01How the process works
In carburising, parts are heated in a carbon rich atmosphere so carbon diffuses into the surface, then quenched and tempered. Nitriding diffuses nitrogen at lower temperature without quenching, giving less distortion and a hard compound (white) layer.
Effective case depth, surface hardness and microstructure (retained austenite, carbides, white layer thickness) are the acceptance features. They are measured on sections of production parts or representative coupons in each load.
- Cleaning and masking. Parts cleaned; areas masked.
- Diffusion. Carburising or nitriding cycle.
- Quench. For carburised parts.
- Temper. Stress relief and hardness adjustment.
- Testing. Case depth traverse, hardness, microstructure.
02What typically goes wrong
| Defect | Typical cause | How it is found |
|---|---|---|
| Shallow or deep case | Time, temperature, carbon potential | Hardness traverse |
| Low surface hardness | Decarburisation, retained austenite | Microhardness, metallography |
| Excess white layer | Nitriding potential | Metallography |
| Distortion | Quench, fixturing | Dimensional check |
| Soft spots | Masking, contamination | Hardness survey |
| Grinding burn after case hardening | Grinding parameters | Nital etch |
03Where an inspector should look
01
Before production
- Case depth definition (e.g. 550 HV)
- Coupon arrangement
- Masking requirements
02
During production
- Atmosphere control records
- Furnace charts
03
After production
- Case depth traverse per load
- Surface hardness
- Microstructure on samples
04Standards and references
ISO 18203 (case depth determination), ISO 2639, CQI-9, EN 10084 (case hardening steels), EN 10085 (nitriding steels).
Standards are named for orientation. The applicable edition and acceptance criteria are those in your contract and specification.
05How we support buyers of case hardening parts
Manufacturing and Special Process AuditsProcess audits of casting, machining, welding, heat treatment, plating and moulding, with VDA 6.3 style evaluation.
Material Verification and Certificate ReviewMaterial identification, PMI, hardness checks and technical review of EN 10204 certificates against material standards.