Tool wear and machinability of HIPed P/M and conventional cast duplex stainless steels

In this study, active wear and failure mechanisms of TiN-coated cemented ca rbide tools with internal coolant supply when drilling of HIPed P/M Duplok 27 and conventionally-produced duplex stainless steel ASTM A8190 1A have be en investigated. Stainless steels are often considered as poorly machinable materials. In P/M-produced duplex stainless steels, there are more hard ox ide particles causing machining difficulties from the wear point of view. H igh strength and work hardening rate cause also difficulties from the machi ning point of view. In this study, drilling tests carried out by using a ma chining centre and optical microscope are presented. Chips were analysed by SEM electron microscopy and EDS-analysis. The machinability of duplex stai nless steels is examined based on tool life and cutting speed presented by upsilon -T-diagrams. The effect of cutting speed and the differences betwee n powder metallurgically and conventionally-produced duplex stainless steel s are also analysed by chip formation and tool wear mechanisms. Based on th e 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 mm, can be applied from machinabi lity point of view. P/M duplex stainless steels with hard oxides decrease m achinability. Tool wear criterion, VB-value of 0.3 mm, is reached after dri lling time of 10 min, when 50 m/min cutting speed and 0.2 mm/r feed rate ar e utilised. (C) 2001 Elsevier Science B.V. All rights reserved.