Introduction to Welding Corten Steel for Modern Outdoor Projects

Introduction to Welding Corten Steel

Corten steel, sometimes known as weathering steel, has become a popular material for modern outdoor projects like planters, sculptures, and architectural accents. The rustic,weathered look of corten steel comes from its chemical composition. When exposed to the elements, corten steel forms a stable rust-like appearance called a patina. While this quality is ideal for creating durable, low maintenance outdoor structures, it does require some special considerations when it comes to welding and fabrication. In this article we’ll look at what you need to know to successfully weld corten steel for your next landscape or architectural project.

What is Corten Steel?

Corten steel is a weathering steel alloy material originally developed to eliminate the need for painting structural steel. It contains small amounts of copper, chromium, silicon and phosphorus added to steel. This special combination causes the material to form a rich, rust-like appearance when exposed to weather and the elements. The rust layer that develops provides a protective finish that slows down future corrosion. Corten steel is also known by other trademarked names like Cor-Ten or weathering steel.

Benefits of Corten Steel

There are several advantages to using corten steel in outdoor applications:

• No painting required - The weathered patina finish eliminates the need for paint
• Long lasting - The rust patina protects the base material from further corrosion
• Low maintenance - Corten requires occasional cleaning but no repainting
• Aesthetically pleasing - The rustic, vintage look is ideal for modern landscapes
• High strength - Corten has comparable strength to common structural steels

Challenges of Welding Corten Steel

Working with corten steel poses some unique challenges when it comes to welding and fabrication:

• Preheating is required - Corten has a higher carbon equivalent than common mild steel
• Special electrodes are needed to prevent cracking - Low hydrogen or nickel-based electrodes are recommended
• Post-weld treatment is needed - Special coatings or weathering processes ensure consistent patina formation
• Cut edges require extra protection - Uncoated edges are more prone to water corrosion

How to Weld Corten Steel

Welding corten steel can produce excellent results, but the process requires more skill and planning compared to standard carbon steel. Here are some important tips for successfully welding weathering steel:

Choose an Appropriate Welding Process

The most common welding methods for corten steel are:

• Shielded Metal Arc Welding (SMAW) - Slow, versatile, good for indoor use, can use various electrodes
• Gas Metal Arc Welding (GMAW) - Fast, excellent for outdoor use, limited electrodes
• Flux Core Arc Welding (FCAW) - Compromise between SMAW and GMAW, moderate speed and electrode options

Use Low Hydrogen Electrodes

Low hydrogen or nickel alloy electrodes are essential for welding corten steel. Standard mild steel electrodes are prone to cracking and inferior corrosion resistance. Common low hydrogen electrodes include E7018, E7028, E7018-1, and E309L.

Preheat the Steel

Corten steel must be preheated before welding to 200-250°F to drive out moisture. Slow heating to this temperature range prevents damage and facilitates welding. The preheat temperature should be maintained throughout the welding process.

Allow Proper Cool Down Time

Slow cooling after welding is critical to prevent cracks in the welded corten steel. Allow the steel to cool very gradually to under 300°F before it is exposed to room temperature air. Insulating weld areas can help maintain a slow cooling rate.

Apply Post-Weld Treatment

Applying a corrosion resistance coating to welds helpsweathering steel achieve an even, consistent patina. Phosphate treatments, paints, and epoxy coatings are commonly used. Weld areas can also be treated to simulate the patina using chemical or heating methods.

Corten Steel Welding Technique

Follow these best practices when welding corten steel:

1. Clean surfaces - Remove paint, oil, rust, and other contaminants from the joint area
2. Preheat to 200-250°F - Use a temp stick, crayon or pyrometer to monitor temperature
3. Make stringer bead welds - Avoid weaving to limit heat input and distortion
4. Use interpass cooling - Allow plates to cool between weld passes
5. Weld in flat position - Avoid overhead or vertical positions when possible
6. Peen welds - Use a chipping hammer to relieve stress and smooth welds
7. Slow cool under insulation - Cover welds until temperature drops below 300°F
8. Apply post-weld treatment - Phosphate, paint or chemically age the welded area

Common Corten Steel Welding Problems

Flaws like cracking and porosity can occur in corten steel welds when the special welding requirements are not followed. Some potential problems include:

• Undercut - Excessive melt-through along the weld toe
• Spatter - Sparks and metal particles deposited on the weld surface
• Porosity - Holes and voids trapped in the solidified weld
• Cracking - Fractures in the weld or adjacent base metal

Proper preheating, electrode selection, and cooling rate are key to avoiding defects.

Finish Work for Corten Steel Projects

After successfully welding weathering steel, a few final steps are recommended to complete the project:

Remove Slag

Chip, grind or wire brush welds to remove leftover slag material. This improves the visibility of the welds for inspection.

Blend and Polish Welds

Grind visible welds smooth for a flush, blended appearance. Polish welds and surrounding areas to prepare for protective coatings.

Add Sealers and Topcoats

Apply clear sealers or topcoats to help finished projects achieve an even, consistent rusted appearance once exposed to the weather.

Weathering Treatment

Special chemical solutions or heat can be used to artificially form the corten patina on welds and uncoated areas.

Conclusion

With the right welding techniques and finishes, corten steel can create stunning durable structures with minimal maintenance. By following the recommendations for electrodes, preheating and controlled cooling, your next corten project is sure to impress. With its signature rustic appearance and high strength, weathering steel is an ideal material for modern landscape and architectural designs built to last.

FAQs

What type of welder is best for corten steel?

Shielded metal arc welding (SMAW) and flux core arc welding (FCAW) are most commonly used for welding corten steel. Both methods allow for versatile electrode options. Gas metal arc welding (GMAW) is also effective but has fewer electrode choices.

What electrodes work best for welding corten steel?

Low hydrogen electrodes designed for welding weathering steel should be used. Common choices are E7018, E7028, E7018-1, and E309L. Avoid mild steel electrodes.

Is preheating required for welding corten steel?

Yes, corten steel must be preheated to 200-250°F before welding to prevent cracking. This temperature should be maintained throughout the welding process.

How should I finish welds on corten steel?

Welds should be cleaned, ground smooth, and treated with a phosphate coating, sealant, or specialized weathering solution to achieve an even patina finish.

How long does it take for the rust patina to form on corten steel?

Natural weathering to form an even rust finish can take several months. Artificial chemical or heat treatments can accelerate the patina formation in just a few hours.