GB/T 30834-2022 PDF in English
GB/T 30834-2022 (GB/T30834-2022, GBT 30834-2022, GBT30834-2022)
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Rating and classifying of inclusions in steel - Scanning electron microscope method
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Standard test methods for rating and classifying inclusions in steel -- Scanning electron microscope
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GB/T 30834-2022: PDF in English (GBT 30834-2022) GB/T 30834-2022
GB
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
ICS 77.040.99
CCS H 24
Replacing GB/T 30834-2014
Rating and classifying of inclusions in steel - Scanning
electron microscope method
ISSUED ON: OCTOBER 12, 2022
IMPLEMENTED ON: FEBRUARY 01, 2023
Issued by: State Administration for Market Regulation;
Standardization Administration of the People's Republic of China.
Table of Contents
Foreword ... 3
1 Scope ... 5
2 Normative references ... 5
3 Terms and definitions ... 6
4 Overview ... 7
5 Equipment ... 9
6 Calibration and verification of equipment ... 10
7 Sampling ... 10
8 Specimen preparation ... 10
9 Test steps ... 11
10 Inclusion classification, rating and statistics ... 13
11 Inspection report ... 16
12 Precision and bias ... 18
Annex A (informative) Typical acquisition conditions for SEM ... 19
Annex B (informative) Typical examples for test results of Method 1 ... 21
Annex C (informative) Typical examples for test results of Method 3 ... 23
Annex D (informative) Typical examples for test results of 80CL rare earth treated steel
... 25
Annex E (informative) Typical examples for test results of X80 pipeline steel ... 27
Annex F (informative) X-ray counting and chemical classification statistics ... 29
Rating and classifying of inclusions in steel - Scanning
electron microscope method
1 Scope
This document specifies the equipment for evaluating and classifying non-metallic
inclusions in steel by scanning electron microscope (SEM), calibration and verification
of equipment, sampling, specimen preparation, test procedures, inclusion classification,
rating and statistics, test reports, precision and bias.
This document recommends three inspection methods. Method 1 mainly classifies
inclusions according to their morphology. Method 2 mainly classifies inclusions
according to their chemical composition. Method 1 and Method 2 are suitable for
microscopic evaluation of non-metallic inclusions larger than 2μm in rolled or forged
steel with a compression ratio greater than or equal to 3. Method 3 is used to determine
the specific details of a certain type of inclusion such as volume fraction, number
fraction and other stereological parameters. It is suitable for the statistical classification
of inclusions of all sizes (including below 2μm) in various slabs or steel products.
2 Normative references
The following referenced documents are indispensable for the application of this
document. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
GB/T 10561, Steel - Determination of content of nonmetallic inclusions -
Micrographic method using standards diagrams
GB/T 13298, Inspection methods of microstructure for metals
GB/T 17359, Microbeam analysis - Quantitative analysis using energy dispersive
spectrometry
GB/T 18876.1, Standard practice for determining the metallographic constituent
and inclusion content of steels and other metals by automatic image analysis - Part
1: Determining the inclusion or second-phase constituent content of steels and other
metals by automatic
GB/T 18876.2, Standard practice for determining the metallographic constituent
and inclusion content of steels and other metals by automatic image analysis - Part
2: Determining the inclusion ratings of steels by automatic image analysis and
stereology
GB/T 27788, Microbeam analysis - Scanning electron microscopy - Guidelines for
calibrating image magnification
GB/T 30067, Standard terminology relating to metallography
3 Terms and definitions
For the purposes of this document, the terms and definitions defined in GB/T 30067 as
well as the followings apply.
3.1 acquisition analysis rules
The conditions for terminating X-ray acquisition (count, time or both), the list of
elements to be analyzed, the number of fields or particles to be analyzed, the shape of
particles to be analyzed, and so on.
NOTE: Typical acquisition conditions for SEM (see Annex A).
3.2 post-acquisition analysis rules
The elemental composition that identifies the chemical classification of the inclusions.
