ASTM_B_795_-_13.pdf

Designation:B79513Standard Test Method forDetermining the Percentage of Alloyed or Unalloyed IronContamination Present in Powder Forged(PF)SteelMaterials1This standard is issued under the fixed designation B795;the number immediately following the designation indicates the year 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()indicates an editorial change since the last revision or reapproval.1.Scope*1.1 This test method covers a metallographic procedure fordetermining the 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 The values stated in SI units are to be regarded asstandard.No other units of measurement are included in thisstandard.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 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:2B243 Terminology of Powder MetallurgyE3 Guide for Preparation of Metallographic SpecimensE177 Practice for Use of the Terms Precision and Bias inASTM Test MethodsE691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test Method3.Terminology3.1 DefinitionsDefinitions of powder metallurgy termscan be found in Terminology B243.Additional descriptiveinformation is available in the Related Material Section of Vol02.05 of the Annual Book of ASTM Standards.3.2 Definitions of Terms 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 for metallographic ex-amination.4.2 The polished and etched sample is examined micro-scopically at a magnification of 100 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.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 iron 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-chaser 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 100.1This test method is under the jurisdiction of ASTM Committee B09 on MetalPowders and Metal Powder Productsand is the direct responsibility of Subcommit-tee B09.11 on Near Full Density Powder Metallurgy Materials.Current edition approved Oct.1,2013.Published November 2013.Originallyapproved in 1988.Last previous edition approved in 2007 as B795 07.DOI:10.1520/B0795-13.2For 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.*A Summary of Changes section appears at the end of this standardCopyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 7.Sampling7.1 Take a metallographic specimen from the powder forgedmaterial.The polished surface of the specimen should be notless than that required to superimpose 2500 grid points at amagnification of 100.Multiple sections are permitted in orderto obtain the necessary area for measurement on small parts ortest pieces.7.2 The polished 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.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 inPractice E3 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