The name "ferrous metals" and "nonferrous metals" is often misunderstood. Black metals must be black, but they are not. There are only three ferrous metals: iron, manganese and chromium. And neither of them three is black! Pure iron is silvery white; manganese is silvery white; chromium is grey. Because the surface is often rusty iron, a mixture of magnetite and brown covered with a layer of black ferric oxide, is looked black. So people call it "black metal"". Often referred to as "black metallurgical industry", mainly refers to the iron and steel industry. Because the most common alloy steel is a steel and chromium steel, so, people manganese and chromium can be considered as a "black metal".
According to the color and property of metals, metals are classified into ferrous and non-ferrous metals. Ferrous metals mainly refer to iron, manganese, chromium and their alloys, such as steel, pig iron, iron alloy, cast iron and so on. Metals other than ferrous metals are called nonferrous metals.
Metal is a big family. There are 86 kinds of metal in the world now. People usually divide metal into two major categories, ferrous and non-ferrous metals.
