Convert as you wish: Hardness is no longer stupid and unclear!

In the fastener industry, whether it is production or sales personnel, not to mention technical personnel, they all need to be exposed to the hardness of different materials. Sometimes the hardness representation methods are different, and we need to convert each other. But nine out of ten people can't handle these things for a while.

Conversion of different types of indentation hardness. In practical applications, we may obtain hardness through several different test methods. In order to facilitate comparison, it is necessary to convert different hardness. So far, people have carried out some research on the conversion of hardness, but most of the conversion formulas are put forward under the guidance of practical experience, and there is no recognized conversion system.

The following are some domestic research results on hardness conversion.

1. Conversion of Knoop hardness and Vickers hardness

(1) Based on the fact that objects of the same hardness have equal resistance to the two Knoop indenters, the stresses of the two Vickers and Knoop indenters under load are respectively derived, and then according to σHKu003d σHV is obtained: HVu003d0.968HK. This formula is measured under low load, and the error is relatively large. In addition, when the hardness value is greater than HV900, this formula has a large error and loses its reference value.

(2) After deduction and revision, the conversion formula of Knoop hardness and Vickers hardness is proposed as

Verified by actual data, the maximum relative conversion error of this formula is 0.75%, which has a high reference value.

2. Conversion of Rockwell hardness and Vickers hardness (Guide: How to make stainless steel fasteners not rust, and do the four points to save worry)

(1) The Qvarnstorm conversion formula proposed by HansQvarnstorm

After correction, the conversion formula of Rockwell hardness and Vickers hardness is obtained as:

This formula is converted with the ferrous metal hardness standard data published by our country, and its HRC error is basically within the range of ±0.4 HRC, and its maximum error is only ±0.9HRC, and the maximum calculated HV error is ±15HV.

(2) According to the stress σHRCu003dσHV of different indenters, the formula is obtained by analyzing the relationship between Rockwell hardness and Vickers hardness indentation depth

This formula is compared with the conversion value of the national standard experiment. The error between the calculation result of the conversion formula and the standard experiment value is ±0.1HRC.

(3) According to the actual experimental data, the conversion of Rockwell hardness and Vickers hardness was discussed using linear regression, and the formula was obtained:

This formula has a small application range and large error, but it is easy to calculate and can be used when the accuracy is not high.

3. Conversion of Rockwell hardness to Brinell hardness

(1) Analyze the relationship between Brinell indentation and Rockwell indentation depth, and obtain the conversion formula according to the stress of the indenter σHRCu003dσHB:

The calculation result is compared with the national standard experimental value, and the error between the conversion formula calculation result and the standard experimental value is ±0.1HRC.

(2) Use linear regression to get the formula based on actual experimental data

The formula error is too large and the range of use is too small, but the calculation is simple, and it can be used when the accuracy is not high.

4. Conversion of Brinell hardness and Vickers hardness

The relationship between Brinell hardness and Vickers hardness is also based on the formula σHBu003dσHV. The conversion result of this formula is compared with the conversion value of the national standard, and the conversion error is ±2HV.

5. Conversion of Knoop hardness to Rockwell hardness

Because the corresponding curve of Knoop hardness and Rockwell hardness is similar to a parabola[7], the approximate conversion formula obtained from the curve is

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