Eli5: why is steel so special?


What makes steel such a universally used metal? If we didn’t have steel, what’s the next most universally applicable metal?

In: 5

It’s a hard, sturdy metal, perfect for construction. Most metals on the periodic table are actually quite soft. Steel is iron plus carbon, which makes it stronger, and suitable for construction. There are some strong metals you could use, like tungsten or titanium, but the benefit of steel is that both iron and the carbon necessary (coal) are very, verywidely available, and therefore very cheap (comparatively).

Your closest reasonable substitute would probably be iron, the base of steel, but it’s much more prone to rust, and shorter lives. To make some things like beams, you could use would, but they’re not as long lasting or as durable. Additionally, steel is more versatile, making things like tubes and shapes that wood can’t.

When you talk about materials, you have several things to consider and you very often need to compromise between them:

Is it cheap?

Is it durable?

Is it easy to make items with this material?

What are you going to use it for?

Steel is ubiquitous because it scores a “good enough” for everything. Take the transition from the bronze age to the iron age for example. Bronze can be cast at a much lower temperature than Iron or Steel. So it’s much easier to make items with bronze than with iron. However, bronze is a mixture of tin and copper and tin is pretty rare and thus pretty expensive. On top of that, bronze is relatively “soft” for a metal, so you cannot always use it. Iron on the other hand is very cheap. Like dirt cheap, because you have so much of it everywhere in Earth’s crust. So everyone with an oven in 1000 BC could smelt using iron because they likely had an iron source nearby. However, it is very easy to oxidize (=rust) which can happen during the smelting process. So Iron gets a high score in pricing, but a low score in durability or easiness of use.

And then came Steel. Now, steel is very hard, so you can use it for pretty much anything. Steel is primarily iron, so it’s also very cheap. With the carbon alloying you use (+other metals like chromium), you also prevent rusting, so it’s also durable. People then started to use steel more and more.

So it’s always a matter of compromising. If you need a lot of it and you need it to be durable, the price becomes a problem, so you use steel. If you don’t need a lot but you need it extra-durable, you’ll probably use nickel or chromium. If you need something for electric conduction, you’ll use copper or gold. If you need something very light, you’ll use aluminum.

All metals have an application, but when it comes to pricing, steel beats them all.

Steel has two great things going for it:

* It’s strong
* It’s cheap

This is actually why ironwork ingredients become popular in the first place; early ironwork was probably worse than bronze at the same time, but iron was more common than copper or tin.

Iron and carbon (the main ingredients of steel) are both very abundant. For reasons related to how nuclear fusion works(!), iron is the most common metal on Earth and the second most common in the crust. Aluminum, the most common metal in the crust, is more expensive to make and not as strong in many ways, though it other ways it is stronger and lighter. (As an aside, aluminum is more abundant in the crust despite being less abundant on the planet because iron is heavier and so sank down further when the Earth was still young and hot and mostly liquidy).

Still, steel has a good combination of strength, hardness, and flexibility, and we know how to make different kinds with lots of different properties very well.

If we didn’t have iron, aluminum is probably the most likely substitute, as it’s also strong and relatively inexpensive. We could probably develop alloys with all kinds of different properties, except magnetism (generally speaking, only iron, nickel, and cobalt can be magnetic).

The thing is that aluminum is impossible to purify from ore in large quantities before electricity, but we’ve been making some form of steel for about 2000 years and iron at least 2000 years before that!

Before about 150 years ago, steel was not yet cheap and people used wrought iron and cast iron for similar applications (like making railways, bridges, some large buildings, etc), though they weren’t as good.