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GB/T 3488.2-2018: Hard metals -- Metallographic determination of microstructure -- Part 2: Measurement of WC grain size
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Hard metals -- Metallographic determination of microstructure -- Part 2: Measurement of WC grain size
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Basic data | Standard ID | GB/T 3488.2-2018 (GB/T3488.2-2018) | | Description (Translated English) | Hard metals -- Metallographic determination of microstructure -- Part 2: Measurement of WC grain size | | Sector / Industry | National Standard (Recommended) | | Classification of Chinese Standard | H16 | | Classification of International Standard | 77.160 | | Word Count Estimation | 18,171 | | Date of Issue | 2018-07-13 | | Date of Implementation | 2019-04-01 | | Issuing agency(ies) | State Administration for Market Regulation, China National Standardization Administration | GB/T 3488.2-2018: Hard metals -- Metallographic determination of microstructure -- Part 2: Measurement of WC grain size
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Hardmetals--Metallographic determination of microstructure--Part 2. Measurement of WC grain size
ICS 77.160
H16
National Standards of People's Republic of China
Metallographic determination of cemented carbide microstructure
Part 2. Measurement of WC grain size
Part 2. MeasurementofWCgrainsize
(ISO 4499-2.2008, IDT)
Published on.2018-07-13
Implementation of.2019-04-01
State market supervision and administration
China National Standardization Administration issued
Foreword
GB/T 3488 "Metal phase measurement of cemented carbide microstructure" is divided into four parts.
--- Part 1. Metallographic photos and descriptions;
--- Part 2. Measurement of WC grain size.
--- Part 3. Metallographic determination of microstructures of Ti(C,N) and WC cubic carbide-based cemented carbides;
--- Part 4. Metallographic determination of porosity, non-combined carbon defects and decarburization phases.
This part is the second part of GB/T 3488.
This part is drafted in accordance with the rules given in GB/T 1.1-2009.
This section uses the translation method equivalent to the ISO 4499-2.2008 "metallographic determination of cemented carbide microstructures Part 2. WC
Measurement of grain size.
The documents of our country that correspond to the international documents consistently referenced in this section are as follows.
---GB/T 3848-2017 Determination method of hard alloy coercivity (magnetic) force (ISO 3326.2013, IDT);
---GB/T 3850-2015 Density of sintered metal materials and hard alloys (ISO 3369.2006, IDT);
--- GB/T 3849.1-2015 Hard alloy Rockwell hardness test (A scale) Part 1. Test method (ISO 3738-1.
1982, IDT);
--- GB/T 3849.2-2010 Hard alloy Rockwell hardness test (A scale) Part 2. Preparation and calibration of standard test blocks
Standard (ISO 3738-2.1988, IDT);
--- GB/T 3488.1-2014 Metallographic determination of microstructures of cemented carbide - Part 1. Metallographic photographs and descriptions
(ISO 4499-1.2008, IDT);
---GB/T 3489-2015 Metallographic determination of cemented carbide porosity and non-combined carbon (ISO 4505.1978, MOD).
This part was proposed by the China Nonferrous Metals Industry Association.
This part is under the jurisdiction of the National Nonferrous Metals Standardization Technical Committee (SAC/TC243).
This section drafted by. Xiamen Golden Heron Special Alloy Co., Ltd., Zigong Cemented Carbide Co., Ltd., Chongyi Zhangyuan Tungsten Industry Co., Ltd.
Limited Company, Zhuzhou Cemented Carbide Group Co., Ltd., Nonferrous Metals Technology and Economic Research Institute.
The main drafters of this section. Fan Zhirui, Jiang Yuanxiang, Sun Xiaotong, Jiang Yong, Cao Wanli, Liao Shilan, Zhao Shengzhi, Wu Yanhua.
Metallographic determination of cemented carbide microstructure
Part 2. Measurement of WC grain size
1 Scope
This part of GB/T 3488 provides the measurement of cemented carbide grain sizes by metallographic detection techniques using optical or electron microscopy.
A guide to the method of inch.
This section applies to WC/Co cemented carbide sintered bodies (also known as cemented carbide or cermet) with WC as the hard phase.
Used to measure grain size and its distribution by the cut line method.
This section mainly includes the following four aspects.
--- Calibration of the microscope to ensure measurement accuracy;
--- Linear analysis to obtain enough statistically significant data;
--- Analytical methods to calculate representative averages;
--- Report to meet modern quality reporting requirements.
