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Similar standardsGB/T 6394-2017: Determination of estimating the average grain size of metal---This is an excerpt. Full copy of true-PDF in English version (including equations, symbols, images, flow-chart, tables, and figures etc.), auto-downloaded/delivered in 9 seconds, can be purchased online: https://www.ChineseStandard.net/PDF.aspx/GBT6394-2017GB NATIONAL STANDARD ICS 77.040.99 H 24 Replacing GB/T 6394-2002 Determination of estimating the average grain size of metal Issued on. FEBRUARY 28, 2017 Implemented on. NOVEMBER 01, 2017 Issued by. General Administration of Quality Supervision, Inspection and Quarantine of the People's Republic of China; Standardization Administration of PRC. Table of ContentsForeword... 3 Introduction... 5 1 Scope... 6 2 Normative references... 6 3 Terms and definitions... 7 4 Symbols... 8 5 Overview and application... 10 6 Sampling... 12 7 Sample preparation... 12 8 Determination method... 13 9 Grain size of non-equiaxed grain... 26 10 Grain size of sample containing two or more phase structures... 29 11 Grain size report... 31 12 Precision and deviation... 32 Appendix A (Normative) Grain size formation and display method... 34 Appendix B (Normative) Statistical technique - Calculation of confidence interval and relative error of grain size measurement results... 41 Appendix C (Informative) Grain size measurement basis... 451 Scope1.1 This standard specifies the expression and determination methods of the average grain size of metal structure, including the comparison method, area method and interception method; it is applicable to the single-phase structure; however, after being specified, it is also applicable to the determination of the average grain size of the certain type in the multi-phase or multi-component sample. If the histomorphology of the non-metallic material is similar to the metal structure in the rating chart, it may also make reference to it. 1.2 This standard uses the grain area, diameter or intercept length of the unimodal distribution (similar to the lognormal distribution) to determine the average grain size of the sample, AND it is not applicable to the grain size of the bimodal distribution. The evaluation of double grain size is as shown in GB/T 24177.For the determination of individual coarse grains on a fain grain substrate, SEE YB/T 4290. 1.3 This standard applies only to the measurement of the plane grain size measurement, AND it is not applicable to the three-dimensional grain size, that is, the measurement of three-dimensional grain size. 1.4 This standard is only used as a recommended test method, AND it shall cannot determine whether the test material is received or suitable for the range of use.2 Normative referencesThe following documents are essential to the application of this document. For the dated documents, only the versions with the dates indicated are applicable to this document; for the undated documents, only the latest version (including all the amendments) are applicable to this Standard. 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 definitionsThe terms and definitions as defined in GB/T 30067 AND the following terms and definitions apply to this document. 3.1 Grain boundary It refers to, for the polycrystalline material, a narrow region transitioning from one crystal direction to the other crystal direction, thereby separating the adjacent grains. 3.2 Grain It refers to the entire area surrounded by grain boundaries, that is, the area within the original grain boundary observed on the two-dimensional plane, or the volume surrounded by the original grain boundery on the three-dimensional object. For twin-grain boundary materials, the twin-grain boundary is not considered. 3.3 Grain size It refers to the measurement of the size of grain, which is evaluated or determined by different methods, is usually expressed using the length, area, volume, or grain size level, AND the grain size as expressed using the grain size level is independent of the measurement method and the unit of use. 3.4 Micro-grain size number The micro-grain size number G is defined as. 3.5 Macro-grain size number Gm The macro-grain size level Gm is defined as.4 SymbolsThe symbols and descriptions used in this standard are as shown in Table 1.5 Overview and application5.1 This standard specifies the basic method for determining the average grain size. comparison method, area method and intersection method. 5.2 Comparison method. comparison method does not need to count grain, intersection or intercept. 