What is effective case depth?

The depth below the surface where hardness falls to an agreed value, usually 550 HV (about 52 HRC). Drawings should state it, e.g. 0.8–1.0 mm (0.0315–0.0394 inch) effective case depth.

Which steels can be carburised?

Low-carbon steels and alloy case-hardening steels such as 20MnCr5, EN353, EN36 and SAE 8620. Medium- and high-carbon steels are through hardened instead.

Does carburising cause distortion?

Yes, some, because of the high temperature and quench. Precise gears and bores are usually ground after hardening.

Case carburising: process, case depth and steels used

Case carburising adds carbon to the surface of a low-carbon steel part at high temperature, then quenches it. The result is a very hard, wear-resistant surface over a tough core, which is ideal for gears, pins and shafts that face both wear and shock.

Quick facts

Temperature: About 880–950 °C, then quench
Case depth: Typically about 0.3–2 mm (0.0118–0.0787 inch), chosen for the part
Surface hardness: About 58–62 HRC after quench and temper
Core: Tough, usually about 30–45 HRC
Steels: 20MnCr5, EN353, EN36, SAE 8620, 16MnCr5
Usually priced: Per kg or per batch

The process

Carburise in a gas or sealed-quench furnace until carbon reaches the case depth wanted
Quench in oil, directly or after reheating
Temper at about 150–200 °C
Shot blast and check hardness and case depth on a sample
Grind or finish critical sizes, leaving allowance for it

Carburising or carbonitriding?

Carburising: deeper cases for gears, shafts and heavily loaded parts
Carbonitriding: carbon plus nitrogen at a lower temperature; thinner, harder cases with less distortion for small parts

What to tell the heat treater

Steel grade
Effective case depth (to a set hardness, e.g. 550 HV) and surface hardness
Core hardness if it matters
Areas to keep soft (copper plating or paint stop-off), such as threads
Quantity and part weight

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Related job work

Machines

Induction hardening machine

Materials

Questions

What is effective case depth?: The depth below the surface where hardness falls to an agreed value, usually 550 HV (about 52 HRC). Drawings should state it, e.g. 0.8–1.0 mm (0.0315–0.0394 inch) effective case depth.
Which steels can be carburised?: Low-carbon steels and alloy case-hardening steels such as 20MnCr5, EN353, EN36 and SAE 8620. Medium- and high-carbon steels are through hardened instead.
Does carburising cause distortion?: Yes, some, because of the high temperature and quench. Precise gears and bores are usually ground after hardening.

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 9 October 2026.