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Annealing process in brief

Short answer

Annealing involves heating steel 30–50°C above its upper critical temperature, soaking, and then cooling very slowly in the furnace. This softens the steel, improves ductility and machinability, relieves internal stresses, and produces a uniform coarse pearlite and ferrite structure.

Describe annealing.

Annealing is a heat treatment in which steel is heated to about 30-50 C above its upper critical temperature (the critical range is 723-910 C, depending on the carbon content), held (soaked) there for a sufficient time, and then cooled very slowly, usually in the furnace itself.

Purposes

  • Softens the steel and improves ductility and machinability.
  • Relieves internal stresses and refines the grain.
  • Gives a uniform structure (coarse pearlite and ferrite).
 Temp
  ^      _______  <- soak (above upper
  |     /       \    critical temp)
  |    /         \
  |   /           \___ slow furnace
  |  /                  cooling
  +-----------------------------> Time

Types: full annealing, process annealing (below the lower critical temperature), stress-relief annealing, spheroidising and isothermal annealing.

✓ Answer checked by Claude Opus 5.5 (high effort)

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