In this study, active wear and failure mechanisms of TiN-coated solid carbide drills with internal coolant supply when drilling of powder matallurgically produced P/M Duplok 27 and conventionally produced duplex stainless steel ASTM A8190 1A have been investigated. Stainless steels are often considered as poorly machinable materials and normally recognized as difficult materials to machine because of their high toughness, low thermal conductivity and high degree of work hardening. In P/M produced duplex stainless steels there should be more hard particles causing machining difficulties from the wear point of view. High strength, work hardening rates and irregular wear cause problems from the machining point of view. In this study drilling tests carried out by using a machining centre and optical microscope are presented. Chips were analysed by SEM electron microscopy. The machinability of duplex stainless steels is examined based on tool life and cutting speed presented by vT-diagrams. The effect of cutting speed and the differences between powder metallurgically and conventionally produced duplex stainless steels are also analysed based on chip formation and tool wear mechanisms. According to the cutting tests, cutting speeds of 20...100 m/min, feed rate of 0.15...0.25 mm and solid carbide drills, diameter of 8.6 nun, can be applied from machinability point of view. P/M duplex stainless steels with hard oxide particles decrease machinability. Tool wear criterion, VB-value of 0.3 mm, is reached after drilling time of 10 min, when 50 m/min cutting speed and 0.2 mm/r feed rate are utilised. Tool life is rapidly shortened when using higher cutting speeds and feed rates.
