Alloy 17-4 PH is a Precipitation Hardening (PH) stainless steel. This alloy combines strength, corrosion resistance and good fabrication.

It consists of max. 0.07% C, 1% Mn, 1% Si, 15.5-17.5% Cr, 3.0-5.0% Ni, 3.0-5.0% Cu, 0.15-0.45% Cb+Ta.

Precipitation harding is essentially a method of increasing hardness and strength, accomplished by a three-step heat treatment consisting of solution treatment, rapid cooling and controlled reheating (aging).

There are 3 classes of PH grades : martensitic, austenitic and semiaustenitic. Alloy 17-4 PH is a martensitic grade, wich means they have a martensitic structure.

However, the weldability of this alloy is excellent. It is not crack sensitive (low carbon content) or susceptible to hot cracking associated with other copper-bearing stainless steels. The most outstanding property : ability to withstand welding without preheating to prevent cracks and excessive hardness

Any of the arc and resistance welding processes can be used. But, the weld should not be subjected to high levels of stress from severely restrained joint. Weldment design should be given the same attention required for any high strength alloy steel to avoid concentration of residual stress.

Fillerless fusion welds are possible with GTAW.
Welding filler material : W17-4PH electrodes/fillers. When weld deposit is not required to have an equivalent strength level to that of the base material, type 308L stainless steel filler can be used.

If 17-4 PH is welded to carbon or low alloy steel it is necassary to minimize dilution by appropriate welding technique (no weaving) to avoid hot cracks due to carbon content.

Hope this helps ...