Which surface hardening method uses nitrogen by heating with ammonia?

Which surface hardening method uses nitrogen by heating with ammonia?

• A. Nitriding
• B. Carburising
• C. Normalising
• D. Case hardening

Answer: (A)

Nitriding is the surface hardening method that uses nitrogen supplied from ammonia. Heating steel in an ammonia-containing atmosphere at moderate temperatures allows nitrogen to diffuse into the surface and form hard nitride compounds, yielding a very hard, wear-resistant layer with good fatigue life. This process operates at lower temperatures and with less distortion than carburising, which introduces carbon from a carbon-rich environment and is often followed by quenching. Normalising is a different heat-treatment approach that refines the grain by heating above critical temperature and air-cooling, not diffusion of alloying elements to the surface. Case hardening is a broader term for surface hardening, but when nitrogen is used from ammonia, the specific method is nitriding.

Nitriding is the surface hardening method that uses nitrogen supplied from ammonia. Heating steel in an ammonia-containing atmosphere at moderate temperatures allows nitrogen to diffuse into the surface and form hard nitride compounds, yielding a very hard, wear-resistant layer with good fatigue life. This process operates at lower temperatures and with less distortion than carburising, which introduces carbon from a carbon-rich environment and is often followed by quenching. Normalising is a different heat-treatment approach that refines the grain by heating above critical temperature and air-cooling, not diffusion of alloying elements to the surface. Case hardening is a broader term for surface hardening, but when nitrogen is used from ammonia, the specific method is nitriding.