Why Is Cast Iron Cookware Brittle?

Have you ever asked why is cast iron cookware brittle?

It’s true that one of the benefits of using cast iron is it’s durable and long-lasting.

On the other hand, it’s also true that cast iron is brittle, meaning it can break.

So it would be good to understand why and what you can do to keep that from happening.

Allow me to explain.

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There are several factors that go into explaining why cast iron is brittle. First is the carbon content. The higher the carbon, the more brittle the cookware will be. Additionally, the presence of graphite flakes gives cast iron a weaker tensile strength. Think of cast iron as having similar properties to glass. Both are hard, and both are brittle, making them susceptible to breaking if dropped.

1. Cast Iron Has Higher Carbon Content

As this question gets into physics and chemistry, I must rely on experts to find an answer.

What is Carbon?

a nonmetal element that exists in different forms: solid, graphite, diamond
the graphite form is what’s in cast iron
graphite is the only nonmetal element that conducts electricity (which isn’t important to cast iron cookware)

A science advisor in Physics Forums says, “Cast Iron is an old technology, a low-cost material, with 2.06% to 6.67% carbon. The carbon is introduced from the fuel during smelting. The excess carbon takes the form of graphite flakes that weaken the material and make it brittle.

Carbon is needed to make the cast iron hard because the iron itself isn’t.

2. The Presence of Graphite in Cast Iron

Graphite is a form of carbon, as mentioned above.

One metallurgy enthusiast on Quora explains the presence of graphite this way, “Grey cast iron is brittle because of the graphite flakes present in it. The flakes with pointed ends act as stress raisers. These flakes then behave as cracks causing brittle fracture when load is applied.”

In other words, graphite contributes to why cast iron is brittle

3. Cast Iron Has Weaker Tensile Strength

Tensile strength has to do with the resistance of the material to breaking under tension.

Compare that with compression strength which is the resistance of a material to breaking under compression.

According to Reliance Foundry, cast iron “cannot be bent, stretched, or hammered into shape, since its weak tensile strength means that it will fracture before it bends or distorts. It does, however, feature good compression strength.”

4. Cast iron Has Properties Similar to Glass

Cast iron cookware is generally made using gray cast iron (as opposed to white, ductile, or malleable).

The properties have to do with its hardness, toughness, and ductility.

Each type of cast iron has different properties, and gray has properties most similar to glass in that it’s hard but can break.

You’ve already seen the various reasons cast iron is brittle, but there is a reason why gray cast iron is still the most used.

Once again, I will quote Reliance Foundry: “Gray iron is not as ductile as other forms of cast iron and its tensile strength is also lower. However, it is a better thermal conductor and has a higher level of vibration damping. It has a damping capacity that is 20–25 times higher than steel and superior to all other cast irons. Gray iron is also easier to machine than other cast irons, and its wear resistance properties make it one of the highest volume cast iron products.

Torsion Test Demonstration: Cast Iron and Carbon Steel

Ways Cast Iron Cookware Can Break

Truthfully, much of what I wrote has little to do with cast iron cookware itself because it is made thick and not prone to breaking.

I mean, no one purposely tries to break their cast iron skillet or thinks that dropping is an okay thing to do.

Funnily though, should you like to know how to break one, see How to Break a Cast Iron Frying Pan – 3 Steps

All kidding aside, the reason cast iron cookware is thick is that it would break much more easily if it were thinner.

However, that doesn’t mean it can’t break (or warp or crack).

Therefore, it’s good to know the ways it can happen so you can avoid doing those things.

If you store your pan in an upper cabinet, and it accidentally drops when you are taking it out, it is more likely to break than if it falls a shorter distance. But dropping it is never a good idea!
Another way cast iron might break is when transporting or shipping. If you don’t pack the cookware properly, I’ve seen pictures of handles broken off.
High heat is more likely to cause warping, but it’s been known to cause cracking or breaking as well.
And sudden temperature change such as putting a hot skillet in cold water is sure to have an adverse effect on your cast iron pan.

That being said, there are times when you might want to break cast iron. It probably won’t be your cookware, but, as you know, many other things are made of cast iron.

For example, in the video below, this man needed to break up some radiators to take them in for scrap.

How to Break Up Old Cast Iron

Final Thoughts

Well, that’s all I have.

And since I am not an expert on the properties of cast iron cookware, I hope you have enjoyed hearing from some who are.

Why is cast iron cookware brittle?

Because the carbon turns into graphite and affects the tensile strength during the smelting process.

But, just because it’s brittle, that in no way makes it inferior cookware.

In the words of one Quora user, cast iron is a “unique and wonderful material with properties no other metal has.”

Have you ever broken your cast iron skillet? If so, how did it happen?