Which one of the following property is imparted on steel by annealing?

Diffusion Annealing

• In this process, hypo-eutectoid, eutectoid, and hyper-eutectoid steel are heated uniformly and the component is held at a temperature between 1000 °C – 1200 °C and then cooled very slowly in the furnace in order to remove the heterogeneity in the composition of heavy castings.
• During this, a coarse grain structure produced.
• A homogenous structure appears.
• To increase material properties, it goes through full annealing after diffusion annealing.

Full Annealing

• Full annealing consists of heating the steel component to about 50 °C – 70 °C above the critical temperature, holding it for a sufficient length of time, and cooling the same in the furnace.  
• Adopted for steel casting and ingots.
• The coarse structure produced during solidification break down to a much smaller size.
• Machinability and ductility increases.
• Hardness is reduced.
• All structural imperfection gets removed.

Spherodise Annealing

• In this method heating can be done in three ways:
  • Prolonged heating just below the lower critical temperature followed by relatively slow cooling
  • Alternately heating and cooling the work-piece to just above and below the lower critical temperature.
  • Short heating at a high temperature followed by relatively slow cooling.
• Conversion of hard lamellar or network carbides of high-carbon steels into globular or spherical shapes.
• Improve machinability and ductility.

Process Annealing

• This process involves heating of steel to a temperature just below the lower critical temperature (723 °C) of steel.
• Usually, cold worked steel has high hardness and low ductility making it difficult to work.
• Deformed grains in cold working get reoriented.
• Hardness is lowered and ductility also increases.