Most stainless steels have good weldability if some key issues are understood and addressed, correct procedures are followed and expert advice is obtained if the organisation is inexperienced, says gases and welding products supplier Afrox manufacturing industries team applications development manager Arnold Meyer.
Speaking during a webinar hosted by Creamer Media on the Essentials of Stainless Steel, held on August 26, Meyer focused on three key issues in welding 304L and 316L austenitic stainless steel and 2205 duplex stainless steel.
Solidification cracking (or hot cracking) in the weld metal upon solidification can be experienced when welding stainless steel grades 304L and 316L .
Should this occur, the solution for 304L is to weld with 308L type electrodes and rods to ensure the composition of the weld metal will place it in the FA region of the Welding Research Council (WRC) 1992 diagram with and without dilution. For 316L, the solution is to weld with 316L type electrodes and rods with the composition of the weld metal in the FA region of the WRC 1992 diagram.
Pitting can also occur owing to carbon contamination from carbon steel when welding 304L and 316L . Meyer suggests physically separating carbon steel and stainless steel welding operations.
This is in addition to using dedicated stainless steel wire brushes and carbide free abrasives – grinding and sanding discs.
Another key issue faced when welding 304L and 316L is discolouration and scaling owing to high temperature oxidation of chromium.
Meyer says to use HP Argon as backing gas for open roots, especially in pipe welding.
Good-quality welding electrodes and shielding gas to protect the weld metal is also recommended and the weld should be cleaned, pickled and passivated afterwards.
When welding 2205, getting the phase balance right in the weld metal – 40% to 60% ferrite, balance austenite, can be an issue.
The solutions is to weld with 2209 type electrodes and rods, as 2209 has increased nickel content to stabilise the austenite phase for rapid cooling during welding.
Further, the heat input needs to be controlled. A higher heat input requires more austenite, while a lower heat input requires more ferrite.
The use of long arcs or long contact-tip-to-work-distances should also be avoided, says Meyer, adding that nitrogen contamination will strongly promote austenite formation.
Stainless steel grade 2205 can also be subject to pitting, owing to carbon contamination from carbon steel, and discolouration and scaling, owing to the high temperature oxidation of chromium, and the solutions there for is the same as that of austenitic steels.