1、Designation: B 796 07Standard Test Method forNonmetallic Inclusion Content of Powders Intended forPowder Forging (PF) Applications1This standard is issued under the fixed designation B 796; the number immediately following the designation indicates the year oforiginal adoption or, in the case of rev
2、ision, 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 method fordetermining the nonmetallic inclusion level of
3、 powders in-tended for powder forging (PF) applications.1.2 The test method covers repress powder forged testspecimens in which there has been minimal lateral materialflow ( 1%). The core region of the powder forged testspecimen shall contain no porosity detectable at 1003.1.3 This test method is no
4、t suitable for determining thenonmetallic inclusion level of powder forged test specimensthat have been forged such that the core region containsporosity.At the magnification used for this test method residualporosity is hard to distinguish from oxide inclusions. Too muchresidual porosity makes a me
5、aningful assessment of the inclu-sion population impossible.1.4 The test method may be applied to materials that containmanganese sulfide (admixed or prealloyed) provided the nearneighbor separation distance is changed from 30 m to 15 m.NOTE 1The test method may be applied to powder forged parts whe
6、rethere has been a greater amount of material flow provided:The near neighbor separation distance is changed, orThe inclusion sizes agreed between the parties are adjusted for theamount of material flow.1.5 This standard does not purport to address all of thesafety concerns, if any, associated with
7、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:2E3 Guide for Preparation of Metallographic SpecimensE 768 Guide for P
8、reparing and Evaluating Specimens forAutomatic Inclusion Assessment of Steel3. Summary of Test Method3.1 A section representing the core region is cut from thepowder forged test specimen and mounted for metallographicgrinding and polishing.3.2 The polished sample is examined microscopically at amagn
9、ification of 1003 and a note made of inclusions largerthan a predetermined size.3.3 The maximum Ferets diameter is used to determineinclusion size. A Ferets diameter is a caliper diameter asillustrated in Fig. 1.3.4 The fragmented nature of some inclusions means thattheir size determination is somew
10、hat complicated. The conceptof near neighbor separation is used in determining inclusionsize. If an inclusion is within a certain distance of its neigh-boring particles, it is considered a member of an inclusioncluster or agglomerate. Detected features within 30 m of oneanother are considered part o
11、f the same inclusion. The conceptis illustrated schematically in Fig. 2.3.5 The nonmetallic inclusion level of the test specimen isreported as the number of inclusions per 100 mm2greater thanor equal to the predetermined size.4. Significance and Use4.1 The extensive porosity present in pressed and s
12、interedferrous materials masks the effect of inclusions on mechanicalproperties. In contrast, the properties of material powder forgedto near full density are strongly influenced by the composition,size, size distribution, and location of nonmetallic inclusions.4.2 The test for nonmetallic inclusion
13、s in powder forgedsteels is useful as the following:4.2.1 Characteristic to classify or differentiate one grade ofpowder from another.4.2.2 Means of quality comparison of powders intended forpowder forging, lot to lot.4.3 Significant variations in nonmetallic inclusion contentwill occur if:4.3.1 The
14、 powder used to form the test specimen does notmeet powder forging quality standards for nonmetallic inclu-sion content.1This 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 De
15、nsity Powder Metallurgy Materials.Current edition approved Oct. 1, 2007. Published November 2007. Originallyapproved in 1988. Last previous edition approved in 2002 as B 796 02.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. F
16、or 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 standard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.4.3
17、.2 Processing of the powder forged test specimen hasbeen carried out under conditions that do not permit oxidereduction or allow oxidation of the test specimen, or both.5. Apparatus5.1 Equipment for the metallographic preparation of testspecimens.5.2 A metallographic microscope permitting observatio
