GB/T 21931.1-2025 PDF English
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GB/T 21931.1: Historical versions
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| GB/T 21931.1-2025 | 320 | Add to Cart | Auto, 9 seconds. | Ferronickel - Determination of carbon content - Infrared absorption method after induction furnace combustion | Valid |
| GB/T 21931.1-2008 | 140 | Add to Cart | Auto, 9 seconds. | Nickel, ferronickel and nickel alloys -- Determination of carbon content -- Infrared absorption method after induction furnace combustion | Valid |
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GB/T 21931.1-2025: Ferronickel - Determination of carbon content - Infrared absorption method after induction furnace combustion
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GB NATIONAL STANDARD OF THE PEOPLE’S REPUBLIC OF CHINA ICS 77.100 CCS H 11 Replacing GB/T 21931.1-2008 Ferronickel - Determination of Carbon Content - Infrared Absorption Method after Induction Furnace Combustion (ISO 7524.2020, MOD) Issued on: AUGUST 29, 2025 Implemented on: MARCH 1, 2026 Issued by. State Administration for Market Regulation; Standardization Administration of the People’s Republic of China.
Table of Contents
Foreword... 3 Introduction... 5 1 Scope... 6 2 Normative References... 6 3 Terms and Definitions... 7 4 Principle... 7 5 Reagents and Materials... 7 6 Instruments and Equipment... 8 7 Sampling and Sample Preparation... 9 8 Analytical Procedures... 10 9 Precision... 13 10 Test Report... 14 Appendix A (informative) Comparison of Structural No. between This Document and ISO 7524.2020... 15 Appendix B (informative) Technical Differences between This Document and ISO 7524.2020 and Their Causes... 17 Appendix C (informative) Characteristics of Commercial High-frequency Induction Furnace Infrared Carbon Analyzer... 18 Appendix D (normative) Flowchart of Specimen Analysis Result Acceptance Procedures... 20 Appendix E (informative) Raw Data from Common Precision Test... 21 Ferronickel - Determination of Carbon Content - Infrared Absorption Method after Induction Furnace Combustion WARNING. personnel using this document shall have practical experience in formal laboratory work. This document does not address all potential safety issues. Users are responsible for taking appropriate safety and health precautions and ensuring compliance with relevant national regulations.1 Scope
This document specifies the method for determining the carbon content in ferronickel using the infrared absorption method after induction furnace combustion. This document applies to the determination of carbon content in ferronickel, determination range (mass fraction). 0.001% ~ 2.5%.2 Normative References
The contents of the following documents constitute indispensable clauses of this document through the normative references in the text. In terms of references with a specified date, only versions with a specified date are applicable to this document. In terms of references without a specified date, the latest version (including all the modifications) is applicable to this document. GB/T 6379.1 Accuracy (trueness and precision) of Measurement Methods and Results - Part 1. General Principles and Definitions (GB/T 6379.1-2004, ISO 5725-1.1994, IDT) GB/T 6379.2 Accuracy (trueness and precision) of Measurement Methods and Results - Part 2. Basic Method for the Determination of Repeatability and Reproducibility of a Standard Measurement Method (GB/T 6379.2-2004, ISO 5725-2.1994, IDT) GB/T 6379.3 Accuracy (trueness and precision) of Measurement Methods and Results - Part 3. Intermediate Measures of the Precision of a Standard Measurement Method (GB/T 6379.3- 2012, ISO 5725-3.1994, IDT) GB/T 8170 Rules of Rounding off for Numerical Values & Expression and Judgement of Limiting Values GB/T 25050 Ferronickel Ingots or Pieces - Sampling for Analysis (GB/T 25050-2010, ISO 8050.1988, IDT) GB/T 25051 Ferronickel Shot - Sampling for Analysis (GB/T 25051-2010, ISO 8049.1988, IDT)3 Terms and Definitions
The following terms and definitions are applicable to this document. 3.1 flux Primarily used to lower the melting point of the sample, making it easier to melt and flow at high temperatures, thus ensuring the full release of carbon and sulfur. 3.2 promoter Typically used to accelerate chemical reactions, and increase the reaction rate, thus enabling carbon and sulfur to be converted into detectable gaseous products more quickly.4 Principle
