A treatment in which steel is held in a nitrogen-bearing atmosphere below the A₁ transformation temperature to form hard nitrides in the surface layer. No quenching is needed and distortion is small.
Japanese name: 窒化処理
Nitriding appears in 3 practice questions across 2 topics, including Surface treatment and tribology, Fracture mechanics and fatigue.
Answer: C. Nitrogen diffuses in at about 500–570 °C, in the ferrite region below A₁, and fine nitrides harden the surface without quenching, so distortion is small
Nitriding introduces nitrogen from the surface, for example by decomposing ammonia, and is carried out at about 500–570 °C, below the A₁ transformation temperature (727 °C). Nitrogen diffuses through ferrite and combines with Al, Cr, Mo, V and similar elements to form fine nitrides, and the surface reaches hardnesses above 1000 HV. With no phase transformation or quenching, dimensional change and distortion are small, so parts can be treated after finish machining. A compound layer of iron nitrides (the white layer) forms at the outermost surface, with a diffusion layer beneath it. In carbon steels without alloying elements, nitrogen may diffuse deeper, but few hard fine nitrides form, so the hardness does not rise much. On the other hand, the case is about 0.1–0.5 mm, thinner than with carburizing, and treatment often takes several tens of hours, which are drawbacks.
Nitriding introduces nitrogen from the surface, for example by decomposing ammonia, and is carried out at about 500–570 °C, below the A₁ transformation temperature (727 °C).
Which statement about nitriding, such as gas nitriding, app…Carburizing, nitriding and induction hardening also harden the surface layer and introduce compressive residual stress, so they raise fatigue strength.
Which surface treatment can be expected to improve the fati…The solubility limit of carbon in ferrite is at most about 0.02%, and hardening without quenching in the low-temperature ferrite region is a feature of nitriding.
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