5.4 Intersection method. intersection method is to count the number of the intercept between the test line (or grid) of known length and the grain or the number of intersection between the test line (or grid) and the grain, AND to calculate the unit length intercept count NL or the intersection count PL, so as to determine the grain size level G. 5.6 In the event of a dispute, the intersection method is used as the arbitration method. 5.7 Low-carbon steel cold-rolled sheet ferrite grain size is determined in accordance with the provisions of GB/T 4335. 5.8 A single grain cannot be determined on the basis of the standard rating chart. Because the composition of the standard rating chart takes into account the relationship between the cut plane and the grain three-dimensional arrangement, it shows the arrangement distribution of grain from the minimum to the maximum, which reflects the representative normal distribution results. Therefore, the rating chart cannot be used to determine a single grain. 5.9 When determining the grain size, it shall be recognized that the determination of grain size is not a very accurate measurement. Because the metal structure is the accumulation of three-dimensional grain of different sizes and shapes. 5.10 The grain size and position in the microstructures are randomly distributed. The randomly measured average grain size is only representative if moving the field of view without intention and placing the measurement grid.6 Sampling6.1 The samples for determination of grain size shall be cut from the material of delivery status. The sampling position and amount shall follow the requirements of the product standard or the technical conditions. 6.2 It shall not cut samples from the region as affected by cutting or heating. It is not allowed to cut sample using such method as possible to change the grain structure.7 Sample preparation7.1 As for the sample having processing deformation grain, it shall inspect the test surface parallel to the processing direction (longitudinal section), AND if necessary, it shall also inspect the test surface perpendicular to the processing direction (cross section). As for the equiaxed grains, it may select randomly the test surface. 7.2 In case of inspection of ferritic steel austenite grain size, it is required for the sample to be subjected to heat treatment (SEE Appendix A), AND the specific method shall follow the requirements of the product standard or technical conditions. However, if the product standard or technical conditions do not specify these requirements, the carburizing steel shall adopt the carburizing procedure, AND the other steel may adopt the direct hardening procedure or the oxidization procedure. In case of inspection of the ferrite grain size and austenitic steel grain size, the sample generally does not require heat treatment. 7.3 It is not allowed for the grain size sample to be subjected to repeated heat treatment. 7.4 The samples for carburizing treatment shall be removed of the decarburized layer and scale. 7.5 The grinding and etching of the sample shall be carried out in accordance with GB/T 13298.The etching of the sample shall make the majority of the grain boundaries fully visible (SEE Appendix A).8 Determination method8.1 Comparison method 8.1.1 General requirements 8.1.1.1 The comparison method evaluates the average grain size by comparing it to the standard rating chart. It is applicable to the recrystallized material of equiaxed grains. 8.1.1.5 As for the evaluation of grain size, it shall randomly select three or more representative fields of view from the sample section to measure the average grain size, AND report it using the level which best represents the grain size distribution of the sample. 8.1.1.6 If the grain is found to be uneven in the sample, after overall observation, if it is an accidental or individual phenomenon, it may not be calculated. If it is common, it shall calculate the area percentage of different levels of grain in the field of view. If the area occupied by the dominant grain is not less than 90% of the area of the view field, it shall only record the number of levels of this grain. 8.1.1.7 When using the comparison method, if it requires re-inspection, it may change the magnification factor, in order to overcome the subjective bias that may be included in the initial inspection results. 8.1.2 Evaluation of micro-grain size 8.1.3 Evaluation of macroscopic grain size 8.1.3.1 For particularly coarse grain, it is determined by the use of macro-grain size, AND the magnification factor is 1-times. 8.1.3.2 When the grain is small, it is preferable to use a slightly higher magnification factor M to evaluate the macro-grain size. If the rated grain size number is G'm, the macro-grain size level Gm is calculated in accordance with the formula (4). 