5. Main incidents

5.1 Overheating

This phenomenon is caused by heating to too high a temperature, or holding at the quenching temperature for too long. It results in a significant re-solution of carbides and a coarsening of the austenitic structure. This treatment may be aggravated by the onset of melting at the grain boundaries, in which case the steel is burnt, resulting in considerable embrittlement. It can be easily detected by the following means:

• observation of the fracture grain: overheated zones can be distinguished by the presence of shiny facets...