Corten is another name for weathering steel. Essentially, it is steel that rusts nicely and develops a beautiful patina that is desirable to many. It contains minimal amounts of Chromium, Nickel, and Copper, which gives it its weather resistance, making it suitable for use on structural applications. If you are interested in learning how to weld Corten steel, then keep on reading. In this article, we’ll discuss how to weld Corten steel as well as topics like how to choose the right filler wire.
Weathering steel does not prevent rust. In fact, the material alters the way the rust affects the structure. The presence of chromium, nickel, and copper add to the material weather resistance. It allows for the rust to dry quicker and thicker, developing a beautiful patina.
However, instead of weakening the structure, the rust forms a paint-like layer over the material. The coating protects the un-reacted material from the atmosphere, and it allows the material to retain its load-bearing capacity and thickness for longer.
Many sculptors and architects prefer it for aesthetic reasons. The natural patina that it develops over time adds a rustic charm and character to many structures.
The precautionary requirements for welding Corten are similar to that of welding mild steel. The only significant difference is that you may need a different filler wire than you would typically use. The AWS classified 6013, used for mild steel, is not acceptable for Corten.
The two types of welding procedures that you can effortlessly use are Metal Inert Gas and basic Arc Welding or shielded metal arc welding (SMAW).
Metal Inert Gas Welding
MIG uses a filler wire and an electric arc to join two pieces of metals together. The arc flows between the filler wire and the base metal, producing heat to melt the two and join them together. When MIG welding Corten, you should choose the filler metal wisely to achieve the optimal color match.
We suggest that for plates that are 0.10 cm thick or thinner, you should use an E7018 or an SG2 MIG wire. They provide enough dilution from the plates to join weathering steel together. E7018 and SG2 MIG wire work particularly well for single-pass welds.
If you are working on joints that require a double pass or are thicker than 0.10 cm, then you should use a filler wire that either has 1 % Nickel and 0.5% Copper or contains 2.5% Nickel. A filler wire that contains mild steel instead of either Nickel or Copper also works well in terms of color match.
In arc welding, you create an electric arc between the base metal and the filler electrode. The heat generated from the arc melts the material joining the two together. It is, however, trickier as it needs the welder to hold the electrode and the torch at the same time.
It does offer more flexibility as it allows you to weld metals of varying thicknesses without making many adjustments to the electrode and the process in general. You can also utilize the TIG process to weld Corten.
When welding weathering steel, you follow the same primary guidelines that you need to follow for mild steel. In TIG welding, you use a tungsten electrode in combination with separate filler wire. The most common welding rods for mild steel are the E60XX and E70XX line.
You will need a sharper electrode point as you will need to concentrate heat at the weld seam specifically. When welding steel structures, the heat direction is essential as opposed to aluminum, as heat dissipates more quickly.
Make sure that the diameter of the electrode is about half the thickness of the metal you’re working on. You must also set the welder to Direct Current and straight polarity, with the electrode having a negative charge.
When welding weathering steel, you need to understand the material and then choose the appropriate filler wire. The wrong filler metal can not only decrease the tensile and yield strength, but it can also take away the anti-corrosion properties. For load-bearing structures like iron bridges, such a lapse in judgment can produce catastrophic results.
Choosing the Right Filler Wire
There are few properties to consider when choosing the right filler wire.
- Any specific requirements that exist
- Level of strength and impact toughness you require
- Weld position
- Whether it will be painted or not
- Required weld size
- Color match
An essential property out of all is the level of strength needed. Most weathering steel applications stick between 50 KSI yield and 70 KSI tensile. However, they can go up to 100 KSI tensile in certain applications. The filler metal must, at the very least, meet the basic mechanical properties of the base metal.
To be able to make the right choice, the welder must be aware of the exact specifications and grade of weathering steel they are working with.
Besides design requirements, you also need to keep in mind specific welding codes and technical instructions as laid out by different technical authorities. AWS guidelines D 1.1 and D 1.5 provide detailed information on the dos and don’ts when working with Corten steel. It also lists the appropriate methods that serve different environments and applications.
Weathering steel is available in various tensile strengths. Each type has its own properties that make it suitable for a different purpose. Filler metal requirements vary by need and purpose of use. You have to match the tensile strength of the filler metal, its yield strength, and its toughness to the design requirements. You must make a decision after proper evaluation. Otherwise, you may end up with a weak or inconsistent filler wire that takes away from the load-bearing capacity of the metal while also ruining the overall aesthetic appearance of the structure.
To start the selection process, you need first to identify where you will place the filler metal. Is your structure exposed to atmospheric conditions? Will it be painted?
Structures left exposed to the atmosphere tend to rust quickly and will require the use of corrosion-resistant filler wire. You don’t need to worry about the corrosion in structures that have a protective coating of paint or aren’t exposed to wind and rain.
The most common filler metals for Corten include:
Filler wires with carbon steel. You can use any of the following.
- E70C-6 M
They are small in size and lower on the strength grade. They prove ideal for use on single pass joints on thinner sheets as they do not have any significant alloying metals.
In single-pass welds, the base undergoes substantial dilution. The filler wire, when mixed with the diluted base, picks up the alloying metals. The process brings out anti-corrosion properties similar to the base material itself.
You can also use filler wires that have low alloy composition like WX, B2, or CX. They include but are not limited to E81T1-W2, ER80S-Ni1, E80C-Ni1, E8018-C3, and so on. You will use low alloy metal fillers when you need to add anti-corrosion properties to the base metal.
In more significant multi-pass welds, welders prefer the use of low alloy filler metals. In multi-pass welds, there is minimal base metal dilution, and thus, they rely on filler metals with some alloy composition to build corrosion resistance in the end product.
Low alloy filler metals have a higher tensile and yield strength than carbon steel. With them, you can directly match the properties of the filler material to that of the base. Welders typically use a low alloy that includes a nominal percentage of nickel. They are one of the cheapest options with acceptable properties.
How Long will Corten Steel Last?
One of the most common uses of Corten steel is in shipping containers. They have to endure really tough weather conditions as they are transported via sea. They bear heavy winds, rain, and seawater and yet manage to last a long time.
Shipping containers last around 15 years, and they undergo a significant amount of wear and tear. If you use them in moderate settings that do not put them through high levels of abuse, they may last you decades.
How do you Make Corten Steel?
You can make Corten steel by mixing a few different steel alloys. It contains chromium, nickel, and copper, and steel and is created in sheet forms, ideally around 0.25 inches thick. Many architects prefer it because the material is meant to stand wear and tear. It eliminates the need for additional paint, which is an added plus in many cases.
What is S2G MIG Wire?
It is a copper-coated Filler wire that can be used to join mild and medium tensile materials. It is used for welding low carbon steel and structural steel with the same level of intensity as the former. You use an S2G MIG wire for weld jobs in steel structures, bridges, engineering machinery, automobile manufacturing, boiler manufacturing, metal products manufacturing, coal mining manufacturing, and various other industries.