The test portion is heated and burned in the oxygen stream of an induction furnace. Under the action of the flux and promoter, carbon is converted into carbon dioxide or carbon monoxide, which is carried by the oxygen stream to an infrared absorption cell. The absorption of infrared light at a specific wavelength is measured by an infrared detector, and the carbon content is determined based on the change in infrared energy received by the detector.5 Reagents and Materials
5.1 Oxygen Purity at least 99.5% (mass fraction). 5.2 Alkali Asbestos Particle size. 0.7 mm ~ 1.2 mm, used for absorbing carbon dioxide. 5.3 Anhydrous Magnesium Perchlorate [Mg(ClO4)2] Particle size. 0.7 mm ~ 1.2 mm, used for absorbing moisture. 5.4 Glass Wool Filter Place glass wool in a dedicated reagent tube to filter dust and particulate matter generated during high-frequency induction combustion and protect detection components at the back end from contamination. 5.5 Flux Common fluxes are tin, copper with tin, copper or tungsten. 5.6 Promoter Common promoters are copper, iron, tungsten or nickel. Some materials act as both fluxes and promoters. Both the flux and promoter used shall have a low carbon content and shall be simultaneously used in the calibration procedures. Various factors (oxygen, crucible, flux and promoter) contribute to the carbon blank value. When the carbon content of the sample to be determined is 0.1% (mass fraction), it is required that the blank value shall not exceed 0.0005% (mass fraction); when the carbon content of the sample to be determined is > 0.1% (mass fraction), it is required that the blank value shall not exceed 0.001% (mass fraction). 5.7 Certified Reference Materials/Samples of Steel or Ferronickel Carbon content (mass fraction) is 0.001% ~ 2.6%.6 Instruments and Equipment
6.1 Carbon Analyzer 6.1.1 High-frequency induction furnaces and infrared absorption carbon determinators are available from multiple instrument manufacturers. The instruments and equipment shall be operated in accordance with the manufacturer’s instructions. In accordance with the manufacturer’s specifications, a pressure regulator is required to control the oxygen pressure entering the instrument’s combustion furnace. 6.1.2 Oxygen shall be purified using a quartz tube filled with alkali asbestos (5.2) and anhydrous magnesium perchlorate (5.3). In standby mode, a flow rate of approximately 0.5 L/min shall be maintained. 6.1.3 A glass wool filter (5.4) shall be installed between the high-frequency induction furnace chamber and the analyzer and replaced as necessary. The furnace chamber, furnace column, and filter screen shall be frequently cleaned to remove oxide residues. 6.1.4 The instrument manufacturer may recommend setting up a pre-combustion program before oxygen intake. During the pre-combustion, the test portion is in a red-hot state. When oxygen is introduced during the combustion stage, the temperature will significantly rise. 6.1.5 The temperature reached during combustion depends on the furnace and the type and quantity of metal in the crucible. After melting, the specimen is maintained at a high temperature ( > 1,700 °C) to ensure complete transfer of carbon dioxide from the furnace to the infrared analysis cell. 6.1.6 After the instrument has been idle for several hours or after cleaning the furnace or filter, the instrument shall be stabilized in accordance with the steps described in 8.1. NOTE. Appendix C provides characteristics of commercial instruments. 6.2 Ceramic Crucible A ceramic crucible is required to hold the sample and other necessary additives for the subsequent melting process. The crucible shall be dimensionally accurate and fit the support, so that the test portion in the crucible is precisely within the heating induction coil. Typical dimensions of the crucible are. ---Height. 25 mm; ---Outer diameter. 25 mm; ---Inner diameter. 20 mm; ---Wall thickness. 2.5 mm; ---Bottom thickness. 8 mm; ---Crucible lid aperture. greater than 10 mm. The crucible and crucible lid shall conform to the instrument manufacturer’s specifications, be able to withstand the combustion temperatures in the induction furnace and not produce carbonaceous chemicals, so as to meet the blank value requirements specified in the document. To eliminate the potential influence of carbon contamination from the crucible on the determination, the crucible shall be incinerated in a high-temperature furnace purged with air or oxygen at 1,100 °C for at least 1 hour, then, cooled and stored in a desiccator or sealed container. Alternatively, a resistance furnace with a combustion tube purged with oxygen can be used for crucible pre-treatment in a similar manner. 6.3 Crucible Clamps Special clamps used for holding the ceramic crucible.7 Sampling and Sample Preparation
