What is annealing of steel: a process in which steel is heated, kept warm and then cooled slowly to obtain a nearly balanced structure.

1.Complete annealing

Process: Heating above Ac3 30-50℃→insulation→cooling with furnace to below 500℃→air cooling to room temperature.

Purpose: To refine the grains, uniformize the structure, improve plastic toughness, eliminate internal stress, and facilitate mechanical processing.

2.Isothermal annealing

Process: Heating above Ac3 → Insulation → Quick cooling to pearlite transformation temperature → Isothermal stay → Transform to P → Air cooling after release;

Purpose: Same as above. But the time is short, easy to control, and deoxidation and decarburization are small. (Applicable to alloy steel and large carbon steel parts with relatively stable supercooling A).

3.Spheroidizing annealing

Concept: It is a process that spheroidizes cementite in steel.

Object: eutectoid steel and hypereutectoid steel

Craftsmanship:

(1) Isothermal spheroidizing annealing: heating to 20-30 degrees above Ac1 → insulation → rapid cooling to 20 degrees below Ar1 → isothermal → cooling with the furnace to about 600 degrees → air cooling after leaving the furnace.

(2) Ordinary spheroidizing annealing is heated to 20-30 degrees above Ac1 → heat preservation → very slowly cooled to about 600 degrees → air-cooled out of the furnace. (Long cycle, low efficiency, not applicable).

Purpose: to reduce hardness, improve plasticity and toughness, and facilitate cutting.

Mechanism: Turn flake or reticular cementite into granular (spherical) shape

Note: During annealing and heating, the structure is not completely transformed, so it is also called incomplete annealing.

4.Stress relief annealing

Process: Heating to a certain temperature below Ac1 (500-650 degrees) → keeping warm → slowly cooling to room temperature.

Purpose: Eliminate residual internal stress in castings, forgings, weldings, etc., and stabilize workpiece dimensions.