Carbon steel is one of the frequently used materials in welding because it is not only strong but affordable and versatile as well. This material is used in various industries from pipelines to construction and household machinery. But, welding carbon steel has certain challenges as well. They need to be handled to ensure high quality and durability.

Since there are different types of carbon steel, heat reacts differently with each. For example, low-carbon steel is easier to weld compared to high-carbon steel. Selecting the right technique, heat treatment, and filler materials helps cope with welding challenges.

So, understanding the different properties of carbon steel is important. We will discuss how to weld carbon steel, its types, challenges, right welding techniques, and so much more.

What is Carbon Steel?

Carbon steel is basically an alloy of iron and carbon with some amount of sulfur, manganese, and silicon. The amount of carbon present in these alloys determines their hardness and strength. High carbon steel has a higher carbon content, offering greater strength and hardness, but makes welding difficult because of reduced ductility.

There are three main categories of carbon steel based on composition, especially carbon content. These are high-carbon steel, medium-carbon steel, and low-carbon steel (mild carbon steel containing 0.60%-1.50%, 0.30%-0.60%, and up to 0.30% carbon content, respectively.

The lesser the amount of carbon content in carbon steel, the more its weldability. Also, low-carbon steel is less prone to welding defects like cracking and porosity. Certain properties affect the welding of carbon steel.

Properties Affecting Welding Carbon Steel

So, carbon steel welding depends on factors like composition, heat response, and mechanical properties. It’s important to understand these factors to appropriately select welding techniques to minimize defects like cracks, porosity, and distortion.

1.Strength, Ductility, & Hardness

Strength is any material’s ability to tolerate force without shattering or breaking. Strength is increased by increasing the carbon content.

However, it decreases ductility. Ductility is the stretching or deforming ability of any metal without breaking. Low carbon content increases ductility and makes carbon steel easily weldable.

On the other hand, hardness is the resistance to wear and indentation. High-carbon steel is more prone to cracks while welding since it is very hard.

2.Effect of Carbon Content on Welding

As mentioned, carbon content plays a huge role in determining the efficiency and ease of weldability in carbon steel.

Low-carbon steel is the easiest form of carbon steel to weld because it has the minimum amount of carbon in it. It reduces the risks of cracks and hardening. You can weld it without pre and post-welding heating treatments.

Moderate carbon steel has more carbon content and is prone to cracking. Preheating the material and controlling heat input help in achieving high-quality welds. To maintain strength, it’s important to select the right filler material.

As the name indicates, high-carbon steel has the highest carbon content, which means it can easily crack.

So, you need to perform slow cooling, pre-welding heating, and post-welding heating treatment (sometimes) to minimize brittleness and relieve residual stress.

3.Impurities & Alloying Elements

Carbon is undoubtedly the most important factor that determines the weldability of the materials. However, other alloying elements present in carbon steel also have some influence.

For example, manganese helps in reducing brittleness and enhancing toughness, which makes welding quite durable.

Silicon helps prevent oxidation during welding and improves strength. Phosphorus and sulfur do offer good properties but increase the chances of cracking. Meanwhile, nitrogen and oxygen lead to porosity.

4.Heat Affected Zone (HAZ)

The area surrounding the weld is affected by extreme heat and is called the heat-affected zone (HAZ).

It undergoes notable temperature changes, altering the material’s properties. This zone is very important in high-carbon and medium-carbon steel because excess heat leads to heating, distortion, and residual stress.

All of them cause cracking and structural failure and make steel more brittle.

5.Controlling Cracking & Distortion

Welders use multiple techniques to control cracking, distortion, and other welding defects. The most common techniques are preheating, post-welding heating treatments, and interpass temperature control.

Preheating not only slows down the rate of cooling for reducing hardness but also helps reduce the risks of cracking.

Post-welding heat treatments relieve residual stress and improve the high-carbon microstructures of the material. On the other hand, interpass temperature control controls the heat-affected zones and workplace cool down and, in return, minimizes stress buildup.

Types of Carbon Steel & Their Challenges

There are three types of carbon steel based on carbon content. Not all of these types are created equal.

So is their welding method/technique. The welding challenges increase as you increase the carbon content in these types because it decreases ductility and enhances hardness.

We will discuss the types in detail and see what welding challenges they face.

1.Welding Low-Carbon Steel

Low-carbon steel is famously called mild steel and contains up to 0.30% carbon. Because of its low carbon content, it is the easiest type to weld. It is very ductile, and its hardness is also low. There are multiple structural applications of this carbon steel type, including pipelines and automotive manufacturing.

As low-carbon steel doesn’t get hard too much during the welding process, you don’t have to perform preheating treatments. The three most common welding techniques used for welding low-carbon steel are stick welding, MIG, and TIG.

However, there is this one challenge that needs to be taken care of, which is avoiding contaminations as it weakens the weld to a greater extent. For this, you must clean the surface of the material to get rid of dust, dirt, and rust and prevent weak joints and porosity.

It is also recommended to control heat input to avoid excessive distortion. This is particularly important for thinner metal sheets. Though mild steel is easy to weld, worker negligence can lead to welding defects.

