ASTM E() – Standard Test Methods for Determining Average Grain Size Using Semiautomati. Purchase your copy of ASTM E – 97() as a PDF download or hard copy directly from the official BSI Shop. All BSI British Standards. The ASTM Designation: E–97 requires five hundred data points for a given sample and this analysis is time-consuming and tedious for the.
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A number in parentheses indicates the year of last reapproval. The test methods may be applied to specimens with equiaxed or elongated grain structures with either uniform or duplex grain size distributions.
Either semiautomatic or automatic image analysis devices may be utilized to perform the measurements. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. Current edition approved Nov. Originally approved in Last previous edition approved in as E — 97 No further reproductions authorized.
Summary e11382 Test Methods 4. These measurements are made for a large number of grains, or all of the grains in a given area, within a microscopical? A large number of measurements over several?
These devices relieve much of the tedium associated with manual measurements, thus permitting collection of a larger amount of data and more extensive sampling which will produce better statistical de? The presence of twin boundaries can be tolerated when semiautomatic digitizing tablets are utilized but measurement errors are more likely to occur. Etching techniques and etchants that do not delineate twin boundaries are preferred for these specimens.
Discrimination of grain boundaries but not twin boundaries using image amendment techniques may be possible with some automatic image analyzers. Such techniques may be employed if the operator can demonstrate their reliability. These features should be removed from the? Wstm deep etching with such etchants to bring out 1e382 fainter boundaries should not be done because deep etching creates excessive relief deviation from planar conditions and will bias certain measurements, particularly grain intercept lengths and grain areas, performed by automatic image analysis and also measurements made with a digitizing tablet.
Use of high magni? For such structures, use the lowest possible magni? Consequently, the imaging system must be kept clean. Prior to analysis, center the light source as described in the operating instructions for the microscope and adjust the?
Digital correction methods for nonuniform illumination may be used subsequently; however, these methods should not be used in lieu of proper microscope alignment and adjustment. If a digitizing tablet is utilized for the measurements, illumination modes other than bright? For example, for optically anisotropic materials that are difficult to etch, crossed polarized light may be required to observe the grain structure.
Such images exhibit grain contrast or color differences between grains rather than grain boundary delineation.
These images, which usually exhibit low light intensities, can be measured using a digitizing tablet but may be more difficult to measure with automatic image analyzers. A variety of approaches can be employed. Aastm simplest is to? Alternatively, the grid can be placed on an eyepiece reticle. The cursor is moved over the tablet surface and the microscopist can see the illuminated cross hairs in the cursor through the eyepieces over the?
A third approach is to transfer the microstructural image, test grid image and cursor image to a television monitor. The microscopist moves the cursor across the tablet surface while watching the monitor to make the appropriate measurements.
For counting grain boundary intersections or grains intercepted, a circular test grid, such as described in Test Methods E, may be used. For measuring intercept lengths, a test grid with a number of astj spaced straight, parallel lines is used. Use of a programmable stage prevents bias in?
For automatic image analysis, the computer also controls all of the operations except, perhaps, focusing automatic focusing is optional.
Graphical data may be produced with either a printer or plotter, as desired. High levels of humidity must be avoided as staining of specimen surfaces may occur during, or before, analysis. Very low levels of humidity must also be avoided as static electricity may damage electronic components. Vibrations, if excessive, must be isolated, particularly for automatic image analysis.
Sampling location and frequency should be based upon agreements between manufacturers and users. However, the presence of an equiaxed grain structure in a wrought specimen can only be determined by examination of a plane of polish parallel to the deformation axis.
Consequently, preparation of longitudinally oriented specimens, where the plane-of-polish is parallel to the deformation axis or grain elongation direction, is recommended.
If the grain structure is not equiaxed but elongated, then grain size measurements on specimens with different orientations will vary. In this case, the grain size must be determined on longitudinal, transverse, and planar surfaces, or radial and transverse surfaces, depending on the product shape, and averaged, as described in Annex A1, to obtain the mean grain size.
If directed test lines rather than random are used for intercept counts on non-equiaxed grains in plate or sheet type specimens, the required measurements can be made using only two principle test planes, rather than all three, due to the equivalence of test directions, as described in A1.
