Carburising vs Induction Hardening
Both processes give a hard surface over a tough core, and they are not interchangeable. Carburising adds carbon to a low carbon steel; induction hardening simply heats a steel that already has enough carbon. That difference drives everything else.
Carburising diffuses carbon into low carbon steels such as 20MnCr5 over hours at 900–950°C, producing a uniform 0.6–1.5 mm case following the full contour. Induction hardening heats the surface of steels already containing 0.35% carbon in seconds, hardening selected zones with far less distortion.
- Carburising temperature
- 900 – 950 °C, hours
- Induction temperature
- Surface only, seconds
- Carburising case
- 0.6 – 1.5 mm, full contour
- Induction case
- 1 – 5 mm, selected zones
- Distortion
- Carburising higher
- Suitable steels
- Low carbon vs ≥0.35% carbon
Carburising vs Induction Hardening at a glance
Quotable facts from Avadh Techno Forge, Gundasara, Gondal, Rajkot.
- Carburising temperature: 900 – 950 °C, hours
- Induction temperature: Surface only, seconds
- Carburising case: 0.6 – 1.5 mm, full contour
- Induction case: 1 – 5 mm, selected zones
- Distortion: Carburising higher
- Suitable steels: Low carbon vs ≥0.35% carbon
| Factor | Carburising | Induction hardening |
|---|---|---|
| Suitable steels | Low carbon (20MnCr5, EN353) | 0.35% carbon and above |
| Cycle time | Hours | Seconds |
| Case coverage | Full contour, uniform | Selected zones only |
| Typical case depth | 0.6–1.5 mm | 1–5 mm |
| Distortion | Significant | Low |
| Best for | Gear teeth, splines | Journals, cam lobes, rods |
Different Starting Materials
Carburising requires a low carbon grade — 20MnCr5, 16MnCr5, EN353 — into which carbon is diffused at 900–950°C over hours. Induction hardening requires a steel that already carries roughly 0.35% carbon or more, and simply heats and quenches its surface in seconds.
- Carburising: low carbon steels only
- Induction: 0.35% carbon minimum
- Carburising takes hours
- Induction takes seconds
Case Depth and Uniformity
Carburising produces a uniform case following the whole part contour, typically 0.6–1.5 mm, ideal for gear teeth where every flank and root must be hardened equally. Induction hardening follows the coil, so it hardens selected zones — a journal, a cam lobe, a spline — leaving the rest untouched.
Distortion and Cost
Carburising heats the entire part for hours, so distortion is significant and grinding stock must be planned. Induction hardening heats a thin surface layer briefly, so distortion is far lower, cycle time is seconds, and unit cost at volume is lower.
Topics covered on this page
- carburising vs induction hardening
- case hardening comparison
- induction hardening vs carburizing
- which hardening process
Based on work carried out at our own forging plant at Gundasara, Gondal, Rajkot — operating since 2008.
Questions Answered
Which process should I use for gears?
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Carburising, because it hardens every tooth flank and root uniformly following the contour.
Which for shafts and cam lobes?
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Induction hardening, which targets journals and lobes selectively while leaving the rest of the shaft tough.
Which causes more distortion?
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Carburising, because the whole part is heated for hours. Induction heats only a thin surface layer briefly.
Can EN8 be carburised?
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Not usefully — it already carries too much carbon. EN8 is induction hardened instead.