Rockwell hardness (Rockwellhardness), which is composed of rockwell (S.P.R ockwell) in 1921, is to use the rockwell hardness tester determination by the hardness value of the metal material. The value has no unit and is only represented by the code name "HR".
There are three different criteria for HRA, HRB, and HRC in rockwell hardness. It is called ruler A, ruler B, ruler C.
HRA is 60 kg load and 120 ° diamond cone forcer, finding the hardness is used for high hardness of the material. For example: hard alloy.
HRB is the hardness of a steel ball with 100Kg payload and 1.59mm diameter, which is used for the hardness of medium materials. For example: annealed steel, cast iron, etc.
HRC load is 150 kg and 150 ° diamond cone forcer, finding the hardness for high hardness of the material. Quench steel, etc
The measurement method is that, under the regulation of the loads, the steel ball or diamond indenter vertical pumped to the surface of the test material, produce dent, according to the indentation depth, load after using the formula of rockwell hardness HR = (K H)/C can calculate the rockwell hardness. Rockwell hardness is displayed on the dial of the durometer, which can be read directly.
In the above formula, K is constant, K= 0.2mm when the diamond head is pressed, and K= 0.26mm when the steel ball heads are quenched. The depth of indentation of the test piece after the main load was relieved by H; C is also constant. In general, C=0.002 MM. It can be seen that the lower the indentation, the higher the HR value, the higher the hardness of the material. For hardness higher knives, knives the world general HRC to represent the blade hardness, such as 60 HRC, represents the test load of 1471.1 N, use vertex Angle is 120 ° diamond cone head, participants indentation depth of the material is 0.08 MM.
Generally speaking, the higher the hardness, the higher the anti-wear ability, but the greater the brittleness. The hardness of high speed steel is 62~ 66HRC, high performance high speed steel 63~ 70HRC, hard alloy cutting tool 70~ 75HRC.
