Welding Corten Steel

Corten is a trade name for Weathering Steel. In other words its steel that still goes rusty but it rusts a nice colour and it resists the spalling black lumps that fall off ordinary mild steel.

Corten contains small amounts of Chromium, Nickel and Copper which impart the weather resistance. It is used mostly in structural applications.

Many buildings appear to have been painted orange but in reality are untreated corten steel.

Stickleback Sculpture by Alan Ross
Corten is often used in outdoor sculpture. Stickleback by artist Alan Ross

When welding Corten the precautions are similar to mild steel except that you may need a special filler material to produce the weathering steel weld. (6013s are not acceptable.)

  • If the plate is 10mm thick or less, and the weld is a single pass (eg a fillet weld), you can use an E7018 or SG2 MIG wire. This is because you will get enough dilution from the plate to render the weld weathering.
  • If it's greater than 10mm thick or a multi-pass weld you need to use a filler containing approximately 1% Nickel and 0.5% Copper (otherwise mild steel), or one containing 2.5% Nickel (otherwise mild steel).

This will result in a weld which will “weather” like the plate.

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