How to Weld Corten Steel

Corten steel, also known as weathering steel, can be welded using standard arc welding processes. The main issue is not whether the steel can be welded, but how the weld is designed and which filler metal is used for the finished joint.

Filler selection depends on the steel grade, joint design, thickness, weld size, number of passes, required strength, and whether the weld must develop corrosion resistance and a colour similar to the surrounding weathering steel.

At COR10 Steel Byron Bay, we consider the steel, the joint and the final use before choosing the welding method for each custom piece. A decorative screen, a planter and an exposed structural connection can all require different welding decisions.

Corten Steel Welding

Corten is a weathering steel designed to form a protective oxide layer when the surface is exposed to suitable wet and dry conditions. The weathered surface is part of the steel rather than a paint coating.

Like other structural steels, weathering steel can be welded by conventional processes. The welding procedure, filler metal and joint detail should be chosen for the specific grade and service conditions.

For structural work in Australia, welding must also meet the requirements of the applicable welding standard and project specification.

MIG Welding Corten Steel

MIG welding, or gas metal arc welding (GMAW), is widely used for Corten fabrication because it offers good control and high productivity.

For standard solid steel wire, a shielding gas such as 75% argon and 25% carbon dioxide is commonly used. The correct gas, however, depends on the wire manufacturer’s specification.

The filler metal is the more important choice. Carbon-steel wires such as ER70S-3 and ER70S-6 can be suitable for some joints, while low-alloy nickel-bearing wires such as ER80S-Ni1 can be selected where the weld requires better atmospheric corrosion performance and closer colour matching.

TIG Welding Corten Steel

TIG welding, or gas tungsten arc welding (GTAW), gives close control over the arc and weld pool. It can be useful for small joints, thin sections and visible fabrication where appearance and heat control matter. The filler rod should be selected for the steel grade and the required weld properties.

ER80S-Ni1 is one low-alloy option used for suitable ASTM A588 weathering-steel applications where good atmospheric corrosion resistance is required.

Stick Welding Corten Steel

Stick welding, or shielded metal arc welding (SMAW), is useful where gas shielding is difficult to maintain, including some site and outdoor work.

Common electrodes such as E7018 may be suitable for applications where the required weld strength and other design conditions allow them. Weathering-steel electrodes such as E7018-W1 and E8018-W2 are available where the weld must provide closer corrosion or colour characteristics.

For structural work, electrode selection should follow the applicable welding procedure and standard rather than a general rule based only on the word Corten.

Flux-Cored Welding

Flux-cored arc welding (FCAW) is often used where a higher deposition rate is useful.

Weathering-steel flux-cored wires are available for suitable Corten grades. One example is ESAB Dual Shield 8100-W, which ESAB classifies as AWS A5.29 E81T1-W2C/W2M and describes as a flux-cored wire developed for weather-proof steel.

The exact wire and shielding gas should always be confirmed against the manufacturer’s current specification.

Choosing Corten Filler Metal

Corten steel does not automatically require a special filler metal for every weld.

The correct choice depends on what the weld must do in service. Two questions are especially important:

1. Does the weld need similar mechanical and atmospheric corrosion performance to the parent steel?
2. Does the weld need to develop a similar colour and patina?

Where a matching patina is not required, conventional carbon or low-alloy fillers may be suitable when selected to meet the requirements of the joint.

Where similar atmospheric corrosion resistance and colour are important, weathering-steel or nickel-bearing low-alloy fillers may be more suitable.

Base Metal Dilution

Dilution is one of the main reasons filler selection becomes more complex with weathering steel.

During welding, part of the parent steel melts into the weld pool. Its alloying elements then become part of the deposited weld metal.

In a small single-pass weld, dilution can be relatively high. This can improve the corrosion and colour characteristics of a conventional filler.

In a larger multi-pass weld, later passes contain less parent-metal dilution. As a result, the weld metal in those passes may not have the same corrosion behaviour or colour as the surrounding weathering steel unless a suitable low-alloy filler is used.

BlueScope notes that C-Mn consumables may be suitable for general structural welding where a matching patina is not required, while nickel-bearing low-alloy consumables may be needed where similar corrosion resistance and patina are required, particularly for multi-run welds.

Common Filler Metals for Weathering Steel

The following examples are commonly associated with weathering-steel fabrication. They are examples only, not a universal selection chart.

ER80S-Ni1 is manufactured for suitable ASTM A588 weathering-steel applications, while ESAB lists E7018-W1 and E8018-W2 products for weathering-steel work.

Weld Size and Number of Passes

Weld size affects dilution and therefore can influence filler selection.

A small single-pass weld can contain a greater proportion of alloying elements from the parent plate. In a multi-pass weld, the later passes receive less dilution from the base metal.

For this reason, two joints made from the same Corten plate can require different filler-metal choices.

The final decision should be based on the steel grade, joint design, required weld properties and applicable welding procedure.

Weld Colour and Patina

A welded area does not always weather to exactly the same colour as the surrounding Corten plate.

This is especially important in visible architectural and decorative work. The final appearance can be affected by filler chemistry, dilution, grinding, surface condition and exposure.

Where colour matching matters, a suitable weathering-steel or nickel-bearing filler can help produce a closer result.

BlueScope specifically notes that colour retention across welds can be achieved through suitable electrode selection and provides separate guidance for matching weathering-steel weld appearance.

Thin Corten Plate

Thin plate can behave differently during welding because a small weld may contain a relatively high proportion of parent-metal dilution.

