In the machinery 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.
The 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 hardnesses. Mechanical Professor WeChat: jixiejiaoshou, the content is good and worthy of attention. 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.
Introduction to Hardness:
Hardness refers to the ability of a material to resist the pressing of hard objects into its surface. It is one of the important performance indicators of metal materials. Generally, the higher the hardness, the better the wear resistance. Commonly used hardness indicators are Brinell hardness, Rockwell hardness and Vickers hardness.
1. Brinell hardness (HB)
Press a hardened steel ball of a certain size (usually 10mm in diameter) into the surface of the material with a certain load (usually 3000kg) and keep it for a period of time. After the load is removed, the ratio of the load to the indentation area is the Brinell hardness value ( HB), the unit is kilogram force/mm2 (N/mm2).
2. Rockwell hardness (HR)
When HB>450 or the sample is too small, the Brinell hardness test cannot be used and the Rockwell hardness measurement can be used instead. It uses a diamond cone with an apex angle of 120° or a steel ball with a diameter of 1.59 and 3.18mm, which is pressed into the surface of the material to be tested under a certain load, and the hardness of the material is obtained from the depth of the indentation. According to the hardness of the test material, it can be expressed in three different scales:
· HRA: It is the hardness obtained with a 60kg load and a diamond cone indenter, used for extremely hard materials (such as cemented carbide, etc.).
· HRB: It is the hardness obtained by using a 100kg load and a hardened steel ball with a diameter of 1.58mm. It is used for materials with lower hardness (such as annealed steel, cast iron, etc.).
· HRC: It is the hardness obtained with a 150kg load and a diamond cone indenter. It is used for materials with high hardness (such as hardened steel, etc.).
3 Vickers hardness (HV)
With a load of less than 120kg and a diamond square cone indenter with an apex angle of 136°, it is pressed into the surface of the material, and the surface area of the material indentation pit is divided by the load value to obtain the Vickers hardness HV value (kgf/mm2).
Note: In Rockwell hardness, A, B, C in HRA, HRB, HRC, etc. are three different standards, called scale A, scale B, and scale C.
The Rockwell hardness test is one of several common indentation hardness tests used today. The initial pressure of the three scales is 98.07N (10kgf), and finally the hardness value is calculated based on the indentation depth. Ruler A uses a spherical cone diamond indenter, and then pressurizes to 588.4N (60kgf); Ruler B uses a steel ball with a diameter of 1.588mm (1/16 inch) as the indenter, and then pressurizes to 980.7N (Total 100kgf); while scale C uses the same spherical cone diamond as scale A as the indenter, but the pressure after pressure is 1471N (total 150kgf). Therefore, ruler B is suitable for relatively soft materials, while ruler C is suitable for harder materials.
Practice has proved that between various hardness values of metal materials, there is an approximate corresponding relationship between the hardness value and the strength value. Because the hardness value is determined by the initial plastic deformation resistance and the continued plastic deformation resistance, the higher the strength of the material, the higher the plastic deformation resistance and the higher the hardness value. However, the conversion relationship of various materials is not consistent.
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 deduced separately, and then calculated according to σHK=σHV : HV=0.968HK. 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 derivation and modification, 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
(1) The Qvarnstorm conversion formula proposed by Hans·Qvarnstorm
After correction, the conversion formula of Rockwell hardness and Vickers hardness is:
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 σHRC=σHV of different indenters, the formula is obtained by analyzing the relationship curve between Rockwell hardness and Vickers hardness indentation depth
picture
This formula is compared with the national standard experimental conversion value. The error between the conversion formula calculation result and the standard experimental value is ±0.1HRC.
(3) According to the actual experimental data, the conversion between Rockwell hardness and Vickers hardness was discussed using linear regression, and the formula was obtained:
picture
The use range of this formula is small, the error is large, but the calculation is simple, and it 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, according to the stress σHRC of the indenter
=σHB gives the conversion formula
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) According to the actual experimental data, use the linear regression method to obtain the formula
The formula error is too large and the application range 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 σHB=σHV. The conversion result of this formula is compared with the national standard conversion value, 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
This formula is more accurate and can be used as a reference.
Hardness conversion formula
1. Shore hardness (HS) = Boehre hardness (BHN)/10+12
2. Shore hardness (HS) = Rockwell hardness (HRC) + 15
3. Boehler hardness (BHN) = Rocker hardness (HV)
4. Rockwell hardness (HRC) = Boehler hardness (BHN)/10-3
Hardness measurement range:
HS<100
HB<500
HRC<70
HV<1300
Hardness test is the simplest and most feasible test method in mechanical performance test. In order to replace certain mechanical performance tests with hardness tests, a more accurate conversion relationship between hardness and strength is required in production.
Practice has proved that between various hardness values of metal materials, there is an approximate corresponding relationship between the hardness value and the strength value. Because the hardness value is determined by the initial plastic deformation resistance and the continued plastic deformation resistance, the higher the strength of the material, the higher the plastic deformation resistance and the higher the hardness value.
The following is a quick calculator made by this site based on the empirical formula obtained from the experiment. It has a certain practical value, but when the data is required to be more accurate, it still needs to be measured through the experiment.
Use the Brinell hardness indentation diameter to directly convert the Rockwell hardness of the workpiece
At the production site, due to the limitation of testing instruments, the Brinell hardness tester is often used to measure the hardness of large quenched parts. If you want to know the Rockwell hardness value of the workpiece, the usual method is to first measure the Brinell hardness value, and then find the corresponding Rockwell hardness value according to the conversion table. This method is obviously a bit cumbersome. So, can the Rockwell hardness value of the workpiece be directly calculated based on the indentation diameter of the Brinell hardness tester? The answer is of course yes. According to the conversion table of Brinell hardness and Rockwell hardness, an empirical formula that is simple to calculate and easy to remember can be summed up: HRC = (479-100D)/4, where D is the Φ10mm steel ball indenter pressed against the workpiece under a pressure of 30KN The measured value of the diameter of the indentation. The error between the calculated value of this formula and the converted value is within the range of 0.5 to -1. This formula is very convenient to use in the field
