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GB/T 224-2019 English PDF (GBT224-2019)

GB/T 224-2019 English PDF (GBT224-2019)

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GB/T 224-2019: Determination of the depth of decarburization of steels

This Standard specifies requirements for sampling, determination method and test report of steel decarburization. This Standard is applicable to measuring depths of decarburization of steel (blank) and its parts. 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 224-2019
NATIONAL STANDARD OF THE
PEOPLE REPUBLIC OF CHINA
ICS 77.040.99
H 24
Replacing GB/T 224-2008
Determination of the depth of
decarburization of steels
(ISO 3887:2017, Steels - Determination of the depth of decarburization, MOD) ISSUED ON: JUNE 04, 2019
IMPLEMENTED ON: MAY 01, 2020
Issued by: State Administration for Market Regulation;
Standardization Administration of the People's Republic of
China.
Table of Contents
Foreword ... 3
1 Scope ... 6
2 Normative references ... 6
3 Terms and definitions ... 7
4 Sampling ... 9
5 Determination method ... 11
6 Test report ... 18
Annex A (Informative) Typical structural photo example of decarburization depth determined by metallographic method ... 20
Foreword
This Standard was drafted in accordance with the rules given in GB/T 1.1-2009. This Standard replaces GB/T 224-2008 ?€?Determination of depth of
decarburization of steels?€?.
Compared with GB/T 224-2008, the main technical changes in this Standard are as follows:
- deleted the term ?€?ferrite decarburization depth?€? and its definition (Clause 3 of Edition 2008);
- modified ?€?sampling?€? (see Clause 4 of this Edition, third paragraph in 4.1, 4.2.2, 4.4.1 and 4.4.2 of Edition 2008);
- added average method (see 5.2.3 of this Edition);
- added specific contents of microscopic knoop hardness method and
microhardness indentation (see 5.3.1 of this Edition);
- added electron probe method (see 5.4.4 of this Edition);
- added glow spectroscopy (see 5.4.5 of this Edition);
- added precise digits that different measurement methods correspond to decarburization depths (see Clause 6 of this Edition).
This Part uses redrafting method to modify and adopt ISO 3887:2017 ?€?Steels - Determination of the depth of decarburization?€?.
Technical differences and reasons between this Standard and ISO 3887:2017 are as follows:
- about normative references, this Standard made an adjustment on
technical differences, so as to adapt to technical conditions of China. See Clause 2 ?€?Normative references?€? for the adjustment. Details are as follows: ?€? used GB/T 4340.1 that adopted international standard to replace ISO
6507-1 (see 5.3.3);
?€? used GB/T 18449.1 that adopted international standard to replace ISO
4545-1 (see 5.3.3);
?€? used GB/T 20126 that adopted international standard to replace ISO
15349-2 (see 5.4.2.2);
Determination of the depth of
decarburization of steels
1 Scope
This Standard specifies requirements for sampling, determination method and test report of steel decarburization.
This Standard is applicable to measuring depths of decarburization of steel (blank) and its 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 4340.1-2009, 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 - Knoop hardness test - Part 1: Test method (GB/T 18449.1-2009, 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 defined in GB/T 30067 as well as the followings apply.
3.1 decarburization
Loss of carbon on steel surface. Such loss of carbon includes:
a) partial decarburization: carbon content on surface of steel sample is reduced below carbon content of substrate, and is greater than solid
solution limit of carbon in ferrite at room temperature;
b) complete decarburization: is also called as ferrite decarburization; surface carbon content of sample is lower than maximum solid solubility of carbon in ferrite; only ferrite exists.
NOTE: Complete decarburization described in b) has only ferrite structure. It shall use metallographic method to determine.
3.2 depth of functional decarburization
Distance from sample surface to point of specified carbon content or point of hardness level. Specified carbon content or hardness level shall be based on that use performance is not affected by decarburization (for example, minimum carbon content specified in product standard).
3.3 depth of total decarburization
Distance from sample surface to the point of which carbon content is equal to substrate carbon content. It is equal to the sum of partial decarburization and complete decarburization.
See Figure 1 for different decarburization zones.
W - width;
A - area of inspection surface of steel plate or rectangular sample.
Figure 4 -- Typical sampling method for steel plate and rectangular steel 4.4 Sample for chemical analysis shall have a sufficient length, so as to ensure quantity of turnings that are continuously increased by chemical analysis. Or it shall have a large enough area to meet spectral analysis area.
5 Determination method
5.1 General
5.1.1 Selection of determination method and its precision depend on product?€?s degree of decarburization, microstructure, carbon content as well as part?€?s shape. Final product usually uses following methods to measure depth of decarburization:
a) metallographic method (see 5.2);
b) microhardness method (see 5.3); it can use Vickers hardness or Knoop hardness;
c) determination method for carbon content can be chemical analysis method (see 5.4.2), direct spectroscopy reading method (see 5.4.3), electron
probe method (see 5.4.4) or glow spectroscopy method (see 5.4.5).
5.1.2 Determination methods in 5.1.1 all have their own application scopes. The method for determination shall be determined by product standard or agreed by both parties. Where it is not specified, it shall use metallographic method. 5.2 Metallographic method
5.2.1 General
This method is, under optical microscope, to observe structure change of sample from surface to substrate as carbon content varies. It is applicable to type of steel that has annealing or normalizing (ferrite-pearlite) structure. It can be conditionally used for those hardened, tempered, rolled or forged products. 5.2.2 Sample preparation
