Alpha single-phase brass (from H96 to H65) has good plasticity and can withstand cold and hot working, but it is easy to show medium temperature brittleness during forging and other hot working. Its detailed temperature scale varies with the difference of zinc content, usually between 200 and 700 C. Therefore, the temperature of hot working should be higher than 700 C. The main reason for the occurrence of medium temperature brittle zone of single phase alpha brass is that there are two ordered compounds Cu3Zn and Cu9Zn in the alpha phase zone of the Cu-Zn alloy system, which change orderly when heated at medium and low temperature and make the alloy brittle. Otherwise, there are trace lead and bismuth harmless impurities in the alloy and copper constitute eutectic thin films with low melting point scattered on the grain boundary, and intergranular fracture occurs during hot processing. Theoretical notes show that the medium temperature brittleness can be effectively eliminated by adding trace cerium. Two-phase brass (from H63 to H59) exhibits a beta solid solution based on electronic compound CuZn in addition to a phase with good plasticity. The plasticity of the beta phase is very high at low temperature, while the toughness and brittleness of the beta'(ordered solid solution) phase at low temperature. Therefore (alpha + beta) brass should stop forging in hot state. Beta brass containing more than 46%-50% zinc can not stop pressure processing because of its hard and brittle nature.