Question: Discuss the process of cyaniding and nitriding in detail

Subject Material Technology

Topic Heat Treatment Processes

Difficulty Level High

mt(63) • 695 views
modified 12 months ago  • written 12 months ago by gravatar for Atharv Inamdar Atharv Inamdar650


  1. Cyaniding is a case-hardening process that is fast and efficient; it is mainly used on low-carbon steels. The part is heated to 871-954 °C in a bath of sodium cyanide and then is quenched and rinsed, in water or oil, to remove any residual cyanide. Reactions are as follows:

    2NaCN + O2 → 2NaCNO

    2NaCNO + O2 → Na2CO3 +CO + N2

    2CO → CO2 + C

  2. This process produces a thin, hard shell (between 0.25 - 0.75 mm, 0.01 and 0.03 inches) that is harder than the one produced by carburizing, and can be completed in 20 to 30 minutes compared to several hours so the parts have less opportunity to become distorted.

  3. It is typically used on small parts such as bolts, nuts, screws and small gears. The major drawback of cyaniding is that cyanide salts are poisonous.


  1. Nitriding heats the steel part to 482–621 °C in an atmosphere of ammonia gas and dissociated ammonia.

  2. The time the part spends in this environment dictates the depth of the case. The hardness is achieved by the formation of nitrides.

  3. Nitride forming elements must be present for this method to work; these elements include chromium, molybdenum, and aluminium.

  4. The advantage of this process is that it causes little distortion, so the part can be case-hardened after being quenched, tempered and machined. No quenching is done after nitriding

written 12 months ago by gravatar for Atharv Inamdar Atharv Inamdar650
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