (that is, a field of view) of the polished and etchedspecimen. Count and record the number of grid points fallingupon contaminant particles; if necessary, a separate count maybe kept to d
21、istinguish between alloy contamination and unal-loyed iron contamination in low-alloy steel parts, or, types ofalloy contaminant in iron or carbon steel parts. (See Note 1.)Counting of randomly selected discrete fields should be con-tinued until at least 2500 grid points have been superimposedon the
22、 specimen. The total number of points falling oncontaminant particles for all fields counted shall be divided bythe total number of grid points superimposed and multiplied by100 to determine the area percentage of contamination.NOTE 1Any grid point that falls on a contaminant particle boundaryshould
23、 be counted as one half. To avoid bias, questionable points shouldbe counted as one half.9. Report9.1 Report the area percentage of contaminant to the nearest0.1 %.10. Precision and Bias10.1 The precision and bias that can be expected through theuse of this test method is currently under review by S
24、ubcom-mittee B09.11 on Near Full Density Powder Metallurgy Ma-terials.11. Keywords11.1 cross product contamination; powder forging (P/F);powder forged (P/F) parts; powder forged (P/F) steelsFIG. 1 Illustration of Iron and Low-Alloy Contaminants in P/F-4650B 7952ASTM International takes no position r
25、especting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standard 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.Thi
26、s standard is subject to revision at any time by the responsible technical committee and must be reviewed every five years andif 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 Inte
27、rnational Headquarters. Your comments will receive careful consideration at a meeting of theresponsible technical committee, which 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
28、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).FIG. 2 Illustration of Low-Alloy Contaminant in P/F-1060B 7953
