Recrystallisation behaviour of Fe base ODS alloys

Developments in higher temperature exchangers and other applications require high strength as well as oxidation resistance. In order to meet such requirements, Dour Metal has developed the 0DM new range of oxide dispersion strengthened (ODS) iron based alloy. Compositional and thermomechanical manipulations can be used to develop the structure enabling (be service temperature to be increased up W about 1200°C.
In both Ni and Fe base ODS materials, an optimization of the structure is required to obtain the best high temperature creep resistance. This consists in minimizing the grain boundaries density and misorientation between adjoining grains.
ODS Fe base alloys and Ni base alloys differ as follows:
- for alloys with high stacking fault energy (as ferritic steel) the phenomenon involved during hot deformation is dynamic recovery
- for alloys with low stacking energy (as Ni alloys and austenilic steels) the phenomenon is dynamic recrystallization.
The texture obtained during recovery is weIl marked and leads to 10w angle boundaries. A static treatment in bot furnace is then enough to develop the secondary dynamic recrystallization.
Dynamic recrystallization leads to randomly oriented grains with high angle boundaries. A secondary dynamic recrystallization is then more difficult and oriented recrystallization leading to an oriented texture must be favoured by creating a thermal gradient during the treatment.
The paper discusses some results on (lie evolution of the texture during treatments on ODS Fe base alloy tubes. It is pointed out that to obtain the temperature, it is important to control the thermomechanical treatments from recrystallization treatment.