In most cases except for thin sheet or wire specimensa minimum polished surface area of mm2 0. Adjust the stage movement so that the interface between adjacent specimens is avoided, that is, is not in the? Guidelines and recommended practices are given in Practice E3. All scratches and smearing must be removed, although very? Scratches from grinding, or from polishing with abrasives larger than about 1-? Excessive relief, pitting or pullout must be avoided.
Specimens must be carefully cleaned and dried after polishing. Other treatment conditions, such as as-hot rolled, as-hot forged, or as-cold drawn, may be tested as required but it must be recognized that the grain structure for these conditions may not be equiaxed.
Unmounted specimens generally should have a surface area much larger than required for measurement to facilitate leveling, if automatic image analysis is to be utilized, as described in The choice of the proper etchant depends on the composition and heat treatment condition of the specimen. For automatic image analysis, a? Test Methods E and Ref 1 3 list many suitable etchants.
A very high degree of grain boundary delineation is required. Grain contrast 1 and tint etchants 1,2 are very effective because they generally provide full delineation of the grain structure. For such specimens, semiautomatic digitizing tablet measurements are preferred. Certain electrolytic etching techniques, 3,4 as summarized in Ref 1 will delineate the grain boundaries but not the twin boundaries thus permitting use of automatic image analysis.
The nature of the heat treatment is usually important, particularly the tempering temperature, if used. Subjecting the specimen to a temper embrittlement cycle may enhance the etch response, but this treatment is not helpful if the amounts of P, Sn, As, and Sb are very low.
In general, coarse-grained specimens are more easily etched for prior-austenite grain size. Reference 1 provides guidance for development of prior-austenite grain boundaries. In general, it is difficult to reveal the prior-austenite grain boundaries to the level required for automatic image analysis, unless the image can be edited successfully prior to measurement, and measurements with a digitizing tablet may be preferable. Again, this technique works best with relatively coarse-grained steels.
However, these techniques must be used with caution because skeletonization can produce false grain boundaries and watershed segmentation may not produce grain boundaries between two adjacent grains with similar color or gray level. Light pen, mouse, or trackball editing of images to complete missing grain boundaries before measurement is an acceptable technique, although slow. If enlargements are used, the magni?
ASTM E1382 – 97(2015)
A sufficient number of? Calibration and Standardization Then, make enlargements of the grain structure images using the same enlarger setting. Alternatively, determine the degree of enlargement by comparing the size of features on the enlargement to their size on the contact print.
Repeat this process for a number of features in the image. Determine the average enlargement factor of the measured features and multiply this value by the magni? Semiautomatic Digitizing Tablet Avoid an excessively high number of grains per photograph as counting accuracy may be impaired. To minimize operator fatigue, and to ensure measurement accuracy, the smallest grain on the photomicrograph should be about 5 mm in diameter.
Take the micrographs at random, that is, without bias in the? Fix each micrograph to the tablet surface, for example using masking tape, to prevent movement during analysis. Drop the measurement grid onto the photograph to prevent placement bias. Tape the grid corners to the micrograph or tablet surface to prevent movement during measurement. With an inverted-type microscope, simply place the specimen face down on the stage plate and hold it in place with the stage clamps.
With an upright-type microscope, place the specimen on a slide and level the surface using clay or plasticene between the specimen and slide. To avoid problems with adherent tissue paper, follow the alternate leveling procedure described in Practice E Procedure section. For manual stage movement, move the x- and y-stage controls without looking at the image.
If a programmable stage is available, set the stage controls to sample the image in a systematic manner. If an excessively high number of grains are present in the image, measurement precision will be impaired.
For accurate measurement of intercept lengths or grain areas, the smallest grains should be at least 5 mm in diameter on the television monitor 9 for a typical — mm 12—13 in. Counting accuracy will be impaired if the number of grains visible is excessively high smaller apparent size in the? There may be other possible methods, or other equivalent procedures, that can be used to measure grain size.
The operator should evaluate the precision and accuracy of such methods on specimens carefully evaluated by one or more of the recommended methods before utilizing an alternate method or procedure. It should be recognized that slight differences in grain size ratings may be obtained using different methods because different aspects of the grain structure are being assessed. Also, minor deviations from equiaxed conditions may accentuate these differences.
Methods based on the average grain area or the number of grains per unit area are directly related to the total length of grain edges per unit volume, LV.
Methods based on the mean intercept length or the number of grain boundary intersections per unit length are directly related to the grain boundary surface area per unit volume, SV.