1、Designation: B 931 03Standard Test Method forMetallographically Estimating the Observed Case Depth ofFerrous Powder Metallurgy (P/M) Parts1This standard is issued under the fixed designation B 931; the number immediately following the designation indicates the year oforiginal adoption or, in the cas
2、e 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 A metallographic method is described for estimating theobserved case depth of ferrous powd
3、er metallurgy (P/M) parts.This method may be used for all types of hardened cases wherethere is a discernible difference between the microstructure ofthe hardened surface and that of the interior of the part.1.2 This standard does not purport to address all of thesafety concerns, if any, associated
4、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:B 243 Terminology of Powder Metallurgy2E 407 Practice for Microet
5、ching Metals and Alloys33. Terminology3.1 DefinitionsDefinitions of powder metallurgy (P/M)terms can be found in Terminology B 243. Additional descrip-tive information is available in the Related Material section ofVol 02.05 of the Annual Book of ASTM Standards.3.2 The metallographically estimated o
6、bserved case depth isdefined as the distance from the surface of the part to the pointwhere, at a magnification of 100X, there is a discernibledifference in the microstucture of the material.4. Summary of Test Method4.1 The powder metallurgy part is sectioned and the surfaceprepared for metallograph
7、ic evaluation. The metallographicspecimen is etched and the distance is measured from thesurface of the part to the point at which a discernible differencein the microstructure of the material is observed.5. Significance and Use5.1 The engineering function of many P/M parts mayrequire an exterior po
8、rtion of the part to have a hardened layer.Where case hardening produces a distinct transition in themicrostructure, metallographic estimation of the observed casedepth may be used to check the depth to which the surface hasbeen hardened.6. Apparatus6.1 Equipment for the metallographic preparation o
9、f testspecimenssee Appendix X1.6.2 Metallographic Microscope, permitting observation andmeasurement at a magnification of 1003.7. Reagents and Materials7.1 Etchants such as 2 to 5 % nital, nital/picral combina-tions, or other suitable etchants. For more information onsuitable etchants refer to Pract
10、ice E 407.8. Test Specimens8.1 Cut a test specimen from the P/M part, perpendicular tothe hardened surface at a specified location, being careful toavoid any cutting or grinding procedure that would affect theoriginal microstructure.8.2 Mounting of the test specimen is recommended forconvenience in
11、surface preparation and edge retention. Edgeretention is important for proper measurement of the observedcase depth.9. Procedure9.1 Grind and polish the test specimen using methods suchas those summarized in Appendix X1.9.2 Etch the specimen with etchants such as 2 to 5 % nitalor nital/picral combin
12、ations.9.2.1 Observed Case Depth:9.2.1.1 Examine the surface region of the part at a magni-fication of 1003.9.2.1.2 Measure the distance from the surface of the part tothe point where there is a discernible difference in the micro-structure of the material.NOTE 1The nature and amount of intermediate
13、 transformation prod-ucts will depend on the material being heat treated, its density, and thetype of surface hardening treatment being used. The sharpness of thechange in the microstructure at the point of transition will therefore vary.The microstructure expected at this transition point should be
14、 agreedbetween the producer and user of the part. Magnifications higher than1003 may be used to check the microstructure of the part in the region of1This test method is under the jurisdiction of ASTM Committee B09 on MetalPowders and Metal Powder Products and is the direct responsibility of Subcom-
15、mittee B09.05 on Structural Parts.Current edition approved Oct. 1, 2003. Published October 2003.2Annual Book of ASTM Standards, Vol 02.05.3Annual Book of ASTM Standards, Vol 03.01.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.the t
16、ransition zone. However, the metallographic estimate of the observedcase depth shall be made at a magnification of 1003.10. Report10.1 Report the following information:10.1.1 The type of material and case measured,10.1.2 The type of etchant used,10.1.3 The location of the measurement, and10.1.4 The
17、metallographically estimated observed casedepth to the nearest 0.1 mm.11. Precision and Bias11.1 The precision that can be expected through the use ofthis test method is currently under review by SubcommitteeB09.05 on Structural Parts.12. Keywords12.1 case depth; observed case depth; P/M; powdermeta
