  In modern accelerators, stringent requirements are placed on the materials
used for vacuum systems. Their physical and mechanical properties,
machinability, weldability and brazeability are key parameters. Adequate
strength, ductility, magnetic properties at room as well as low temperatures
are important factors for vacuum systems of accelerators working at cryogenic
temperatures. In addition, components undergoing baking or activation of
Non-Evaporable Getters (NEG) or directly exposed to the beam impose specific
choices of material grades for suitable outgassing and mechanical properties in
a large temperature range. Today, stainless steels are the dominant materials
of vacuum systems. The reasons for specific requirements in terms of
metallurgical processes are detailed for obtaining adequate purity, inclusion
cleanliness and fineness of the microstructure. In many cases these
requirements are crucial to guarantee the final leak tightness of the vacuum
components. Innovative manufacturing and material examination technologies are
also treated.
