Relationship between induction frequency and quenching depth (hardening depth)

The quenching depth (hardening depth) depends on the output frequency of induction heater. Generally, higher frequency will bring smaller quenching depth (shallower).
The relationship between the frequency f and the heating depth δ has the following empirical formula:
δ=20/√f(20°C)；δ=500/√f(800°C)。

d/mm	f/KHZ
0.76	450
1.14	200
2.11	100
2.26	50
3.20	25
5.08	10
9.27	3
16.05	1
22.71	0.5
37.85	0.18
65.53	0.06