Hot and Cold Impact Strength
Steels may fissure when exposed to abrupt temperature changes, whether during tempering or usage. Hot and cold impact strength is closely related to toughness, heat dilation and conductivity and tensile resistance. Fissures are produced when the thermal stresses affecting the steel are higher than its tensile resistance.
Design and surface quality of tools is of the greatest importance, since surface flaws, sharp changes or overlapping surfaces may produce high stress concentrations.
We must also note that non-metallic inclusions, especially needle-shaped are also great localized concentrators of stress.
