Carbonitride
Case & surface hardening · Thermochemical diffusion
Carbonitriding diffuses both carbon and nitrogen into low-carbon steel in the austenitic range, then quenches and tempers the surface to martensite.
Reference page — Carbonitride is not in the instant-quote configurator. Upload the part, name the treatment in the notes with the call-out below, and an engineer quotes it with the part.
Carbonitride at a glance
Four scores, each 0–100 against every heat treatment in this catalog. Hardness is derived from the HRC target (20 HRC = 0, 70 HRC = 100) — treatments without a hardness target (anneals, stress relief, HIP, cryo) are not rated. Toughness, dimensional stability and cost are FabDigit's engineering assessment.
What is Carbonitride?
Carbonitriding diffuses both carbon and nitrogen into low-carbon steel in the austenitic range, then quenches and tempers the surface to martensite. It is a high-volume route to a shallow 52–62 HRC case on small fasteners, stampings, gears, and pins.
How it works
Low-carbon steel is heated in a carbon-bearing furnace atmosphere with added ammonia, commonly between 820 and 900 °C. Carbon and nascent nitrogen diffuse into austenite; nitrogen increases case hardenability, allowing a hard case with a milder oil or gas quench. The process runs cooler and for less time than conventional carburizing, so its case is shallower. After direct quenching, a 150–200 °C temper reduces quench stress while retaining wear hardness. Atmosphere carbon potential, ammonia addition timing, load temperature, retained austenite, case porosity, and quench rate all require control.
Why specify it
- Creates about 52–62 HRC on economical low-carbon steels
- Provides a shallow 0.075–0.75 mm effective case
- Uses lower temperature and shorter time than deep carburizing
- Nitrogen raises case hardenability for small mass-produced parts
Where it falls short
- Practical case depth is generally no more than about 0.75 mm
- Long or nitrogen-rich cycles can create retained austenite and porosity
- Quenching still creates distortion and crack risk
- Not a substitute for deep carburized cases under heavy contact loads
The Carbonitride cycle
Typical furnace parameters from the governing specifications and shop practice; the heat treater sets the exact recipe from the alloy, section size and required result.
| Temperature | 820–900 °C (1,508–1,652 °F) — Austenitic gas carbonitriding range; 845–870 °C is common. |
|---|---|
| Soak | 0.5–6 h — Short cycles are typical; time is limited by the shallow-case application and nitrogen control. |
| Cooling | Oil quench |
| Atmosphere | Endothermic gas / ammonia |
| Door to door | 3–10 h — Includes heat-up, diffusion, quench, wash, and temper. |
Stages
- 1Preclean and load at temperature
- 2Establish carbon potential
- 3Add ammonia after the load stabilizes
- 4Direct oil quench
- 5Temper at 150–200 °C
What Carbonitride does to the part
| Hardness | 52–62 HRC — Typical final surface-hardness classes reported for gas-carbonitrided steel. |
|---|---|
| Case depth | 0.08–0.75 mm — Effective case depth to 50 HRC per SAE J423; ISO 2639 uses 550 HV1 for CHD. |
| Toughness | The low-carbon core remains comparatively ductile, but excess nitrogen and retained austenite can reduce case integrity. |
| Distortion | Medium risk. Lower processing temperature and mild oil quench reduce movement relative to deep carburizing, but do not eliminate it. |
| Surface after treatment | Dark quenched surface with light scale unless a controlled bright process and wash are used. |
| Machining sequence | Finish most geometry first; allow light grinding only where the minimum 0.075–0.75 mm case remains. |
Specifications for Carbonitride
The documents a drawing cites to define this treatment. Each links to a page explaining the standard, its classes and the tests it invokes.
| Standard | Role | Classes used | Status |
|---|---|---|---|
Steels — Determination and verification of the depth of carburized and hardened cases | Alternative | — | Active |
Test and related methods: ASTM E18 (Standard Test Methods for Rockwell Hardness of Metallic Materials), ASTM E384 (Standard Test Method for Microindentation Hardness of Materials), SAE J423 (Methods of Measuring Case Depth), AMS 2750 (Pyrometry), AMS 2759 (Heat Treatment of Steel Parts, General Requirements).
Drawing call-out
GAS CARBONITRIDE TO 58–62 HRC; 0.25–0.45 MM EFFECTIVE CASE DEPTH TO 50 HRC PER SAE J423 ON ALL EXPOSED SURFACES; OIL QUENCH AND TEMPERWhich alloys take Carbonitride?
