The process of obtaining spherical grains of Fe₃C in steel in the process of annealing is known as _______. 

Concept:

Annealing: Heating the steel to austenite temperature + 50°C, held for some time period and cooled slowly in the furnace.

Characteristics:

• To reduce hardness
• To improve machinability
• To increase ductility
• To relieve internal stresses
• To refine grain size 

Spheroidizing:

• Heat the metal to slightly above the critical temperature, hold them at this temp for a period of time, and then letting them cool in the furnace.
• Spheroidizing produces a rounded or globular form of carbide so option 2 is correct.
• It is used for medium and high-carbon steel. It improves ductility, machinability , and formability.

Full annealing:

• Metal is heated above the upper critical temperature & held there until the temperature of the workpiece is uniform throughout, and finally cooling the workpiece at a slow controlled rate in a furnace so that the temperature of the surface and that of the centre of the workpiece is approximately the same.

Benefits of annealing are:

• relieve stresses
• increase softness, ductility and toughness
• Reduce hardness and brittleness
• produce a Coarse pearlite microstructure

Process annealing: 

• The metal is heated below the Lower critical temp. i.e. Recrystallization temp. and cooled in the furnace. Its main purpose is to relieve residual stresses of low carbon steel. 

Normalizing: 

• Heat the steel from 30°C to 50°C above its upper critical temp, held about fifteen minutes and then allowed to cool down in still air. The homogeneous structure provides a higher yield point, ultimate tensile strength and impact strength with lower ductility to steels.

Main objective:

• Mechanical properties of steels are better than those produced by annealing.
• Residual stresses are relieved only partly
• Fine grains are formed
• Strength and hardness is more