2.Welding Medium Carbon Steel

Medium carbon steel has a carbon content of 0.30% to 0.60%. Since it is stronger and harder compared to low-carbon steel, it is more susceptible to cracking and other welding defects if mishandled.

This type of carbon steel has several applications in the manufacturing of gears, axels, and machinery as wear and strength resistance are very critical in these industries.

Unlike mild steel, this carbon steel demands careful preheating control and cooling rates. Preheating treatment slows down the rate of cooling and reduces the chances of cracking in the heat-affected area.

The temperature of preheating is set according to the material thickness and its carbon content. It typically has a range of 250 °F to 500 °F.

If medium carbon steel is cooled very rapidly, it forms a hard microstructure very soon during welding, leading to increased brittleness and weld failure.

To address this issue, post-welding heat treatments (PWHT) are performed to enhance toughness and relieve residual stress. Also, it is very important to select the right filler material that maintains structural integrity and is compatible with the base material.

3.Welding High Carbon Steel

As the name indicates, it has the most amount of carbon in it. High-carbon steel has a carbon content of 0.60% to 1.50%, increasing hardness and strength even more than medium-carbon steel.

Though it is the strongest type, it is the toughest to weld because of its hardness. There are multiple applications of high-carbon steel in high-strength components, springs, and cutting tools because they need extreme durability.

Among some welding challenges, the primary concern is cracking because of rapid cooling. So, preheating is a good option to fix this. Preheat at temperatures ranging from 500 °F to 800 °F, which reduces the temperature difference between weld and base material. This, in return, reduces internal stresses.

Another thing to consider is selecting the appropriate filler material. It is advised to use a low-carbon filler as it is easy to weld and significantly prevents the heat-affected zone from getting extremely heated.

Also, you need to control cooling as well. For this, cover the entire weld with insulating materials to slow down the rate of cooling. You can use thermal blankets or sand for this purpose.

Post-welding heating treatment (PWHT) is necessary to bring back some ductility and soften the hardened areas.

This step is called tempering or stress relieving. It involves the heating of the welded areas again at lower temperatures and then waiting for a while to let them cool very slowly.

If you skip this step, it can increase the chances of brittleness of the material, leading to failure under stress.

Best Welding Methods for Carbon Steel

Since carbon steel has a wide number of applications, welders must select a welding technique that guarantees high-quality weld that is not only durable but also free of defects.

The following are the types of welding methods used for carbon welding.

Stick Welding

Stick Welding

Stick welding or shielded metal arc welding (SMAW) is among the most used welding methods because it is easy to perform and versatile. During this process, a flux-coated electrode is used that produces a shielding gas when melted by the torch. It protects the weld from external contaminants.

Gas Metal Arc Welding

Gas Metal Arc Welding

Also called MIG, this method is very efficient and can be automated. A continuous wire feed is used as an electrode. There is an external shielding gas for protection against contaminants. It produces minimal slag and is faster method.

Gas Tungsten Arc Welding

Gas Tungsten Arc Welding

This method is highly applicable to obtain precision where high-quality welds are required. A shielding with a non-consumable tungsten electrode is used in TIG welding. It produces cleaner and more controlled welds because of more control over heat input. The best part is that you can do welding with or without using filler material.

Flux-Cored Arc Welding

Flux-cored Arc Welding

Flux-cored arc welding is similar to gas metal arc welding. However, it uses a tubular wire electrode filled with flux to produce its own shielding gas. That’s why it is perfect for outdoor settings and heavy-duty applications. It works quite well for thicker carbon steel and gives deeper penetration.

Oxy-Fuel Welding

It is also called simple gas welding. It uses a flame produced by burning acetylene and oxygen to melt and fuse carbon steel. It is not very frequently used nowadays, but it has limited applications. It doesn’t require an electric current and is portable.

The welds it produces are not good quality. Also, it is not good for thicker materials.

How to Weld Carbon Steel?

Welding of Carbon Steel

Welding carbon steel is a step-by-step method where every step needs to be done carefully. Proper execution is important to make sure there are minimum welding defects, and the welding quality is maintained.

1. Preparation of Metal Surface

Metal surface preparation ensures high-quality welds. If you don’t get rid of oil, grease, paint, dirt, and rust, it will lead to porosity. So, start by cleaning the surface using a wire brush, chemical cleaner, or a grinder.

Prepare edges of thicker carbon steel sections. The bevel angle must be within 30 to 45 degrees based on the welding technique.

Position and fix the workpieces accurately using tack welds or clamps to guarantee there is no misalignments.

2. Select the Right Electrode or Filler

Low-carbon steel uses E6010 and E7018 electrodes for shielded metal arc welding. Whereas, for MIG welding, ER70S-6 is a good option. Pre and post-weld heating treatments are needed for medium carbon steel.

Meanwhile, they use electrode E7018 or ER80S-D2. On the other hand, since high-carbon steel is brittle and hard, it uses a nickel based electrode or a stainless steel electrode to reduce cracking. For this type, slow cooling and preheating are also necessary.

