B, Rockwell Hardness (HK) Rockwell hardness test with the Brinell hardness test, are indentation test method. The difference is that it is the depth of the indentation measured. That is, under the influence of the initial test force (Fo) and the total test force (F), the indenter (gold
steel cone or steel ball) is pressed into the surface of the specimen, and after the specified holding time, The test force is calculated using the measured residual indentation depth increment (e). The value is an unknown number, expressed in symbol HR, the scale used is A, B, C, D, E, F, G, H, K and other 9 scales. Which is commonly used in steel hardness test scale is generally A, B, C, that is, HRA, HRB, HRC. The hardness value is calculated by the following formula: HR = 100-e when tested with A and C scale HR = 130-e where e - residual depth of indentation is incremented, Unit 0.002mm said, that is, when the indenter axial displacement of a unit (0.002mm), that is equivalent to Rockwell hardness change a number. The greater the e value, the lower the hardness of the metal, and vice versa the higher the hardness. The above three scales apply as follows: HRA (diamond cone head) 20-88 HRC (diamond cone head) 20-70 HRB (diameter 1.588mm steel ball head) 20-100 Rockwell hardness test is widely used , Where HRC is used in steel pipe standards after Brinell hardness HB. Rockwell hardness can be applied to the determination of very soft to very hard metal material, which makes up the Buchner method is not, than the Brinell method is simple, can be directly from the hardness of the dial read out the hardness value. However, due to its indentation is small, so the hardness value is not as accurate as the Brinell method.