There isn't a fixed number of "ferrous metals" because the term is somewhat broad. It generally refers to metals containing iron, but the exact definition can vary. Here's a breakdown:

Technically: There's only one ferrous metal: Iron (Fe).

Practically: "Ferrous metals" often include alloys of iron with other elements, like:

* Steel: An iron alloy with carbon (usually less than 2%). This is the most common ferrous metal, with various types depending on the other elements added.

* Cast Iron: Iron with a higher carbon content than steel, making it harder and less ductile.

* Stainless Steel: Steel containing chromium for corrosion resistance.

* Nickel Steel: Steel with nickel added for strength and toughness.

* Other Iron Alloys: Various other alloys are possible with elements like manganese, molybdenum, etc.

So, while there's technically only one ferrous metal (iron), the term is often used to encompass various iron alloys, making the number of "ferrous metals" effectively very large.