NOTE: For Method 1 and Method 2, in addition to setting the elemental composition of the
chemical classification of inclusions, it is also necessary to set the type of inclusion (class A, class
B or class C) to which each chemical classification belongs.
3.3 chemical classification
Set the category to which inclusions belong based on elemental composition.
NOTE: It can be broadly classified, such as sulfide, alumina, and silicates. It can also be finely
classified, such as calcium sulfide, calcium silicate, and anorthite.
3.4 aspect ratio; AR
The ratio of the longitudinal and transverse directions of the extension of the inclusions.
3.5 stringer
A single inclusion that is highly extended in the direction of deformation. Two or more
type A or type C inclusions, three or more type B inclusions, and these two or more
inclusions must be arranged in a row, parallel to the direction of the thermal processing
axis. The center line of offset stringer inclusions is less than or equal to 15μm. The
distance between any two adjacent inclusions is less than or equal to 40μm.
3.6 Feret's diameter
chemical classification should be indicated in the inspection report.
4.4 Method 1 and Method 2 provide a quantitative evaluation method for each type of
inclusion and each width series of inclusion levels (level 0~5) in half-level increments.
4.5 Method 3 specifies procedures for analyzing and counting inclusions by size and
chemical classification. Method 3 is used to determine and record some basic
stereological parameters of inclusions, such as the area fraction of sulfides and oxides,
the number of sulfides or oxides per square millimeter. Method 3 is not used for rating.
5 Equipment
5.1 The scanning electron microscope should be equipped with the following
accessories:
- Image acquisition software: It can acquire images.
- Sample stage: Computer control, X-Y direction motor drive. Automatic sample
stage is recommended. Manual operation is also possible. Pay attention to the
continuity of the field of view when operating manually.
- Energy spectrometer: Its resolution should meet the requirements of GB/T 17359.
According to the set parameters, the electron beam and sample stage can be
controlled, and images and spectra can be collected. The chemical composition
analysis of inclusions can be carried out.
- Backscattered electron detector: One or more thresholds can be set to distinguish
between matrix and inclusions.
5.2 The requirements for automatic feature analysis software are as follows:
- It should be possible to set analysis conditions for chemical classification. It should
be possible to characterize by elemental composition, size and morphology.
- It should be able to distinguish stringer and single spherical oxide. Then distinguish
stringer oxides according to different forms (type B or type C). It can measure the
length of various stringer inclusions in each field of view. Classify all spherical
oxides separated from type B or type C stringer inclusions into type D or type DS
oxides. After separation of various types of inclusions (type A, type B, type C, type
D), the automatic feature analysis software should also be able to measure the
diameter of a single inclusion or the width of a stringer inclusion. Classify each
type of inclusion as fine or coarse.
- It can connect the stringer inclusions across the boundary of the field of view.
6 Calibration and verification of equipment
6.1 The magnification of the scanning electron microscope should be regularly
calibrated and verified according to GB/T 27788.
6.2 Calibration of energy spectrometer should be carried out according to the provisions
of GB/T 17359.
6.3 The energy resolution of the spectrometer should be regularly verified in accordance
with GB/T 17359.
7 Sampling
7.1 The sampling methods of Method 1 and Method 2 should be carried out according
to the provisions of GB/T 10561. The sampling method of Method 3 should be carried
out according to the agreement between the supplier and the purchaser. In any case, the
polished surface should be parallel to the axis of thermal processing.
NOTE: If the angle between the polished surface and the thermal processing axis is greater than 6°,
it will have a great influence on the length measurement of non-metallic inclusions.
7.2 If the product standard does not specify, if the non-metallic inclusions in rolled or
forged steel are classified and rated according to Method 1 and Method 2, the polished
surface is generally cut at 200mm2. At least 160mm2 test area should be guaranteed. If
the inclusions in various slabs or steels are classified and counted according to Method
3, the test area should be determined according to the analysis requirements. It is
recommended that the specimen area be relatively larger so that the measurement can
be performed within a specified area away from the edge of the specimen.