18、nand measurement up to a magnification of 1003 using lightwith a wavelength of 544 nm (green filter), an objective lenswith a magnification of from 83 to 12.53, and a numericalaperture between 0.16 and 0.20.NOTE 2Defining the light optics used is important because thisdetermines the features that wi
19、ll be resolved, and all detected features areincluded in the assessment of inclusion size.6. Test Specimen Preparation6.1 Mix the powder that is intended for use in a powderforging application with an appropriate amount of graphite andlubricant.6.2 Press a cylindrical compact to a specified green de
20、nsityand heat the compact to the desired forging temperature usinga furnace with a suitable reducing gas atmosphere.6.3 Transfer the heated cylindrical compact to a pre-heateddie in a fast-acting press and repress forge the cylinder.6.4 The relationship between the diameter of the greencompact and t
21、he diameter of the forging die shall be such thatthe lateral flow during the repress forging operation is 1%.7. Sampling7.1 A metallographic sample shall be removed from thepowder forged test specimen, austenitized, and quenched.7.2 The polished surface of the sample to be examined shallbe not less
22、than 350 mm2(0.54 in.2) in area. Multiple sectionsare permitted in order to obtain the necessary area for mea-surement.7.3 The polished surface shall be parallel to the direction offorging, that is, parallel to the direction of travel of the forgingpunch, and shall represent the core region of the t
23、est specimen.8. Procedure8.1 Preparation of SpecimensIn polishing the specimens,it is highly important that a clean polish be obtained and thatthe inclusions not be pitted, dragged, or obscured. It isrecommended that the procedures described in Practice E3andGuide E 768 be followed. Automated grindi
24、ng and polishingprocedures are recommended. Examine specimens in theas-polished condition, free of the effects of any prior etching,if used.8.2 Measurement of Nonmetallic Inclusion Content:8.2.1 Survey at least 350 mm2(0.54 in2) of the surface of thepolished specimen at a magnification of 1003 using
25、 light witha wavelength of 544 nm (green filter), an objective lens with amagnification of from 83 to 12.53, and a numerical aperturebetween 0.16 and 0.20.8.2.2 Size detected inclusions on the basis of near neighborseparation. Features within 30 m of one another are consid-ered to be part of the sam
26、e inclusion.8.2.3 For individual features less than 30 m in size, threesuch features within 30 m of one another are required toconstitute an inclusion aggregate.8.2.4 Add an individual feature less than 30 m in size to aninclusion larger than 30 m, provided both features are within30 m of one anothe
27、r. Examples are given in Figs. 3 and 4.8.2.5 Measure and record the number of inclusion particlesaccording to the principle of near neighbor separation and sizedusing the maximum Ferets diameter that are as follows:8.2.5.1 Greater than or equal to 30 m but less than 100 min length,FIG. 1 Schematic i
28、llustration of Ferets diameter.FIG. 2 Schematic illustration of the “near neighbor” concept andmaximum Ferets diameter.FIG. 3 Example of a spotty oxide inclusion. The maximum Feretsdiameter is indicated.B7960728.2.5.2 Greater than or equal to 100 m but less than 150 min length, and8.2.5.3 Greater th
29、an or equal to 150 m in length.9. Report9.1 Report the number of nonmetallic inclusions per100 mm2that are as follows:9.1.1 Greater than or equal to 30 m but less than 100 m inlength.9.1.2 Greater than or equal to 100 m but less than 150 min length.9.1.3 Greater than or equal to 150 m in length.9.2
30、The total area examined.10. Precision and Bias10.1 The precision and bias that can be expected through theuse of this test method is currently under review by Subcom-mittee B09.11.11. Keywords11.1 nonmetallic inclusions; powder forged (PF) steel partsSUMMARY OF CHANGESCommittee B09 has identified th
31、e location of selected changes to this standard since the last issue (B796-02)that may impact the use of this standard.(1)Anew section Test Specimen Preparation has been added asSection 6 . Subsequent sections have been renumbered.ASTM International takes no position respecting the validity of any p
32、atent 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.This standard is subject to revisi
33、on 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 International Headquarters. Your co
34、mments 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 below.This standard is copyrigh
35、ted 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. 4 Example of a discontinuous sulphide inclusion. Themaximum Ferets diameter is indicated.B796073
