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Option 2 : A - 1, B - 3, C - 2, D - 4
Explanation:
Annealing:
- Annealing is heating of steel to austenite temperature and then cooling slowly in the furnace.
- Annealing results in the formation of ferrite, spheroidal cementite and coarse pearlite.
- All the phase constituents are relatively soft and therefore this is known as softening treatment and produces relatively lower hardness values while ductility increases.
- Purpose of annealing:
- to reduce hardness, relieve internal stress
- improves machinability
- it refines grain size.
Nitriding:
- Nitriding is a case of the hardening process in which nitrogen (Ammonia) instead of carbon is added to the surface of the steel.
- Nitriding heats the steel part to 482-621°C (900 -1,150°F) in an atmosphere of ammonia gas and dissociated ammonia.
- The time the part spends in this environment dictates the depth of the case.
- No quenching is done after nitriding.
Normalizing:
- Heat the steel from 30°C to 50°C above its upper critical temp, hold about fifteen minutes, and then allow to cool down in still air.
- The homogeneous structure provides a higher yield point, ultimate tensile strength, and impact strength with lower ductility to steel.
- The main purpose of normalizing is to refine grain size.
- Main objective:
- Refine grain size in metal, improve strength and hardness, reduce ductility
- Remove cold work stress.
- Remove dislocations due to hot working.
Martempering:
- In this martensite is formed and quenching is done in two medium
- First quenched in water to a temperature of 300 - 400°C and then quickly transferred to a less intensive medium like oil or air where they are held until they are completely cooled.
- The purpose of the second medium is to reduce internal stress associated with the austenite to martensite transformation.
- Used for the heat treatment of C-steel tools like taps, disc, milling cutters, etc. to improve hardness of the whole mass
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