Thickness should therefore not be considered on its own. Weld size, joint design, heat input and the number of passes also affect the finished weld.

This is another reason to select the filler from the complete welding procedure rather than from plate thickness alone.

Heat-Affected Zone

The heat-affected zone (HAZ) is the area beside the weld that is heated but does not melt.

Welding can change the structure and properties of this region. The extent of the change depends on the steel grade, thickness, heat input, cooling conditions and joint design.

Control of heat input and hydrogen can be important where there is a risk of delayed or hydrogen-assisted cracking.

Preheating Corten Steel

There is no single preheat temperature that applies to every Corten weld.

SSAB identifies several factors that affect preheating and interpass temperature, including:

• Carbon equivalent of the steel
• Combined thickness of the joint
• Hydrogen content of the consumable
• Welding heat input
• Joint geometry and restraint

Low-hydrogen consumables can reduce the risk of hydrogen cracking and may reduce the need for preheating. The actual preheat temperature should come from the applicable welding standard, qualified procedure or manufacturer guidance for the specific steel and consumable.

Heat Input

Heat input affects both the weld metal and the surrounding HAZ.

Very high heat input can change the HAZ and, in some weathering-steel conditions, increase the risk of hot cracking. Very low heat input can also affect preheat requirements.

Current, voltage and travel speed should therefore be set from a qualified welding procedure and consumable data rather than copied from a general online chart.

BlueScope notes that some weathering steels can have increased hot-cracking risk at higher heat inputs and recommends appropriate procedure qualification where required.

Preparing Corten Before Welding

The joint should be clean before welding.

Oil, grease, dirt, loose scale and other contaminants can affect the welding process and the final surface.

Surface preparation also matters when a consistent patina is required. SSAB recommends scale removal where an even-looking weathered surface is desired.

The amount and method of cleaning should follow the welding procedure and the required finish.

Grinding Corten Welds

Grinding changes the surface around the weld.

A freshly ground area may weather at a different rate from the surrounding mill surface for a period of time. On visible work, grinding and cleaning should therefore be treated as part of the final finish.

For architectural Corten products, the goal is not simply to remove excess weld metal. The finished surface should also sit well with the surrounding weathered steel.

Corten Welding and Water

Weathering steel needs suitable wet and dry cycles to develop its protective surface.

Moisture trapped in joints, crevices or enclosed details can create a different corrosion environment and can interfere with proper weathering.

Good drainage, ventilation and joint design are therefore important in outdoor Corten fabrication.

Australian weathering-steel guidance recommends avoiding moisture traps and designing details so the steel can dry out between wet periods.

Welding Corten Planters

Corten planters often include welded corners, bases, seams and drainage openings.

The weld has to hold the shape of the planter while the design still allows water to leave the structure. Poor drainage can keep moisture against the steel for too long.

For this reason, welding and drainage should be considered together during fabrication.

Welding Corten Screens

Corten screens can contain many cut edges, brackets, returns and support joints.

Because the cut pattern is often the main feature, visible welds should not distract from the design. Joint position, filler choice and finishing can all affect the finished appearance.

This becomes more important when several panels are installed together and need to weather in a consistent way.

Welding Corten Signs and Numbers

Corten signs often use small welded supports, brackets and frames.

Our 3D Numbers are one example of custom Corten fabrication where the joints support the finished form without becoming the main visual feature.

Our 3D Letters use the same approach for custom names, words and signs.

Custom Corten Fabrication

A custom Corten product can combine cutting, bending and welding in one fabrication process.

Our 3D Custom Parcel Box is one example. The final result depends on the complete design and fabrication process rather than steel thickness alone.

We consider the shape, joints, surface finish and installation environment before deciding how a custom piece should be made.

Decorative Corten Welding

Decorative Corten work places extra focus on the visible surface.

Planters, screens, sculptures, signs and architectural features can all contain exposed welds. In these applications, the appearance of the weld can matter almost as much as its mechanical performance.

That is why filler selection, joint placement, grinding and surface preparation should be considered as part of the overall design.

Structural Corten Welding

Structural Corten welding has additional requirements.

The filler must provide the required mechanical properties, while the joint design, welding procedure, inspection and applicable standards must also be considered.

Australian guidance states that welding of weathering steel structures is subject to the applicable requirements of AS/NZS 1554, with the exact requirements depending on the structure and construction category. ASI Technical Note TN008 also explains the relationship between AS 4100 and the AS/NZS 1554 series for welding consumables and weld design.

A decorative welding approach should not be transferred directly to a load-bearing structure without checking the relevant design and welding requirements.

Corten with Other Metals

Corten can be used with other metals, but the connection needs careful design.

When different metals are in contact in a wet environment, galvanic corrosion can become a concern. Isolation, suitable fasteners and good joint design can reduce the risk.

This matters when Corten panels, frames or fixing systems include stainless steel, aluminium or other metals.

What We Check Before Welding

We start with the exact steel grade.

We then consider thickness, joint design, weld size and the number of passes. These factors affect dilution, heat flow and filler selection.

The final environment also matters. A small decorative weld hidden inside a product has different requirements from an exposed structural connection.

Getting a Corten Welding Quote

To help us assess a Corten welding job, provide the steel grade when it is known.

Include the thickness, dimensions and number of parts. A drawing or clear sketch can also help us understand the joint.

Tell us where the product will be installed and whether the weld will remain visible.

For custom work, details about grinding, brackets, frames and the required finish help us plan the fabrication and provide a more accurate quote.