Grain size measurement according to astm standards

Methods for microscopic grain size measurements according to ASTM standards and codes.

1. Grain Size Measurement According To ASTM Standards Jabin Mathew Benjamin 13MY04 Dept. of Metallurgical Engineering

2. ASTM standard E112-10 Determination of planar grain size A microscopically-determined grain size of No. 1 has 1.000 grains/in 2 at 100X

3. Comparison Procedure Comparison of the grain structure to a series of graded images Wall chart Clear plastic overlays An eyepiece reticle. Use with a 10X objective The following chart was used to make this image METHODS FOR DETERMINING THE AVERAGE GRAIN SIZE ASTM METHODS E 112 PCN 12-501 120-10 Plate 1B Untwinned Grains 100X

4. Repeatability and reproducibility of ±1 grain size number. Specimens consisting of equiaxed grains. Comparison Charts Plate I— Untwinned grains (flat etch). Plate II—Twinned grains (flat etch) Plate III—Twinned grains (contrast etch) Plate IV—Austenite grains in steel

5. Planimetric or Jeffries’ Procedure Involves an actual count of the number of grains within a known area. Number of grains per unit area, N A , is used to determine the ASTM grain size number, G. Repeatability and reproducibility of ±0.25 grain size units Require marking off of the grains as they are counted.

6. Relationship Between Magnification Used and Jeffries’ Multiplier, f, for an Area of 5000 mm2 (f= 0.0002 M 2 )

7. Intercept Procedure Actual count of the number of grains intercepted grain boundary, per unit length of test line Lineal intercept length, used to determine the ASTM grain size number, G. Repeatability and reproducibility are less than ± 0.5 grain size units. Faster than the planimetric method for the same level of precision. Structures consisting of elongated grains.

8. Heyn Lineal Intercept Procedure The number of grains intercepted by one or more straight lines sufficiently long to yield at least 50 intercepts. Intercept Intersection Circular Intercept Method Automatically compensate for departures from equiaxed grain shapes Ambiguous intersections at ends of test lines are eliminated

9. ASTM No. 0 has a mean intercept size of 32.00 at 100X.  l o = 32.00mm

10. Reference Abrams , H., “Grain Size Measurement by the Intercept Method ,” Metallography , Vol 4, 1971, pp. 59–78 . “Methods for determining the average grain size” ASTM methods E 112 PCN 12-501 120-10

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