18、llurgyAPPENDIX(Nonmandatory Information)X1. SAMPLE PREPARATIONX1.1 The methods described in this appendix are provenpractices for metallographic preparation of porous P/M mate-rials. It is recognized that other procedures or materials used inpreparation of a sample may be equally as good and can beu
19、sed on the basis of availability and preference of individuallaboratories.X1.2 Method 1:X1.2.1 The porous samples should be free of oil or coolant.Remove any oil using Soxhlet extraction. Mount and vacuumimpregnate samples with epoxy resin, to fill porosity and toprevent the pickup of etchants. Use
20、a sample cup or holder toform the mount. Pour epoxy resin over the sample in the cup toa total depth of about 0.75 in (19 mm). Evacuate the cup tominus 26 in. of mercury (88 kPa) and hold at that pressure for10 min. Then restore ambient air pressure to force the resin intomost of the sample. Cure at
21、 room temperature or at 122F(50C).X1.2.2 Grind on 240, 400, and 600 grit wet SiC paper, on arotating wheel, and change the polishing direction 90 aftereach paper. Etch samples for 1 min in their normal etchant, forexample, 2 % nital, to begin to open the porosity. Roughpolishing for 8 to 12 min tota
22、l on 1 m alumina (Al2O3), longnapped cloth (for example Struers felt cloth), at 250 rpm, and300 gf load, using an automated polisher opens smeared pores.This rough polishing opens and exaggerates the pores. Toreturn the pores to their true area fraction, polish for 4 min at125 rpm on a shorter nap c
23、loth (for example Struers MOLcloth), with 1 m diamond paste. Final polishing is done for 20to 30 s using 0.05 m deagglomerated alumina, and a longnapped cloth (for example, Buehler Microcloth), at 125 rpm,and 75 gf load, on an automated polisher. Polishing may alsobe done by hand for the times indic
24、ated. The first twopolishings require moderate pressure and the final polishrequires light pressure.X1.2.3 The metallographic structure should be free ofsmeared porosity. Generally at 800 to 10003, the edge of asmeared over pore will appear as a thin gray line outlining oneside of the pore, and occa
25、sionally outlining most of the pore.X1.3 Method 2:X1.3.1 The specimen should be carefully selected so that itis representative of the region of interest. After selection, thespecimen may require sectioning to provide a workable speci-men. Sectioning may be made employing an abrasive ordiamond wheel.
26、X1.3.2 Heat should be avoided to prevent occurrence ofpossible changes in microstructure. If slow feeds are employed,a coolant may not be necessary to avoid temperature buildups.If abrasive wheels are used, then a coolant is often necessary toavoid overheating of the specimen.X1.3.3 If a coolant is
27、employed, it may be retained withinthe pores. The lubricant must be removed prior to the prepa-ration of the specimen for examination. This may be accom-plished by using a Soxhlet extractor or an ultrasonic cleaner.The extraction condenser is the most efficient and the leastexpensive.X1.3.4 Generall
28、y, specimens to be evaluated for case depthare mounted to provide edge retention. There are many kinds ofmounting compounds available. Most common materials in-clude epoxies (powder or liquid), diallyl phthalate, or Bakelite.Of these, Bakelite is sometimes preferred because it is harderand therefore
29、 provides improved edge retention. Bakeliterequires equipment to apply heat and pressure, whereas theepoxies do not.X1.3.5 After mounting, the specimen is ground to provide aflat, stress-free surface. A belt grinder is generally used firstwith care to prevent heating of the specimen. Grit size isdep
30、endent on the preference of the metallographer, althoughfiner grits are preferred.X1.3.6 The specimen is then hand ground on four emerypapers, generally of 240, 320, 400, and 600 grit.X1.3.7 Etch samples for 1 min in their normal etchant, forexample, 2 % nital, to begin to open the porosity.X1.3.8 W
31、et polishing follows hand grinding and etching.Several polishing media are employed including diamondpaste, magnesia, alumina, etc. Grit size varies between 1 and0.3 m and is applied to nap-free cloths such as nylon. Toremove remaining scratches and stress, a soft cloth with finerpolishing compound
32、is employed. Generally a short nappedB931032cloth is preferred. A fine 0.5 m alumina is recommended. Forbest results, and to ensure complete freedom of pores fromworked metal, repeat the polishing and etching procedure.Final polishing generally requires 3 to 5 min.X1.3.9 Automated polishing equipmen
33、t is also available.Automated polishing is accomplished by moving the specimenacross a polishing cloth in an abrasive solution undergoingvibrating action. Cloths and abrasives available are numerousand are generally selected by experience of the metallographer.X1.4 Two additional schemes for the pre
