ASTM_B_390_-_92_2006.pdf

Designation:B 390 92(Reapproved 2006)Standard Practice forEvaluating Apparent Grain Size and Distribution ofCemented Tungsten Carbides1This standard is issued under the fixed designation B 390;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(e)indicates an editorial change since the last revision or reapproval.1.Scope1.1 This practice for the visual comparison and classifica-tion of the apparent grain size and distribution of cementedtungsten carbides is limited to cemented tungsten carbides thatcontain approximately 6,10,and 18%cobalt.1.2 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:2B 657 Guide for Metallographic Identification of Micro-structure in Cemented CarbidesB 665 Guide for Metallographic Sample Preparation ofCemented Tungsten Carbides3.Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 apparent grain sizethe average diameter of a tung-sten carbide particle as measured on an etched metallographi-cally polished surface of a specimen of sintered cementedcarbide.The apparent grain size is expressed in micrometresand is generally reported as a range.4.Significance and Use4.1 The apparent size and distribution of tungsten carbidegrains in cemented carbides affects the materials wear resis-tance and fracture.For a given chemical composition,anincrease in the average grain size will result in increasedtoughness and decreased wear resistance.This practice illus-trates representative micro-structures for a wide range oftungsten carbide-cobalt grades.This is not intended to be usedas a specification for carbide grades;producers and users mayuse the micrographs and the grain size chart as a guide indeveloping their own specifications.5.Specimen Preparation5.1 Specimens shall be prepared for metallographic exami-nation in accordance with a procedure suitable for this type ofcemented carbides.NOTE1A suitable procedure is described in Test Method B 657 andPractice B 665.6.Procedure6.1 Examine metallographically the entire surface of anetched specimen at a magnification of 1500 diameters.Select arepresentative area and make a comparison with the photomi-crographs in Figs.1-3.6.2 The nominal analyses of the cemented tungsten carbidesamples that were used to prepare the nine photomicrographsshown in Figs.1-3 are as follows:6.2.1 Fig.1Tungsten carbide plus 6%cobalt,6.2.2 Fig.2Tungsten carbide plus 10%cobalt,and6.2.3 Fig.3Tungsten carbide plus 18%cobalt.6.3 The grain size for each of these specimens may bedesignated as follows:Type FFine grain,Type MMedium grain,andType CCoarse grain.7.Evaluation7.1 The grain size rating of a cemented tungsten carbidespecimen is accomplished by selecting the photomicrographsin Figs.1-3 that most nearly match the field observed on thespecimen being evaluated(see Appendix X1).7.2 A range of numerical values for various concentrationsof tungsten carbide particles,even though arbitrary,is sug-gested in Table 1.8.Report8.1 After visual comparison of a specimen with the photo-micrographs contained in this practice,the apparent grain sizeof a particular specimen shall be rated relative to one or moreof the photomicrographs.Cobalt contents should always bespecified.For example,a cemented tungsten carbide specimen1This practice is under the jurisdiction of ASTM Committee B09 on MetalPowders and Metal Powder Products and is the direct responsibility of Subcom-mittee B09.06 on Cemented Carbides.Current edition approved April 1,2006.Published April 2006.Originallyapproved in 1962.Last previous edition approved in 2000 as B 390 92(2000).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.1Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959,United States.Copyright by ASTM Intl(all rights reserved);Thu Apr 16 05:00:31 EDT 2009Downloaded/printed byLaurentian University pursuant to License Agreement.No further reproductions authorized.containing approximately 6%cobalt,having a fine grain sizeand a grain size distribution similar to the one shown in Fig.1(a)would be reported as Type 6-F.The“F”indicates a finegrain size and the“6”identifies the cobalt content.9.Precision and Bias9.1 Visual comparison of cemented carbide microstructureswith the Carbide Grain Size Chart is subjective.No precisionand bias statement can be made for this practice.10.Keywords10.1apparent grain size;cemented carbides;cementedtungsten carbides;grai