This section describes this recommended technique through a measurement case analysis (see Appendix A).
This section does not apply to the following aspects.
--- Determination of size distribution;
--- Shape determination, still need more in-depth study before the shape determination.
Coercivity can sometimes be used to measure grain size, but this method only involves metallographic methods. This method is suitable for cemented carbide and is not suitable
Used in powders. However, the method can in principle also be used to determine the average size of the powder that can be mounted and sampled.
2 Normative references
The following documents are indispensable for the application of this document. For dated references, only dated versions apply to this article.
Pieces. For undated references, the latest edition (including all amendments) applies to this document.
ISO 3326 Hard alloy coercivity (magnetic) force measurement method [Hardmetals-Determinationof(themagnetization)
Coercivity]
ISO 3369 Densified sintered metal materials and cemented carbide density determination methods (Impermeablesinteredmetalmaterials
andhardmetals-Determinationofdensity)
ISO 3738-1 Hardmetals Rockwell hardness test (A scale) Part 1. Test methods [Hardmetals-Rockwel
Hardnesstest(scaleA)-Part 1.Testmethod]
ISO 3738-2 Hardmetals Rockwell hardness test (A scale) Part 2. Preparation and calibration of standard test blocks [Hardmetals-
Rockwelhardnesstest(scaleA)-Part 2.Preparationandcalibrationofstandardtestblocks]
ISO 3878 Hardmetal Vickers Hardness Test Method (Hardmetals-Vickershardnesstest)
ISO 4489.1978 Inspection rules and test methods for cemented carbide products (Sinteredhardmetals-Samplingandtes-
Ting)
ISO 4499-1 Metallographic determination of microstructures - Part 1 . Metallographic photographs and descriptions (Hardmetals-Metal-
lographicdeterminationofmicrostructure-Part 1. Photomicrographsanddescription)
ISO 4505 Carbide Porosity and Metallographic Determination of Non-Calcium Carbon (Hardmetals-Metalographic Determinationof
Porosityanduncombinedcarbon)
3 terms, definitions, abbreviations, symbols and units
3.1 Overview
There are many terms used to describe the grain size of a powder or cemented carbide. For example, the following terms are often used in various publications and reports.
Nanoscale grain nanocrystalline nanophase microcrystalline fine
Submicron ultrafine and fine
Medium/fine medium/coarse thick
None of these terms has been agreed upon by powder or cemented carbide users and producers, and their size range is not clear.
Therefore, it is recommended to use the terms defined in 3.2 and their size ranges as discussed by the Cemented Carbide Association.
If the number of representative crystal grains is.200 to 300, the grain size error measured by the cut line method is about 10%. because
Therefore, care should be taken when the measured value is at the edge of the classification level. When the measured value falls within 10% of the edge of each grade, it is recommended to press the following
Description.
E.g.
0.19μm described as nano/ultrafine 0.21μm described as ultrafine/nano
0.75μm is described as submicron/thin 0.85μm described as fine/submicron
1.29μm described as fine/medium 1.31μm described as medium/fine
2.4μm Description Medium/Coarse 2.6μm Description as coarse/medium
3.2 Terms and definitions
The following terms and definitions apply to this document.
3.2.1
Nano nano
WC grain size < 0.2μm
Note. Measured using the average cut line method described in this section.
3.2.2
Ultrafine ultrafine
0.2μm ≤ WC grain size < 0.5μm
Note. Measured using the average cut line method described in this section.
3.2.3
Submicron submicron
0.5μm ≤ WC grain size < 0.8μm
Note. Measured using the average cut line method described in this section.
3.2.4
Fine fine
0.8μm ≤ WC grain size < 1.3μm
Note. Measured using the average cut line method described in this section.
3.2.5
Medium
1.3μm ≤ WC grain size < 2.5μm
Note. Measured using the average cut line method described in this section.
3.2.6
Coarse coalse
2.5μm ≤ WC grain size ≤ 6.0μm
Note. Measured using the average cut line method described in this section.
3.2.7
Super thick extracoarse
WC grain size >6.0μm
Note. Measured using the average cut line method described in this section.
3.3 Symbols, abbreviations and units
The following symbols, definitions, and units apply to this document, as detailed in Table 1.
