sciroccos1111,
I recommend using US parent material equivalents when posting on this forum.
That is, ASTM A 405 Grade P24, instead of the European designation 14MoV6-3.
This might inspire the AWS forum experts to maybe rather chime in - which surely will happen soon.
Also, I strongly assume that you may have an approved welding procedure available before pell-mell starting to weld.

Certainly you're right saying that this material, employed decades ago, is "difficult" to weld.
As a result from long-term service, however, repairs may become likely at present.

Achieving creep resistance through mainly V-carbide precipitation, heat treatment in general may be assessed fundamental; e.g. when replacing a piece of pipe within some existent operating system. That is, when to achieve homogeneous carbide distribution between replaced parent- weld- and existent parent material. The former; i.e. the genuine parent metal is certainly unpredictable in this respect, even due to its long-term use. Hence, PWHT is crucial, since the whole joint carbide precipitation has to match for providing similar behaviour.

Literature states PWHT temperatures of ~ 700°C recommended for such cases.

For any other 690°C ≤ t ≤ 720°C is known to me being employed.
The lower limit has to be considered resulting in somewhat limited toughness. In general A_c_1 should not be exceeded since leading to long-term creep resistance degradation.
Using baked basic coated consumables low hydrogen annealing is – usually – not required.

Anyway, repair welding of this parent metal and achieving guarenteed long-term creep resistance values may remain a truly intricate task at all.

Maybe this can prove helpful:
http://ommi.co.uk/PDF/Articles/62.pdf

EDIT:
Perhaps this can help as well: http://upetd.up.ac.za/thesis/submitted/etd-05042005-134949/unrestricted/00dissertation.pdf

Hi sciroccos1111

When you mention "hydrogenation", I am assuming that you are referring to hydrogen bake-out. (Also called de-gassing.) Please correct me if I am wrong.

Hydrogen bake-out is typically done under the following conditions:

1) The service conditions of a component, that needs repair, has introduced hydrogen into the metal. - The hydrogen bake-out operation under these circumstances would be done before starting any repair welding.
2) The welding operation itself has introduced hydrogen into the weld metal and adjacent HAZ. - The hydrogen bake-out operation under this case would be done after welding, but before allowing the welded area to cool down to ambient temperatures.

As you can see, in neither of these cases would it make sense to perform the hydrogen bake-out just before PWHT, after the component has cooled to ambient temperatures, as the PWHT operation itself would act as a hydrogen bake-out.

These materials are typically welded as follows:

1) Apply pre-heat.
2) Weld, always maintaining pre-heat.
3) Allow to cool to a temperature low enough to allow the martensite transformation to complete, but not low enough to allow hydrogen cracking to take place. (Typically 150degC.)
4) Perform PWHT without allowing temperature to go down to ambient.

I hope that helps.

Regards
Niekie