Top two hits from a Google search using the term "17-4 PH data sheet".
17-4 is weldable, but you would need to re-solution heat treat prior to age treatment.
"The precipitation hardening class of stainless
steels is generally considered to be
weldable by the common fusion and resistance
techniques. Special consideration is
required to achieve optimum mechanical
properties by considering the best heattreated
conditions in which to weld and
which heat treatments should follow
welding. This particular alloy is the most
common member of the class and is generally
considered to have the best
weldability. When a weld filler is needed,
AWS E/ER 630 is most often specified.
AK Steel 17-4 PH Stainless Steel is well
known in reference literature and more
information can be obtained in this way."
Alloy 17-4PH can be welded by the following welding processes: SMAW, GTAW, PAW, and GMAW. SAW should not be used without preliminary testing (to check freedom of cracks and toughness of the weld metal).
Due to a ferrite delta primary type of solidification, the hot cracking risk of the weld metal or the HAZ is reduced.
Generally, no preheating must be done, and interpass temperature must be limited to 248°F (120°C). The better toughness is obtained in the weld after a complete heat treatment (solution annealing + precipitation hardening).
Adding to previous posts:
It is not advisable to weld 17-4PH in hardened condition ( H900 to H1025). Generally best condition to be welded is in the solution treated condition or over H1100 condition. Pre heating is not necessary but Post Weld Heat Treatment is necessary. Select the same aging cycle as it was in the pre-welded condition or it can be aged after welding in the solution annealed condition.
Welding 17-4PH in the hardened condition can be done but should be avoided in the H900-H1025 range. Everyone else is right, full strength (same a bulk material) requires solution HT then age. Often we weld in condition A and then age. Risk of SCC is lower than the as welded condition but higher than resolution HT + age method.
