GROUP MEMBERS

Muhammad Kamran Sadiq

Muhammad Ismail

Muhammad Kamran

Waqar Rafiq

CASE HARDENING

CASE HARDENING OR SURFACE HARDENING 

Case hardening or surface hardening is the process of hardening the surface of a metal object while allowing the metal deeper underneath to remain soft, thus forming a thin layer of harder metal (called the "case") at the surface.

For steel or iron with low carbon content, which has poor to no hardenability of its own, the case hardening process involves infusing additional carbon into the case.

Case hardening can provide a part that will not fracture (because of the soft core that can absorb stresses without cracking) but also provides adequate wear resistance on the surface.

SHACKLE OF A LOCK

Flame and induction hardening: Flame or induction hardening are processes in which the surface of

the steel is heated to high temperatures (by direct application of a flame, or by induction heating) then cooled rapidly, generally using water; this creates a "case" of martensite on the surface.

 A carbon content of 0.3–0.6 wt% C is needed for this type of hardening.

Applications:

MECHANICAL GEARS

CARBURIZING

Carburizing is a process used to case harden steel with a carbon content.

Carbon content is between 0.1 and 0.3 wt% C.

Steel is introduced to a carbon rich environment and elevated temperatures for a certain amount of time, and then quenched so that the carbon is locked in the structure

It is a diffusion-controlled process, so the longer the steel is held in the carbon-rich environment the greater the carbon penetration will be and the higher the carbon content.

Only a portion of a part can also be carburized either by protecting the rest by a process such as copper plating, or by applying a carburizing medium to only a section of the part.

TYPES OF CARBURIZING

On the basis of carbon source, there are three types of CARBURIZING

1. Pack Carburizing:

If carbon source is a Solid the process is called Pack Carburizing. Packing low carbon steel parts with a carbonaceous material and heating for some time diffuses carbon into the outer layers. 2. Liquid Carburizing:

If carbon source is a Liquid then Part is placed in a bath of a molten carbon-containing material, often a metal cyanide 3. Gas Carburizing:

If carbon source is a Gas the process is called Gas Carburizing. Gas carburizing involves placing the parts in a furnace maintained with a methane-rich interior.

NITRIDING 

Nitriding heats the steel part to 482–621 °C (900–1150 °F) in an atmosphere of ammonia gas and dissociated ammonia.

The hardness is achieved by the formation of nitrides.Nitride forming elements include chromium, molybdenum,

and aluminium.The advantage of this process is that it causes little

distortion, so the part can be case hardened after being quenched, tempered and machined.

APPLICATIONS OF NITRIDING

CrankshaftCam follower Camshaft

InjectorsDie casting tools Extrusion Dies

CYANIDING

The part is heated to 871-954 °C (1600-1750 °F) in a bath of sodium cyanide and then is quenched and rinsed, in water or oil, to remove any residual cyanide.

2NaCN + O2 → 2NaCNO

2NaCNO + O2 → Na2CO3 +CO + N2

2CO → CO2 + C

Cyaniding 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.

Parts have less opportunity to distort as the process completes in 20-30 minutes.

Cyanide salts are poisonous which is it’s big drawback

NUTS BOLTS AND SCREWS

APPLICATIONS OF CYANIDING It is typically used on small parts.

Following parts can be case hardened by cyaniding process

SMALL GEARS

CARBONITRIDING

Carbonitriding is a metallurgical surface modification technique that is used to increase the surface hardness of a metal, thereby reducing wear.

If the part is to be quenched, it is heated to 775–885 °C (1427–1625 °F); if not, then the part is heated to 649–788 °C (1200–1450 °F).

Nitrogen is adsorbed at the surface and diffuses into the workpiece along with carbon.

Atoms of carbon and nitrogen diffused interstitially into the metal, create barriers to slip, increasing the hardness and modulus near the surface.

APPLICATIONS OF CASE HARDENING

Engine Camshaft Rifle Bolt Firing Pins

Self Driving screws Single Action Revolver