ASTM_B_797_-_15.pdf

Designation:B79715Standard Test Method forSurface Finger-Oxide Penetration Depth and Presence ofInterparticle Oxide Networks in Powder Forged(PF)SteelParts1This standard is issued under the fixed designation B797;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 method fordetermining the maximum depth of surface finger-oxide pen-etration and the concentration of subsurface interparticle oxidenetworks in critical areas of powder forged steel parts.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 Document2.1 ASTM Standards:2E3 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 Definitions of Terms Specific to This Standard:3.1.1 surface finger-oxidessurface finger-oxides are sur-face oxides that follow prior particle boundaries into a powderforged part from the surface and cannot be removed byphysical means such as rotary tumbling.Examples of surfacefinger-oxides are shown in Fig.1.3.1.2 interparticle oxide networksinterparticle oxide net-works are continuous or discontinuous oxides that follow priorparticle boundaries in powder forged parts.Examples ofinterparticle oxide networks are shown in Fig.2.4.Summary of Test Method4.1 A section representing both surface and subsurfaceregions of a critical area is cut from the powder forged part andmounted for metallographic grinding and polishing.4.2 For surface finger-oxide penetration,the polished andunetched sample is examined microscopically at a magnifica-tion of 400 to 500.The maximum depth of penetration ofsurface finger-oxides is measured.4.3 For interparticle oxide network concentration,the pol-ished and unetched sample is examined microscopically at amagnification of 200 to 500 to determine the presence ofinterparticle oxide networks.5.Significance and Use5.1 The presence of surface finger-oxide penetration andinterparticle oxide networks are two of the properties used toevaluate powder forged steel parts for proper processing.Maximum acceptable depths of penetration of surface finger-oxide penetration and acceptable concentrations of subsurfaceinterparticle oxide networks depend on the component and itsservice environment.5.2 Results of tests may be used to qualify parts forshipment.6.Apparatus6.1 Equipment for the metallographic preparation of testspecimens.6.2 A metallographic microscope permitting observationand measurement up to a magnification of 500.7.Sampling7.1 A metallographic specimen shall be removed from thepowder forged part to cover each designated critical area.Critical areas shall be defined by the applicable part drawing orthe purchaser order.Specimens shall be taken from the powderforged part in the condition in which it is to be supplied.The1This test method 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 Oct.1,2015.Published November 2015.Originallyapproved in 1988.Last previous edition approved in 2007 as B797 93(2007).DOI:10.1520/B0797-15.2For 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 FIG.1 Example of Surface Finger-Oxide Penetration Extending Inward from the Powder Forged Part Surface(Shown more clearly athigh magnification.)B797 152 FIG.2 Example of Interparticle Oxide Networks Within a Powder Forged Part(Shown more clearly at high magnification.)B797 153 polished surface of the specimens shall be parallel to theforging direction,that is,parallel to the direction of travel ofthe forging punch.8.Procedure8.1 Preparation of SpecimensIn mounting the specimenfor grinding and polishing,protection from rounding the edgeof the part is essential.In polishing the specimen it is importantthat a clean polish be obtained and that edge detail of the partnot be destroyed.Specimens shall be