GB/T 9450-2025 Determination of the case hardening depth for steel English, Anglais, Englisch, Inglés, えいご
This is a draft translation for reference among interesting stakeholders. The finalized translation (passing through draft translation, self-check, revision and verification) will be delivered upon being ordered.
ICS 25.200
CCS J 36
National Standard of the People's Republic of China
GB/T 9450-2025
Replaces GB/T 9450-2005
Determination of the case hardening depth for steel
Issue date: 2025-08-29 Implementation date: 2026-03-01
Issued by the General Administration of Quality Supervision, Inspection and Quarantine of the People's Republic of China
the Standardization Administration of the People's Republic of China
Contents
Foreword
1 Scope
2 Normative References
3 Terms and Definitions
4 Symbols and Abbreviations
5 Principle
6 Test Equipment
7 Test Specimens
8 Measurement Methods
9 Evaluation of Results
10 Test Report
Appendix A (Normative) Interpolation Method for Determining Case Hardening Depth
References
Determination of the Case Hardening Depth for Steel
1 Scope
This document specifies the principle, test equipment, specimens, measurement methods, evaluation of results, and test report for determining the case hardening depth of steel parts after carburizing or carbonitriding followed by quenching and tempering.
This document applies to workpieces that have undergone carburizing or carbonitriding and subsequent quenching and tempering heat treatment.
2 Normative References
The following documents contain provisions that, through reference in this text, constitute essential requirements for this document. For dated references, only the edition cited applies; for undated references, the latest edition (including all amendments) applies.
GB/T 4340.1 Metallic Materials—Vickers Hardness Test—Part 1: Test Method
GB/T 4340.2 Metallic Materials—Vickers Hardness Test—Part 2: Verification and Calibration of Hardness Testers
GB/T 7232 Terminology for Metal Heat Treatment
GB/T 18449.1 Metallic Materials—Knoop Hardness Test—Part 1: Test Method
GB/T 18449.2 Metallic Materials—Knoop Hardness Test—Part 2: Verification and Calibration of Hardness Testers
3 Terms and Definitions
Terms and definitions defined in GB/T 7232 and the following apply to this document.
3.1 Case Hardening Depth (CHD)
The perpendicular distance from the surface of the workpiece to the point where the Vickers hardness value is 550 HV (or equivalent Knoop hardness value).
Note: The case hardening depth is usually measured after carburizing or carbonitriding followed by quenching. If measured after quenching and tempering, this shall be noted in the test report.
4 Symbols and Abbreviations
The symbols and abbreviations given in Table 1 apply to this document.
Table 1 Symbols and Abbreviations
5 Principle
The hardened layer depth is determined based on the hardness gradient on a cross-section perpendicular to the workpiece surface. The hardened layer depth is derived from the hardness distribution curve versus distance from the surface using graphical analysis.
6 Test Equipment
Vickers hardness testing shall be performed, and the hardness tester shall be inspected and calibrated in accordance with GB/T 4340.2. Upon agreement between relevant parties, Knoop hardness testing may also be used, and the hardness tester shall be inspected and calibrated as per GB/T 18449.2.
7 Specimen
Unless otherwise agreed, the hardened layer depth shall be measured on a cross-section of the workpiece or specimen under the following conditions:
The tested cross-section shall be perpendicular to the longitudinal axis of the workpiece. If no longitudinal axis exists, testing may be performed on a cross-section perpendicular to a surface of the workpiece after agreement between relevant parties.
For thin hardened layers (≤0.3 mm), step specimens (as shown in Figure 1) or wedge specimens (as shown in Figure 2) may be used with reduced test loads upon agreement. Each step of the step specimen shall be 0.05 mm or 0.10 mm in height from the surface to the substrate, requiring precision grinding. Step specimens are used when the hardened layer depth is approximately known, and the measurement method shall comply with Appendix A.
7.2 When specimen testing is adopted upon agreement between relevant parties, the material and heat treatment process of the specimen shall be identical to those of the workpiece.
7.3 The testing surface of the specimen shall be polished and free from corrosion. During specimen preparation, cutting shall be performed using gentle techniques to ensure minimal damage. The specimen shall be securely held to maintain well-defined edges. Appropriate grinding materials shall be used during polishing to remove surface damage caused by cutting or grinding, ensuring that the testing surface hardness remains unaffected and rounded edges are avoided. The testing surface shall be polished to allow accurate measurement of hardness indentations. Smaller test loads require higher surface preparation quality.