8 Specimen preparation
8.1 Specimen preparation should be carried out in accordance with the provisions of
GB/T 10561 and GB/T 13298.
8.2 The surface of the specimen after polishing should not be disturbed by man-made
pollution, foreign matter, scratches. During polishing, the true shape of the inclusions
cannot be changed by excessive protrusions, pits or tearing.
8.3 In general, inclusions are more likely to remain in the quenched specimen than the
annealed specimen. For treatable steels, if sufficient inclusions do not remain in the
annealed specimen, the specimen should be subjected to standard heat treatment. The
tempering temperature should be relatively low. After heat treatment, the oxide layer
should be removed. Longitudinal specimens should be reground to below the
decarburized layer.
lead, it is recommended to set multiple thresholds. It is recommended to set image
grayscale compensation during operation, for example, the software automatically
adjusts the image grayscale to be consistent with the initial contrast at intervals of 5min,
thereby ensuring the consistency of identification of inclusions.
NOTE: Use the same contrast setting. Different analysts will get the same or similar results when
testing the same specimen. The reproducibility of test results can be guaranteed. Use appropriate
threshold setting to ensure the accuracy of inclusion identification.
9.6 Control the sample stage according to the procedure recommended by the
manufacturer. Set the analysis area of the specimen to be tested. For specimens with
irregular shapes and it is difficult to ensure that the detection surface is flat, if a special
horizontal specimen seat is not used to fix the specimen, it is recommended to use
multiple Z-axis position points to locate the analysis area. For the testing and analysis
of multiple specimens of thin plates, it is recommended to use the setting of multiple
regions for one analysis (interface regions where multiple specimens are superimposed
are not included in the analysis).
9.7 Set the post-acquisition analysis rules:
- Set chemical classification. For example, in Method 1, at least two chemical
classifications should be set: sulfide and oxide. In Method 2, at least three chemical
classifications should be set: sulfide, alumina, silicate. Additional categories can
also be set according to needs, for example, calcium silicate inclusions are similar
to class B inclusions in appearance and have similar hazards, so they can be
classified as class B inclusions. The chemical classification and the main inclusion
types to which it belongs should be given in the report.
- Specify the peak intensity that the X-ray spectrum should satisfy. Peak intensity
includes one or more of the following parameters: spectral peak intensity range,
peak-to-background ratio, peak intensity ratio, element content percentage, or other
chemical parameters that characterize certain types of inclusions.
9.8 Set image and energy spectrum analysis parameters, such as minimum/maximum
size of inclusions, critical aspect ratio, spectrum range, X-ray acquisition mode. Annex
A lists typical acquisition conditions for SEMs. The parameters are set as follows:
a) Under the selected magnification, select the appropriate image resolution. It
should be ensured that the pixel size is no larger than the size of the inclusion of
interest.
b) According to GB/T 10561, the critical aspect ratio AR of Method 1 and Method 2
adopts 3.
c) In Method 3, it is recommended to use the two conditions of the number of
inclusions and the detection area to terminate the analysis. When any one of these
conditions is met, the analysis is automatically terminated. Use two conditions to
terminate the analysis. When the inclusion content in the steel is low, it can ensure
that the detection area is large enough to be representative. When the content of
inclusions in the steel is high, the testing time can be ensured to improve the
testing efficiency.
9.9 Run automated scan detection.
9.10 Identify inclusions by chemical composition, morphology and width according to
the steps specified in 10.1 (Method 1) and 10.2 (Method 2). Calculate levels based on
length, count or diameter. Then store the results and generate inspection reports. Or
follow the steps specified in 10.3 (Method 3) to identify inclusions by chemical
composition, shape and width. Statistical analysis is carried out based on certain
conditions. Generate test reports.
9.11 Save the raw data. The raw data should include the size, shape, composition,
location and other information of all inclusions.
NOTE: Raw data can be processed later.
10 Inclusion classification, rating and statistics
10.1 Method 1: Morphology classification
10.1.1 Method 1 adopts the same inclusion classification as GB/T 10561. The
characteristic spectrum is used to confirm and distinguish the inclusions.
