Taper turning of super duplex stainless steel: tool life, tool wear and workpiece surface roughness

Abstract

The combination of several alloying elements in the super duplex stainless steels (SDSS) provides high corrosion resistance, high strain-hardening coefficient and low thermal conductivity. These properties make them usually used in industries from oil and gas segment. On the other hand, the same properties reduce their machinability, because they cause the formation of built-up edge and a large notch wear on the tools used to cut these steels. The goal of this work was to develop the best combination of machining strategies, tool geometries and cutting feeds, using high pressure coolant jet (70 bars), aiming long tool life and high process productivity, allied to the lowest surface roughness possible. To achieve this goal, two machining strategies (longitudinal and taper cutting) were tested in combination with two indexable insert geometries (conventional and wiper) and different feeds for turning of SDSS-SAF-2507. The condition using the conventional insert in longitudinal cutting with low feed rate presented the longest tool life among all the conditions tested, with low roughness values. In opposition of what is stated in the literature, notch wear was not preponderant to the end of tool life even in longitudinal cutting and, consequently, the use of taper cutting strategy did not improve tool life. Built-up edge was formed in all conditions where wiper inserts were used.