8 Measurement Method
8.1 Hardness indentations shall be made along one or more parallel lines perpendicular to the surface of the workpiece or specimen within a width (W) of 1.5 mm (see Figure 3). The spacing between parallel lines shall comply with GB/T 4340.1 or GB/T 18449.1.
8.2 The distance between two adjacent indentations (Δd) shall be at least 3 times the length of the indentation diagonal (see Figure 3). The difference in distance between adjacent indentation centers and the surface (e.g., dₑ - dᵢ) shall not exceed 0.1 mm, with a measurement precision of ±25 μm for the distance from the indentation center to the surface. The measurement accuracy of each indentation diagonal shall meet the requirements of GB/T 4340.2 or GB/T 18449.2. The center of the first indentation shall be at least 2.5 times the indentation diagonal length away from the surface.
8.3 Vickers or Knoop hardness testing shall be performed with test loads ranging from 0.9807 N to 29.42 N, with 9.807 N being commonly used.
8.4 Hardness testing shall be conducted under a high-quality optical microscope with adequate illumination. The microscope shall provide sufficient magnification to ensure clear and undistorted indentation corners.
8.5 Hardness testing shall be performed on two or more test bands on the specimen surface, with their positions selected by agreement between relevant parties. A hardness gradient curve shall be plotted for each test band after testing.
9 Result Evaluation
9.1 Following the measurement method in Chapter 8, a hardness distribution curve (as shown in Figure 4) shall be plotted. The distance from the surface where the curve intersects 550 HV shall be taken as the carburized-quenched hardened layer depth.
9.2 If the hardness at a distance 3 times the hardened layer depth from the surface exceeds 450 HV, a higher limiting hardness value (in 25 HV increments) may be adopted upon agreement between relevant parties.
9.3 The carburized-quenched hardened layer depth shall be measured on two test bands. If the two results fall within 10% deviation, the larger value shall be taken as the valid result. If the deviation exceeds this range, additional testing shall be performed.
9.4 When the carburized-quenched hardened layer depth has been approximately determined, the method provided in Appendix A may be used.
Standard
GB/T 9450-2025 Determination of the case hardening depth for steel (English Version)
Standard No.
GB/T 9450-2025
Status
to be valid
Language
English
File Format
PDF
Word Count
6000 words
Price(USD)
180.0
Implemented on
2026-3-1
Delivery
via email in 1~3 business day
Detail of GB/T 9450-2025
Standard No.
GB/T 9450-2025
English Name
Determination of the case hardening depth for steel
GB/T 9450-2025 Determination of the case hardening depth for steel English, Anglais, Englisch, Inglés, えいご
This is a draft translation for reference among interesting stakeholders. The finalized translation (passing through draft translation, self-check, revision and verification) will be delivered upon being ordered.
ICS 25.200
CCS J 36
National Standard of the People's Republic of China
GB/T 9450-2025
Replaces GB/T 9450-2005
Determination of the case hardening depth for steel
Issue date: 2025-08-29 Implementation date: 2026-03-01
Issued by the General Administration of Quality Supervision, Inspection and Quarantine of the People's Republic of China
the Standardization Administration of the People's Republic of China
Contents
Foreword
1 Scope
2 Normative References
3 Terms and Definitions
4 Symbols and Abbreviations
5 Principle
6 Test Equipment
7 Test Specimens
8 Measurement Methods
9 Evaluation of Results
10 Test Report
Appendix A (Normative) Interpolation Method for Determining Case Hardening Depth
References
Determination of the Case Hardening Depth for Steel
1 Scope
This document specifies the principle, test equipment, specimens, measurement methods, evaluation of results, and test report for determining the case hardening depth of steel parts after carburizing or carbonitriding followed by quenching and tempering.
This document applies to workpieces that have undergone carburizing or carbonitriding and subsequent quenching and tempering heat treatment.
2 Normative References
The following documents contain provisions that, through reference in this text, constitute essential requirements for this document. For dated references, only the edition cited applies; for undated references, the latest edition (including all amendments) applies.
GB/T 4340.1 Metallic Materials—Vickers Hardness Test—Part 1: Test Method
GB/T 4340.2 Metallic Materials—Vickers Hardness Test—Part 2: Verification and Calibration of Hardness Testers
GB/T 7232 Terminology for Metal Heat Treatment
GB/T 18449.1 Metallic Materials—Knoop Hardness Test—Part 1: Test Method
GB/T 18449.2 Metallic Materials—Knoop Hardness Test—Part 2: Verification and Calibration of Hardness Testers
3 Terms and Definitions
Terms and definitions defined in GB/T 7232 and the following apply to this document.
