1、Designation: E2567 16aStandard Test Method forDetermining Nodularity And Nodule Count In Ductile IronUsing Image Analysis1This standard is issued under the fixed designation E2567; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, th
2、e 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.INTRODUCTIONDuctile cast iron, also known as nodular cast iron, and spherulitic or spheroidal graphitic iron, isproduced
3、 with graphite in a spherulitic form. Nodularizing elements, such as magnesium, cerium,lithium, sodium etc., are added to a molten metal bath of proper chemical composition to producediscrete particles of spheroidal-shaped graphite. The control of graphite shape is critical to nodulariron properties
4、.Areproducible measurement method is required for evaluation of the cast product andto control process variability. Shape is a difficult parameter to assess using standard chart methods,unless the shape is very close to well-recognized geometric shapes. Nodule density is also difficult toassess by c
5、hart methods as nodule size is also a variable and the chart cannot depict nodule densityvariations for nodules of all possible sizes. Stereological and metrological methods provide unbiasedtechniques for assessing structural variations. These procedures are best performed by image analysissystems t
6、hat eliminate operator subjectivity, bias and inaccuracies associated with manual applicationof stereological and metrological methods. The metallographic sectioning plane will cut through thenodules at random, producing images of graphite nodules with circular or near-circular peripherieswith a ran
7、ge of diameters.1. Scope1.1 This test method is used to determine the percentnodularity and the nodule count per unit area (that is, numberof nodules per mm2) using a light microscopical image ofgraphite in nodular cast iron. Images generated by otherdevices, such as a scanning electron microscope,
8、are notspecifically addressed, but can be utilized if the system iscalibrated in both x and y directions.1.2 Measurement of secondary or temper carbon in othertypes of cast iron, for example, malleable cast iron or ingraphitic tool steels, is not specifically included in this standardbecause of the
9、different graphite shapes and sizes inherent tosuch grades1.3 This standard deals only with the recommended testmethod and nothing in it should be construed as defining orestablishing limits of acceptability or fitness for purpose of thematerial tested.1.4 The values stated in SI units are to be reg
10、arded asstandard. No other units of measurement are included in thisstandard.1.5 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 determ
11、ine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2A247 Test Method for Evaluating the Microstructure ofGraphite in Iron CastingsE3 Guide for Preparation of Metallographic SpecimensE7 Terminology Relating to Metallography3. Terminology3.1 Definit
12、ionsFor definitions of terms used in this testmethod, see Terminology E7.3.2 Definitions of Terms Specific to This Standard:1This test method is under the jurisdiction of ASTM Committee E04 onMetallography and is the direct responsibility of Subcommittee E04.14 on Quanti-tative Metallography.Current
13、 edition approved April 1, 2016. Published May 2016. Originallyapproved in 2011. Last previous edition approved in 2016 as E256716. DOI;10.1520/E256716A.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMSt
14、andards volume information, refer to the standards Document Summary page onthe ASTM website.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States13.2.1 MFDMaximum Feret Diameter3.2.2 minimum size requirementthe size threshold belowwhich gra
15、phite particles are eliminated from the analysis.3.2.3 nodulea discrete graphite particle that exceeds boththe required minimum size and shape factor as defined by thismethod.3.2.4 nodule counttotal number of graphite particlesmeeting the definition of a nodule in the area of interest (AOI).3.2.5 no
16、dule density (Nodule count/unit area)number ofnodules per mm2.3.2.6 nodularitydegree of roundness, or closeness to acircular periphery, of a graphite particle in ductile iron basedupon the shape factor.3.2.7 percent nodularity by areathe total area of particlesdefined as nodules which meet the minim
17、um size requirementsdivided by the total area of all particles which meet theminimum size requirements, expressed as a percentage. See8.10.3.2.8 shape factora number between 0.00 and 1.0 result-ing from formula (Eq 2) of this method.3.2.9 spherulitic graphitein cast iron, a small, spheroidal-shaped
18、crystalline carbon body with a radial growth structure.4. Summary of Test Method4.1 This test method uses an image analyzer to measure thedegree of roundness of graphite particles, viewed on a metal-lographic sectioning plane, that are above a minimum size inorder to determine percent nodularity and
19、 nodule density. . Acommon objective used for the analysis is 10x, for an overallmagnification of approximately 100x. Higher magnificationobjectives (20x or more, for an overall approximate magnifi-cation of 200x) can be used to characterize small nodules, anda 5x magnification objective (approximat
20、e overall magnifica-tion of 50x) can be used to characterize very large nodules. Themagnification used shall be in accordance to purchaser-supplieragreement and, shall be reported in the final report (see9.18).Threshold settings are established by the operator, and can beinfluenced by factors such a
21、s polishing technique, illuminationintensity and uniformity, and lamp voltage and stability.5. Significance and Use5.1 Qualitative measurement of “nodularity” and “nodulecount” using visual estimations has been practiced for manyyears. These methods suffer from poor reproducibility andrepeatability.
