Stainless and Nickel Alloy Welding

The general techniques and procedures for welding are similar for all stainless and nickel alloys. Individual alloys, or families of alloys, may require more restrictive procedures and processes, but the guidelines below form a solid foundation for joining these alloys by welding.

Proper Joint Design – If the joint is being made without filler metal, butting the edges together is preferred. Otherwise, the joint should be designed to allow a gap so that filler metal can properly mix with the base metal. In addition, heavier thicknesses should be beveled to insure full penetration and a proper ratio of filler to base metal.

GTAW or TIG – Gas tungsten arc welding using a tungsten electrode with our without filler metal. Filler wire is usually a bare, straight18” – 36” long wire.

GMAW or MIG – Gas metal arc welding where the filler metal is the electrode and is consumed. Filler metal is a bare solid wire usually on a spool of at least 25#.

SMAW – Shielded metal arc welding uses covered (stick) electrodes which create a slag to protect the weld during solidification. Inert gas coverage of the arc is not required.

SAW – Submerged arc welding is a high deposition rate process using a solid bare spooled wire with the arc protected by a recycling granular flux.

FCAW – Flux core arc welding uses a spooled hollow wire filled with a flux to protect the weld during solidification.  Used in conjunction with a shielding gas when welding most stainless or nickel alloys.

Clean, Sound Metal – Surface contamination such as paint, grease, oil or rust can result in weld defects or poor weld corrosion resistance.  Iron contamination from tools or handling can also affect weldability. If repairs are being made to material that has been in service, the condition of the material can influence weldability.  Common examples are stress corrosion or carburization.  A loss of mechanical properties due to thermal history during service can also influence weldability.

Proper Filler Material – Even when a filler metal that matches the base metal composition exists, consideration of the use of higher alloyed filler may be justified.  In some alloy systems, like the duplex or 6% Mo type materials, the suggested filler metal is more highly alloyed than the base metal to offset the effects of segregation during weld solidification.

Shielding Gas – Stainless steels and most nickel alloys oxidize very rapidly.  This is good for corrosion resistance, but the weld area must be protected from oxygen during welding.  Pure argon is used for GTAW and helium can be added to the gas mix to increase weld speeds. Argon is often used for GMAW.  Adding helium to the argon improves bead contour, while a small amount of CO2 (1/2% to no more than 2-1/2%) will stabilize the arc. Gas mixes with up to 25% CO2 may be used for flux core wires.  If the back side of the root pass is not accessible or will not be ground and re-welded from the opposite side, it should be protected from oxidation by purging with an inert gas or nitrogen.

 

Heat Input – Except for heavier sections of the martensitic or PH stainless steels, preheating is not desired and interpass temperatures should be held below 300⁰ F.  The heat input for austenitic and nickel alloys should be kept moderately low since these materials are sensitive to solidification cracking.  Stringer type beads should be used with minimal weaving.  Excessive heat input is also detrimental to duplex alloy welds, but welding these alloys also requires maintaining sufficient heat input to form enough austenite upon solidification.

More detailed welding information specific to particular alloys is available on our website or available through our metallurgical help desk.