Table 1 Symbols, abbreviations and units
Symbol abbreviation unit
A area mm2
dWC WC grain arithmetic mean intercept μm
ECD equivalent diameter mm
L line length mm
The arithmetic mean length of the LI cut line μm
Li measured single cut length μm
∑li The sum of the measured lengths of each single cut line μm
N is the number of grain boundaries that are crossed
n Number of WC grains that have been intercepted
m magnification -
Mmax maximum magnification -
Mmin minimum magnification -
Sm measurement size mm
Sa actual size mm
4 General
This section gives the best method for measuring the average WC grain size. This section recommends using the line method to obtain data and measure samples.
It should be prepared by the preparation method of ISO 4499-1.
The properties of cemented carbides depend on the microstructure and change during the manufacturing process, which in turn is affected by the properties of the raw material powder.
Understanding the microstructure is the key to controlling and improving the performance of the product, so it is important to measure the properties of the microstructure, especially the grain size and ruler.
Inch distribution.
The metallographic preparation and etching methods in ISO 4499-1 (see references [1] to [4] for details) are as important as the grain size measurement method.
The main type of cemented carbide is WC/Co, in which Co is the binder phase. In addition, the method is also applicable to cubic phase carbides or TiC
Or Ti(C,N) is a matrix of cemented carbide.
The most straightforward method for measuring the grain size of WC is to first polish and etch the metallographic cross section, then use quantitative metallographic detection techniques to calculate
The area or the cut line method is used to measure the average value of the grain size.
There are three ways to define the average grain size.
--- Length (the length of the line across the grain section);
--- Area (the cross-sectional area of the grain);
--- Volume (single grain volume).
First calculate the value of each measurement parameter (length, area, volume), and then divide the sum of the parameter values by the total number of these parameters to calculate the level
Mean.
Among them, the most commonly used data is the length parameter. It can be used to obtain data in several ways, such as the parallel line method in ASTME 112 [12].
Or round method.
--- The line method, also known as the Heyn method, traverses the grain by drawing a straight line;
--- Equivalent diameter method 1), first measure the grain area, and then calculate the equivalent diameter.
1) For equiaxed grains, the equivalent diameter (ECD) can be converted to the cut length (LI) using equation (1).
LI= A = π/4ECD (1)
ECD=1.13LI is obtained;
This expression is discussed in references [1] and [5].
Another method is established by Jefferies, which counts the number of grains per unit area. It can be converted if needed
Equivalent diameter.
It is worth noting that.
--- Point/area count cannot provide distribution information;
The --Jefferies method does not apply to multiphase materials such as cemented carbide.
This section recommends the use of the line method to measure the grain size of cemented carbide.
5 instruments
The measurement of the grain size is determined by microscopic image. Reference method for optimal preparation of sample surface for imaging
ISO 4499-1, ASTMB657 [10] and ASTMB665 [11].
Cemented carbide microstructure images are typically obtained using optical microscopy or scanning electron microscopy (SEM). For accurate measurement, it is best to use
Scan the image of the electron microscope. Especially for materials containing coarse grains, the cross-section of the edge of the image can only be refined by scanning electron microscopy.
Measured.
Manual or semi-automatic image analysis is often used to obtain the length of the cut line. For some images with coarse grain or good contrast, you can use
Automated analysis software for analysis; but for most materials, especially fine-grained materials, it is difficult to obtain very sharp images, therefore,
Automatic analysis is generally not used.
For ultra-fine and nano-scale materials, it is quite difficult to obtain good quality photos using conventional tungsten wire electron source scanning electron microscopy.
For these materials, field emission scanning electron microscopy (FESEM) is recommended. This device can significantly improve the image resolution, enough to measure the average
A material with a cross-sectional dimension of 0.1 μm to 0.2 μm. For finer grained materials, it may be necessary to use a transmission electron microscope (TEM). however,
This is extremely demanding on sample and sample preparation (see reference [7] for details). For these materials, in order to get good photo quality,
It is important to focus on the preparation of the sample, which is usually better with a combination of corrosion methods (see ISO 4499-1).
6 calibration
In order to obtain reliable quantitative measurements, the image is calibrated with a micrometer or ruler traceable to national standards. Scanning electron microscopy most often
The micrometer used is a SIRA grating. The grating is formed by dividing a line of 197 pieces/mm to 2160 pieces/mm. However, these gratings
The (ruler) is also calibrated and traceable to national standards (see Reference [8] for details).
For optical microscopes, the same objective lens (built-in rate converter or focal length) and illumination should be used to observe the scale image. For
For maximum resolution, the microscope should use Kohler illumination.
