How to weld stainless steel
Stainless steels can be readily welded, as long as a suitable welding procedure specification (WPS) is defined and followed. The WPS is a document that guides welders to accepted procedures for preparation, weld conditions and filler metals, to achieve consistent welds. The specification is typically validated by initially undertaking a series of test welds, with samples subject to microstructural, mechanical and corrosion testing.
Given the variety of stainless steels, there are a large number of welding procedure specifications in existence, often company-specific reflecting their in-house processes, the part geometry and end use. Stainless steels can be affected by the formation of deleterious phases when exposed to elevated temperatures.
Generally speaking, austenitic stainless steels are relatively straightforward to weld, whereas ferritic stainless steels are more challenging. Duplex and super duplex stainless steels are somewhere in between – the harmful sigma phase can form if the part is exposed to elevated temperatures, resulting in a dramatic loss of impact strength and corrosion resistance in the weld and heat affected zone (HAZ) either side. To avoid elevated temperatures during welding, the weld heat input and inter-pass temperature should be moderated. A guide to the welding of Ferralium super duplex stainless steel is available here.
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