Heat treatment

Heat treatment refers to a permanent change in structure and properties caused by the action of heat.

The most important processes are: Annealing, hardening, quenching and tempering, nitriding and hardening of the edge zone.

Annealing is the heat treatment of a workpiece at a fixed temperature, talking into account a certain holding period and subsequent slow cooling.

A distinction is made between the following annealing processes:

  • Normal annealing is mainly carried out after previous hot forming of components. The normalizing process is intended to achieve a fine-grained ferrite-pearlite microstructure. In this way, coarse-grained and uneven microstructures can be transformed into new, homogeneous and fine structures. Annealing takes place at 750°C to 950°C, depending on the C content.
  • Stress relief annealing serves to reduce residual stresses in the workpiece as a result of cold forming, structural transformation, thermal stress or machining. Stress relief annealing is usually performed between 550°C and 650°C with sufficiently long holding times and subsequent very slow cooling. There are no significant changes in the microstructure or mechanical properties.
  • Soft annealing means annealing at a temperature of 680°C zo 750°C followed by slow cooling to achieve the softest possible condition. This is to produce granular perlite, a soft microstructure which provides the best workability in non-cutting forming and machining.
  • Recrystallization annealing is used when a structure distorted by cold deformation is to be returned to an undistorted structural state.
  • Diffusion annealing is a long term annealing at 1050°C to 1250°C. It is used to reduce the differences in concentration that occur when casting large cast iron workpieces.


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