GB/T 9450-2025Steel — Determination of Case Hardening Depth After Carburizing or Carbonitriding

Foreword

This Document was drafted as per the rules specified in GB/T 1.1-2020 Directives for Standardization – Part 1: Rules for the Structure and Drafting of Standardizing Documents.

This Document replaced GB/T 9450-2005 Steels - Determination and Verification of the Depth of Carburized and Hardened Cases. Compared with GB/T 9450-2005, the major technical changes of this Document are as follows besides the structural adjustments and editorial modifications:

a) Change the scope (see Clause 1 of this Edition; Clause 1 of the 2005 Edition);

b) Change the provisions of the determination items (see Clause 4 of this Edition;

Clause 4 of the 2005 Edition);

change the determination principle (see Clause 5 of this Edition; 5.1 and 5.2 of the 2005 Edition);

d) Add provisions of test equipment (see Clause 6 of this Edition);

e) Change the provisions of specimens (see Clause 7 of this Edition; 5.3.1 and f) Change the test methods (see Clause 8 of this Edition; 5.3.3 of the 2005 edition);

g) Change the provisions of result evaluation (see Clause 9 of this Edition; 5.4 of h) Change the content of the test report (see Clause 10 of this Edition; Clause 7 of i) Delete the clause of "verification" (see Clause 6 of the 2005 Edition).

j) Add The interpolation method for case hardening depth (see Appendix A of this Edition).

Please note some contents of this Document may involve patents. The issuing agency of this Document shall not assume the responsibility to identify these patents.

This Document was proposed by and under the jurisdiction of National Technical Committee on Heat Treatment of Standardization Administration of China (SAC/TC 75).

Fengdong Heat Treatment & Surface Engineering Research Co., Ltd.; Zhejiang Shuanghuan Driveline Co., Ltd.; Chongqing Gearbox Co., Ltd.; Dalian Huarui Heavy Industry Group Co., Ltd.; Beijing Petroleum Machinery Co., Ltd.; Taiyuan Heavy Industry Transit Equipment Co., Ltd.; Jiangsu Kingkind Industrial Furnace Co., Ltd.; Shanghai Railway Certification (Group) Co., Ltd.; Zhejiang Guojian Testing Technology Co., Ltd.; Guangdong Fengdong Neturen Co., Ltd.; Zhejiang Juyue Gear Co., Ltd.; Gospell Thermal Systems Jiangsu Co., Ltd.; Zhejiang Qiujing Technology Co., Ltd.; Hangzhou Advance Gearbox Group Co., Ltd.; Suzhou Nuclear Power Research Institute Co., Ltd.; Guilin Fuda Co., Ltd.; Changshu Tiandi Coal Mine Machinery Equipment Co., Ltd.; Qingdao Yidong Coal Mine Machinery Manufacturing Co., Ltd.; Hunan Southern Aerospace High Precision Transmission Co., Ltd.; Chongqing Jingyanxin Jukui Technology Co., Ltd.; Shenyang Jiayu Vacuum Technology Co., Ltd.; Shanghai United Roller Bearings Co., Ltd.; Jinan Heavy Industries Group Co., Ltd.; Nanjing Technology and Equipment Manufacturing Co., Ltd.; Nanjing Chuangli Transmission Machinery Co., Ltd.; Jiangsu Shendun Engineering Machinery Co., Ltd.; Jianhu Jintuo Mechanics Manufacture Co., Ltd.; and Changzhou New District Hehai Heat Treatment Engineering Co., Ltd.

Chief drafting staffs of this Document: Xu Yueming, Li Qiao, Shi Yousen, Zhang Zhao, Hu Zhaonan, Cao Fengjiao, Li Ruxue, Zhao Xinglong, Chen Weidong, Liu Guoyong, Wang Hui, Xia Xiaoyu, Shi Tianzhen, Zou Chaohui, Xia Mingdao, Zhou Huanhui, Lai Yunting, Li Bin, Yuan Yuedong, Leng Gang, Qi Ling, Chen Andong, Wang Jiajie, Fan Linhua, Xu Jingwei, Liu Hongyan, Liu Wei, Xu Changfei, Yang Jian, Yin Heping, Han Yongzhen, Wang Qin, Wei Xiaolin, Peng Tian, Chen Decai, Xu Wentian, Ma Shitao, and Ling Dehua.

