Ductility and brittleness at high temperatures
Damage and ductility in forming

Here, as in the rest of the article, we shall confine ourselves to the case of forming, leaving aside problems specific to creep.

In the high-temperature range, damage due to the presence of inclusions is generally limited by dynamic restoration or recrystallization mechanisms, which reduce stress concentrations and can even plug up microcavities already formed.

On the other hand, at low strain rates, encountered, for example, in the continuous casting process (slab bending) or in certain closed die-forging operations, damage is often observed at the grain boundaries. This phenomenon is linked to the notion of equicoherence temperature T_e. Below this temperature, plastic deformation of a polycrystalline aggregate takes place essentially within the grains. Above T_e, on the other hand, intergranular sliding is easier than grain deformation. As the equicohesion temperature...