Welding chromoly is different from welding other common metals. The unique chemistry of chromoly and the high heat output of the welds, make chromoly uncooperative for most welders. But with a few tricks, anyone can learn how to weld chromoly effortlessly. Chromoly is often used as a substitute for carbon steel in production because it’s also easy to work with, affordable, and resistant to rust and corrosion.
It’s often used in applications where corrosion resistance is just as important as strength or impact resistance, like in marine hardware or agricultural equipment. In this article we will discuss some tips and tricks you should know before tackling your next project with welding chromoly steel pipe, angle bars or profiles.
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What is Welding Chromoly?
Chromoly is a type of high strength, high alloy steel. The key word in this sentence is “high strength”, as compared to “low alloy” steels, which are still affordable, but not quite as strong as “high strength” steels. Chromoly can be welded to a wide variety of metals, including cast iron, aluminum, and even stainless steel. It’s a good choice for applications where you need extra strength and resistance to corrosion, but not as much impact resistance as other options like stainless.
Can you weld chromoly to mild steel
Yes, you can weld chromoly to mild steel. However, you should be aware of certain material properties when welding chromoly to mild steel and other common metal types. The weld joint should be of good mechanical appearance, meaning there should be no cracks, spatter, or excessive filler material. You can also see the beads and slag on the weld.
The joint should be of adequate weld metal thickness, meaning it should be thick enough to withstand the stress placed on it by the load. Mild steel welds are not prone to corrosion, but if you weld to an iron or steel surface, you will require a passivation process to protect the welded joint from electrochemical attack.
Understanding the Chromoly Material
Chromoly is a high strength steel alloy made up of iron, chromium, and aluminum. It’s often used in the automotive, aviation and mining industries due to the robustness of the material, while maintaining low weight. Chromoly is an iron alloy that is 15 percent chromium and seven percent aluminum. It’s often referred to as high chromium ferritic material, or high chromium ferritic steels due to the addition of chromium to the iron.
High chromium steels are very durable, but they have a higher tendency to begin fretting or crevice corrosion, where the oxide layer on the surface of the material is compromised and the metal is more susceptible to attack by corrosive chemicals. Overall, chromoly is a very durable and robust material, but it’s worth mentioning that you should be aware of the material properties when welding chromoly to mild steel.
Pre-Weld Preparation
Before welding chromoly to mild steel, you will want to remove any scale or oxides from the surface of the metal, and prepare the weld joint for welding. If the surface of the mild steel pipe is rusty, this will cause a lot of issues during the welding process. If you have to weld rusty steel, you will have to thoroughly clean the weld joint of any rust before welding. You can clean the rust off of mild steel by scrubbing the surface with a wire brush, then rusting off the surface with a solution of muriatic acid.
Hardened and Tempered Steel
When welding chromoly to mild steel, you will want to pay attention to the joint temperature and welding parameters to ensure the welded joint is not too hot. If the weld joint is too hot, the joint will crack and break under load. On the other hand, if the weld joint is too cool, it may not be strong enough to withstand the load. This is where a little metallurgy can help you get the best weld possible. Stainless steel is a type of alloy, often referred to as a hardenable steel. When welding stainless steel to chromoly, you will want to ensure the weld joint is shielded from high temperatures.
To ensure a good weld joint shielded from high temperatures, you can weld a protective layer of steel between the two metals. This layer of steel is called a pre-heat or pre-heating shield, and it should be welded just to the side of the weld joint.
How to welding chromoly to mild steel- Key Things to Know
You will want to use a low-hydrogen, low-alloy gas such as argon, helium or krypton. The weld joint should be of adequate weld metal thickness, meaning it should be thick enough to withstand the stress placed on it by the load. You will want to use a small filler spool of weld wire and a small filler wire feeder to feed the weld wire to the weld joint. Feed the weld wire to the weld joint slowly and evenly. You will also want to preheat the joint just to the side of the weld joint with a thinner shield before welding.
Start with a small base metal thickness
Chromoly is often used as a substitute for carbon steel in production because it’s also easy to work with, affordable, and resistant to rust and corrosion. You will find that welding chromoly to mild steel is a little more challenging than welding carbon steel to mild steel. The challenge is that chromoly is less forgiving than carbon steel and has a high heat output, so you’ll need to be a little more cautious during welding. You can mitigate these challenges by welding with a smaller base metal thickness. This will generate less heat, making the weld joint stronger, and provide you with more control over the weld joint.
Wrapping up
Chromoly is often referred to as a hardenable steel. This means that chromoly is more forgiving than other high-strength steels, like stainless steel. This means you need to be careful during welding but it also means the weld joint is more likely to be strong and durable, compared to welding mild steel to stainless steel.
