Study Mech

The case hardening process is used to harden the outer surface of the material, the inner surface of the material remains soft. hence this process is also called surface hardening. The type of case hardening process is as follows Carburizing Nitriding Cyaniding Carburizing In the carburizing process, specimens are heated beyond the upper critical temperature in sealed containers having an atmosphere of carbon (C). Heating is continued for 4 to 10 hours, depending upon the depth of penetration required. Hence, carbon diffuses into the surface layer. Nitriding The nitriding process is similar to carburizing, but instead of carbon (C), nitrogen (N ₂ ) is used as a hardening agent in nitriding. The nitriding process is carried out in the ammonia atmosphere. The nitriding process requires less temperature compared to carburizing but requires more heating time compared to carburizing. Cyaniding In the cyaniding process, sodium cyanide (NaCN) is used as a hardening agent. Hence both carbon (C...

Quenching also called Hardening, is a heat treatment process in which steel is heated up to austenite temperature (above it's critical temperature), hold for some time and then cooled in water, oil or molten salt (rapid cooling). Due to rapid cooling, it results very hard structure - martensite (hardest form of Steel). fig.- steel component quench in oil. Due to hardening process hardness of steel increases and bitterness also increases. (brittleness increases hence hardened Steel nay not directly use). Quenching is always follow by tempering process. Due to rapid cooling in hardening process metal shape shrink, internal residual stresses are setup. That's the reason why hardening is follow by tempering.

know the Heat Treatment...! Heat treatment is defined as the operations involving the heating and cooling of a metal or an alloy within a solid-state to obtain desire properties (physical or chemical) without change composition. The heat treatment process is carried out to change the grain size, modified the crystal structure of the material, and relieve the stress set up in the material after hot or cold working. Heat treatment also uses in many manufacturing processes, eg. glass working. The heat treatment process is performed in the furnace or oven with a controlling the environment of step-by-step heating and cooling within a specific period of time, apart from this the gases are used to control the furnace environment in some processes.  Fig.1 - Heat treatment process of gears Heat treatment consists of heating of metal near of above re-crystallization temperature of the material, hold for a particular time, and then finally cooling the metal in some medium which may be air, ...