What is the difference between induction hardening and through hardening?

Induction hardening hardens only the surface where needed; through hardening heats and quenches the whole part, strengthening its whole section.

Which steels can be induction hardened?

Medium-carbon and alloy steels such as EN8, EN9, C45, EN19 and 42CrMo4. Low-carbon steels need case hardening instead.

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Induction hardening machine

Also called: induction hardener, induction heating machine, scanning hardening machine, induction quenching

An induction hardening machine heats the surface of a steel part in seconds with a high-frequency copper coil, then quenches it with water or polymer. Only the surface hardens, about 50–60 HRC depending on the steel, while the core stays tough: ideal for shafts, gears and pins.

Quick facts

Heating: High-frequency electromagnetic induction from a copper coil
Typical steels: Medium-carbon and alloy steels: EN8, EN9, C45, EN19, 42CrMo4
Surface hardness: About 50–60 HRC depending on the steel
Case depth: Typically about 1–5 mm, set by frequency and time
Modes: Scanning (coil moves along the part) or single shot
Strength: Fast, local, little distortion

Typical work

Shafts and axles: bearing seats and splines
Gear teeth and sprockets
Pins, rollers and cams
Machine slideways
Crankshaft journals

Points to know

The steel needs enough carbon (about 0.35% or more) to harden
Mark on the drawing which surfaces to harden, the hardness range and case depth
Coils are made to fit the part, so new shapes may need a new coil

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Questions

What is the difference between induction hardening and through hardening?: Induction hardening hardens only the surface where needed; through hardening heats and quenches the whole part, strengthening its whole section.
Which steels can be induction hardened?: Medium-carbon and alloy steels such as EN8, EN9, C45, EN19 and 42CrMo4. Low-carbon steels need case hardening instead.

The figures on this page are typical values for guidance, written by Diemeco from standard engineering practice. They are not a specification: confirm grades and properties with the relevant standard or the supplier's mill test certificate, and tolerances with your workshop. Last checked 8 October 2026.