 A reduction in fracture toughness may also be attributed to the embrittlement effect of impurities , or for body @-@ centred cubic metals , from a reduction in temperature . Metals and in particular steels have a transitional temperature range where above this range the metal has acceptable notch @-@ ductility while below this range the material becomes brittle . Within the range , the materials behavior is unpredictable . The reduction in fracture toughness is accompanied by a change in the fracture appearance . When above the transition , the fracture is primarily due to micro @-@ void coalescence , which results in the fracture appearing fibrous . When the temperatures falls the fracture will show signs of cleavage facets . These two appearances are visible by the naked eye . Brittle fracture in steel plates may appear as chevron markings under the microscope . These arrow @-@ like ridges on the crack surface point towards the origin of the fracture . 
