Tungsten is a rare metal with high melting point, which can improve the high temperature hardness of steel. It belongs to the group VI B of the sixth cycle (the second long cycle) in the periodic table of elements. Tungsten is a silver-white metal with a steel-like appearance. Tungsten has high melting point, low vapor pressure and low evaporation rate. The chemical properties of tungsten are very stable. It does not react with air and water at room temperature. Without heating, hydrochloric acid, sulfuric acid, nitric acid, hydrofluoric acid and aqua regia of any concentration have no effect on tungsten. When the temperature rises to 80 100 C, all the above acids except hydrofluoric acid have weak effect on tungsten. Tungsten can dissolve rapidly in the mixed acid of hydrofluoric acid and concentrated nitric acid at room temperature, but it does not work in alkali solution. In the presence of air, tungsten can be oxidized to Tungstate by molten alkali. In the presence of oxidants (NaNO3, NaNO2, KClO 3, PbO 2), the reaction of tungstate formation is more intense. It can combine with oxygen, fluorine, chlorine, bromine, iodine, carbon, nitrogen and sulfur at high temperature, but not with hydrogenation.