GB/T 6394-2017 PDF English
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Determination of estimating the average grain size of metal
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| GB/T 6394-2002 | English | 170 |
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Metal-methods for estimating the average grain size
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GB/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/GBT6394-2017
GB
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 Contents
Foreword... 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... 45
1 Scope
1.1 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 references
The 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 definitions
The 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 Symbols
The symbols and descriptions used in this standard are as shown in Table 1.
5 Overview and application
5.1 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 Sampling
6.1 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 preparation
7.1 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 method
8.1 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 grain
9.1 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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