Choosing the Right Frequency for Induction Hardening Applications
Learn how frequency impacts heat penetration, case depth, and hardness during the induction hardening process.
In induction hardening, one parameter makes all the difference between a perfect case depth and a failed part — frequency. It directly controls how deep and fast heat penetrates into the metal surface, determining the hardness, strength, and fatigue life of the component.
At Thakur Induction, we customize frequency selection for every component and material to ensure optimal hardening depth, minimal distortion, and superior surface finish.
What Is Frequency in Induction Hardening?
Frequency refers to the number of times the alternating current (AC) changes direction per second in the induction coil, measured in Hertz (Hz). Higher frequency leads to shallow heat penetration, while lower frequency results in deeper heat penetration due to the "skin effect."
| Frequency | Typical Range | Heating Depth | Application |
|---|---|---|---|
| High Frequency (HF) | 100–500 kHz | 0.5 – 2 mm | Gears, pins, thin components |
| Medium Frequency (MF) | 10–100 kHz | 1.5 – 6 mm | Shafts, spindles, camshafts |
| Low Frequency (LF) | 1–10 kHz | 5 – 20 mm | Large rollers, axles, crankshafts |
High Frequency Induction Hardening
High frequency (100–500 kHz) is used for shallow case depths (0.5–2 mm). It's ideal for small or thin components like gears and pins, offering rapid heating and minimal distortion.
Medium Frequency Induction Hardening
Medium frequency (10–100 kHz) is the most common method, providing case depths between 1.5 mm and 6 mm. It's perfect for automotive shafts, crankshafts, and agricultural parts made from EN8, EN19, and EN24 steels.
Low Frequency Induction Hardening
Low frequency (1–10 kHz) is for large, heavy-duty components requiring deep hardening up to 20 mm, such as large axles and rollers. The heating is slower but penetrates deeper.
How Frequency Affects Case Depth and Hardness
| Parameter | Low Frequency | Medium Frequency | High Frequency |
|---|---|---|---|
| Case Depth | Deep (up to 20 mm) | Medium (1.5–6 mm) | Shallow (0.5–2 mm) |
| Heating Speed | Slow | Moderate | Very Fast |
| Distortion Risk | Low (slow heating) | Controlled | Very Low |
| Precision | Low | Moderate | High |
| Typical Application | Axles, rollers | Shafts, spindles | Gears, pins, tools |
Practical Examples from Industrial Applications
| Component | Steel Grade | Frequency Used | Case Depth | Result |
|---|---|---|---|---|
| Gear Teeth | EN8 | High (300 kHz) | 1 mm | Hard surface, no distortion |
| Drive Shaft | EN19 (4140) | Medium (30 kHz) | 3 mm | Deep, fatigue-resistant case |
| Axle Roller | EN24 (4340) | Low (5 kHz) | 8 mm | Uniform deep hardness |
| Camshaft Lobe | EN19 | Medium (20 kHz) | 2 mm | High wear resistance |
Conclusion: The Right Frequency Defines the Right Hardness
Choosing the right frequency is the key to achieving the perfect balance between surface hardness and core toughness. At Thakur Induction, we use advanced frequency control systems to deliver industry-leading heat treatment job work for Ludhiana and all of Punjab.
Need Frequency-Controlled Induction Hardening?
Contact Thakur Induction for precision induction hardening job work using the right frequency for your material and component type.