Toughness is an important performance tool steel, toughness, impact test determines the material force in breaking down the ability of rupture. The higher the toughness of the material, the smaller the risk of brittle fracture, thermal fatigue strength is also higher. For a measure of the tendency to brittle fracture die, significance and impact toughness test.      Impact toughness refers impact notch impact on the cross-sectional area of the absorbed energy, while the impact energy refers to the provisions of the specimen shape and size when the next action in the impact test force to break the power absorbed. Charpy impact test has u-notch impact test (open into u-notch specimens), v-notch Charpy impact test (sample open into v-notch) and Izod impact test. Many factors influence the impact toughness. Different materials mold steel impact toughness vary greatly, even if the same kind of material, due to the state of different organizations, different grain sizes, different stress state is not the same impact toughness. Usually the more coarse grains, the more serious carbide segregation (ribbon, mesh, etc.), the more coarse martensite steel etc. will induce brittle. Different temperatures, impact toughness is not the same. Generally, the higher the temperature, the higher the impact toughness, and under some very tough steel at room temperature, when the temperature dropped to minus 20 ~ 40 ℃ when the steel becomes brittle. In order to improve the toughness of steel, must take reasonable forging and heat treatment processes. Forging should break as carbides and carbide segregation reduce or eliminate, prevent grains grow excessively, the cooling rate is not too high when the heat treatment and quenching, to prevent the internal stress. Die before or during use should take some measures to reduce internal stress.