Join stainless by electric arc welding with a stainless filler rod and low heat input, because heat held near the weld lets chromium carbides form beside it and the steel there loses its corrosion resistance. Forge welding at 1,100 °C with borax flux is described as possible but difficult, and nothing in this wiki shows it working, so treat it as unproven and use brazing, riveting or a cast part instead where you can.
Part of Stainless Steel Production
Joining stainless steel by arc welding, forge welding or alternatives, and keeping the heat-affected zone corrosion-resistant.
The Weld Zone Is Where Stainless Fails
The carrier gives two routes. Forge welding: heat to 1,100 °C, flux with borax and strike fast, noting that the chromium oxide layer resists welding and the flux must dissolve it. Electric arc welding: much easier, with a stainless filler rod and low heat input to limit carbide formation in the heat-affected zone.
The reason for the low heat is Carbon Control. Metal held in the carbide-forming range beside the weld can form chromium carbides, locking up chromium and leaving a strip beside the weld that rusts or corrodes even though the weld itself is sound. I recall the range as roughly 450-850 °C for austenitic steel and cannot source it; the carrier does not state it. The cure for austenitic is Solution Annealing of the whole weldment.
What You Need
- An arc welding supply. The corpus has no article on building one; I cannot source a village design.
- Stainless filler rod of a compatible family, kept dry and clean.
- Clean joints: no oil, paint or mill scale.
- Dedicated stainless wire brush and grinding discs; carbon-steel ones leave iron in the surface.
- For forge welding: a forge reaching 1,100 °C and borax (Flux Materials).
Method: An Arc Weld With Low Heat
Step 1: Clean and fit the joint. Remove oil and scale back to bright metal with a stainless brush.
Step 2: Weld in short beads and let the part cool between them, so heat does not build up. The carrier’s rule is low heat input.
Step 3: Clean the weld. Remove scale and heat tint with a stainless brush, then passivate (Passivation Treatment).
Step 4: Solution anneal austenitic assemblies if the equipment exists.
Alternatives To Welding
- Brazing: Metalworking and Soldering gives brazing as 600-900 °C. I recall that stainless needs a flux that attacks the oxide film, and that brazing can pass through the sensitization range; I cannot source either.
- Riveting and folded seams: no heat in the weld zone at all.
- Casting the part whole (Investment Casting).
Common Mistakes
- Using carbon-steel filler. The joint rusts and stains the neighbouring stainless.
- Welding continuously. Heat builds up and widens the sensitized zone.
- Treating a forged-welded seam as pressure-rated. Vessels for steam or acid need a proven, tested procedure; see Vessel Construction, which sets requirements for welds on pressure vessels.
Safety
Arc, fume and hot metal
Arc welding emits ultraviolet that burns eyes and skin in seconds and fumes that carry chromium compounds; I recall hexavalent chromium in stainless weld fume as a recognised lung carcinogen but have no corpus source. Use a dark welding filter, cover skin, and keep fume away from the face outdoors or under a draught. The supply is high-current: dry gloves and boots, and a disconnect within reach of a second person. Borax flux and forge welding involve metal at 1,100 °C.
What’s Next
- Learn next: Solution Annealing - recovering corrosion resistance after welding
- Combine with: Passivation Treatment - cleaning and restoring the film