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Material property-changing operation where martensite in the material is softened so that the hardness decreases slightly, without drastically reducing the amount of martensite.

Illustration of Annealing

The process

The material should be pretreated before processing for e.g. quenching to obtain the desired proportion of martensite in the material.

A: The material is heated to a temperature slightly below its lower critical transformation temperature.

B: The temperature is held for a certain time and results in slight change in microstructure and reduction of some internal stresses thus decreasing the hardness. The temperature controls how much of material’s hardness will be reduced and depends on the composition of the material.
The temperature should not be too high to prevent the martensite in the material from transforming into something softer.

C: The material is air cooled finally to room temperature.

The process also increases the corrosion resistance slightly.