3. Set the Right Parameters

Each type of carbon steel has a certain set of parameters to be welded precisely. For instance, stick welding is performed at 75 to 200 amperes current with an electrode angle of 10-15 degrees. You need to maintain a uniform speed to prevent undercutting.

Voltage for MIG welding should be 18 to 24V with a wire speed of 250-500 inches per minute. For TIG welding, keep the current 50-200 amperes. It uses a 100% argon gas as shielding gas to produce cleaner welds. Whereas FCAW is performed at 18-26V with a wire feed speed of 200-450 inches per minute.

You need to control heat input and distortion as carbon steel has a tendency to expand and contract when it comes in contact with heat. Preheating medium carbon steel at 250 °F to 500 °F reduces cracking.

4. Perform Welding

Start the arc properly for stick welding by striking the electrode like a match stick. Whereas keep the arc length steady for TIG and MIG.

Make sure the bead size is consistent. Perform multiple passes as needed or in case of thicker materials.

Welding Carbon Steel to Stainless Steel

Welding carbon steel to stainless steel faces a lot of challenges as there is quite a difference in the composition of both types of steel.

Not only composition, but they also have different thermal conductivities and different corrosion resistance levels, as well.

Both of these materials are widely used in industries for multiple applications, particularly in those areas where you need the resistance properties of stainless steel but the strength of carbon steel.

Such applications are chemical processing equipment, structural components operating under harsh conditions, and pipelines.

Difference Between Carbon Steel and Stainless Steel

The main difference between stainless and carbon steel lies in their composition. Carbon steel is made of iron and carbon, along with some alloy elements like manganese, sulfur, and silicon. Though it is quite strong, it is highly susceptible to rusting in the presence of moisture or humidity.

On the other hand, stainless steel has chromium (at least 10.5%), forming a protective oxide coating outside the surface of the material and preventing it from getting corrosion and rust. It has heat resistance properties as well because of the presence of alloys like nickel.

However, stainless steel has lower thermal conductivity, and it expands to a greater extent when exposed to heat as compared to carbon steel. Hence, stainless steel is likely to bend or twist and distort during welding.

Moreover, both are different in terms of dilution. When the molten metals get mixed during welding to form a weld, stainless steel alters the properties of the weld. This can cause brittleness and corrosion if not managed properly.

Problems During Welding Carbon Steel to Stainless Steel

Since they are not similar to each other, their welding faces certain challenges like different melting points, thermal expansion mismatch, carbon migration, and corrosion concerns.

Carbon steel has a lower melting point than stainless steel when heated. It makes the stainless steel brittle and prone to cracking.

Weld distortion and residual stress are increased in the weld because stainless steel has more thermal expansion compared to carbon steel.

Carbon migration is also common in this fusion. During fusion, carbon from carbon steel migrate into stainless steel and diffuse there, making the stainless steel materials prone to cracking.

Last, if you use the wrong filler material, there is a high chance that the weld will corrode quickly.

Choose the Right Welding Technique

Choosing the right method for welding carbon steel to stainless steel is important. Like standard welding, there are certain welding techniques that are more suitable for this type of fusion.

These include shielded metal arc welding (stick welding), gas tungsten arc welding (GTAW), gas metal arc welding (GMAW), and flux-cored arc welding (FCAW).

Stick welding (SMAW) is an affordable method, but you need to select the electrode material very carefully as it avoids carbon migration from carbon steel to stainless steel. Gas tungsten arc welding (GTAW) offers higher precision and quality, and that’s why it is suitable for critical applications.

Gas metal arc welding (GMAW) is perfect for large-scale applications. However, you need to select an appropriate shielding gas so that the oxidation is minimal. Flux-cored arc welding (FCAW) needs a specific flux composition to handle two dissimilar metals but is very suitable for outdoor settings.

Select the Right Filler

When you choose the right filler material, you choose a stranger and corrosion-free welds. It makes sure there is no carbon migration and the integrity of both metals remains maintained.

There are some common filler materials used for welding carbon steel to stainless steel, such as:

312 stainless steel filler for better crack resistance properties as it contains nickel and chromium.
309 stainless steel filler offers a perfect balance of corrosion resistance and strength. Hence, the most frequently used filler.
Nickel-based fillers provide good heat resistance when welded at higher temperatures. One example of such filler is Inconel 625.

Conclusion

Welding carbon steel is an important skill as it has multiple applications in metal fabrication, automotive, industrial applications, and construction. It’s essential to pick the right welding technique, whether you are welding low-carbon steel, medium-carbon steel, or high-carbon steel.

The four main types of techniques used for welding carbon steel are shielded metal arc welding, gas metal arc welding, gas tungsten arc welding, and flux-cored metal arc welding.

However, you need to properly follow all the steps of welding starting from cleaning the surface to post-welding heating treatments. It’s necessary to control heat input and perform pre and post-welding treatments to ensure stronger bonds particularly for medium and high-carbon steel.

If the welders follow all welding steps carefully and apply best practices, it can guarantee high-quality welds that tolerate not only stress, temperature, and pressure but also have minimum to no defects.

Welding Carbon Steel – Process, Methods, & Challenges