The need for alternate energy sources has led to the develop- ment of
prototype fusion and MHD reactors. Both possible energy systems in
current designs usually require the use of magnetic fields for plasma
confinement and concentration. For the creation and maintenance of large
5 to 15 tesla magnetic fields, supercon- ducting magnets appear more
economical. But the high magnetic fields create large forces, and the
complexities of the conceptual reactors create severe space
restrictions. The combination of re- quirements, plus the desire to keep
construction costs at a mini- mum, has created a need for stronger
structural alloys for service at liquid helium temperature (4 K). The
complexity of the required structures requires that these alloys be
weldable. Furthermore, since the plasma is influenced by magnetic fields
and since magnet- ic forces from the use of ferromagnetic materials in
many configur- ations may be additive, the best structural alloy for
most applica- tions should be nonmagnetic. These requirements have led
to consideration of higher strength austenitic steels. Strength
increases at low temperatures are achieved by the addition of nitrogen.
The stability of the austenitic structure is retained by adding
manganese instead of nickel, which is more expensive. Research to
develop these higher strength austenitic steels is in process, primarily
in Japan and the United States.