For scanning electron microscopy, the observation of the scale image should be the same as the observation of the cemented carbide sample (acceleration voltage, working distance, aperture).
7 section line method to measure grain size
7.1 Overview
This section recommends using the arithmetic mean of the cut lines to define the WC grain size. This is the easiest way to summarize all the data.
To quantify the distribution range.
The cut line method draws a straight line across the calibrated microstructure image. For single-phase materials, the starting and ending points of the line can be
Therefore, the position of the straight line is L at any position on the image, and the number of grain boundaries passing through is N. Therefore, the average cut length L is.
LI=L/N (2)
It can be seen from the above formula that only the average length of the cut line is calculated, and the distribution of the grain size cannot be obtained.
For two-phase materials, such as cemented carbide (α phase and β phase), the wire cutting method is not easy to operate because the length of the wire for each phase requires a single
Independent measurement, but it can provide the distribution of grain size. Draw a straight line on the calibrated carbide metallographic photo, cross-section WC
For the grain, the length of the wire is measured using a ruler (where i = 1, 2, 3, n, corresponding to the 1, 2, 3, n grains). Recommended at least statistics
In order to reduce the error to 10% or less, it is preferable to count.200 crystal grains or more.
The grain size of the average intercept is defined as follows.
Dwc=∑li/n (3)
The cemented carbide grain size is generally between 0.1 μm and 10 μm. Due to a certain measurement error, it is recommended that the grain size value is large.
A 1-bit fraction is reserved at 1.0 μm, and a 2-bit fraction with a value less than 1.0 μm is retained. For example. 3.4 μm and 0.18 μm.
See Appendix A for measurement examples.
7.2 Sampling
7.2.1 Product sampling
The appropriate sampling method should be chosen for testing. Random sampling method, randomly select one sample in a batch of samples, each sample is selected
The probability is the same (see Ref. [9] for details).
Perform the following test, ISO 4489.1978 Chapter 4 states "the determination of the performance of cemented carbide grades, usually take one sample in a batch
It is enough".
--- Determination of coercive force (ISO 3326);
--- Determination of density (ISO 3369);
--- Determination of Rockwell hardness (ISO 3738-1 and ISO 3738-2);
--- Determination of Vickers hardness (ISO 3878).
In special cases, tests that can be performed.
--- Determination of microstructure (ISO 4499);
--- Determination of porosity and non-combined carbon (ISO 4505).
7.2.2 Selection of microstructure
The choice of microstructure has a great influence on the accuracy of the measurement results.
a) General measurement area selection
The photos used for analysis should be randomly selected and representative. The number of photos is recommended to be at least 4 sheets to ensure a summary analysis time
The number of grains is not less than.200.
b) Grain size measurement of homogeneous materials
In this case, a series of photos are taken from the sample determination position for summary analysis to ensure that at least.200 are measured per position.
Grain. This measurement is allowed because the effect of grain size on the error is greater than the measurement error caused by the different positions.
The error is proportional to 1/N, where N is the number of grains per position).
c) non-homogeneous materials
In this case, the microstructure of the sample is not uniform from one field of view to the next, given that the grains are scattered,
To get more than.200 measurements, a good measure is to increase the number of photos analyzed.
Photo magnification should be selected to control 10 to 20 WC grains across each field of view, allowing measurement error for a single line
Within 10%. It is generally allowed to draw 3 or 4 straight lines on a single photo without any single cross-section of any single WC die. Most
The organization of cemented carbide is isotropic, so it is not important to draw parallel lines. If it is anisotropic, it is best to draw a line at random and allow
Let them intersect (see Reference [11] for details). Therefore, each image should be able to obtain about 50 lines.
7.3 Measurement error
7.3.1 Systematic error and random error
7.3.1.1 There are several sources of measurement error.
--- systematic errors, such as generated during the calibration process of the microscope;
--- Random error, such as in the process of data transmission or calculation of the actual intercept;
---Statistical errors, such as due to the randomness of the microstructure.
7.3.1.2 The cause of the systematic error may be due to the calibration of the image magnification. Usually, the magnification of an optical microscope is one
Single value. However, if the calibration is performed with different calibration lengths or different operators, the measurement results will change, and the average release is required.
Large magnification and standard deviation. The systematic error of the SEM is greater because there is no fixed adjustment step size for its magnification.