22、 The introduction of computer-aided image analy-sis enables metallographers to measure and count individualparticles of interest in a microstructure with a high degree ofprecision. This greatly reduces measurement variations com-pared to visual estimation methods (see, for example, TestMethod A247).
23、5.2 This method defines a procedure for measuring thenumber of nodules and the quality of nodularity of spheruliticgraphite in a cast iron microstructure. The specimens locationin a casting or cast test specimen, and the orientation of theplane-of-polish, are governed by product standards. When apro
24、duct standard is not defined, choose the test locationrandomly or at specific systematically chosen depths asneeded. The plane-of-polish may be parallel or perpendicularto the solidification direction, or chosen at random, dependingupon the needs of the study.5.3 This test method may be used to dete
25、rmine variationswithin a given test specimen, within a given location in acasting, between different locations in a casting, or for the samelocation in different castings over time. Results from this testmethod may be used to qualify material for shipment inaccordance with guidelines agreed upon bet
26、ween purchaserand manufacturer or can be used to monitor process quality orproduct variations.5.4 Measurements are performed using a computer-controlled automatic image analysis system.5.5 A minimum number of specimens and a minimumsurface area to be evaluated may be defined by producer-purchaser ag
27、reement, provided at least 500 particles meetingthe minimum size requirements are measured. The number ofparticles analyzed shall be indicated in the final analysis report(see 9.6).6. Test Specimens and Statistical Sampling6.1 Test Specimens:6.1.1 The number and location of test specimens, and theor
28、ientation of the plane-of-polish, should be defined by productstandards or by producer-purchaser agreements. When this isnot possible, the metallographer should use common-senseengineering analysis to decide on the number of specimensbased upon the size of the casting, or the number of castings inth
29、e lot. The plane-of-polish may be chosen at random, orparallel or perpendicular to the solidification direction, depend-ing upon the information required. The number and locationsof test specimens, and the orientation of plane-of-polish, can bedefined by product standards or producer-purchaser agree
30、-ments.6.1.2 Each specimen should have a surface area largeenough to provide a number of fields-of-view at the requiredmagnification. In general, a 10 10 mm surface area, or itsequivalent area, is an acceptable approximate specimen size.6.1.3 It is recommended to avoid sampling in the near-surface r
31、egion, as this region will exhibit large variations ingraphite structure as compared to areas further below thecasting surface.6.2 Specimen Preparation:6.2.1 Metallographic specimen preparation must be care-fully controlled to produce an acceptable quality surface forimage analysis. Guidelines for p
32、reparing metallographic speci-mens are given in Guide E3.6.2.2 Mounting of specimens is not required, but mayfacilitate identification coding or grinding and polishing.6.2.3 The polishing procedure must remove all deformationand damage induced by the cutting and grinding procedure.Scratches and smea
33、red graphite or matrix must be removed byfinal polishing with an abrasive of about 1 m or less in size.Scratches must be small enough so as not to be detected duringthe thresholding step in the image analysis procedure.E2567 16a26.2.4 Excessive relief between constituents on the plane-of-polish and
34、excessive pitting or pullout of the soft graphite mustbe avoided. Graphite retention is critical. Specimens must becarefully cleaned and dried after polishing. Castings cancontain shrinkage cavities and seepage of liquids or abrasivesfrom these voids must be prevented.6.2.5 Graphite shall be examine
35、d in the unetched condition.Etching the specimen is unnecessary and can lead to difficultiesin segmenting the graphite from other microstructural features.It may not be possible to separate graphite from voids.6.2.6 The preparation must be of sufficient quality to revealthe exact periphery of each n