34、paration of sin-tered ferrous materials, one manual and the other automated,are discussed. The first method, basic manual preparation, hasmost likely been used to prepare more samples for metallo-graphic examination than any other single method. The as-sumption is made that the sample has been mount
35、ed andpre-ground to give a planar surface. Vacuum impregnation withan epoxy resin is recommended for samples to be used in casedepth measurement.X1.4.1 Basic Manual Sample Preparation:X1.4.1.1 Grind samples using progressively finer abrasivepapers.(a) Routinely, 240, 320, 400, then 600 grit (U.S. St
36、andarddesignation) SiC abrasive paper strips are used.(b) Lubricate and cool the sample with a continuous flow ofwater.(c) Rotate the sample 90 before proceeding to the nextpaper.(d) Clean the surface of the sample with a soft cloth orpaper towel before grinding on each paper.NOTE X1.1Do not progres
37、s to the next paper strip until all evidenceof the previous step has been removed.X1.4.1.2 Etching prior to polishing. This step is optional.(a) Etch with 2 or 5 % nital prior to the first polishing step.(b) Rinse with running water and dry with filtered, dry,compressed air.X1.4.1.3 Coarse polishsin
38、gle step.(a) Use a slurry made of distilled or deionized water with1mAl2O3. Polish using a Nylon cloth.(b) Charge the cloth with the slurry at the start of the cycleand periodically as the cloth becomes dry.(c) Pressure applied to the sample should be moderate toheavy and movement should be counter
39、to the direction of thepolishing wheel.(d) Wash the sample with soap and water using a softmaterial such as cotton.(e) Rinse with running water.(f) Dry the surface using filtered, dry, compressed air.(g) Repeat this step until the porosity appears to be openand the appearance of the specimen is unif
40、orm from edge toedge.(h) Periodically clean the cloth. Keep the surface free ofbuilt-up slurry and polishing debris.X1.4.1.4 Fine polishsingle step.(a) Use a slurry made of distilled or deionized water and0.05 m Al2O3. Polish using a soft, napped, fine, polishingcloth.(b) Charging of the cloth, pres
41、sure applied to the sample,direction of sample movement, and cleaning of the sample aresimilar to the conditions used in coarse polishing.(c) Use short polishing times to minimize rounding andrelief.(d) Perform the operations described in X1.4.1.3(d), (e),and (f).X1.4.1.5 Dry the sample in a vacuum
42、chamber in order toremove entrapped moisture.X1.4.1.6 Remove any stains by washing with soap andwater.(a) Dry with compressed air.X1.4.2 Basic Automated Sample Preparation:X1.4.2.1 Clamp or set the samples in the multi-sampleholder.(a) Try to prepare materials with similar composition andhardness at
43、 one time.X1.4.2.2 Grind samples using progressively finer abrasivepapers.(a) Use 240, 320, 400, then 600 grit (U.S. Standarddesignation) SiC paper disks. The use of interrupted cutcomposite disks in place of most of the grinding papers is alsoacceptable. The disk is usually charged with 15 or 30 md
44、iamond spray.(b) Cool and lubricate with a continuous flow of preparedfluid.(c) Use pressure of 40 to 55 kPa and a time no longer than30 s.(d) Rinse the platen and sample before progressing to thenext paper.(e) Dry the samples using filtered, dry, compressed air.X1.4.2.3 Etching prior to polishing.
45、This step is optional.(a) Etch with 2 or 5 % nital prior to the first polishing step.(b) Rinse with running water and dry with filtered, drycompressed air.X1.4.2.4 Coarse polish using two steps.(a) Polish using 6 m diamond polish on a hard cloth, thatis, Nylon or chemotextile.(b) Polishing time shou
46、ld be approximately 3 min, at apressure of 40 to 55 kPa.(c) Charge the cloth at the start of the cycle and at oneminute intervals using aerosol propelled diamond spray.(d) Ultrasonically clean the samplesdo not remove fromthe holder.(e) Wash polished surfaces using soap and water.(f) Dry the surface
47、 using compressed air.(g) Polish using 3 m diamond polish on a second hardcloth, that is, woven or synthetic silk.(h) Polishing time should be 2 to 3 min at a pressure of 40to 55 kPa.(i) Repeat steps X1.4.2.4(c) through (f) as described above.(j) Take care not to contaminate the cloth used in thesec
48、ond step of coarse polishing with polish and debris from thefirst step.X1.4.2.5 Fine polish.(a) Polish using 1 m diamond polish on a soft nappedcloth.(b) Polishing time should be 1 to 2 min.B931033(c) Perform steps X1.4.2.4(c) through (f) as describedabove (use pressure toward the low end of the ran
49、ge).X1.4.2.6 Dry the sample in a vacuum chamber in order toremove entrapped moisture.X1.4.2.7 Remove stains by washing with soap and water.(a) Dry with compressed air.ASTM International takes no position respecting the validity of any patent 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 revision at any time by the responsible te
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