How to Weld Cast Steel | Everything You Need to Know

I’ve done a lot of welding, but when I get to weld on cast steel it’s like the first time every time. I get the nerve-racking shakes that I had on my first welding test. In theory cast steel looks easy to weld, but in reality, it’s not that simple.

The secret to welding cast steel is understanding the metallurgy of the material and knowing how your filler metals will interact with it. In this article, I’ll give a basic overview of cast steels, an introduction to the different types of welding processes used for them, and step-by-step welding cast steel.

What is cast steel?

What is cast steel?

Cast steel is a group of steels with specific properties and chemical compositions. They generally fall into the category of alloy steels, but many times they are also considered as strucural or low alloy steels as well.

The main difference between cast steel and other types of steel is that it’s created in a mold rather than an ingot. This allows for more complex shapes to be created from a single metal billet instead of having to pour multiple ingots at once to create a multi-sided object.

How They make Cast Steel Shape?

Making a cast steel shape starts out by heating up metal billets until molten enough to pour into a mold. Once the heat source has been removed the liquid metal hardens back into solid form which creates your final cast steel shape. 

The type of heating used to melt the metal can have a large effect on your final product as well. Here are just a few of the most common types:

Carbon and charcoal – This is an old-fashioned process that still is used in some parts of China today. It produces a low-quality cast steel, but it is a good process for creating lower carbon steel with high carbon content.

Electric arc furnace – This is the most common type of oven used to melt downcast steel today. It’s called an “arc” furnace because of how electricity is used in its creation, but in many cases gas can be co-fired with the molten metal to help reduce this effect.

Nitrogen – This is a modern process where nitrogen and carbon are injected into the molten metal to create a nitrogen-rich environment in your final product. It helps produce solid, high-quality cast steel with a very fine and uniform microstructure. 

Carbon, Oxygen, Nitrogen – This is an even newer process where the metal is placed into a vacuum chamber and heated up to very high temperatures. The oxygen and nitrogen are then injected which creates an extremely clean, uniform steel with fewer contaminants than other methods.

How to tell the difference between cast iron and cast steel?

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How to select Welding Amperage?

This can be a little tricky because both types of metal have a lot in common. They are both malleable, gray/black metals that harden when cooled down. When you look at cast iron and cast steel side by side it can be difficult to tell which is which. 

  • Chemical compositions – Cast irons typically contain a higher carbon content than cast steels. This means they tend to be more brittle and not as strong. They also contain a high percentage of iron oxide in their chemical makeup. Cast steels typically contain more alloy metals like nickel, molybdenum, chromium, and manganese. These all help strengthen or otherwise alter the properties of the final product, but they also take up more volume as well as alter the resulting color.
  • Look – The shape of a piece of metal will usually give some indication as to whether it’s cast iron or steel. Cast steel tends to have a slightly smoother, more refined or polished look to it while cast iron will have a rougher “gritty” texture.
  • Sparks – When you use a grinder to cut metal or remove rust, sparks will fly. You can tell if it’s cast steel by the sparks that come off of it when you grind on it. If the sparks are bright and light-colored then you’re probably looking at cast steel. If they’re dark and “dirty” looking then the piece is more likely cast iron.
  • Weight – If you know the weight of an object and it’s size, you can determine with a good degree of accuracy whether it’s cast steel or not. Cast iron will weigh less than cast steel of the same size due to its lower carbon content

What kind of metal would I make out of Cast Steel?

The answer to this question really depends on the type of cast steel you’re using. Here are a few common examples, but there are certainly others:

Cold Finish Steel – Cold finish steel is the most commonly used alloy when making tools and industrial hardware. It’s used to make things like shovels, spades, ax heads, automotive parts, and much more.

Lead Cast Steel – This type of cast steel is a very soft iron/carbon alloy that is used for making bullets. It’s melted in huge vats and poured into molds which are then allowed to solidify in the air without being moved during cooling–producing a “free-machining” metal.

Liquid Cast Steel – This alloy gets its name because it’s basically a liquid form of steel that can be used for casting objects without the need to reheat it after pouring. Welding this type of metal can be very difficult due to how thin and fluid-like it is. It’s often used in oil wells, engines, pumps, and various other parts.

Molten Cast Steel – This is a very high-quality alloy for making pieces of metal that require extreme amounts of strength and durability. It’s typically made out of liquid steel, but can also be solidified in special furnaces to create it as well. It’s used in the construction industry for things like bridges or skyscrapers

Stainless Steel – A special alloy used in knife making. It’s created by adding chromium to the molten steel mixture which helps make it rust-resistant and very durable.

Bright Cast Steel – This is a strong alloy-type of steel used to make things like train rails and streetcar tracks. It’s cast in large molds and allowed to solidify with the help of gravity rather than being cooled quickly.

These are just some examples out of dozens, but they give you an idea as to how versatile cast steel can be.

