Induction hardening frequency is the frequency of the alternating current delivered by the induction power supply. It affects how fast the magnetic field alternates, how induced current distributes in the workpiece and the skin effect - and therefore the heat-source distribution and heating depth.
This article gives no fixed frequency ranges and promises no case depth or hardness outcomes. Frequency must be confirmed against material, part size, target depth, coil and measured results.
What Frequency Means
Frequency is the number of complete alternations of the current per second, expressed in Hz or kHz on hardening equipment.
For engineers it is not an isolated electrical figure but a process parameter that shapes how induced current distributes inside the workpiece.
Frequency and Current Distribution
Induction heating relies on an alternating electromagnetic field to induce current in the part. As frequency changes, the current distribution changes too.
This relates to the skin effect: generally, higher frequency concentrates current near the surface, while lower frequency lets the heat-affected region reach deeper. Actual results still depend on material, temperature, geometry and coil.
Frequency Affects Heating Depth
Because frequency shapes current distribution, it shapes heat distribution and heating depth - closely tied to the target case depth in hardening.
But depth is never set by frequency alone. Power, heating time, scan speed, coil structure, cooling and material hardenability all contribute.
Why Frequency Alone Is Not Enough
At the same frequency, different parts can give different results, because of:
- Different material grades
- Different cross-sections
- Different coil structures
- Different coupling gaps
- Different heating times
- Different power outputs
- Different spray-quench conditions
Claiming "frequency X suits depth Y" invites misjudgment.
How to Approach Frequency Selection
Consider together:
- Target effective case depth
- Material grade and hardenability
- Part diameter, thickness or cross-section
- Heating mode (single-shot or scanning)
- Coil structure
- Machine power capability
- Heating time or scan speed
- Hardness-gradient and metallographic results
Frequency selection should serve the final measured outcome, not a number on the datasheet.
Summary
Frequency is a key parameter for current distribution, skin effect and heating depth in induction hardening - but it does not decide case depth by itself. Analyze it together with power, time, coil, material, cooling and measured results.