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