What is steel? And how is it related to iron?

by Jason Crawford · April 9, 2017 · 1 min read

Here’s another example of my staggering ignorance of basic technology.

I heard long ago that steel is an alloy of iron and carbon. Only recently did I learn that cast iron is also an alloy of iron and carbon—and that steel actually has a lower carbon content than cast iron: under 2% carbon for steel, vs. more like 3–4% for cast iron. So steel is, in a sense, more iron than “iron”. Pure iron, it turns out, is too soft and not very useful.

One site helpfully explains:

When we talk about “steel”, we usually mean “steels”; broadly speaking, steels fall into four groups: carbon steels, alloy steels, tool steels, and stainless steels. These names can be confusing, because all alloy steels contain carbon (as do all other steels), all carbon steels are also alloys, and both tool steels and stainless steels are alloys too.

That clears that up!

As an aside, another mistaken notion I had was that steel was invented in the 19th century. I thought this because I had an idea that early trains and tracks were made of iron, and later converted to steel. But it turns out steel has been made since antiquity—what was invented in the 19th (or early 20th?) century was cheap steel, that is, better processes for manufacturing steel more cheaply and reliably.

Social media link image credit: Flickr / włodi, CC BY-SA 2.0