Sample is ground and polished according to GB/T 13298. However, rounding and curling are not allowed on sample edge. For this purpose, sample can be mounted or fixed in holder. If necessary, surface of testing sample can be plated with a layer of metal to protect it. Automatic or semi-automatic sample measurements at random (at least five). Take average value of these
measurement values as depth of total decarburization. For bearing steel, tool steel, spring steel, measure depth of total decarburization at the deepest. Averaging method measures the first point at the deepest uniform
decarburization zone. Then, starting from this point, surface is equally divided into several parts. If there are no special regulations, at least it shall be divided into four equal parts. At the end position of each part, measure depth of decarburization at the deepest. Take average value of these measurements (at least four) as depth of total decarburization and report it. Averaging method is applicable to steels such as bearing steel, tool steel, spring steel that have high requirements for decarburization.
If there are no special provisions in product standard or technical agreement, when measuring, those deep decarburization points (such as cracks or folds, workpiece corners, etc.) in sample caused by steel defects shall be excluded (but defects shall be noted in test record).
5.2.3.2 Determination of complete decarburization
Determination method of complete decarburization is same with 5.2.3.1.
5.2.3.3 Determination of functional decarburization
Determination method of functional decarburization is same with 5.2.3.1. Judgement of functional decarburization is determined in product standard or agreed by parties concerned.
5.2.3.4 Typical structural photo of decarburization depth determined by metallographic method
Refer to Annex A for typical structural photo example of decarburization depth determined by metallographic method.
5.3 Microhardness method
5.3.1 General
This method is to measure distribution gradient of microhardness value in cross section that is perpendicular to surface of sample.
This method is only applicable to hardened, tempered or heat treated eutectic steel of which decarburization is rather deep. Meanwhile, it is also used for situation where decarburization is completely in hardened zone to avoid hardness fluctuation caused by incomplete quenching. This method is not applicable to low-carbon steel.
Depth of decarburization is specified as distance from surface to the point that has reached required hardness value (dispersion of measurement needs to be considered into estimation).
In principle, it shall perform four groups of measurements at a position where they are as far as possible from each other. Use average value of their measurements as depth of decarburization.
Measurements limit of depth of decarburization can be:
a) from sample surface to position where hardness value is specified in product standard or technical agreement;
b) from sample surface to position where hardness value is stable;
c) from sample surface to a certain percentage of position where hardness value is stable.
Which kind of measurement limit used is specified in product standard or agreement of both parties.
5.4 Determination method of carbon content
5.4.1 General
This method is to determine distribution gradient of carbon content in a direction perpendicular to surface of sample.
5.4.2 Chemical analysis method
5.4.2.1 General
This method is applicable to sample that has proper geometry, for example, cylinder or polyhedron with planar body.
NOTE 1: Sample is usually not heat-treated. If it is really necessary, after proper consultation, appropriate heat treatment can be carried out, but it is guaranteed not to affect depth of decarburization.
NOTE 2: This method is not applicable to partial decarburization.
5.4.2.2 Sample preparation
Use machining method to, parallel to surface of sample, strip sample chips of which each layer is 0.1mm thick. Take care to prevent any pollution. Remove oxide film in advance. Collect metal sample chips stripped from each layer. Determine carbon content in accordance with GB/T 20126 or ISO 9556.
Determination of depth of total decarburization is from surface to position where carbon content is stable. Depth of complete decarburization is according to agreement between supplier and purchaser. Conduct four groups of
determinations at a position where distance between each other is as far as possible. Take average value of determination values as depth of
decarburization.
5.4.5 Glow spectroscopy method
5.4.5.1 General
This method is in accordance with GB/T 19502 and GB/T 22368. This method is applicable to round sample of which depth of decarburization does not exceed 100??m, diameter is between 20mm ~ 100mm or square sample of
which side length is between 20mm ~ 100mm. Plane size of sample shall meet requirements for glow spectrometer.
5.4.5.2 Sample preparation
Use suitable solvent (analytically-pure acetone or ethanol) to rinse sample surface to remove oil or other residues. During rinsing, it can use wet soft non- woven fabric to gently wipe sample surface. After rinsing, it can use inert gas (argon or nitrogen) or clean oil-free compressed air to blow sample dry. Gas piping must not be in contact with surface of sample.
5.4.5.3 Measurement
Depth curve of carbon content goes from sample surface to position where substrate carbon content is stable. Depth of total decarburization is determined by depth curve of carbon content.
Determination of depth of total decarburization is from surface to position where substrate carbon content is stable, for example, to position where substrate carbon content is. Depth of total decarburization can be according to agreement between supplier and purchaser. Conduct four groups of determinations at a position where distance between each other is as far as possible. Take average value of determination values as depth of decarburization.
6 Test report
Test report shall contain the following information:
a) number of samples and sampling parts;
b) specific determination method if it does not use metallographic most serious view field method;

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