This Document was first-time published in 1988; first-time revised in 2005; and it is secondtime revised hereby.

1 Scope

This Document specifies the principles, test equipment, specimens, determination methods, result evaluation, and test report of the case hardening depth for steel.

This Document applies to workpieces that have been carburized or carbonitrided and then quenched, tempered and heat treated.

2 Normative References

The provisions in following documents become the essential provisions of this Document through reference in this Document. […]

3 Terms and Definitions

3.1 Case hardening depth; CHD

The vertical distance from the workpiece surface to the location with boundary hardness of 550 HV Vickers hardness (or equivalent Knoop hardness).

quenching. If measured after quenching and tempering, this shall be noted in the report.

4 Symbols and Abbreviated Terms

The symbols and abbreviated terms given in Table 1 apply to this Document.

5 Principle

The hardened layer depth is determined based on the hardness gradient along a cross section perpendicular to the workpiece surface.

The hardened layer depth is determined graphically from the hardness distribution curve as a function of distance from the surface.

6 Test Equipment

The Vickers hardness test is used for testing. The hardness tester shall be inspected and calibrated in accordance with the provisions of GB/T 4340.2. […]

7 Specimen

7.1 Unless otherwise agreed, the hardened layer depth shall be measured on a cross section of the workpiece or specimen that meets the following conditions: workpiece. If there is no longitudinal axis, test shall be performed on a cross section perpendicular to the workpiece surface at a certain location by agreement between the parties involved. b) For thin hardened layers (≤0.3 mm), a step specimen (see Figure 1) or a wedge specimen (see Figure 2) shall be used by agreement, and a lower test force shall be used for hardness test. The step specimen has each step height of 0.05 mm or 0.10 mm from the workpiece surface to the substrate and requires precision grinding. Step specimens are used when the hardened layer depth is roughly determined. The determination method is in accordance with the provisions of Appendix A. a Actual depth d is given by the Formula d = lsinα. b Test depth l varies with slope (d/l). 7.2 When specimens are used for test as agreed upon by the relevant parties, the material and heat treatment process of the specimens shall be the same as those of the workpieces. 7. […]

8 Test Methods

8.1 Conduct hardness indentation tests on one or more parallel lines perpendicular to the workpiece or specimen surface within a width (W) of 1.5 mm, as shown in Figure 3. The distance between the parallel lines shall comply with the provisions of GB/T4340.1 or GB/T18449.1. 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 from the center of adjacent indentations to the surface (e.g., d2 d1) shall not exceed 0.1 mm; and the measurement accuracy of the distance from the center of the indentation to the surface shall be ±25 μm. The measurement accuracy of each indentation diagonal shall meet the requirements of GB/T 4340.2 or GB/T 18449.2. The distance d1 from the center of the first indentation to the surface shall be at least 2.5 times the length of the indentation diagonal. 8.3 When conducting Vickers or Knoop hardness tests, the applicable test force range is 0.9807 N to 29.42 N, with 9.807 N typically used. 8. […]

9 Evaluation of Results

9.1 According to the test methods in Clause 8, draw the hardness distribution curve shown in Figure 4. The distance from the surface corresponding to 550 HV on the curve is the case hardening depth.

9.2 For hardness values greater than 450 HV at a depth three times the hardened layer depth from the surface, a boundary hardness greater than 550 HV shall be used, with increments of 25 HV, upon agreement between the parties involved.

9.3 The case hardening depth shall be measured on two wide test strips. If the two test results are within a 10% tolerance, the larger of the two results shall be considered valid. If this tolerance is exceeded, the test shall be repeated.

9.4 When the case hardening depth has been roughly determined, the method in Appendix A shall be used.