Metal is a substance with luster, good electrical conductivity, thermal conductivity and mechanical properties, and has a positive temperature coefficient of resistance. Metal is a big family, there are 86 kinds of metal in the world. Usually, according to the characteristics of the color and nature of the metal, the metal is divided into two categories: black metal and non-ferrous metal. Ferrous metals mainly refer to iron and its alloys, such as steel, pig iron, ferroalloy, cast iron, etc. Metals other than ferrous metals are called non-ferrous metals.

The name ferrous metal and non-ferrous metal often makes people misunderstand that ferrous metal must be black, but it is not. There are three kinds of ferrous metals: iron, manganese and chromium. And none of them are black. Pure iron is silvery white; Chromium is silvery white; Manganese is off-white. Because the surface of iron is often rusted, covered with a mixture of black ferric oxide and tan iron oxide, it looks black. So people call it "black metal." Often said "ferrous metallurgy industry", mainly refers to the iron and steel industry. Because the most common alloy steels are manganese steel and chromium steel, manganese and chromium are also counted as "black metals".

In addition to iron, manganese, chromium, other metals, are considered non-ferrous metals