ramesh 0010

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Constitution of Alloys 65 Disadoantages : (i) Requires high power. (ii) Only suitable for ductile materials. (iii) Requires intermediate annealing for large deformation. 2.8.2 Hot Working : Hot working is defined as a plastic deformation that is carried out at a temperatureabove recrystallisation temperature where recovery process occur simultaneously during the defor- mation. Due to hot working grainsare re?ined which fesult in an increase in ductility and roughness. Aduantagesand disaduantages of hot working : Som.e of the advantages and disadvantages of hot working of metals are given below : Adoantages : (i) Extensive deformation is possible because of increased plasticity. (ii) Intermediate annealingis not requiredbecause of no strain hardenirig. (iii) Power requirements for the process are less. (iv) Mechanical properties are improved as a resultof grain refinement. (v) The porosity is largely eliminated and the impurities are uniformly distributed throughout the volume. Dlsqduantages : (i) Tooling cost is high. (ii) Surface finish is usually poor, because of the scale formation on the surface'of the metal. (iii) Close dimensional tolerance cannot be maintained. kln Working : Fiastic deformation carriredout at a temperature below recrystallisation and above room nrnperature is called warm working. When compared to hot working it offers the advantage d improved dimensionalcontrol and higher quality surfaces; and comparedto cold working il offers advantagesof extensivedeformation without intermediate annealing. The temperature ranges for cold, warm and hot working of metals in terms of th'eir melting point (T,n) are given below : Cold working, T Warm working, T Hot working, T <0.37 m - 0.3 to 0.5 T m >0.67 m hapter-2)

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Page 1: Ramesh 0010

Constitution of Alloys 6 5Disadoantages :

( i ) Requires high power.

( i i ) Only sui table for duct i le mater ia ls.

( i i i ) Requires intermediate anneal ing for large deformat ion.

2.8.2 Hot Working :

Hot working is defined as a plastic deformation that is carried out at a temperature aboverecrystallisation temperature where recovery process occur simultaneously during the defor-mation. Due to hot working grains are re?ined which fesult in an increase in ductility androughness.

Aduantages and disaduantages of hot working :

Som.e of the advantages and disadvantages of hot working of metals are given below :

Adoantages :

(i) Extensive deformation is possible because of increased plasticity.

(ii) Intermediate annealing is not required because of no strain hardenirig.

(ii i) Power requirements for the process are less.

(iv) Mechanical properties are improved as a result of grain refinement.

(v) The porosity is largely eliminated and the impurities are uniformly distributedthroughout the volume.

Dlsqduantages :

(i) Tooling cost is high.

(ii) Surface finish is usually poor, because of the scale formation on the surface'ofthe metal.

(ii i) Close dimensional tolerance cannot be maintained.

kln Working :

Fiastic deformation carrired out at a temperature below recrystallisation and above roomnrnperature is called warm working. When compared to hot working it offers the advantaged improved dimensional control and higher quality surfaces; and compared to cold workingil offers advantages of extensive deformation without intermediate annealing.

The temperature ranges for cold, warm and hot working of metals in terms of th'eirmelting point (T,n) are given below :

Cold working, T

Warm working, T

Hot working, T

< 0 . 3 7m

- 0 .3 to 0 .5 Tm

> 0 . 6 7m

hapter-2)