Recrystallisation behaviour of Fe base ODS alloys

peer reviewedDevelopments 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

Silicon carbide fibers and particles reinforced aluminium alloys produced by stir casting

peer reviewedThis study is concerned with the solidification processing of aluminium alloys reinforced by short fibers and particles of SiC. The reinforcements have been introduced and dispersed into aluminium alloys melts by the vortex method. The commercial alloys (2024, 319) containing elements such as Cu or Mg chosen to provide adequate wetting have been used and compared. The samples have been examined both in the as-cast or as-rolled and heat treated conditions (T6). Examinations of the mechanical properties by statistical analyses show that both SiC chopped fibers and particles increase significantly the mechanical properties of the alloys especially at high temperature

Study of composite aluminium alloys produced by stir casting

peer reviewedSolidification processing of aluminium alloys reinforced by short fibers and particles of SIC was studied. The reinforcements were introduced and dispersed into aluminium alloys melts by the vortex method. The paper describes the fabrication process used to provide adequate bonding between reinforcemments and liquid matrix. The commercial alloys (2024, 319) containing element such as Cu or Mg chosen to provide adequate wetting were used and compared. The samples were used in the as-cast state or after hot rolling. The samples were examined both in the as-cast or as-rolled and heat treated conditions (T6). The specimens were submitted to microstructural examinations (optical and SEM) density measurements and mechanical property evaluation. Examinations of the results by statistical analyses show that both SIM chopped fibers and particles increase significantly the mechanical properties of the alloys especially at high temperature. However it is shown that the behaviour of the different alloys is strongly different. The effect reinforcement depends on the nature of the alloy and can be related to microstructural features

Review of hot shortness problems in copper-containing steel

The problem of hot shortness is first briefly discussed in terms of the recycling of scraps and the occurrence of various residual elements in steel. The phenomenon is then defined and described as a function of the factors influencing its different stages : copper solubility in austenite, copper phase melting point, wettability of the liquid copper rich phase, oxidation, furnace atmosphere, occlusion and diffusion. The effect on these phenomena of other residual or alloying elements is discussed. The paper concludes with the different ways to minimize the hot shortness problems and with hints on the more efficient use of copper containing scraps

Mechanical properties and recrystallisation behaviour of Fe base ODS alloys

peer reviewedDevelopments in higher temperature exchangers and other applications require high strength as well as oxidation resistance at very high temperature. In order to meet such requirements, Dour Metal has developed ODM new range of oxide dispersion strengthened (ODS) iron base alloys realised by powder mechanical alloying. Compositional and thermomechanical manipulations can be used to develop the structure enabling the service temperature to be increased up to about 1200°C. An optimization of the structure is required to obtain the best high temperature creep resistance. This consist in minimizing the grain densities and the misorientation between adjoining grains. The paper will discuss some results on evolution of the texture during different thermomechanical treatments on ODS Fe base tubes. Typical rupture strength will be presented for temperature ranging from 900 to 1100°C. The emphasis will be given to alloy ODM 751 which most recent work has been performed