The joining of steels and especially stainless steel is a totally different
process than diffusion bonding of pure materials.   First, stainless steel
is an alloy that is in a metastable thermodynamic condition.  Therefore,
when heated above the Ae1 or the Ae3 temperatures the crystal structure
changes.  Also, the solubility of all the alloying elements change in the
new crystal structure and a whole cascade of precipitates, intermetallics
and disorder phases appear.  Metallographically it is a beautiful thing to
see, but in the end the bond properties go to crap.  Homogenous welding of
stainless is done (stainless to stainless with no filler metal), high
temperature in an inert environment supplied by an electron beam, resistance
heating current or laser beam holds the two ends together long enough that
heating melts a volume of material and it solidifies.  Solidification is
rapid and total energy input low to avoid changing the properties of
adjacent base material too much.  However, you will always have a
solidification microstructure.  Second, what in the world are you making
that you want to diffusion bond stainless steel?  Are you trying to make a
stainless steel lined mems reactor?  Cool, but if you need a diffusion bond
process to make your mems structure maybe look at single phase materials for
your lining, for example nickel, tantalum, zirconium or copper are good
materials that offer corrosion resistance.

Rob