# Conversion Between Various Hardness Value

Although hardness is applied widely, it is not the independent basic capacity of material. What kind of resistanting power that specific hardness represents relies on the test method it applies, that is hardness type. For example, the plunging hardness represents material's ability of resistanting transformation, and characterization method of hardness represents material's ability of resistanting fracture etc. Visible hardness has no exact physical significance. Therefore, there is no conversion formula between various kinds of hardness values.

Under the circumstance, a certain hardness value should be converted to a needed hardness value. After long time practicing and accumulating datas, people get some hardness conversion formulas by mathematical methods. Certainly, these formulas are all experimental, and conversion relations between experimental data of average and approximate value. The result has certain reference value.

Approximate conversion formulas of several hardness values are as follows:

1. Relations between HB and HV

When HB≤400， HB≈HV

When HB＞400， HB＜HV

2. Relations between HB and HR

HB=4030/130-HRF

HB=7300/130-HRB(40＜HRB＜100)

HB=333000/(100-HRA)2(55＜HRA＜70)

HB=1520000-4500HRC/(100-HRC)2(20＜HRC＜40)

HB=25000-10(57-HRC)2/100-HRC(50＜HRC＜60)

3. Relations between HV and HRC

HV=2×106/(112-HRC)2

4. Relations between HB and HS

HB=αHS

In the formula, α is different according to different materials(see Tab.1), HS is the Shore hardness  value tested by a diamond indenter. If a steel ball indenter is applied, the result should multiply by 0.56 to convert to Shore hardness value with diamond indenter.

Tab.1 Coefficient α between HB and HS of Some Kinds of Steel 