Can you weld cast steel?

Of course, you can. Many people choose to weld cast steel parts because it’s such a durable metal that holds up really well to heat and pressure during the welding process. If you prefer stick welding, use an E7018 welding rod for best performance. I highly recommend TIG welding explained later on but your metal must be perfectly clean.

Forney 30681 E7018 AC Welding Rod, 3/32-Inch, 5-Pound

What to consider before welding cast steel?

There are some things to consider before you weld your first cast steel.

Size

Smaller cast steel parts are much easier to weld than large ones. Even the tiniest crack or deformation in your casting can cause problems later on. You should take great care when welding small pieces together to make sure that you’re completely removing any warpage, cracks, or mistakes.

Rapidity

Cast steel is very difficult to work with when it comes to welding. As such, you’ll want to take special care not to let your weld pool cool too quickly, or else the steel might crack. This is much less of a need for low carbon castings or those that contain manganese which tends to make them harder than typical cast iron.

Safety

When working with any kind of metal, you should always wear protective clothing and safety equipment.

Have an emergency plan in place before starting any welding job where you use this material, especially if you’re doing anything more complicated than basic welding.

Service conditions

High heat and poor strength at high temperatures are just two of several issues that can come up when you’re working with cast steel. Since it has such a low melting point, any change in service conditions can lead to cracks or deformations.

Working conditions

Just like service conditions, the work environment will play a role in how successful your welding job turns out. If it’s too hot or cold for your alloy this might complicate things and cause unpredictable results. Also, certain factors like humidity or moisture can drastically affect cast steel’s ability to hold together when welding.

Distortion

Distortion is a big problem when it comes to welding cast steel. Cast irons have a very high level of distortion compared with other metals, and this is even more significant when you’re dealing with higher carbon contents.

You should take special care when working with any kind of cast steel product that the surrounding temperatures won’t cause any problems during or after your welding job.

Some basic tips for you to avoid distortion are:

  • Use a sandbag or similar tool to keep your cast steel cool and still during welding.
  • Hold parts together as you weld instead of relying on the clamps alone.
  • Allow time for any changes in temperature before continuing work.
  • Use a MIG welder with low heat input at the lowest wire feed speed possible.
  • Use a wire that’s an appropriate size for the amount of current you’re using.
  • Don’t grind away any of your cast steel until after you’ve finished welding it together.
  • You should consider using stainless steel filler material instead of plain steel when welding cast steel to avoid these problems and make sure that the final product retains its strength and corrosion resistance for many years ahead.

Preheating difficulties

If the temperature of your cast steel is too low, it can cause problems when you’re trying to weld it together. To prevent this from happening, you should preheat your cast steel or at least allow a long enough time for it to warm up.

This is especially true when you’re welding thicker materials since their heat conductivity is less effective than thinner pieces.

NOTE: Remember that the higher the carbon content, the more heat it will require to make your cast steel reach a welding temperature.

Cast steel types

There are many different kinds of cast steel that vary in terms of carbon content, alloy composition, and heat treatment.

Low Carbon cast steel

Low Carbon cast steel contains less than 0.3% carbon, which means that it’s much softer and more malleable than other types of cast steel. It is the easiest to weld and machine, but also the most sensitive to cracking during cooling.

Medium Carbon cast steel

This type contains from 0.3% to 0.5% carbon . It’s harder, more wear-resistant, and less likely to crack during cooling. You can also make it easier to machine or grind compared to low-carbon cast steel.

High Carbon cast steel

This type contains more than 0.5% of carbon and it’s extremely hard to weld or machine. You need to increase the amount of heat applied during welding, use special equipment for it, and use a higher amperage than other cast steels.

NOTE: Any kind of break or crack can be fatal when working with this type of material because high carbon steel is very brittle, which means that it will not deform before it cracks or breaks.

How do you weld cast steel?

When it comes to welding cast steels, your best option is going to be the GMAW process. The FCAW and TIG/GTAW processes can also be used, but they will generally require more preparation and post-processing than GMAW.

The key to welding cast steels is patience. You cannot rush the process or else you will severely weaken the final product, if not ruin it completely. Slow, steady heat application works best with this material type which means using a low welding speed rate at an extremely low heat input.

This is because when you weld cast steel, your weld puddle cools very quickly. If you try to force too much heat into it or apply the heat at an excessive rate, the entire puddle will rapidly solidify and become useless.

The key here is to allow time for the energy in your welding arc to transfer into your puddle. It should be absorbed slowly, evenly, and patiently. Too fast or forceful of heat input will only cause the puddle to solidify before you can even get it started.

NOTE: Once your cast steel welding project is complete, make sure you clean out the weld heat affected zone extremely well. The process used for this varies depending on the type of alloy you are working with.