3.1 Case Hardening Depth (CHD)
The perpendicular distance from the surface of the workpiece to the point where the Vickers hardness value is 550 HV (or equivalent Knoop hardness value).
Note: The case hardening depth is usually measured after carburizing or carbonitriding followed by quenching. If measured after quenching and tempering, this shall be noted in the test report.
4 Symbols and Abbreviations
The symbols and abbreviations given in Table 1 apply to this document.
Table 1 Symbols and Abbreviations
5 Principle
The hardened layer depth is determined based on the hardness gradient on a cross-section perpendicular to the workpiece surface. The hardened layer depth is derived from the hardness distribution curve versus distance from the surface using graphical analysis.
6 Test Equipment
Vickers hardness testing shall be performed, and the hardness tester shall be inspected and calibrated in accordance with GB/T 4340.2. Upon agreement between relevant parties, Knoop hardness testing may also be used, and the hardness tester shall be inspected and calibrated as per GB/T 18449.2.
7 Specimen
Unless otherwise agreed, the hardened layer depth shall be measured on a cross-section of the workpiece or specimen under the following conditions:
The tested cross-section shall be perpendicular to the longitudinal axis of the workpiece. If no longitudinal axis exists, testing may be performed on a cross-section perpendicular to a surface of the workpiece after agreement between relevant parties.
For thin hardened layers (≤0.3 mm), step specimens (as shown in Figure 1) or wedge specimens (as shown in Figure 2) may be used with reduced test loads upon agreement. Each step of the step specimen shall be 0.05 mm or 0.10 mm in height from the surface to the substrate, requiring precision grinding. Step specimens are used when the hardened layer depth is approximately known, and the measurement method shall comply with Appendix A.
7.2 When specimen testing is adopted upon agreement between relevant parties, the material and heat treatment process of the specimen shall be identical to those of the workpiece.
7.3 The testing surface of the specimen shall be polished and free from corrosion. During specimen preparation, cutting shall be performed using gentle techniques to ensure minimal damage. The specimen shall be securely held to maintain well-defined edges. Appropriate grinding materials shall be used during polishing to remove surface damage caused by cutting or grinding, ensuring that the testing surface hardness remains unaffected and rounded edges are avoided. The testing surface shall be polished to allow accurate measurement of hardness indentations. Smaller test loads require higher surface preparation quality.
8 Measurement Method
8.1 Hardness indentations shall be made along one or more parallel lines perpendicular to the surface of the workpiece or specimen within a width (W) of 1.5 mm (see Figure 3). The spacing between parallel lines shall comply with GB/T 4340.1 or GB/T 18449.1.
8.2 The distance between two adjacent indentations (Δd) shall be at least 3 times the length of the indentation diagonal (see Figure 3). The difference in distance between adjacent indentation centers and the surface (e.g., dₑ - dᵢ) shall not exceed 0.1 mm, with a measurement precision of ±25 μm for the distance from the indentation center to the surface. The measurement accuracy of each indentation diagonal shall meet the requirements of GB/T 4340.2 or GB/T 18449.2. The center of the first indentation shall be at least 2.5 times the indentation diagonal length away from the surface.
8.3 Vickers or Knoop hardness testing shall be performed with test loads ranging from 0.9807 N to 29.42 N, with 9.807 N being commonly used.
8.4 Hardness testing shall be conducted under a high-quality optical microscope with adequate illumination. The microscope shall provide sufficient magnification to ensure clear and undistorted indentation corners.
8.5 Hardness testing shall be performed on two or more test bands on the specimen surface, with their positions selected by agreement between relevant parties. A hardness gradient curve shall be plotted for each test band after testing.
9 Result Evaluation
9.1 Following the measurement method in Chapter 8, a hardness distribution curve (as shown in Figure 4) shall be plotted. The distance from the surface where the curve intersects 550 HV shall be taken as the carburized-quenched hardened layer depth.
9.2 If the hardness at a distance 3 times the hardened layer depth from the surface exceeds 450 HV, a higher limiting hardness value (in 25 HV increments) may be adopted upon agreement between relevant parties.
9.3 The carburized-quenched hardened layer depth shall be measured on two test bands. If the two results fall within 10% deviation, the larger value shall be taken as the valid result. If the deviation exceeds this range, additional testing shall be performed.
9.4 When the carburized-quenched hardened layer depth has been approximately determined, the method provided in Appendix A may be used.
