Why is the finished product of cast steel shot black? The casting is made by melting the steel, pouring it into the sand mold for molding, and then cooling and casting. Therefore, the black on the surface of cast steel shot is the color of iron oxide formed by the chemical reaction between the high-temperature steel surface and oxygen in the air. Ferrous oxide is also called iron oxide. Chemical formula FeO Black powder; Melting point 1369 ± 1 ° C, relative density 5.7; Insoluble in water, alcohol and lye, soluble in acid; It is very unstable. It is rapidly oxidized to ferric oxide when heated in air.

Ferrous oxide can be prepared by heating ferrous compounds such as ferrous oxalate under the condition of isolation from air, or by hydrogen in ferric oxide. Ferrous oxide is mainly used as colorant in glass.