10.1.2 Method 1 first divides inclusions into two categories according to their shape,
that is, their aspect ratio. Inclusions with aspect ratio greater than or equal to 3, with
high ductility, are mainly divided into class A and class C. Inclusions with an aspect
ratio of less than 3, with low or no ductility, are mainly divided into class B, class D,
and class DS. Then, the inclusions with an aspect ratio greater than or equal to 3 are
divided into class A (sulfide, containing sulfur) and class C (silicate, containing oxygen)
according to their chemical composition. Then the inclusions with an aspect ratio less
than 3 are divided into class B, class D and class DS according to the distribution of
clusters (bars) or single particles. Discontinuous stringer inclusions consisting of 3 or
more particles (single particle aspect ratio less than 3) are class B, generally alumina.
Single-grain inclusion particles are class D. Among them, the oversized class D
inclusions with a diameter greater than 13μm belong to class DS.
10.1.3 For class A, class B and class C inclusions, the inclusion centerlines whose
transverse spacing is within 15μm and whose longitudinal spacing is within 40μm
should be regarded as the same stringer. If the widths of the inclusions in the same
stringer are different, the width of the inclusion whose length is dominant should be
taken as the width of the stringer of inclusions.
10.1.4 After classifying various types of inclusions, they are divided into fine series and
10.2 Method 2: Chemical classification
10.2.1 Method 2 mainly classifies inclusions according to their chemical composition.
Sometimes refer to form.
10.2.2 Method 2 divides the inclusions into three classes according to their chemical
composition: A, B and C. Class A inclusions are sulfides (usually manganese sulfide).
Class B inclusions are aluminates (usually alumina). Class C inclusions are silicates.
10.2.3 Generally, the three classifications of A, B, and C have met the requirements. If
you are interested in single-grain inclusions, class D spherical oxides (aspect ratio less
than 3, single particle) can also be separated from the three types A, B, and C according
to the morphology (aspect ratio) and distribution [stringers or single particles] (D) and
class D spherical sulfide (aspect ratio less than 3, single particle) (D sulfide). Class D
inclusions with a diameter greater than 13μm can be classified as class DS. In some
applications, single particle spherical inclusions may not be classified separately.
Instead, they are still classified into class A, class B or class C according to their
chemical composition. The classification of single particle inclusions should be
determined by agreement between supplier and purchaser. However, if the rating is
required, class A, class B and class C inclusions should be divided into stringers and
single particles, that is, class D, class D sulfide and class DS.
10.2.4 After classifying various types of inclusions, they are divided into fine series and
coarse series according to width or diameter (see Table 1). For class A, class B and class
C inclusions, the width of the inclusion whose length is dominant is measured as the
width of the stringer inclusions. For class D and class DS inclusions, measure the
diameter. Class D inclusions with a width less than 2μm (class A, B, C) or a diameter
less than 2μm are not included in the subsequent grade calculations.
10.2.5 For stringer inclusions, if the length exceeds 0.710mm, or the width is greater
than the maximum value of the coarse series (see Table 1), it should be evaluated as
oversized (length, width) inclusions. Record separately. However, these inclusions
should still be included in the rating for this field.
10.2.6 On a testing area of 0.5mm2, measure the total length of class A, class B or class
C stringer inclusions and the total number of class D inclusions. Grades are rated
according to the minimum length or number of each grade given in Table 2. The
measurement should be carried out on a continuous 0.5mm2 testing area.
10.2.7 Composite inclusions (such as oxysulfide or dual-phase inclusions) can be
classified according to chemical composition and content. If the inclusion is mainly
sulfide and its area is greater than 50%, it is classified as class A. If it is mainly non-
deformable oxides (such as alumina inclusions) and its area is greater than 50%, it is
classified as class B. If it is mainly deformable silicate and its area is greater than 50%,
it is classified as class C. For composite inclusions with critical aspect ratio AR< 3, if
they exist alone, they can be classified as class D or class D sulfide.
