When classifying metals, focusing on a particular property is most often used as a way to divide them into two groups. Is this metal ductile or non-ductile? Is it magnetic or not?
When it comes to ferrous metals, one basic quality determines the groups: whether the metal contains iron. If iron makes up a large percentage of its composition, the metal is considered to be ferrous. If it contains no iron, or just trace amounts of it, it will be labeled a non-ferrous metal.
Beyond that, it becomes more difficult to apply general labels on the groups and the metals’ properties. While ferrous metals can range from iron itself to stainless steel, the alloying elements greatly affect the metal’s characteristics. For example, most ferrous metals are magnetic. But austenitic stainless steel is not, due to the high levels of nickel added to the steel for alloying. The nickel allows the steel to form in a crystal structure that is mostly austenite – and austenite is not magnetic.
So although it can be difficult to generalize about all ferrous metals as a group, there are some general characteristics that can be made about them. Ferrous metals are very hard and strong, especially in comparison to non-ferrous ones such as tin or copper. They’re vulnerable to rust due to their high percentage of iron, unless given corrosion resistance through alloying elements or protective coatings. And they’re usually (but not always) magnetic, which makes them very useful for motor and electrical applications.
The most common categories of ferrous metals include:
- Carbon steel: there’s certainly no question of this being a ferrous metal, with over 90% of its composition being made up of iron. It is very hard and can keep a sharp edge, making it well-suited for mechanical uses such as drill bits and blades.
- Cast iron: this metal is exceptionally hard due to its high levels of carbon, but the carbon also makes it quite brittle. For this reason, cast iron is now primarily used for smaller machine components or cookware.
- Stainless steel: the most commonly used type of ferrous metals, especially for consumer goods. The addition of chromium is what makes a steel stainless, and gives it good corrosion resistance. And it’s magnetic, which is why you can stick magnetics on your refrigerator.
- Alloy steel: the properties of this group of ferrous metals can vary much more widely than the others, since the alloy is specifically formulated for a particular purpose. So while alloy steels are ferrous, the added elements allows the metal to be tailored for more strength, ductility, hardness or other property.