Which Process Reaches ~1000 HV Surface Hardness: Nitriding vs Carburizing

If you are asking "which process reaches ~1000 HV surface hardness", the usual answer is the nitriding and nitrocarburizing family, which diffuses nitrogen into the surface to form a very hard layer — around 900–1100 HV in suitably alloyed steels.

Note this is reported in HV (Vickers), not HRC, because the hard layer is thin enough that an HRC indenter punches through. It is measured on a cross-section at low load (e.g. HV0.3, HV0.5) per ISO 6507.

Unlike ordinary hardening, which relies on martensite, nitriding works at low temperature (~500–570°C): nitrogen diffuses in and combines with alloying elements such as chromium, aluminium, molybdenum and vanadium to form fine nitride precipitates throughout the surface. These block dislocation movement and make the surface very hard.

The outermost surface may form a compound layer (white layer) of iron nitrides (ε and γ′) that is hard and resists scuffing, with a diffusion zone beneath that raises hardness and fatigue strength.

Dedicated nitriding steels (aluminium-bearing grades like Nitralloy, or certain tool steels) reach the top of the range, ~1100–1200 HV; ordinary low-alloy steels sit lower.

Carburizing adds carbon at ~850–950°C then quenches to form martensite, giving a ~58–63 HRC surface (about 700–800 HV) and a case depth (CHD) that can run ~0.3–2 mm — good for high contact loads.

Nitriding gives a "harder" surface (~900–1100 HV) but a thinner case, at low temperature and without quenching, so distortion is very low — ideal for high-precision parts.

As a rule of thumb: maximum surface hardness with minimal distortion → nitriding; deep case for high contact/impact load → carburizing.

The ultra-hard nitride layer is usually thin (NHD typically ~0.1–0.6 mm). That is excellent for wear, scuffing resistance and surface fatigue, but gives limited sub-surface "support" for contact pressure.

Under high Hertzian contact, a too-thin case can collapse below the surface (case crushing); there, the deeper case from carburizing is usually the better fit. The choice depends on the actual loading at the surface, not the hardness number alone.

Depth is measured per ISO 18203, with NHD taken to core hardness + 50 HV. State the reference hardness and load when specifying.

For information: V.S. Heat Treatment provides case hardening by carburizing and carbonitriding on a mesh-belt line. We do not run a dedicated nitriding line, so a true nitrided ~1000 HV surface is a separate, specialised gas/plasma nitriding process.

For high-count small parts, carbonitriding is a strong option — it adds both carbon and nitrogen at ~800–870°C, often giving a harder, more wear-resistant case than plain carburizing, well suited to screws, pins and small parts that need a hard surface at controlled cost.

Whichever process is chosen, define the target surface hardness (HV) and case depth clearly, then confirm with cross-section micro-hardness and case-depth measurement per ISO 18203/ISO 6507. The team can advise on process selection and test points to match the function.