Need more info really, or at least someone like TechnicAl will. If it has been cold worked or is a repair then may need annealing or some other pre weld heat treatment for example. What's happening to it post weld?
ER630 is the usual suspect, 17-7ph sometimes recommended but will be hard to find AFAIK. On the other hand if properties of the weld aren't too critical and it isn't having any PWHT 308L and some other wires are usuable i.e. not particually tricky to physically weld but depends what is desired/needed in the way of properties. Presumably they're fairly important or a simpler alloy would be used?
i agree with hotrodder. You will need to take advice from someone who makes this sort of alloy, Metrode or Bohler are the main suppliers.
There are special procedures to follow but really if you are welding this you need to be informed by whoever gave you the job. There needs to be a welding procedure and tests etc.
17/4 PH is Precipitation Hardening which means it hardens if you allow to slow cool, if you quench it you soften it.....so its the opposite to everything else (just about)