Heat treatment incidents
Heat treatments in the mass of steels. Part 2

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...