1. Purpose

Standardize the operation of the Vickers hardness test to ensure the accuracy and reliability of the test results.

2. Scope

This is applicable to the Vickers hardness test in this laboratory, and the test forces are limited to 5 kilograms and 10 kilograms.

3. Reference

Refer to the following latest edition of standards:

4. Test conditions

The test is generally carried out at room temperature ranging from 10°C to 35°C. For tests with strict temperature requirements, the room temperature should be maintained at 23°C ± 5°C.

5. Test

5.1 Sample

5.1.1 The test specimen should be taken from a representative position, avoiding the heat-affected zone.

5.1.2 The surface of the test specimen should be flat and smooth. There should be no scale or foreign contaminants on the testing surface, and in particular, no grease, unless otherwise specified in the product standard. The quality of the test specimen surface should ensure the measurement accuracy of the diagonal length, and the surface of the test specimen should be polished.

5.1.3 When preparing the test specimen, the influence on the surface hardness of the test specimen caused by factors such as overheating or cold working should be minimized.

5.2 Test method

5.2.1 Press a square-based pyramidal diamond indenter with a specified angle on the two opposite top faces into the surface of the test specimen with a certain test force. After maintaining for the specified time, remove the test force and measure the length of the diagonal of the indentation on the surface of the test specimen.

5.2.2 Hardness representation: The Vickers hardness is represented by HV. The number in front of the symbol HV is the hardness value, and the numbers following the symbol indicate the test force and the duration for which the test force is maintained.

For example: 640HV10/20 indicates that the Vickers hardness value is 640, which is measured under a test force of 10 kgf and with the test force maintained for 20 seconds.

5.2.3 The testing surface of the test specimen, the supporting surface, the surface of the testing stage and the surface of the indenter should be clean. The test specimen should be placed firmly on the testing stage to ensure that there is no displacement or deformation during the testing process. Under no circumstances is it allowed for the indenter to touch the testing stage and the support. There should be no indentations on the supporting surface of the test specimen, the support and the working surface of the testing stage. During the test, it is necessary to ensure that the direction of the test force is perpendicular to the testing surface of the test specimen.

5.2.4 The testing device should not be subjected to impact and vibration during the testing process. The time from the start of applying the force to the completion of applying the entire test force should be between 2 and 8 seconds.

5.2.5 The test force holding time is between 10 seconds and 15 seconds. For test specimens made of special materials, the test force holding time can be extended until the specimen does not undergo plastic deformation. However, it should be noted in the test results, and the error should be within 2 seconds.

5.2.6 The distance from the center of any indentation to the edge of the specimen should be at least 2.5 times the length of the diagonal for steel. The distance between the centers of adjacent indentations should be 3 times the length of the indentation diagonal.

5.2.7 Measure the lengths of the two diagonals of the indentation, and calculate the Vickers hardness value by looking up the table according to their arithmetic mean. The difference between the lengths of the two diagonals should not exceed 5% of the average value of the diagonals. If it exceeds 5%, it should be noted in the test report. The length of the diagonal should be accurate to 1 μm or less.

6. Handling of Invalid Test Specimens

6.1 If the sample is not representative, take a new sample for testing.

6.2 If the roughness of the test specimen does not meet the requirements, reprocess the test specimen.

7. Daily Inspection of the Hardness Tester

7.1 Before using the hardness tester on the same day, the inspector should check the scale that needs to be used for the hardness tester.

7.2 Select a standard hardness block whose hardness value is close to the value to be tested, and perform at least two hardness measurements on the calibrated surface of the standard hardness block. The indentations should be evenly distributed on the surface of the reference block. If the deviation value of each reading is within the allowable range of less than ±3%, the hardness tester is considered to meet the requirements.

8. Precautions

8.1 When the instrument can be used normally, it is absolutely prohibited to disassemble it by oneself. Otherwise, the original precision of the instrument will be damaged.

8.2 When the instrument is stored and in use, it should be kept away from dust, dampness, extreme cold or heat, and environments containing acid and alkali vapors.

8.3 If there is dirt on the surface of the lens, it is necessary to wipe it with soft objects such as degreased cotton, a soft brush, or lens paper. When encountering oil stains or dirt, you can dip a little degreased cotton in a mixture of alcohol and ether and gently wipe it.