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This standard is drafted in accordance with the rules given in the GB/T 1.1-2009
This part replaces GB/T 224-2008 Determination of the Depth of Decarburization of Steels in whole.
The following technical deviations have been made with respect to the GB/T 224-2008 (the previous edition):
— deletion of the term “depth of ferritic decarburization” and its definition (Clause 3 of Edition 2008);
— modification of the “Sampling” (see Clause 4; paragraph 3 of 4.1, 4.2.2, 4.4.1 and 4.4.2 of Edition 2008);
— addition of the average method (see 5.2.3);
— addition of the specific method for measuring the micro-indentation Knoop hardness and micro-hardness impressions (see 5.3.1);
— addition of the electron probe microanalysis (see 5.4.4);
— addition of the glow discharge optical emission spectrometry (see 5.4.5);
— addition of the exact decimal places for different measurements of the depth of decarburization (see Clause 6).
This standard has been redrafted and modified adoption of International Standard ISO 3887:2017 Steels — Determination of the Depth of Decarburization.
Compared with ISO 3887:2017, this standard has the following technical differences and causes:
— The adjustments of technical deviations are made for the normative references in this standard so as to adapt to the technical conditions of China. The adjustment is mainly reflected in Clause 2 "Normative References", with the specific adjustments as follows:
? ISO 6507-1 is replaced by GB/T 4340.1 which is modified adoption of the International Standard (see 5.3.3);
? ISO 4545-1 is replaced by GB/T 18449.1 which is modified adoption of the International Standard (see 5.3.3);
? ISO 15349-2 is replaced by GB/T 20126 which is identical with the International Standard (see 5.4.2.2);
? ISO 14707 is replaced by GB/T 19502 which is identical with the International Standard (see 5.4.5.1);
? addition of references GB/T 30067 (see Clause 3), GB/T 13298 (see 5.2.2), GB/T 15247 (see 5.4.2.3), GB/T 4336 (see 5.4.3.2), GB/T 22368 (see 5.4.5.1);
— addition of the requirements for sample state in Clause 4 "Sampling" (see 4.1), by reason of the sample state has a great influence on the depth of decarburization, so the requirements for sample state are unified to avoid quality disputes;
— addition of requirements of "total test perimeter not less than 35 mm" for large samples and the sampling schematic diagram in Clause 4 "Sampling” (see 4.3 and Figures 2 to 4), which is included in GB/T 224-2008 to improve the operability of sampling;
— addition of the “The depth of total decarburization of bearing steel, tool steel and spring steel shall be measured at the deepest position” (see 5.2.3.1), which had been specified in GB/T 224-2008 and applicable to the national conditions of China;
— deletion of the 5.4.4 of ISO 3887:2017, its contents are included in 5.4.2.3 and 5.4.3.3, respectively;
— modification of treatment method for the test results in 5.4.2 “Chemical analysis” and 5.4.3 “Spectrographic analysis” (see 5.4.2.3), keeping consistent with GB/T 224-2008, and applicable to the national conditions of China.
For the purposes of this standard, the following editorial changes have also been made:
— in order to be consistent with the existing standard series, the standard name is changed to Determination of the Depth of Decarburization of Steels.
— addition of the metallographic structure of surface decarburization of GCr15 (see Figure A.3).
This standard was proposed by China Iron and Steel Association.
This standard is under the jurisdiction of SAC/TC 183 (National Technical Committee on Iron and Steel of Standardization Administration of China).
The previous editions of the standard replaced by this standard are as follows:
— GB 224-1963, GB 224-1978, GB/T 224-1987, GB/T 224-2008.
Determination of the Depth of Decarburization of Steels
1 Scope
This standard specifies the requirements for sampling, measuring methods and test reports of the decarburization of steel products.
This standard is applicable to the determination of the depth of decarburization of steels (billets) and their parts.