Welding Cast Steel Step By Step

Step 1 – Grind surfaces flat enough for good fusion between parts

Grinding out any old brazing joints or cracks in the part before welding it together will make the weld much stronger. It is important to clean both sides of the part evenly and make sure that there are no gaps between them.

Step 2 – Use a filler material with a low-hydrogen content

The choice of filler rod will have a significant impact on the final quality of your weld. You should use a filler rod with the lowest hydrogen content possible.

Step 3 – Preheat if necessary

Preheating your cast steel is recommended for two reasons. It will help ensure that the material reaches welding temperature more quickly and you’ll be able to get your weld started much faster.

Step 4 – Position filler material correctly

When you’re welding cast steels, the filler rod should be placed at an approximately 45-degree angle directly into the weld puddle. The more consistent your arc is, the better.

Step 5 – Take slow, steady welds with short arc lengths

Your goal is to use a robot style of welding in order to maintain a very stable, even heat input and avoid any sudden movements which could drop the temperature of your alloy.

Don’t stop welding until the entire weld is finished. Your filler material should be melted into the steel puddle for maximum strength and durability.

Any excess filler metal on the outside of your weld can be removed with a grinder or other tool after you finish welding.

NOTE: Complex shapes may require several different pieces of cast steel to create the final product.

Step 6 – Clean carefully after welding

Once you’re done, leave everything alone until it cools down enough that reaching into it will only result in pain. As soon as this happens, pick up whatever part has been welded first (probably the one facing upwards) and start removing all excess slag using your wire brush or a chipping hammer.

Once everything has been removed, pick up the other part and do the same thing except this time keep going until you have reached either metal!

NOTE: The slag should come off easily as long as it's cooled down enough so refrain from using too much force otherwise you risk denting or even ruining your weld completely.

Welding cast steels can be done safely as long as you have the right equipment and know how to handle the material.

Tips for welding cast steel

Here are some basic tips that you should always consider when welding cast steel:

  • Use a wire feed welder with low heat input and preheat your material to decrease the risk of cracking.
  • Don’t forget to use stainless steel filler material instead of plain steel in order to prevent distortion and improve the finish quality.
  • Sometimes, depending on the carbon content, you may have to adjust the wire feed speed.
  • Be careful not to let your cast steel get too hot by shielding it or cooling it with water.
  • Keep in mind that thicker pieces of material will need more time for heating and cooling before welding begins.
  • Use a TIG welder instead of an arc welder if the cast steel cracks often—it’s more difficult to work with this kind of material.
  • Always refer to the welding guide for your specific cast steel product.

Basic safety tips

There are a few basic safety tips that you should always consider before welding cast steel:

  • Wear heat-resistant gloves and footwear, as well as a fire-resistant apron and a welding helmet or hood.
  • Wear earplugs and a dust mask because the addition of manganese, sulfur, and phosphorus can produce harmful fumes during welding.
  • Make sure that you’re not breathing in any gases and particles from your cast steel before you start welding.
  • Weld in a well-ventilated area to make sure that the fumes and gases do not affect you or other people in your work environment.
  • Be careful not to touch hot pieces of material before they’re cooled completely without some kind of protection, such as leather gloves and boots.

Check my best 3 welding helmets below:

Can you stick weld cast steel?

You can definitely use stick welding to weld cast steel. However, it’s important that you only do this if you’re experienced with stick welding and know how to do it without causing any damage.

I highly recommend using TIG welding with cast steel instead of MIG or stick welding if you’re not experienced.

NOTE: You Steel can be dirty or not perfectly cleaned when using a stick welder. This is a Great advantage over TIG welding.

Why do I recommend TIG Welding for Cast Steel?

TIG welding is more difficult than MIG or stick welding, but it’s also much safer.

The materials that you can weld using TIG are limited compared to those that your standard arc welder can work with, which is why I recommend trying TIG on simpler pieces of material first before even attempting to weld cast steel.

NOTE: Your metal must be perfectly clean when using TIG welding.

Can you MIG weld cast steel?

You can definitely MIG weld cast steel, but I do not recommend it. This process requires more experience than TIG welding and you will need to use stainless steel filler material instead of plain steel wire.

TIG welding is faster than MIG welding and doesn’t suffer from as many issues such as spatter, which can cause your finished product to look sloppy. It will also put less strain on your arms and wrists.

It’s harder to use a TIG welder with cast steel because of the control that it takes to prevent warping and cracking, but once you do it, you’ll see how well it works and why I recommend using TIG welders for cast steel.

TIP: Read 8 Tips for MIG Welding Beginners

What is the best way to TIG weld cast steel?

The best way to TIG weld cast steel is to treat it like any other type of material.

You need to set up your equipment, which includes using TIG stainless steel rod instead of plain steel.

ER308L - TIG Stainless Steel Rod - 36" x 1/16

You also need to be able to see the difference between the different colors that the metal turns as you heat it up so that you know where not to weld and how long you should wait before welding again.

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