ASTM E930-2018 Standard Test Methods for Estimating the Largest Grain Observed in a Metallographic Section (ALA Grain Size).pdf

1、Designation: E930 18Standard Test Methods forEstimating the Largest Grain Observed in a MetallographicSection (ALA Grain Size)1This standard is issued under the fixed designation E930; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision

2、, 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.This standard has been approved for use by agencies of the U.S. Department of Defense.INTRODUCTIONCommercial materia

3、l specifications sometimes include, in size limits for grain structures, the needfor identification of the largest grain observed in a sample, often expressed as ALA (as large as) grainsize. The methods presented here are for use when the number of large grains is too few formeasurement by Test Meth

4、ods E112. It shall be understood that larger (but unobserved) grains mayexist in the local volume sampled.1. Scope1.1 These test methods describe simple manual proceduresfor measuring the size of the largest grain cross-sectionobserved on a metallographically prepared plane section.1.2 These test me

5、thods shall only be valid for microstruc-tures containing outlier coarse grains, where their population istoo sparse for grain size determination by Test Methods E112.1.3 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of

6、the user of this standard to establish appro-priate safety, health, and environmental practices and deter-mine the applicability of regulatory limitations prior to use.1.4 This international standard was developed in accor-dance with internationally recognized principles on standard-ization establis

7、hed in the Decision on Principles for theDevelopment of International Standards, Guides and Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:2E3 Guide for Preparation of Metallographic SpecimensE7 Terminology

8、 Relating to MetallographyE112 Test Methods for Determining Average Grain SizeE407 Practice for Microetching Metals and AlloysE1181 Test Methods for Characterizing Duplex Grain Sizes2.2 ASTM Adjuncts:ALAGrain Size VisualAid for Comparison Procedure (OneOpaque Print and One Transparency)33. Terminolo

9、gy3.1 Definitions:3.1.1 For definitions of terms used in these test methods, seeTerminology E7.3.2 Definitions:3.2.1 ALA grain, nthe largest grain observed in a randomscatter of individual coarse grains comprising 5 % or less of thespecimen area, where the apparent grain size of the coarsegrain(s) d

10、iffers by 3 or more ASTM grain size numbers fromthe balance of the microstructure.3.2.2 outlier grain, na grain substantially different in sizefrom the predominant grain size in a microstructure; forexample, an ALA grain.4. Significance and Use4.1 The presence of large grains has been correlated wit

11、hanomalous mechanical behavior in, for example, crackinitiation, crack propagation, and fatigue. Thus there is engi-neering justification for reporting the ALA grain size.4.2 These methods shall only be used with the presence ofoutlier coarse grains, 3 or more ASTM grain size numbers1This test metho

12、d is under the jurisdiction of ASTM Committee E04 onMetallographyand is the direct responsibility of Subcommittee E04.08 on GrainSize.Current edition approved Dec. 1, 2018. Published February 2019. Originallyapproved in 1983. Last previous edition approved in 2015 as E930 99(2015). DOI:10.1520/E0930

13、-18.2For 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.3Available from ASTM International Headquarters. Order Ad

14、junct No.ADJE0930.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesThis international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDe

15、velopment of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.1larger than the rest of the microstructure and comprising 5 % orless of the specimen area.Atypical example is shown in AnnexA1 as Fig. A1.1.4.3 These m

16、ethods shall not be used for the determination ofaverage grain size, which is treated in Test Methods E112.Examples of microstructures that do not qualify for ALAtreatment are shown in Annex A1 as Fig. A1.2, Fig. A1.3, andFig. A1.4.4.4 These methods may be applied in the characterization ofduplex gr

17、ain sizes, as instructed in the procedures for TestMethods E1181.5. Sampling5.1 Sampling shall have been performed according to sam-pling procedures in Test Method E112.5.2 The generally intended plane of polish is a plane passingthrough the center of the thickness and exhibiting maximumgrain aspect

18、 ratio.5.3 Other polishing planes which may be more useful orpredictive in specific products or applications are allowed.5.4 An unambiguous description of the plane of polish or areference to a description or drawing of the plane of polishshall be a part of the test report.5.5 Specimens shall be pre

19、pared in accordance with Meth-ods E3 and Practice E407.6. Procedures6.1 In 6.2 a comparison procedure is presented with accu-racy near to 61 ASTM grain size number, for the apparent sizeof the largest grain. For greater accuracy, a measuring proce-dure is described in 6.3.Amanual quantitative method

20、, to serveas referee procedure, is described in 6.4. (The measuringprocedure is especially recommended over the comparisonprocedure when the ALA grain sections shape is substantiallydifferent from those shown in Annex A2.)6.2 Comparison Procedure:6.2.1 Scan the entire microsection at a convenient ma

21、gnifi-cation to locate the larger grains.6.2.2 Position the largest grain in the middle of the micro-scope viewing screen, eyepiece, or on a photomicrograph.6.2.3 Estimate the grain size by comparing theALAgrain toa visual aid that is based on the relationship of area to grain sizeexpressed in Table

22、 1. Examples of visual aids are shown inAnnex A2, with their specifications in Annex A3. Fig. A2.1may be used only at the magnification specified on the aid.NOTE 1The use of Test Methods E112 comparison plates is notallowed, since few of the grain sections illustrated correspond to theaverage area f

