Fracture of cutting tools due to the formation of untempered martensite

Three case studies are presented in which untempered martensite produced during forming or use caused premature failure or failures in unexpected regions. The sources of formation of untempered martensite observed were: laser cutting of circular saws, friction originated from poor fixation of blades, and uncontrolled thermal cycling in the vicinity of a weld. Due to its very high hardness, untempered martensite favors the appearance of microcracks that develop into premature catastrophic failures.