7.1 Sampling shall be performed in accordance with the provisions of GB/T 25050 or GB/T 25051.Sample preparation shall be carried out in accordance with the normally agreed procedures; in case of dispute, the appropriate standard shall prevail. 7.2 Laboratory samples are usually granular, drilling chips, or milling chips, requiring no further processing. 7.3 If laboratory samples are contaminated with oil or grease during grinding or drilling, they shall be cleaned with high-purity acetone and air-dried. 7.4 If the particle size of the laboratory samples significantly varies, then, the specimens shall be obtained after reduction.8 Analytical Procedures
WARNING---the main danger of this test lies in the burns that occur during crucible pre- combustion and in the molten state. Therefore, crucible clamps shall be used throughout the test, and the burned crucible shall be placed in a suitable container. When using oxygen cylinders, their standard safety procedures shall be followed. Localized oxygen enrichment can cause a fire; therefore, it is essential to ensure that oxygen is effectively evacuated from the instrument during combustion. 8.1 Instrument Preparation and Stabilization 8.1.1 In accordance with the manufacturer’s instructions, assemble and prepare the instrument. Perform leak detection tests on the high-frequency furnace and analytical system to ensure that the entire gas path system is leak-free. 8.1.2 Before calibrating the instrument or performing the blank test, weigh-take several samples similar to the specimen to be determined, add appropriate flux and promoter, and ignite them in the instrument’s induction furnace to stabilize the instrument. NOTE. it is unnecessary to use pre-treated crucibles. 8.1.3 Perform several cycle tests with the instrument under oxygen supply, and if necessary, adjust the zero point of the instrument. 8.2 Blank Test and Zero Adjustment 8.2.1 Carbon content 0.1% For this range, weigh-take a certain mass of flux (5.5), accurate to 0.005 g, and place it in a ceramic crucible (6.2). Add a certain mass of low-carbon certified reference material/sample (5.7), and then, weigh-take a certain mass of promoter (5.6) to cover it. The type and mass of flux and promoter used in the blank test shall be consistent with the sample determination method used (see 8.4.1 for details). Record the mass of the reference material/sample. Place the crucible with flux, sample, and promoter on the furnace base support and operate in accordance with the manufacturer’s instructions. Repeat the determination 3 times and take the average result. Subtract the carbon content of the certified reference material/sample from the average result to obtain the blank value. If the blank value is greater than 0.0005% (mass fraction), or its standard deviation is greater than 0.0002% (mass fraction), identify the cause, correct it, and repeat the test. In accordance with the manufacturer’s instructions, input the blank average value into the analytical instrument. NOTE 1.obtained blank reading is the blank value generated by the crucible, flux and promoter. If the analytical instrument does not have an automatic blank correction function, then, each time a result is calculated, manually subtract the blank value from the result shown by the instrument. NOTE 2.another method is to record the blank test reading and use a calibration chart for correction. 8.2.2 Carbon content > 0.1% Blank correction is not required in this range, but the blank value shall be checked and determined. The blank value shall not be greater than 0.001% (mass fraction). If the blank value is greater than 0.001% (mass fraction), identify the cause, correct it, and repeat the test. 8.3 Calibration 8.3.1 Select a series of certified reference materials/samples of steel or ferronickel (5.7) for calibration and verification. The carbon content of the certified reference materials/samples shall have a certain gradient. 