Which materials require fluxes to be welded?

Which materials require fluxes to be welded?

• A. Mild steel and low alloy steel
• B. Aluminum and magnesium
• C. Copper and brass
• D. Cast iron and stainless steel

Answer: (D)

Flux is used in welding to clean the metal surface and shield the weld from air, especially when the base material forms oxide layers or has a metallurgy that’s hard to weld. Cast iron and stainless steel fall into that category. Cast iron oxidizes and contains carbon and graphite in ways that can make the weld brittle or porous unless the slag and deoxidizers in flux are present to protect and stabilize the weld zone. Stainless steel also forms a very reactive chromium oxide layer, and using a flux-equipped filler or flux in the process helps remove impurities, deoxidize the weld pool, and maintain the proper metallurgy so the joint is sound. Other common welding metals are typically welded with shielding gas or with fillers that don’t require the extra flux for protection, so flux isn’t routinely needed in those cases.

Flux is used in welding to clean the metal surface and shield the weld from air, especially when the base material forms oxide layers or has a metallurgy that’s hard to weld. Cast iron and stainless steel fall into that category. Cast iron oxidizes and contains carbon and graphite in ways that can make the weld brittle or porous unless the slag and deoxidizers in flux are present to protect and stabilize the weld zone. Stainless steel also forms a very reactive chromium oxide layer, and using a flux-equipped filler or flux in the process helps remove impurities, deoxidize the weld pool, and maintain the proper metallurgy so the joint is sound.

Other common welding metals are typically welded with shielding gas or with fillers that don’t require the extra flux for protection, so flux isn’t routinely needed in those cases.