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CHT · Carburising, hardening and tempering

Carbon is diffused into the surface of a low-carbon steel, then the part is quenched and tempered: a hard, wear-resistant case over a tough core that takes shock.

Furnace
SQF-1, 2, 3 → TFC

Source · STEP process inspection records

What it does

A hard case where the load is. A tough core behind it.

Gears, pins and shafts fail at the surface first: pitting, wear, contact fatigue. Carburising puts hardness only where it is needed and leaves the core able to absorb shock.

  • Specify it for contact load and wear on case-hardening grades such as 20CrMo and 8620.
  • Tell us surface hardness, effective case depth and the hardness it is measured to (for example 513 HV), and core hardness.
  • Expect some size change and distortion; leave grinding stock where your tolerances are tight, and run a trial charge on a new part first.

Typical cycle

The cycle, as we run it.

CHT Carburising · hardening · tempering
  • Pre-heat430 ± 10 °C · 60 min min.
  • Carburise900 ± 15 °C
  • BoostCP 0.98 %
  • DiffuseCP 0.63 %
  • Harden825 ± 15 °C
  • Quenchoil 110 ± 10 °C
  • Temper170–190 °C · 90 min

STEP typical parameters from process inspection records. Times illustrative; actual cycle per part specification.

Route through the plant

Specifications we control

What goes on the drawing, and how we prove it.

Tighter bands are quoted per part.

Surface hardness
Tested to the scale on your drawing; for example 88–90 HR15N.
Rockwell / HR15N · per sampling plan
Effective case depth
To the depth on your drawing; for example 0.35–0.55 mm, to a limit of 513 HV.
Microhardness traverse · HV0.3 · sectioned sample
Temper start
Within 4 h of the quench, or a snap temper of 140 ± 10 °C for 60 min.
Logged per charge · check TM01
Carbon potential
Held by oxygen probe through carburise and diffuse.
Oxygen probe · digital controller
Case-depth traverseIllustrative · not a measured part
Hardness against depth below the surface. Effective case depth is where the curve crosses the limit hardness.

Typical work

Grades and parts we carburise.

Material grades

  • 20CrMo
  • 8620

Other grades on request.

Part types

  • Pins
  • Gears
  • Shafts
  • Pistons
  • Spools
  • Sleeves
  • Rings
  • Cams
  • Bushes

Next step

Quote a CHT job.

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