Study of the failure of one machining tool

This paper presents the study of the failure of one tool that was broken in two pieces inducing a serious damage in the component that was being machined. The main difficulty for this analysis came up against the need of keeping the broken tool in the as-received condition due to legal requirements. Due to this situation it was not possible obtaining tensile test specimens to determine the strength and ductility of the material or metallographic samples which could reveal its microstructure. Consequently, the study was restricted to observing the fracture surfaces in the scanning electron microscope and identifying by X-ray energy dispersive spectrometry, the nature of the substances which could have played a role in the failure process. This analysis allowed identifying the failure origin was sited on a notch induced on the periphery of the tool in a zone where a section change and a marked stress concentration existed. This notch was covered by a dark substance whose composition was near the same than that of the blueing coating, indicating that it was already opened when this surface treatment was applied. These results, leaded to a conclusion blaming the machining operation previous to the blueing coating for the failure.