Verdict per material family, with the grades that behave differently. Each family links to its datasheets in the material library. Typical grades: 1008, 1010, 1018, 1020, 1117, 12L14.
| Material family | Verdict | Notes |
|---|---|---|
| Yes | Low-carbon plain and low-alloy steels are the intended substrates.
| |
| With care | Sintered low-carbon steel may respond, but porosity and chemistry alter diffusion. | |
| Limited | Only qualified AM low-carbon steel routes should be considered. | |
| No | Aluminum cannot form a carbonitrided martensitic case. | |
| No | Brass cannot tolerate the process temperature. | |
| No | Bronze is outside carbonitriding metallurgy. | |
| No | Cobalt-chrome does not use steel carbonitriding. | |
| No | Copper alloys do not form carbonitrided martensite. | |
| No | The process temperature exceeds magnesium alloy capability. | |
| No | Nickel alloys do not use conventional steel carbonitriding. | |
| No | Precious metals cannot form a carbonitrided steel case. | |
| No | Refractory-metal carbon and nitrogen reactions require separate processes. | |
| No | Conventional carbonitriding is not a stainless-steel process. | |
| No | Carbon and nitrogen pickup can embrittle titanium. | |
| No | Tungsten heavy alloys do not form the intended case. | |
| No | Zinc alloys melt below the process range. |
Design rules for Carbonitride
What to decide on the drawing before the part goes to the heat treater.
- Limit specified effective depth to the practical 0.075–0.75 mm range.Carbonitriding is optimized for shallow cases; deeper cycles increase retained austenite and porosity risk.
- Specify effective depth to 50 HRC or CHD to 550 HV1.The numerical depth is meaningless without its criterion.
- Keep thin edges and sharp notches out of severe quench flow.The enriched case is hard and crack-sensitive immediately after quench.
- Introduce ammonia only after the load reaches temperature.Early ammonia addition causes nonuniform nitrogen uptake and case depth.
- Provide representative coupons for microhardness traverse.Case-depth verification is destructive.
Carbonitride versus the alternatives
Treatments engineers weigh against Carbonitride, and when each wins.
| Treatment | Hardness | Toughness | Stability | Cost | Choose it when |
|---|---|---|---|---|---|
Carbonitride this page | 74 | 50 | 50 | $$ | — |
| 82 | 55 | 35 | $$$ | when more than 0.75 mm effective case or greater contact-load capacity is needed | |
| 68 | 55 | 88 | $$$ | when no transformation quench and lower distortion are required |
Cost, lead time and applications
Relative cost
Carbonitride is a standard-cost treatment ($$) relative to the other heat treatments in this catalog.
Heat treatment is priced per lot with a furnace minimum. The exact figure appears on the instant quote once the part is uploaded.
Lead time
| Added lead time | 3–7 working days |
|---|---|
| Furnace time | 3–10 h |
What Carbonitride is used for
- Small gears
- Washers and stampings
- Fasteners and screws
- Bushings
- Pins and pawls
- Small chain components
Carbonitride — frequently asked
How is carbonitriding different from carburizing?
Carbonitriding adds nitrogen with carbon and commonly runs at 820–900 °C. Its 0.075–0.75 mm case is shallower than typical carburizing but has higher hardenability.
How is carbonitriding different from FNC?
Carbonitriding runs in austenite and is quenched to martensite. Ferritic nitrocarburizing runs near 560–590 °C below Ac1 and does not use a transformation quench.
What hardness does carbonitriding produce?
Small low-carbon steel parts commonly specify about 52–62 HRC. The exact result follows surface carbon and nitrogen, quench rate, retained austenite, and temper.
How deep can carbonitriding go?
The established practical range is about 0.075–0.75 mm. For depths above roughly 0.75 mm, carburizing is normally the more controllable choice.
Does carbonitriding distort parts?
Yes, because the enriched austenitic case is oil quenched. The lower temperature and shallow case generally reduce movement relative to deep carburizing.
Which AMS slash sheet governs carbonitriding?
No applicable AMS 2759 slash sheet was identified for austenitic carbonitriding. AMS 2759/12 and /13 cover gaseous ferritic nitrocarburizing, while AMS 2759/11 covers stress relief.