Abstract

Precipítales present in three modifies HP steels after exposure at I 173K tur HHJÍJh were investigated using scanning and transmission electrón microscopy. Particular attention was paid to the (NbTi)C to G-phase (Ni16Nb6Si7) transformation. The influence of Ti in this transformation is described. The superior properties of the modified HP steel with NT and Ti compared with a single addition of Nb are explained on the bases of the amount of G-phase transformed during aging. It is shown, in this case, that the Ni16Nb6Si7  precipitation and that this silicide is a preferential site for creep damage occurrence.