Nitriding in Heat Treatment of Metals :

Nitriding is a process of producing hard surface layer on alloy steels only. Nitriding consists essentially of heating the steel in an atmosphere of ammonia gas at temperature of 500*C to 650*C without further heat treatment. The ammonia is dissociated and the nascent nitrogen combines with elements in the steel to form nitrides. These Nitrides give extreme hardness to the surface. A hard surface layer usually from 0.2 to 0.4 mm in depth is produced in 50 hours.

Nitriding is the last operation after shaping and heat treatment process.

Thus after forging, the sequence of operations is :

a) Oil hardening at 850*C to 900*C,

b) Tempering at 600*C to 650*C.

c) Rough machining ,

d) Stabilizing ( to remove internal stresses) at 525 *C to 550*C

e) Final Machining and ultimately,

f) Nitriding.

Nitriding is used on many automotive, airplane, and diesel engine wearing parts, as well as on numerous miscellaneous parts such as pump shafts, gauges, drawing dies, gears, clutches, and mandrels. Its use is limited by the expense necessary for the treatment and the comparatively this case obatined.

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Mechinopedia For Mechanical Engineers

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