4. Heat treatment incidents

4.1 Overheating

Overheating results in exaggerated coarsening of the austenite grains, which in turn generates large fracture grains after hardening by quenching.

It may be the result of :

• heating to too high a temperature;

• too long at austenitizing temperature;

• too long at too high a temperature;

• the use of steel insufficiently protected against grain growth (lack of Al addition, for example).

Furthermore, the correlative increase in hardenability can favor the formation of acicular structures as a result of the preferential germination and growth of a phase (ferrite for hypoeutectoid...