1、Designation: B 795 07Standard Test Method forDetermining the Percentage of Alloyed or Unalloyed IronContamination Present in Powder Forged (PF) SteelMaterials1This standard is issued under the fixed designation B 795; the number immediately following the designation indicates the year oforiginal ado
2、ption 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.1. Scope*1.1 This test method covers a metallographic procedure fordetermining the
3、 percentage of alloyed or unalloyed ironcontamination present in powder forged low-alloy steel mate-rials and the percentage of alloyed iron contamination inpowder forged iron and carbon steel materials.1.2 Property values stated in SI units are the standard.1.3 This standard does not purport to add
4、ress all of thesafety 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.2. Referenced Documents2.1 ASTM Standards:2B 243 Termino
5、logy of Powder MetallurgyE3 Guide for Preparation of Metallographic Specimens3. 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 Sta
6、ndards.3.2 Description 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 is taken from thepowder forged material and prepared f
7、or metallographic ex-amination.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
8、 0.1 %.5. Significance 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 i
9、ron particles, 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-c
10、haser and manufacturer or to check the suitability of mixes foruse in powder forging.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 spe
11、cimen from the powder forgedmaterial. The polished surface of the specimen should 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 or test pieces.7.2 The polishe
12、d surface shall be parallel to the direction offorging, that is, parallel to the direction of travel of the forgingpunch, or as specified in the contract or purchase order, andshall represent an area away from the surface of the material.1This test method is under the jurisdiction of ASTM Committee
13、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 Oct. 1, 2007. Published November 2007. Originallyapproved in 1988. Last previous edition approved in 2002 as B 795 93(2002)
14、e1.2For referenced ASTM standards, 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.1*A Summary of Changes section appears at the end of this
15、standard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.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 recom
16、mended that the procedures described inPractice E3be 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
17、 freshly prepared aqueous solution 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 microstructur
18、e. The greater the alloy content, theslower the etching rate; the greater the carbon content, thefaster the etching rate.8.1.2.2 Agood contrast is developed between the matrix andthe contaminant because of a combination of etching andstaining. The areas containing the highest alloy content are thele
19、ast affected. Unalloyed iron will 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 etchd
20、ifferently (see Fig. 1 and Fig. 2).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
21、, a separate count maybe kept to distinguish between alloy contamination and unal-loyed iron contamination in low-alloy steel materials, or, typesof alloy contaminant in iron or carbon steel materials. (SeeNote 1.) Counting of randomly selected discrete fields shouldbe continued until at least 2500
22、grid points have been super-imposed on the 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 fall
23、s on a contaminant particle boundaryshould 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
24、test method is currently under review by Subcom-mittee B09.11 on Near Full Density Powder Metallurgy Ma-terials.11. Keywords11.1 cross product contamination; powder forging (PF);powder forged (PF) parts and test specimens; powder forged(PF) steelsFIG. 1 Illustration of Iron and Low-Alloy Contaminant
25、s in PF-4650B795072SUMMARY OF CHANGESCommittee B09 has identified the location of selected changes to this standard since the last issue (B 795-93(Reapproved 2002)e1) that may impact the use of this standard.(1) Changed “Parts” to “Materials” in title of standard.(2) Changed “parts” to “materials” i
26、n Section 1.1 (two places).(3) Changed “part” to material in Section 4.1.(4) Added, “or to check the suitability of mixes for use inpowder forging.” to Section 5.5.(5) Changed “part” to “material” in Section 7.1 and added “ortest pieces” at the end of the sentence.(6) Changed “part” to “material” in
27、 Section 7.2.(7) Changed “parts” to “materials” in Section 8.2 (two places).(8) Added “and test specimens” after powder forged parts inSection 11.ASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of
28、 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.This standard is subject to revision at any time by the responsible technical committee and must be reviewed every five
29、 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 International Headquarters. Your comments will receive careful consideration at a meeting of theresponsible technical co
30、mmittee, 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 below.This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA
31、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 PF-1060B795073
