Normalising and Annealing

Normalising becomes necessary in case of forged tools. Forging induces undesirable residual stresses, coarse grains and non-uniform structure. These defects are removed by normalising treatment. The normalised tools are machined to exact dimensions. Such machining increases the hardness because of strain hardening. The intermediate annealing from just below A1 temperature is applied upon the tool to remove the effects of strain hardening.

The tools steels have lower thermal conductivity and if the tool is heated at a faster rate distortion and cracking may occur. To avoid such distortion and cracking the tool before any treatment is preheated slowly to temperature between 600 to 800oC. The tool is held at the preheat temperature sufficiently long to allow whole body to come to uniform temperature and then heat to required temperature for any treatment.