23、or that grain size number.6.3 Measuring Procedure (for greater accuracy than withcomparison procedure):6.3.1 Locate and position the largest grain in a microscopeimage or in a photomicrograph, as in 6.2.1 and 6.2.2.6.3.2 Using a measuring eyepiece, internal reticle, or exter-nal scale, as appropriat

24、e, measure the maximum caliper diam-eter and the caliper diameter perpendicular to the maximumcaliper diameter.6.3.3 Multiply the product of these two measurements by0.785, to obtain the area of an ellipse with axes equal to thecaliper diameters at the magnification used.6.3.4 Divide this area by th

25、e square of the magnificationused, to obtain the true grain area at 1X.6.3.5 Compare this area with the grain areas in Table 1. Usethe nearest area in the table to obtain the ALA grain sizenumber, unless the next smaller or the next larger area is agreedupon between the interested parties.6.4 Refere

26、e Procedure (Image Analysis):6.4.1 Photograph the largest grain, using the largest magni-fication that shows the entire grain in the image area. (In caseof uncertainty about which of several grain sections is thelargest, photograph them all and carry out the following stepsfor all of the photographs

27、.)6.4.1.1 Verify that the magnification on the microscopealigns with the magnification selected in the image analysissoftware.6.4.1.2 Using the image analysis software, trace the perim-eter of the grain. This may be accomplished manually or byautomatic detection provided the software has the capabil

28、ity.6.4.1.3 Verify that the perimeter traced best represents thegeometry of the grain and record the area (mm2).6.4.1.4 Compare the area determined with the area columnin Table 1. Use the nearest area in the table to report the ALAgrain size number, unless the next smaller or the next largerarea is

29、agreed upon between the interested parties.6.4.1.5 If necessary, retain the photomicrograph that in-cludes a reference scale.6.5 Alternate Referee Procedure (Manual Overlay):6.5.1 Photograph the largest grain, using the largest magni-fication that shows the entire grain in the image area. (In caseof

30、 uncertainty about which of several grain sections is thelargest, photograph them all and carry out the following stepsfor all of the photographs.)TABLE 1 Relationship of ALA Grain Area to ALA Micro-Grain SizeNumberAArea, mm2Size2.06 00000 or 4.01.46 3.51.03 0000 or 3.00.703 2.50.516 000 or 2.00.365

31、 1.50.258 00 or 1.00.182 0.50.129 00.0912 0.50.0645 1.00.0456 1.50.0323 2.00.0228 2.50.0161 3.00.0114 3.50.00807 4.00.00570 4.50.00403 5.00.00285 5.50.00202 6.00.00143 6.50.00101 7.0AAdapted from Test Methods E112, Table 2.E930 1826.5.2 Apply a transparent overlay containing a square net-work of gri

32、d lines to the photograph, so that the large grain iscompletely covered by the grid. An interline grid spacing of 5mm is recommended. Count the number of grid intersections(points) that fall within the large grain being estimated. Pointsfalling on the grain boundary are counted as one half.6.5.3 Rea

33、pply the overlay to the photo at least four moretimes at different angular placements, each time tallying thegrid intersections as in 6.5.2.6.5.4 The estimated area of the grain section is determinedby the following equation:A 5P!d2M2where:P!= number of points falling within the grain averagedover s

34、everal angles,d2= area of each small square of the grid with spacing d,M = magnification of the photomicrograph, andA = estimated area of the grain section.6.5.5 Compare the area determined with the area column inTable 1. Use the nearest area in the table to report the ALAgrain size number, unless t

35、he next smaller or the next largerarea is agreed upon between the interested parties.6.5.6 Retain the photomicrograph, and record the following:grid points counted for each grid placement, Pi(); total gridpoints counted, Pi(); average number of grid points counted,P!; inter-point spacing in grid, d;

36、 magnification used, M;measured area of ALA grain, A; and the ALA grain sizenumber.7. Precision and Bias7.1 The precision and bias of these methods have not yetbeen determined.8. Keywords8.1 ALA grain; caliper diameter; comparison procedure;ellipse measurement; grain size; largest grain; measuringpr

37、ocedure; metallography; microstructure; outlier grain; point-count procedureANNEXES(Mandatory Information)A1. MICROSTRUCTURAL EXAMPLESNOTE A1.1These figures are taken from Test Methods E1181, AnnexA1.FIG. A1.1 125, ALA Condition Rateable to E930E930 183FIG. A1.2 50, Wide-Range Condition Not Rateable

38、 to E930FIG. A1.3 100, Bimodal Condition (No ALA Grain Present In Course Population)E930 184A2. ALA GRAIN SIZE VISUAL AID FOR 6.2, COMPARISON PROCEDUREFIG. A1.4 100, Necklace Condition (No ALA Grain Present In Course Population)NOTE 1This reduced illustration is for information purposes only.FIG. A2

39、.1 ALA Grain Size Visual AidE930 185A3. DIMENSIONS FOR Fig. A2.1ASTM 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 suc

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44、ve, Danvers, MA 01923, Tel: (978) 646-2600; http:/ of Figures, mmACircle1:2 Ellipse 1:4 EllipseMajor Minor Major MinorA 645 28.7 40.5 20.3 57.3 14.3B 456 24.1 34.1 17.0 48.2 12.0C 323 20.3 28.7 14.3 40.6 10.1D 228 17.0 24.1 12.0 34.1 8.5E 161 14.3 20.2 10.1 28.6 7.2ARounded to nearest 0.1 mm.E930 186