10.2.8 For steel treated with rare earth or calcium, the endogenous inclusions can also
be treated in the same way as in 10.2.2~10.2.7. Set the chemical classification (e.g.,
calcium sulfide, calcium silicate, anorthite, spessartine). Assign the chemical
classification to the main inclusion types.
10.2.9 For specimens containing heavy element inclusions such as RE, Pb, Bi, they
generally contain traditional types of inclusions such as oxides, sulfides, or silicates and
composite inclusions of heavy elements. The automatic statistical software should have
the function of double or multi-threshold gray scale and screening function to ensure
the identification of all inclusions and realize the accurate statistics of heavy element
composite inclusions.
10.3 Method 3: Custom analysis method
10.3.1 Method 3 is recommended when neither Method 1 nor Method 2 is applicable.
Method 3 allows inclusions to be analyzed individually by material and application.
Allow customizing the criteria for chemical classification. The critical aspect ratio can
be properly selected according to actual needs. The termination conditions of the
analysis can be set as the maximum number of inclusions and the testing area.
Inclusions can be further subdivided by morphology.
10.3.2 Method 3 can be used to determine the number and size distribution of inclusions
of a certain chemical composition (such as titanium inclusions in stainless steel) or to
analyze inclusions in as-cast steel. Method 3 can classify inclusions according to special
methods, such as classifying all non-sulfide particles by width in tire cord steel. This
method can also be used in some steels with special restrictions or regulations.
10.3.3 Method 3 can set the relevant chemical classification, size range and
morphological classification, rather than using indirect terms such as A, B, C, and D,
or fine, coarse, and wide. Chemical classification is the taxonomic designation for
inclusions. The size distribution of each type of inclusion can then be determined. The
minimum size for inclusion analysis is not specified in this document but is determined
by the specific application. Higher magnifications can be used to determine small
inclusions that cannot be seen with an optical microscope.
10.3.4 Method 3 can give the volume and number fraction of inclusions in each field of
view, the maximum Feret's diameter of each inclusion and other stereological
parameters. The ratio parameters such as average area and mean free path of inclusions
can also be calculated according to GB/T 18876.1.
11 Inspection report
11.1 The inspection report should include the following:
a) Reference to this document;
Annex F
(informative)
X-ray counting and chemical classification statistics
F.1 X-ray counting statistics
F.1.1 The generation and measurement of X-rays is a statistical process. Electron beams
are irradiated onto the specimen in the scanning electron microscope. If the electrons
carry enough energy, then X-rays may be produced. A programmed beam of X-rays
may then leave the specimen surface and hit the detector. Finally, it will be tested and
counted. Therefore, the measured intensities of specific X-rays vary widely even for
ideal specimens tested by high-quality instruments.
F.1.2 The degree of dispersion of test results is processed by Gaussian software. The
true value of the measured count is determined by the mean . The standard
deviation is also given by . Gaussian distribution shows that 95.4% of the
measured values are distributed in the range of . 99.7% of the measured
values are distributed in the range of . That is, any measured value has a
95% probability of falling within the interval of ; it has 99% probability
of falling within the interval of . In the actual X-ray measurement, if the
number of spectral peak counts exceeds the background count by , considering
the statistical probability of background floating is only 0.3%, then it is considered that
the spectral peak must exist. The 3σ criterion is usually used when defining the
minimum testing limit. The longer the counting time and the number of counts, the
closer the measured value of the spectral peak is to the real value. If the number of
counts I is 10000, assuming I=I°, it is estimated that 99% of the counts will fall in the
interval of 9700~10300, that is, . A variation of ±3% may not have any
effect on the accuracy of inclusion classification. However, if I is only 36, then the
estimated measurement will be off by 50%, leading to misclassification. However, as
mentioned in F.2, if the classification is sufficiently distinct, even a small number of
counts can be accurately classified.
F.2 Termination criteria for X-ray analysis of individual inclusion
......
Source: Above contents are excerpted from the PDF -- translated/reviewed by: www.chinesestandard.net / Wayne Zheng et al.
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