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GB/T 25744-2010 English PDF (GBT25744-2010)

GB/T 25744-2010 English PDF (GBT25744-2010)

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GB/T 25744-2010: Metallographic examination for carburizing quenching and tempering of steel parts

This standard specifies the method for the inspection of the carburizing quenching and tempering metallographic structure of steel parts, the level of the metallographic structure, the determination of the effective depth of hardened layer of the carburizing quenching. This standard is applicable to workpieces, whose effective hardened layer depth is greater than 0.3 mm by carburizing quenching.
GB/T 25744-2010
GB
NATIONAL STANDARD OF THE
PEOPLE REPUBLIC OF CHINA
ICS 25.200
J 36
Metallographic examination for carburizing quenching
and tempering of steel parts
ISSUED ON: DECEMBER 23, 2010
IMPLEMENTED ON: JUNE 01, 2011
Issued by: General Administration of Quality Supervision, Inspection and Quarantine of PRC;
Standardization Administration of PRC.
Table of Contents
Foreword ... 3
1 Scope ... 4
2 Normative references ... 4
3 Terms and definitions ... 4
4 Specimen ... 5
5 Inspection items and inspection methods ... 5
6 Rating of metallographic structure level ... 6
7 Inspection equipment ... 8
8 Inspection report ... 8
Appendix A (Informative) General requirements for the metallographic
inspection of steel gears by carburizing quenching and tempering ... 9 Appendix B (Normative) Martensite level chart ... 11
Appendix C (Normative) Retained austenite level chart (500??) ... 13
Appendix D (Informative) Retained austenite level chart (1000??) ... 15 Appendix E (Normative) Carbide level chart ... 17
Appendix F (Informative) Morphology of inner oxidation ... 20
Appendix G (Normative) Core structure level chart ... 21
Metallographic examination for carburizing quenching
and tempering of steel parts
1 Scope
This standard specifies the method for the inspection of the carburizing quenching and tempering metallographic structure of steel parts, the level of the metallographic structure, the determination of the effective depth of hardened layer of the carburizing quenching.
This standard is applicable to workpieces, whose effective hardened layer depth is greater than 0.3 mm by carburizing quenching.
2 Normative references
The provisions in following documents become the provisions of this Standard through reference in this Standard. For the dated references, the subsequent amendments (excluding corrections) or revisions do not apply to this Standard; however, parties who reach an agreement based on this Standard are
encouraged to study if the latest versions of these documents are applicable. For undated references, the latest edition of the referenced document applies. GB/T 7232 Terminology of metal heat treatment
GB/T 9450 Steels - Determination and verification of the depth of carburized and hardened cases (GB/T 9450-2005, ISO 2639:2002, MOD)
GB/T 13298 Metal - Inspection method of microstructure
3 Terms and definitions
The terms and definitions as defined in GB/T 7232, as well as the following terms and definitions, apply to this standard.
3.1
Core structure
The structure in the area, which is 3 times the depth of the effective hardened layer of carburizing quenching from the surface.
Figure G.1 of Appendix G. The description of rating is as shown in Table 6. 7 Inspection equipment
7.1 The Vickers hardness tester and the standard block shall pass the
calibration. It shall be used within the calibration period.
7.2 The metallurgical microscope or related micrometer scale shall pass the calibration. It shall be used within the calibration period.
8 Inspection report
The inspection report shall generally include the following:
a) Number of this standard;
b) The name of the specimen (product);
c) The identification of marking;
d) The specimen's material designation and process;
e) If the sample is not included in the furnace, description of the sampling location and the direction of the test surface;
f) Inspection results and special descriptions;
g) The signature of the inspector and reviewer, as well as the date of
inspection.
Appendix A
(Informative)
General requirements for the metallographic inspection of steel gears by carburizing quenching and tempering
A.1 Specimen
A.1.1 For the tooth-shaped workpiece, cut at least one complete tooth profile. It may also use cylindrical specimens OR simulated tooth thickness specimens. Cylindrical specimen's size: the minimum diameter is 6 times the modulus, BUT not less than 16 mm. The minimum length is 2 times the specimen diameter. With the consent of the user, it may also a small specimen: the minimum diameter is 3 times the modulus; the minimum length is 2 times the specimen diameter. The thickness of the simulated tooth thickness specimen shall be equal to 1.57 times the modulus of the tooth; its width and length shall be 2.5 times the modulus of the tooth.
A.1.2 The test surface of the tooth profile specimen shall be on the normal section of the tooth.
A.1.3 Except for the above description, all others shall be implemented, in accordance with Chapter 4 of the main text of this standard.
A.2 Inspection items and inspection methods
A.2.1 The measuring position of the effective hardened layer depth of the gear is generally on the normal section of the tooth width, in the direction along the vertical tooth surface at the index circle, OR according to the specific process documents.
A.2.2 The inspection positions of the martensite and retained austenite are within 0.05 mm ~ 0.15 mm, from the surface of the carburized layer at the index circle of the tooth.
A.2.3 The carbide's inspection position is at the sharp corner (tooth angle) of the carburized layer, OR according to the process requirements.
A.2.4 The inspection position of the depth of the oxidization layer, in the surface, is on the tooth root's surface layer of the gear.
A.2.5 The inspection position of the core structure is at the intersection of the center line of the tooth width and the tooth root circle. The recommended inspection positions, for large gears, are as shown in Figure A.1.

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