This standard is applicable to the determination of the surface Rockwell hardness (N and T scale) of metal thermal spray coatings. GB/T 8640-1988 Test method for surface Rockwell hardness of metal thermal spray coatings GB/T8640-1988 Standard download decompression password: www.bzxz.net

Scope of application
National Standard of the People's Republic of China
Metallic thermal spray coatings Rockwell hardness test methodThermal sprayed metallic coatings Rockwell hardness test
This standard applies to the determination of the surface Rockwell hardness (N and T scale) of metallic thermal spray coatings. Reference standards
GB 3773
Technical conditions for surface Rockwell hardness tester
GB 3774
Symbol explanation
Second-class standard surface Rockwell hardness block
. The symbols used in this standard and their explanations are shown in Table 1 and Figure 1, Table 2 and Figure 2. Test with diamond cone (N scale)
Diamond cone top angle (120°)
Diamond cone top curvature radius (0.200mm)Initial load 29.42N (3kgf)
Main load 117.68, 264.78, 411.88 N (12, 27, 42 kgf)Total load (F.+F)
Insertion depth under initial load
Insertion depth increment under main load
UDC 621.793
:620.178.1
GB 8640--88
After removing the main load, the residual increment of the indentation depth under the initial load, the increment is in units of 0.001mm. Surface Rockwell hardness (FN=100-e)
Note: 1) indicates HR15N, HR30N or HR45N. China Nonferrous Metals Industry Corporation approved on January 11, 1988. 536
Implementation on July 1, 1989
GB8640--88
Figure 1 Test with diamond cone (N scale) Figure 2 Test with steel ball (T scale)
Steel ball diameter (1.5875mm)
Initial load 29. 42N(3kgf)
Main load117.68、264.78、411.88N(12、27、42kgf)Total load（F+F）
Insertness under initial load
Insertness increment under main load
After removing the main load, the residual increment of the insertness under initial load, the increment is in units of 0.001mmSurface Rockwell hardness (FT=100e）
Note:1) Table HR15T.HR30T or HR45T37
4 Instrument
4.1 Surface Rockwell hardness tester
GB 8640 --88
Figure 2 Test diagram with steel ball (T scale)
Should meet the technical requirements specified in GB3773. 4.2 Hardness block
The standard surface Rockwell hardness block used to check the hardness tester shall comply with the technical requirements specified in GB3774. 5 Test specimen
5.1 Test specimen size
5.1.1 Spray coating thickness shall comply with the provisions of Table 3 and Table 4. After the test, there shall be no obvious deformation on the back of the test specimen. 538
(not less than)
(not less than)
Surface Rockwell
Hardness value
GB8640-88
Test specimen spray coating thickness (N scale)
HRC value
Surface Rockwell
Hardness value
Equivalent to
HRC value
Table 4 Test specimen spray coating thickness (T scale)
Surface Rockwell
Hardness value
Equivalent to| |tt||HRB value
Surface Rockwell
Hardness value
Equivalent to
HRB value
Surface RockwellWww.bzxZ.net
Equivalent to
HRC value
Surface Rockwell
Equivalent to
HRB value
5.1.2 Other dimensions shall meet the following requirements: The distance between the centers of two indentations or the distance from the center of any indentation to the edge of the specimen shall not be less than 3mm, and at least five points can be measured for each specimen. 5.2 Specimen preparation
5.2.1 The product can be directly used or cut from the product. 5.2.2 Specially made specimens shall comply with the provisions of Table 5. 539
Spraying conditions
Base material
Determined by the sample preparer" Low and medium carbon steel, or agreed by or between the parties concerned
Determined by the sample preparer
GB 8640--88
-Sample base size
E-shaped square
$ 30×20
5.2.3 The surface and back of the sample should be flat and parallel to each other. 5.2.4 The test surface of the sample should be smooth and clean. Shape
40×20×20
Thickness of spray coating
Before machining
After machining
Determined by the sample preparer, or
Conform to the provisions of Table 3 and Table 4
Agreed by the relevant parties
5.2.5 When preparing the sample, any change in the surface state caused by cold or hot processing should be avoided. 6 Test steps and requirements
Before the test, the hardness tester should be calibrated using a second-class standard surface Rockwell hardness block with a hardness value close to that of the sample. 6.1
6.2 Place the sample firmly on the sample table to ensure that no displacement or deformation occurs during the test. 6.3
During the test, the load force must be kept perpendicular to the test surface of the sample. During the test, the test instrument should not be subjected to any impact or vibration. 6.4
6.5 When applying the initial load, the pointer or indicating line does not exceed the specified mark of the hardness tester, otherwise the initial load should be removed and the test should be carried out at another position of the specimen. 6.6 After adjusting the indicating indicator to zero, the main load should be applied within 4 to 8 seconds. 6.7 The initial load and the main load should be applied evenly and steadily on the surface of the specimen without any jumping or impact. 6.8 After the main load is applied, the length of time the total load is maintained should be based on the fact that the pointer or indicating line of the indicating indicator basically stops moving. The total load holding time is recommended as follows:
For specimens that do not continue to deform over time after loading, the holding time is not less than 2 seconds; for specimens that continue to deform over time after loading, the holding time is 6 to 8 seconds; b.
For specimens that are significantly deformed over time after loading, the holding time is 20 to 25 seconds. 6.9 After smoothly removing the main load, maintain the initial load and read the hardness value from the corresponding scale dial. 6.10 The test shall be conducted in the temperature range of 10 to 35°C. 7. Results
7.1 The surface Rockwell hardness value is indicated by the symbol HR. The hardness value is preceded by the total load (expressed in kilograms of force) and followed by the letter indicating the specific hardness scale.
Example I: 70HR30N means that the surface Rockwell hardness value measured by scale N is 70 with a diamond cone indenter at a total load of 294.2N (30kgf).
Example 2: 62HR45T means that the surface Rockwell hardness value measured by scale T is 62 with a steel ball indenter at a total load of 441.3N (45kgf).
7.2 The surface Rockwell hardness value given in the test report shall be accurate to 0.5 Rockwell hardness unit. 7.3 In the test report, for the spray-welded layer, the surface Rockwell hardness values ​​of five consecutive points shall be given for each specimen. For spray coatings, the arithmetic mean of five consecutive points can be given for each specimen, and the lowest and highest values ​​can be given at the same time. 7.4 The surface Rockwell hardness values ​​measured on cylindrical curved surface specimens should be corrected according to Appendix Table A1 and Table A2, and the corrected values ​​are all positive values. 7.5 The test report should include the following:
This standard number;
Specimen number;
Specimen preparation method;
Test results;
Any details that may affect the test results. Dial reading
GB8640---88
Appendix A
Hardness correction value
(Supplement)
Correction value of surface Rockwell hardness of cylindrical curved specimen (N scale) Diameter of cylindrical specimen
Dial reading
GB8640-88
Table A2 Correction value of surface Rockwell hardness of cylindrical curved specimen (T scale) Diameter of cylindrical specimen
Note: These approximate correction values ​​are accurate to 0.5 surface Rockwell hardness value. Unless otherwise specified by agreement, the correction values ​​given in brackets are generally not used. For other diameters and hardness values ​​in Table A1 and Table A2, the correction value can be obtained by insertion method. Additional remarks:
This standard was drafted by the Iron and Steel Research Institute of the Ministry of Metallurgical Industry. The main drafters of this standard are Li Bijun and Jiang Zhenchun. 542
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