8.2 Area method 8.2.1 The area method is to determine the grain size by counting the number of grains N in a given area grid. 8.2.4 If the number of grains in the test circle drops below 50, the grain size assessed by the area method will have deviation, which has a relatively large dispersion. The degree of deviation increases as N decreases from 50. 8.2.5 By measuring the number of grains in the grid N AND observing the magnification M, it may follow the formula (7) to calculate the grain number per square millimeter NA on the actual sample testing surface (1-times). 8.2.6 Grain size number G is calculated in accordance with the formula (8) or (9). OR 8.2.7 SELECT the field of view in accordance with 5.10 in a random and unbiased manner. It is not allowed to deliberately select the typical field of view. From the polishing surface, randomly SELECT the field of view from different locations, to ensure trueness and validity. To ensure that the average value is valid, it shall calculate at least 3 fields of view. 8.3 Intersection method 8.3.1 General requirements 8.3.1.1 The intersection method is to determine the grain size by counting the number of intercepts between the measuring line (or grid) of given length and the grain boundary. 8.3.1.2 The intersection method is simpler than the area method. It is recommended to use the manual counter, to avoid routine errors during counting AND to eliminate deviations that may occur when the count is higher or lower than expected. 8.3.1.3 It shall use the intersection method for the non-uniform equiaxed grains. For non-equiaxed grain size, the intersection method can be used not only to respectively determine the grain size of three mutually perpendicular directions, but also to calculate the overall average grain size. 8.3.1.4 The intersection method is divided into straight-line intersection method and circular intersection method. The circular intersection method can automatically compensate the error produced by the deviation from equiaxed grain without the needs of adding too many field of view, so it overcomes the issues that the intersection at the test line end is not apparent. The circular intersection method is more appropriate as a quality testing method to evaluate the grain size. 8.3.1.5 It is recommended to use the 500 mm measuring grid, AND its size is as shown in Figure 1. 8.3.2 Straight-line intersection method 8.3.2.1 In the grain image, USE one or several straight-lines to form a measuring grid; SELECT the appropriate measuring grid length and magnification, to ensure that at least 50 intersections can be obtained. In accordance with the number of intersections as obtained by the measuring grid, DETERMINE the grain size. 8.3.3 Single circle intersection method 8.3.4 Three circle intersection method 8.3.4.1 The tests show that reliable precision can be obtained when the intersection count of each sample reaches 500.The measurement data is subjected to X2 test, AND the result shows that the intersection count is subjected to a normal distribution, so it is allowed for the measurement value to be subjected to the statistic processing of normal distribution. For each grain size determination result, it may calculate the result deviation and the confidence level (SEE Appendix B).9 Grain size of non-equiaxed grain9.1 General requirements 9.1.1 If the grain shape changes due to processing AND is no longer equiaxed, the grain size of the rectangular bar, plate and sheet material shall be measured along the longitudinal (l), transverse (t) and normal (p) section; AND the grain size of the round bar may be measured along the longitudinal and transverse section. 9.1.2 If the equiaxed deviation is not too large (less than 3.1 shape ratio), measurements can be made using a circular measuring grid on the longitudinal section of the sample. It is recommended to conduct measurement in accordance with the requirements of GB/T 4335. 9.2 Area method When the grain shape is non-equiaxed but elongated, the grain counts are to be performed on the three main sections in the longitudinal, transverse and normal directions. Respectively MEASURE the grain number,, and per square millimeter on the actual sample plane (1-times) along the longitudinal, transverse, and normal section, USE the formula (16) to calculate the average grain number per square millimeter, and then USE the formula (8) to calculate the grain size number G. 9.3 Intersection method 9.3.1 To measure the grain size of non-equiaxed grains, it may use a circular measuring grid to make random measurements on three primary test surfaces, OR otherwise it may use straight-line to perform intercept or intersection count along the 3 or 6 main directions (SEE Figure 3) of the two or three primary test planes. ......Source: Above contents are excerpted from the full-copy PDF -- translated/reviewed by: www.ChineseStandard.net / Wayne Zheng et al. 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