Soldering Nichrome wire to Stainless steel and steel to PCB
Nichrome is very refractory- it melts at around 1400°C- so that's not a problem. 

Both stainless steel and Nichrome have oxide layers that render them impossible to soft solder. It's possible to silver solder (braze) them with high temperatures (eg. a propane torch), silver solder and brazing flux but that's not a lot of use if you want to connect to a PCB since the stainless steel is not soft solderable (the silver solder itself is soft solderable, if I recall correctly). 

Pressure contact is one possibility (a terminal strip or a threaded stud) or you could spot weld or silver solder the Nichrome wire to a copper wire that could then be soft soldered.