8.3.2 If the instrument has multiple carbon detection cells (measurement systems), then, each carbon detector shall be calibrated as described in this section. All test parameters shall be determined for each measurement range. Parameters that need to be determined include whether the crucible is pre-combusted, the type and mass of the flux and promoter, and the weighed mass of the test portion. 8.3.3 For each detection cell (see 8.3.2), weigh-take an appropriate amount (typically 0.50 g) of certified reference material/sample, with a carbon content corresponding to the high point of each operating range; place it in a pre-treated ceramic crucible (6.2). Add the pre-selected flux (5.5) and promoter (5.6) and ignite as described in 8.4.1.Repeat this process twice. If the analytical result is within the range of “certified value 2σ”, then, in accordance with the instrument operating instructions, adjust the final instrument reading, so that it is consistent with the certified carbon content in the certified reference material/sample. NOTE. σ is the standard deviation of the certified reference material/sample, the same applies below. 8.3.4 Analyze the carbon content of certified reference material/samples at least 3 times, with the carbon content falling within the middle of the detection value range, to check the linearity. The result shall be within the range of “certified value 2σ”. 8.3.5 Before proceeding to the next step, any non-compliance shall be corrected. 8.4 Determination 8.4.1 Weigh-take 0.5 g ~ 0.6 g of the specimen to be determined, accurate to 0.001 g, and transfer it to a ceramic crucible (6.2). If necessary, add an appropriate amount of the selected flux (5.5). Then, use an appropriate amount of promoter (5.6) to cover the specimen, and if necessary, cover the crucible. NOTE. the flux and promoter used depend on the performance of the instrument used and the type of sample being analyzed. For ferronickel, use approximately 1.5 g of a tungsten-tin mixture, with a tungsten + tin ratio of (7 ~ 9) + 1.For high-nickel samples, appropriately add pure iron. 8.4.2 Place the crucible and contents on the induction furnace crucible holder, raise it to the combustion position, and lock the system. In accordance with the manufacturer’s instructions, operate the induction furnace. 8.4.3 Record the analyzer readings and repeat the determination at least once. NOTE 1.maintaining a high temperature after sample melting is important to ensure complete transfer of carbon dioxide from the induction furnace to the infrared detection cell. NOTE 2.keep the sample stable during combustion to avoid molten material splashing onto the crucible lid. 8.4.4 Analyze at least twice a certified reference material/sample with carbon content slightly higher or lower than the content of each unknown sample. The corresponding results shall be within the range of “certified value 2σ”. The certified reference material/sample used to check the accuracy of the determination shall be different from the certified reference material/sample used for calibration (see 8.3). 8.4.5 If an abnormal deviation occurs, then, the analytical result is invalid, and the test steps in 8.3 and 8.4 shall be repeated for re-analysis. 8.5 Calculation and Reporting of Analytical Results 8.5.1 Calculation If the instrument is calibrated and automatically compensates for the mass of the test portion, the carbon content of the sample is read directly as a percentage by mass. If the instrument is calibrated based on 0.50 g of test portion without automatic mass compensation, then, each reading must be divided by the corresponding mass of the test portion (unit. g). For certain instruments, it is necessary to plot a calibration chart of instrument readings versus carbon mass (unit. g). The carbon content in the instrument is read and expressed in micrograms on the mass chart. The blank and mass of the detected components are then corrected. 8.5.2 Reporting If the absolute value of the difference between two independent analytical results for the same specimen is not greater than the repeatability limit r, then, the arithmetic mean is taken as the analytical result. If the absolute value of the difference between two independent analytical results is greater than the repeatability limit r, then, additional measurements shall be performed ......Source: Above contents are excerpted from the full-copy PDF -- translated/reviewed by: www.ChineseStandard.net / Wayne Zheng et al.
