Case & surface hardening
Carburize, carbonitride, nitride, nitrocarburize, flame and induction — a hard, wear-resistant skin over a tough core, measured as case depth to a hardness criterion.
7 treatments compared
Cycle temperature, the hardness each delivers, case depth, furnace time and relative cost, side by side. Open a treatment for its full cycle, specifications, compatible alloys and drawing call-out.
| Treatment | Temperature | Hardness | Case depth | Cycle time | Relative cost |
|---|---|---|---|---|---|
Plasma nitriding uses a glow discharge to clean, heat, and diffuse nitrogen into ferrous surfaces. | 400–580 °C | 58–67 HRC | 0.1–0.5 mm | 8–50 h | $$$$ High |
Flame hardening rapidly austenitizes selected steel surfaces with an oxy-fuel flame and immediately quenches them to martensite. | 800–950 °C | 45–65 HRC | 0.5–6 mm | 0.1–2 h | $$ Standard |
Induction hardening uses an alternating magnetic field to austenitize selected steel surfaces, followed immediately by quenching. | 800–950 °C | 48–60 HRC | 0.75–6 mm | 0.02–1 h | $$ Standard |
Carburizing diffuses carbon into low-carbon steel at austenitizing temperature, then quenches and tempers the enriched surface into a hard martensitic case. | 900–955 °C | 58–64 HRC | 0.5–2.5 mm | 8–40 h | $$$ Premium |
Gas nitriding diffuses nitrogen into finished ferrous parts below the transformation temperature, producing a hard compound layer and diffusion zone without quenching. | 495–565 °C | 58–67 HRC | 0.1–0.5 mm | 14–100 h | $$$$ High |
Ferritic nitrocarburizing diffuses nitrogen and carbon into ferrous surfaces below the transformation temperature. | 560–590 °C | 45–65 HRC | 0.05–0.8 mm | 4–12 h | $$$ Premium |
Carbonitriding diffuses both carbon and nitrogen into low-carbon steel in the austenitic range, then quenches and tempers the surface to martensite. | 820–900 °C | 52–62 HRC | 0.08–0.75 mm | 3–10 h | $$ Standard |
Ranges depend on the alloy and the specification called out. A dash means the treatment sets no target for that value.
Where case & surface hardening sits
Cycle temperature against hardness delivered across the heat-treatment library. Other families appear as faint dots. Click a dot to open its page.
Choosing between them? How to choose a heat treatment — best picks by what the part needs, the five things a drawing call-out must carry, and the questions engineers ask.