When it comes to talking about the hardness of material, there are three different scales that are commonly used: the Vickers hardness test, the Brinell hardness test, and the Rockwell hardness test. Each of these tests measure hardness differently, and they all have their own pros and cons. To help navigate the differences between these tests, here’s a breakdown of how each one works, why they are used and the common conversion between the three.
Vickers Hardness Test
The Vickers Hardness Test (VHN) is a common technique used to measure hardness of metals and alloys, such as steel and aluminum. It is based on a diamond indenter, which is applied to the material at a predetermined and applied load. The size of the indentation is then measured and then used to calculate the Vickers Hardness Number. The higher the Vickers Hardness Number, the harder the material.
Brinell Hardness Test
The Brinell Hardness Test (BHN) is a test used to measure the hardness of metals and alloys. It is similar to the Vickers Hardness Test in that it uses an indenter (in this case, a steel ball of specific diameter). This test is usually used for measuring large and thick materials such as castings, forgings, and welded components. Unlike the Vickers Hardness test, it does not rely on the depth of the impression, but instead measures the pressure on the material caused by the indenter. The higher the Brinell Hardness Number, the harder the material.
Rockwell Hardness Test
The Rockwell Hardness Test (HR) is a test used to measure the hardness of materials. This test is unique from the others in that it does not involve an indenter. Instead, it uses three different measurement systems (A, B, and C) which applie varying amounts of force to the material and then measure the material’s response. The higher the Rockwell Hardness Number, the harder the material.
Conversion Between Hardness Tests
Though all three tests measure hardness, they all use different methods so it can often be confusing to convert between them. Fortunately, there are a number of formulas available that can help make the conversion process easier. The most common conversions involve converting between Vickers Hardness (HV) to Brinell Hardness (HB) and Rockwell Hardness (HRC).
When a material’s hardness is measured in terms of Vickers Hardness (HV), it can generally be converted to both a Brinell Hardness (HB) and a Rockwell Hardness (HRC) using the following equation:
HV=HB/1458+48.97 and HV=HRC/302.85+8.905
Conversely, when measuring a material’s hardness in terms of Brinell Hardness (HB), it can be converted to both a Rockwell Hardness (HRC) and a Vickers Hardness (HV) using the following equation:
HB=HVx1458+48.97 and HB=HRCx494.40+3.842
Finally, when measuring a material’s hardness in terms of Rockwell Hardness (HRC), it can be converted to both a Brinell Hardness (HB) and a Vickers Hardness (HV) using the following equation:
HRC=HVx302.85+8.905 and HRC=HBx494.40+3.842
Conclusion
The Vickers, Brinell, and Rockwell Hardness tests are all different tests used to measure different aspects of the hardness of materials. Though they all measure the same thing, each test uses different methods and thus, conversions between the three can often be confusing. Fortunately, there are a number of equations available to help make the conversion process easier. It’s important to understand the differences between the tests and to be familiar with the available equations to ensure accurate results.
