Commonly used HRC, HV, HB hardness comparison table, clear at a glance!

Hardness indicates a material's ability to resist hard objects pressing 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 include Brinell hardness, Rockwell hardness and Vickers hardness. According to the German standard DIN50150, the following is a comparison table between the tensile strength and Vickers hardness, Brinell hardness, and Rockwell hardness of steel in the commonly used range.

The data in this table comes from German standard DIN50150

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 its indentation area is the Brinell hardness value ( HB), unit is kilogram force/mm2 (N/ mm 2).

The difference between HBS and HBW is the difference in the indenter. HBS means that the indenter is a hardened steel ball, which is used to measure materials with a Brinell hardness value below 450, such as mild steel, gray cast iron and non-ferrous metals. HBW indicates that the indenter is carbide and is used to measure materials with a Brinell hardness value below 650.

For the same test block, when other test conditions are exactly the same, the two test results are different. The HBW value is often greater than the HBS value, and there is no quantitative rule to follow.

After 2003, my country has adopted equivalent international standards, canceled the steel ball indenter, and all used carbide ball heads. Therefore, HBS is discontinued and all Brinell hardness symbols are represented by HBW. Many times, Brinell hardness is only represented by HB, which refers to HBW. However, HBS is still seen from time to time in literature papers.

The Brinell hardness measurement method is suitable for cast iron, non-ferrous alloys, and various annealed and quenched and tempered steels. It is not suitable to measure samples or workpieces that are too hard, too small, too thin, and do not allow large indentations on the surface.

2. Rockwell hardness (HR)

When HB>450 or the sample is too small, Brinell hardness test cannot be used and Rockwell hardness measurement is used instead. It uses a diamond cone with a vertex angle of 120° or a steel ball with a diameter of 1.59 or 3.18mm to press into the surface of the material to be tested under a certain load, and the hardness of the material is calculated from the depth of the indentation. According to the different hardness of the test material, it is expressed in three different scales.

HRA: It is the hardness obtained using a 60kg load and a diamond cone intruder, and is used for extremely hard materials (such as cemented carbide, etc.).

HRB: It is the hardness obtained by using a hardened steel ball with a load of 100kg and 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 using a 150kg load and a diamond cone intruder, and is used for materials with very high hardness (such as quenched steel, etc.).

The usage range of HRC scale is 20~70HRC. When the hardness value is less than 20HRC, because the conical part of the indenter is pressed too much, the sensitivity decreases. At this time, the HRB scale should be used instead; when the sample hardness is greater than 67HRC, the pressure on the tip of the indenter is too large, and the diamond is easily damaged. The life of the indenter will be greatly shortened, so HRA scales should generally be used instead.

The Rockwell hardness test is easy and fast to operate and has small indentation. It can test the surface of finished products and harder and thinner workpieces. Due to the small indentation, for materials with uneven structure and hardness, the hardness value fluctuates greatly, and the accuracy is not as high as Brinell hardness. Rockwell hardness is used to determine the hardness of steel, non-ferrous metals, hard alloys, etc.

At the production site, due to limitations of testing instruments, a 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 according to the indentation diameter of the Brinell hardness tester? The answer is of course yes. According to the Brinell hardness and Rockwell hardness conversion tables, an empirical formula that is simple to calculate and easy to remember can be summarized: HRC = (479-100D)/4, where D is the Φ10mm steel ball indenter pressing on the workpiece under a pressure of 30KN Indentation diameter measurements on. The error between the value calculated by this formula and the converted value is in the range of 0.5 to -1. This formula is very convenient to use in the field. You may wish to have a try.

3. Vickers hardness (HV)

Use a diamond square cone intruder with a load within 120kg and a vertex angle of 136° to press into the material surface. Divide the surface area of the indentation pits in the material by the load value, which is the Vickers hardness HV value (kgf/mm2).