Evidence is presented to show that hard inclusions in iron-base alloys degrade machinability by reducing cutting tool life. Machining experiments have been carried out on Fe-C-Silica and Fe-C-Alumina powder metal compacts containing varying amounts of abrasive. In addition, two stainless steels have been compared. One of these was titanium stabilized hence containing hard TiC particles; the other was unstabilized and free of such particles. In all these experiments the tool wear rate increased with volume fraction of hard inclusions. Abrasive wear mechanisms have been identified using detailed metallography. When machining with high-speed steels, rake face wear by abrasion occurs by a plastic plowing process and this is enhanced if the tool is thermally weakened. When machining with cemented carbide tools the results indicate that the temperatures in the crater region are high enough for the same plastic plowing of tool material to occur. By contrast, temperatures at the flank face are 300–400°C lower and the wear processes are of a different nature.

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