How it works
A coil emits a high-frequency electromagnetic field that induces eddy currents in the steel surface, heating just that zone within seconds.
The part is then quenched immediately (often a water spray), so the skin becomes hard martensite while the core stays tough because it never got hot.
Higher frequency means a shallower hardened case depth, so it can be tuned to the job.
Where it fits
- Shafts, pins and dowels needing a wear-resistant skin over an impact-resistant core.
- Localized zones such as thread tips, screw points or contact faces.
- Jobs needing fast, consistently repeatable (automated) cycles.
Best on medium-carbon steel—e.g. S45C, SCM440—with enough carbon to harden the surface.
How it differs from through hardening
Through hardening hardens the whole body—good when the entire part must be hard, but more prone to distortion and more brittle.
Induction hardens only the selected surface, lowering overall distortion and keeping a tough core.
The choice depends on *where* you need hardness and how the part is loaded.
FAQ
Induction vs carburizing?+
Different: induction heats medium-carbon steel that already has the carbon, while carburizing first adds carbon to the surface of low-carbon steel before hardening.
Can case depth be controlled?+
Yes—by tuning frequency, power and time, then verifying case depth with a cross-section hardness traverse.
Can very small parts be done?+
It depends on geometry and the zone to harden. Send a drawing and we will assess suitability.
Free Engineering Tools
- Hardness Converter HRC ↔ HV ↔ HB
- Which Steel Grades Harden — and How Far
- Fastener Weight: pcs ↔ kg
- Finishing Specification Builder for Purchasing and QC
- Salt Spray Test Plan Builder
- Coating thickness → thread fit (GO/NO-GO)
- Hydrogen Embrittlement — is baking required?
- Bolt Tightening Torque & Proof Load
- Thread Engagement Length
- Bolt Size Estimator (from load)
- Bolt Property Class — Mechanical Properties (ISO 898-1)
Related comparison guides
- Case hardening vs Through hardeningCase hardening vs through hardening: which one for screws and bolts?
- Annealing vs Tempering vs NormalizingAnnealing vs tempering vs normalizing: which one does your part need?
- Quenching vs TemperingQuenching vs tempering: two halves of one process
- Carburising vs NitridingCarburising vs nitriding: what a screw, nut or bolt actually gets
- Carbonitriding vs CarburizingCarbonitriding vs carburizing: which case-hardening for fasteners?
- S45C vs SCM440S45C vs SCM440: which steel should you harden?
- SCM435 vs SCM440SCM435 vs SCM440: one alloy step apart, and it shows
- Grade 8.8 vs Grade 10.9 vs Grade 12.9Grade 8.8 vs 10.9 vs 12.9 bolts: what actually differs?
- Class 10.9 vs Class 12.9Class 10.9 vs 12.9: what you gain, and what you take on
Technical content review
Reviewed by the V.S. Heat Treatment QA and production team—heat-treatment and finishing operations since 1994 under an ISO 9001:2015 quality system.
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