1、 Match the measurement range of the hardness tester

The hardness value of the standard hardness block should fall within the effective measurement range of the Vickers hardness tester and cover the typical hardness range of daily measurements.

Vickers hardness testers have different ranges (such as micro Vickers HV0.1-HV10 and macro Vickers HV5-HV100), and corresponding hardness blocks need to be selected. For example, the commonly used HV10 hardness tester should select blocks with hardness values between 100-800HV (to avoid approaching the upper/lower limit of the range, usually taking the range of 20% -80% of the range, with smaller measurement errors).

If it is necessary to measure workpieces with multiple hardness ranges (such as from soft aluminum to quenched steel), it is recommended to use 2-3 standard blocks with different hardness values (such as 200HV, 500HV, 700HV) to calibrate different intervals separately.

2、 Confirm the accuracy level of the hardness block

Select the corresponding level of standard block according to the accuracy requirements of the measurement requirements.

According to the "Verification Regulations for Metal Vickers Hardness Testers" in China, standard hardness blocks are divided into Level 1 and Level 2: Level 1 blocks allow for smaller errors (such as ± 2% error when the hardness is ≤ 300HV); ± 1.5% at 300-1000HV, suitable for high-precision measurement or hardness tester calibration; The error of the 2nd level block is slightly larger (± 3% for ≤ 300HV and ± 2% for 300-1000HV), which is suitable for daily calibration.

International standards (such as ISO6507-2) are similar and classified according to uncertainty. When selecting, the calibration requirements for the hardness tester should be clearly defined (such as selecting level 1 for verification and level 2 for daily point inspection).

3、 Match test force with indentation size

In the Vickers hardness test, the test force (such as 1kgf, 10kgf) will affect the size of the indentation, and it is necessary to choose a hardness block that matches the commonly used test force.

The hardness value marked on the surface of the hardness block corresponds to a specific test force (such as "HV5500" indicating a hardness of 500HV measured with a force of 5kgf), which needs to be consistent with the actual test force used: if a force of 10kgf is commonly used for measurement, it is not possible to calibrate the hardness block with only HV1 marked (differences in indentation size can cause errors).

Pay attention to the compatibility of "force value indentation": For small test forces (such as HV0.2) corresponding to small indentation, it is necessary to choose a hardness block with lower surface roughness (Ra ≤ 0.05 μ m); For large test forces (such as HV50), sufficient thickness of the hardness block is required (to avoid indentation, usually thickness ≥ 10 times the diagonal of the indentation).

4、 Verify the material and surface condition

The hardness block material should be close to the tested workpiece (reducing the influence of substrate differences), and the surface condition should meet the requirements.

Material matching: Carbon steel/alloy steel hardness blocks can be selected for measuring steel parts, and aluminum based hardness blocks can be selected for measuring aluminum alloys. Avoid using hard alloy blocks to calibrate hardness testers for measuring soft metals (differences in filter media may cause hardness value deviations).

Surface condition: Check the surface for scratches, rust, and oil stains, and ensure that the indentation area is flat. If there is damage to the surface, there may be misjudgment during indentation measurement; When stored, it should be sealed and moisture-proof to avoid surface oxidation caused by long-term exposure.

5、 Confirm certificate and validity period

The standard hardness block is a measuring standard instrument that requires a calibration certificate issued by a legal metrology institution and is within its validity period.

The certificate should include information such as hardness value, uncertainty, test force, calibration date, etc. The validity of the certificate should be verified (usually valid for 1 year, and it is recommended to recheck it every six months if frequently used).

Avoid using uncertified or expired hardness blocks: Such blocks may experience hardness decay due to long-term use, leading to calibration failure.

In summary, when selecting a Vickers hardness tester, it is necessary to first clarify the commonly used test force, measurement range, and accuracy requirements, and then match the hardness value, test force, and accuracy level of the hardness block. At the same time, the material, surface condition, and certificate validity should be checked to ensure that the calibrated hardness tester measurement results are accurate and reliable.