This standard is applicable to the determination of grain size of metal materials. Since the purity is based on the geometrical figure of the grain, but on nothing to do with the material itself, therefore, this method can also be used to determine the grain size of the non-metallic materials. The methods for the determination of grain size in this standard include: comparative law, area method and resection.
1.1 Scope
1.1.1 This standard includes metal-methods and representation principle for estimating the average grain size composed completely or mainly of single-phase. At the same time, these methods are also applicable to any organizations similar to the standard rating diagram pattern.
1.1.2 In case the material morphology is similar to any of the standard rating diagram series, comparative law may be adopted; while area method and resection may be adopted in any case.
1.1.3 The comparative law is the easiest for the determination of grain size of equiaxed grain, and the accuracy may meet the requirements for production inspection. If higher accuracy requires, the area method and resection may be adopted. The non-equiaxed grains cannot use comparative law.
1.1.4 The "grain" in this standard refers to the whole region in the grain boundary. In materials with twin crystal, each grain and its internal twin band shall be regarded as one grain.
1.1.5 The size of the sub-grain may be measured by the methods for the determination of grain size.
1.1.6 If any dispute arisen, the resection may be used as the arbitration method.
1.1.7 This standard is not applicable to the determination of deep cold-worked material or grain size of partial re-crystallized deforming alloy. If the grain size of the gentle or moderate cold-worked material must be measured, the material shall be regarded as being composed by non-equiaxed grain.
1.2 Application Summary
1.2.1 When determining the grain size, the operator shall recognize that the determination of the grain size is not a precise measurement. Since the metal structure is accumulated by three-dimensional grains in different sizes and shapes. Although sizes and shapes of these grains are the same, the size of the grain distributed on any section (check surface) through the structure will be varied from the maximum to zero. Therefore, the check surface can never be distributed with grain in even size absolutely, nor two same check surfaces can be present.
1.2.2 If considering the grain counts from statistics: for general application, if each setting area contains more than 100 grains, the area may meet the statistics conditions; for practical determination, the counts may be reduced to be 50 grains for the convenience of counting. Therefore, when determining the grain size, proper magnification and survey area must be selected.
1.2.3 The determination of the grain size shall be made by selecting three or more representative viewing field from the check surface of each test piece. The so called "representativeness" hereof reflects all parts are contributing for the check result, but rather than selecting the viewing field of the average grain size hypothetically. Only in doing so, the accuracy and precision of the testing result are valid.
1.2.4 When comparative law is adopted, the observational magnification shall be changed if re-inspection is a must, so as to overcome the subjective bias likely be carried by the initial testing result.
1.2.5 The differences among the measurement results of different observers may be allowed in the scheduled confidence interval.