7.3.1.3 Random error is mainly generated when measuring a single tungsten carbide grain cut. When different operators measure the same cut line,
Inconsistent selection of the position of the cut line or unclear boundary will bring measurement errors. Random errors are more difficult to quantify than systematic errors.
7.3.1.4 Statistical errors may occur if the microstructure is undersampled, such as too few photomicrographs or too few measured grains. This needs to have
Sufficient statistics are used to average. The size of the average intercept or the measured value of other parameters needs to be calculated repeatedly to average. get
The average value will fluctuate, but as the number of measurements increases, it will get closer to the true value. When the fluctuation of the average is small enough, you can stop
Stop the measurement.
7.3.2 coarse WC grain
Before deciding how much magnification to measure the grain size, first observe whether there are some coarse crystals on the surface of the sample after corrosion.
grain. If too high a magnification is used, these coarse grains may not be suitable for entering the field of view, which may affect the statistics of the measurement results. In theory, the institute
The magnification used should ensure that the largest WC grain imaging (10-20 pixels across the field of view) accounts for up to one-third of the field of view.
General guidelines. In practice, there will always be large grains across the edge of the field of view, making it impossible to measure. However, if you measure enough field of view, and
Using the mean method (see Figure A.4), the effect of large grains will be minimized.
7.3.3 Measurement of minimum intercept
7.3.3.1 Currently, there is no standard for the minimum intercept that can be measured by optical or scanning electron microscopy. For reference, use the instrument used
Resolution to determine the minimum intercept that can be measured. For a specific resolution, the measurable lower limit of the intercept is shown in Table 2. These data represent the best
The highest resolution available under conditions. In practice, it is possible to get lower resolution images, especially due to surface treatment problems.
To get high definition images. Therefore, the minimum intercept that can be measured will become larger. In fact, the smallest intercept that can be measured is the resolution of the instrument.
2 times, the measurement error is also twice the resolution error.
Table 2 measurable minimum intercept
Instrument maximum resolution minimum visible cut length a
Optical microscope
230nmb
350nmc
500nmb
700nmc
Scanning electron microscope
20nmb
200nmc
40nmb
200nmc
Field emission scanning electron microscope
1.5nmb
10nmc
3nmb
20nmc
a When the microscope resolution is maximum. The minimum visible cut length increases as the magnification decreases.
b Calibrate the theoretical resolution of the sample.
c Actual resolution of typical cemented carbide sample images.
7.3.3.2 The length of the cut line is smaller than the recommended minimum intercept, but the measurement error will increase significantly. Usually, the beginning and end of the line
The measurement error is twice the resolution error. In order to make the measurement error less than 10%, the length of the cut line is at least 20 times the theoretical resolution. because
Therefore, the optical microscope must have a measurement error of less than 10% at its maximum numerical aperture when the length of the cut line must exceed 5 μm. If WC
When the length of the grain cut is mostly less than 5 μm, the measurement error will affect the measured average of the cut lines and distort the grain size distribution.
In this case, a scanning electron microscope should be used.
7.3.3.3 Select the magnification to accommodate as many WC grains as possible while also affecting the measurable minimum intercept. In general,
Low magnification (LOM) requires a lower magnification objective and a smaller numerical aperture to reduce resolution. For SEM, lower magnification means electronics
The beam is sampled in larger steps. Table 2 shows the maximum resolution that can be achieved. In order to achieve low magnification, a numerical aperture of 1.3 should be used.
×100 oil immersion objective lens.
8 report
8.1 When giving the grain measurement results, all relevant information should be listed to ensure traceability of the measurement results. For example, a standard
The test report should contain the following.
---sample discription;
---Corrosive agent and corrosion time;
--- Traceability, calibration ticks and calibration certificates;
---Image acquisition equipment. optical microscope, scanning electron microscope or field emission scanning electron microscope;
--- Magnification. one or more times;
---Measure the number of fields of view;
---The total number of cut lines;
--- the arithmetic mean of the cut line;
---Grain size distribution, using the method recommended in this section, if other standards are used, the method needs to be explained;
---Additional note.
8.2 Additional information is necessary to match the quality system. Description of images or photomicrographs that may be involved, if required for archiving,
Source information and customer requested information are also required.
The following additional information is often also involved.
---Maximum cut length;
---The minimum length of the line;
---Maximum grain;
---The numerical aperture of the optical microscope objective lens;
--- Scanning electron microscope acceleration voltage, working distance, aperture and so on.
8.3 Test report style See Appendix B. It is recommended to add a description of the measurement method ...
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