Machinability of Duplex and Super Duplex Stainless Steels

Abstract

This master thesis aims at investigating the machinability of duplex, grade 1.4462 and super duplex stainless steels, grade 1.4410 from a tool wear perspective, assessing factors such as cutting forces, chip thickness, and wear evolution. To investigate it, two types of tests were used: orthogonal and longitudinal with constant spiral cutting length. In orthogonal cutting tests, acquired force measurements, contact lengths, and chip thicknesses were studied. For longitudinal tests, forces and tool wear patterns were analysed when machining stainless steels using di!erent tool grades. The wear formation was investigated using stereo optical microscopy, Scanning Electron Microscopy, and Energy Dispersive Spectroscopy. Orthogonal testing showed correlation between average forces, chip thickness and tool-chip contact length. Significant di!erences in tool-chip contact length between grades GC2220 and GC2025 were observed. Overall super duplex stainless steel machining resulted in higher average cutting forces, lower average chip thickness, and lower contact length as compared to those of the duplex stainless steel. Regarding the cutting tool wear, there is a noticeable variation in type and dimension of wear for di!erent grades. The most frequently occurring wear types were: notch wear, built-up-edge formation and crater wear. There is also a di!erence between wear formation for duplex and super duplex stainless steel, where both size and localization varied, while types of wear remained similar. Among the cutting tool grades GC1205 had the lowest wear and cutting forces, suggesting potential for future implementation of superalloy-intended tools for these materials. The overall flank wear was higher when machining super duplex stainless steel