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 4336 Carbon and Low-alloy Steel — Determination of Multi-element Contents — Spark Discharge Atomic Emission Spectrometric Method (Routine Method)
GB/T 4340.1 Metallic Materials — Vickers Hardness Test — Part 1: Test Method (GB/T 4340.1, ISO 6507-1:2005, MOD)
GB/T 13298 Inspection Methods of Microstructure for Metals
GB/T 15247 Microbeam Analysis — Electron Probe Microanalysis — Guidelines for Determining the Carbon Content of Steels Using Calibration Curve Method (GB/T 15247-2008, ISO 16592:2006, IDT)
GB/T 18449.1 Metallic Materials — Vickers Hardness Test — Part 1: Test Method (GB/T -2009, ISO 4545-1:2005, MOD)
GB/T 19502 Surface Chemical Analysis — Glow Discharge Optical Emission Spectrometry (GD-OSE) — Introduction to Use (GB/T 19502-2004, ISO 14707:2000, IDT)
GB/T 20126 Unalloyed Steel — Determination of Low Carbon Content — Part 2: Infrared Absorption Method after Combustion in an Induction Furnace (with Preheating) (GB/T 20126-2006, ISO 15349-2:1999, IDT)
GB/T 22368 Low-alloy Steel — Determination of Multi-element Contents — Glow Discharge Optical Emission Spectrometry (Routine Method)
GB/T 30067 Standard Terminology Relating to Metallography
ISO 9556 Steel and Iron — Determination of Total Carbon Content — Infrared Absorption Method after Combustion in an Induction Furnace
ISO 14594 Microbeam Analysis — Electron Probe Microanalysis — Guidelines for the Determination of Experimental Parameters for Wavelength Dispersive Spectroscopy
3 Terms and Definitions
For the purposes of this document, the terms and definitions given in GB/T 30067 and the following apply.
3.1
decarburization
reduction of carbon content from the surface zone of the steel The reduction of carbon include:
a) partial decarburization, measured as the distance from the point at which the carbon content exceeds the solubility limit in ferrite, becoming visible as e.g. pearlite, to the point at which there is no more visible difference to the core carbon concentration;
b) complete decarburization, also called ferrite decarburization, measured as the distance between the surface of the product and the point up to which the carbon content is below the solubility limit of carbon in ferrite so that only ferrite is present.
Note: The depth of complete decarburization as described in b) is determined by examination of the microstructure.
3.2
depth of functional decarburization
distance between the surface of the product and the point at which the carbon content or hardness is at the level where the performance of the product would be unaffected by a reduction in carbon content (i.e. at the minimum level specified in the product standard)
3.3
depth of total decarburization
distance between the surface of the product and the point at which the carbon content is that of the unaffected core, the sum of the partial and the complete decarburization
The various bands of decarburization are shown diagrammatically in Figure 1.
Note: If the product has undergone a process involving carburization, the definition of the “core” shall form the subject of an agreement between the parties concerned. The permissible depth of decarburization shall be specified in the appropriate standard covering the product or shall be the subject of an agreement between the parties concerned.
Key:
d1 — the depth of complete decarburization, in millimetres (mm);
d2 — the depth of functional decarburization, in millimetres (mm);
d3 — the depth of partial decarburization, in millimetres (mm);
d4 — the depth of total decarburization, in millimetres (mm);
a — the minimum carbon content specified in the product standard;
b — core carbon content.
Note: The boundaries separating the various types of decarburization are shown as hatched bands with the width of the band illustrating the practical variability in measurements due to the uncertainty of interpretation.
Figure 1 Schematic representation for a typical decarburization
4 Sampling
4.1 Samples shall be inspected in the state of delivery without further heat treatment. If additional heat treatment is required as agreed by the parties concerned, attention should be paid to the prevention of changes in carbon distribution and mass fraction, such as the use of small samples, short austenitization time, neutral protective atmosphere, etc.
4.2 Samples should be taken at locations that are representative of the bulk specimen. The location and number of samples taken depend on the nature of the material to be tested and are defined by agreement between the parties concerned.
Foreword II
1 Scope
2 Normative References
3 Terms and Definitions
4 Sampling
5 Measuring Methods
6 Test Report
Annex A (Informative) Examples of Typical Decarburization Microstructure Measured by Metallographic Method
