Determination of Estimating the Average Grain Size of Metal
1 Scope
1.1 This standard specifies the representation and determination methods for average grain size of metallic structure, including comparison procedure, planimetric procedure and intercept procedure; these methods are applicable to single-phase structure, but they, with specific requirements, may also be applied to determine the average size of a particular type of grain in a multi-phase or multi-constituent specimen. These methods may also be applied to nonmetallic materials with structures having appearances similar to those of the metallic structures shown in the comparison charts.
1.2 This standard is applied to determine the average grain size of specimens with a unimodal distribution (similar to lognormal distribution) of grain areas, diameters or intercept lengths, and is not applicable to the grain size in bimodal distribution. Characterization of duplex grain size is described in GB/T 24177. Test methods for determining individual very coarse grains in a fine grained matrix are described in YB/T 4290.
1.3 This standard deals only with determination of planar grain size. Determination of spatial grain size, that is, measurement of the size of the three-dimensional grains, is beyond the scope of this standard.
1.4 This standard deals only with the recommended test methods and nothing in it should be construed as defining or establishing limits of acceptability or fitness of purpose of the materials tested.
2 Normative References
The following documents for the application of this document are essential. Any dated reference, just dated edition applies to this document. For undated references, the latest edition (including any amendments) applies to this document.
GB/T 4335 Determination of Ferrite Grain Size for Cold Rolled Low Carbon Steel Sheets
GB/T 13298 Inspection Methods of Microstructure for Metals
GB/T 24177 Standard Test Methods for Characterizing Duplex Grain Sizes
GB/T 30067 Standard Terminology Relating to Metallography
YB/T 4290 Test Methods for Estimating the Largest Grain Observed in a Metallographic Section (ALA Grain Size)
3 Terms and Definitions
For the purposes of this document, the terms and definitions defined in GB/T 30067 and the following apply.
3.1
grain boundary
a very narrow region in a polycrystalline material corresponding to the transition from one crystallographic orientation to another, thus separating one adjacent grain from another
3.2
grain
a whole area enclosed by grain boundary, that is, the area within the original grain boundary observed on two-dimensional plane or the volume enclosed by the original grain boundary planes on three-dimensional body. Twin-plane boundary is not considered for materials with twin-plane boundary
3.3
grain size
a magnitude of grain size. Generally, length, area, volume or grain size number are used for representing the grain size estimated or determined with different methods, while the grain size represented by grain size number is unrelated to the measurement method and unit
3.4
micro-grain size number
G
the micro-grain size number G is defined as:
N100=2G-1 (1)
3.5
macro-grain size number
Gm
the macro-grain size number Gm is defined as:
(2)
3.6
grain boundary intersection count
Pi
determination of the number of times a test line cuts across, or is tangent to grain boundaries, which is called the intersection count for short
3.7
grain intercept count
Ni
determination of the number of times a test line cuts through individual grains on the plane tested, which is called the intercept count for short
3.8
intercept length
l
the distance between two grain boundary intersection points on a test line segment that crosses the grain
4 Symbols
The symbols adopted in this standard and their descriptions are given in Table 1.
Table 1 Symbols and Descriptions
5 Generalities and Application
5.1 This standard specifies the basic procedures for determination of average grain size, including comparison procedure, planimetric procedure and intercept procedure.
5.2 Comparison procedure:
Foreword II
Introduction IV
1 Scope
2 Normative References
3 Terms and Definitions
4 Symbols
5 Generalities and Application
6 Sampling
7 Specimen Preparation
8 Determination Procedures
9 Specimens with Non-equiaxed Grain Shapes
10 Grain Size of Specimens Containing Two- or Multi-phase Structure
11 Report on Grain Size
12 Precision and Bias
Annex A (Normative) Establishing and Outlining Method of Grain Size
Annex B (Normative) Statistical Techniques - Calculation for Confidence Interval and Relative Error of Grain Size Determination Results
Annex C (Informative) Measurement Foundation of Grain Size
