Which steel is best for induction hardening?

Medium-carbon steels with about 0.35–0.55% carbon: EN8, C45 and EN9 for ordinary parts, and EN19 or EN24 when the core must also be strong. Low-carbon steels such as EN1A or mild steel do not harden well this way.

How deep is an induction-hardened case?

Usually 1–6 mm (0.0394–0.236 inch). Higher frequency gives a shallower case; lower frequency and longer heating go deeper. The drawing should state the case depth and the hardness at which it is measured.

Do parts need grinding after induction hardening?

Bearing seats and close fits are usually ground afterwards, because the surface moves slightly and scales. Leave about 0.2–0.3 mm (0.0079–0.0118 inch) on diameter for this.

Induction hardening job work: case depth, hardness, cost

Induction hardening heats only the surface of a steel part with a coil carrying high-frequency current, then quenches it at once. The surface becomes hard and wear resistant while the core stays tough. It is fast, local and very common for shafts, pins, gear teeth and guide ways.

Quick facts

Suitable steels: Medium-carbon steels such as EN8, EN9, C45, EN19; cast irons
Surface hardness: About 50–58 HRC (steel and carbon dependent)
Case depth: About 1–6 mm (0.0394–0.236 inch), set by frequency and heating time
Heated zone: Only the areas the coil reaches
Distortion: Low compared with full hardening
Usually priced: Per piece, often per hardened length

How it is done

The part passes through or sits inside a copper coil
High-frequency current heats a thin outer layer in seconds
A water-based quench follows immediately (spray or tank)
Low-temperature tempering (about 150–200 °C) relieves stress
Hardness and case depth are checked on sample pieces

Induction hardening or carburising?

	Induction hardening	Case carburising
Steel	Medium carbon (0.35–0.55% C)	Low carbon (0.15–0.25% C)
Where hardened	Only chosen zones	Whole surface (unless masked)
Time	Seconds per part	Hours in a furnace
Typical use	Shafts, pins, bearing seats	Gears, highly loaded parts

What to tell the heat treater

Steel grade and its current condition (e.g. hardened and tempered EN19)
Zones to harden, marked on the drawing
Surface hardness range, e.g. 52–56 HRC
Effective case depth, e.g. 2–3 mm (0.0787–0.118 inch) at 40 HRC
Zones that must stay soft (threads, keyways, ends)
Quantity, so the coil and fixture can be made

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Questions

Which steel is best for induction hardening?: Medium-carbon steels with about 0.35–0.55% carbon: EN8, C45 and EN9 for ordinary parts, and EN19 or EN24 when the core must also be strong. Low-carbon steels such as EN1A or mild steel do not harden well this way.
How deep is an induction-hardened case?: Usually 1–6 mm (0.0394–0.236 inch). Higher frequency gives a shallower case; lower frequency and longer heating go deeper. The drawing should state the case depth and the hardness at which it is measured.
Do parts need grinding after induction hardening?: Bearing seats and close fits are usually ground afterwards, because the surface moves slightly and scales. Leave about 0.2–0.3 mm (0.0079–0.0118 inch) on diameter for this.

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 15 October 2026.