36、odule in the unetched condition.6.3 Statistical Sampling:6.3.1 At any specific test location, a minimum of 500graphite particles should be analyzed for nodularity. In mostcases it will be required to measure multiple fields of view toachieve the 500 particles per analysis minimum.7. Calibration7.1 I
37、mage analysis software includes a calibration proce-dure to determine the pixel size in the X and Y directions foreach microscope objective (and any fixed zoom factors). If anylinear or area data will be reported the system should becalibrated. Use a certified stage micrometer or one that istraceabl
38、e to a certified stage micrometer, to determine thelinear magnification for each objective (or for each objectiveand each available fixed zoom factor). To determine the pixellength in the X direction, the stage micrometer must be orientedso that its image appears as close to horizontal (0) on themon
39、itor as possible. When it is necessary to calibrate the pixelsize in the Y direction, orient the stage micrometer on the stageso that the scale appears as close as possible to vertical on themonitor. Light intensity and focus should be adjusted toprovide the sharpest image achievable. Always consult
40、 themanufacturers operating manual for the specific calibrationroutine.8. Procedure8.1 Correct illumination is critical in all image analysiswork, and measurement of graphite is no exception.8.1.1 The lamp should be checked for correct alignment andthe illumination intensity should be adjusted to th
41、e levelrequired by the camera. Avoid saturating the camera. If a lightover-flow indicator is available it must be used to set a constantlight intensity. This will increase the repeatability of resultsfrom one analysis to another.8.1.2 If a shading correction is available, it shall be used asit reduc
42、es light variations across the image; this improvesthresholding.8.2 Selection of magnification and measurement field is alsoof great importance.8.2.1 At low magnification, survey the mount forhomogeneity, polishing defects and abnormalities.8.2.2 The default objective magnification used for theanaly
43、sis is 10X which will produce an overall magnification ofapproximately 100X.Ahigher magnification objective (20X ormore) can be used when characterizing microstructures withvery small graphite particles. A 20X objective lens willproduce and overall magnification of approximately 200X.Inversely, a lo
44、wer magnification objective, such as 5X, can beused when analyzing very large graphite particles. A 5Xobjective will produce an overall magnification of approxi-mately 50X. In all cases, the magnification selected shall beagreed upon via a purchaser-supplier agreement and, themagnification of the ob
45、jective used for the analysis shall beindicated in the final report (see 9.18).8.2.3 The industry norm for the minimum size to beconsidered as a nodule is 10 microns MFD. This limit is lowerfor thin walls castings. Other size limit can be used accordingto producer-purchaser agreements. Remove all pa
46、rticles fromthe analysis that have a MFD of less than 10 m. This has theeffect of removing noise, stray pixels, and smaller particles.8.3 Well-defined particles should be visible on the monitor.Digitize the image to be analyzed. This image may haveroutines performed on it either to make the dark nod
47、ules darkeror the white matrix whiter, but the shape and size of the nodulemust be maintained. Smoothing or averaging filters that changethe size or shape of a particle shall not be used.8.4 The densitometer settings, or gray level threshold set-tings (or bit plane overlay), are chosen to segment th
48、e graphiteparticles of interest from the matrix. These threshold settingsmay result in detection of undesired features, such as voids,nitrides or inclusions.Adjust the threshold settings to minimizeor prevent detection of these unwanted features. Some of theundesired constituents that are detected m
49、ay be eliminated ifthey are smaller than the minimum size.8.5 It is important to measure only whole particles. Aproperly sized guard frame shall be used to correctly measuregraphite particles that intersect the edges of the measuringframe.8.6 To qualify a graphite particle as a nodule its shape mustmeet or exceed a certain minimum shape factor value asdefined in 8.88.7 Additional fields-of-view are evaluated until at least 500individual particles are measured.8.8 To determine if a graphite particle above the minimumsize qualifies as a nodule, its shape must be quant
