Metal materials are divided into two categories: one is ferrous metals, including steel, mainly alloys of iron and carbon;
The second is non-ferrous metals, that is, metals other than ferrous metals, such as gold, silver, copper, tin, lead, etc.; non-ferrous metals are further divided into heavy metals, that is, metals with larger specific gravity, such as tungsten, lead, etc., and light metals, that is, higher specific gravity. Small metals, such as magnesium, aluminum, etc.; rare metals, that is, more precious and rare metals, such as platinum, gold, radium, etc.