Abstract
In this study, the wear mechanisms and tribological performance of uncoated and coated carbide tools were investigated during the turning of super duplex stainless steel (SDSS)—Grade UNS S32750, known commercially as SAF 2507. The tool wear was evaluated throughout the cutting tests and the wear mechanisms were investigated using an Alicona Infinite Focus microscope and a scanning electron microscope (SEM) equipped with energy dispersive spectroscopy (EDS). Tribo-film formation on the worn rake surface of the tool was analyzed using X-ray Photoelectron Spectroscopy (XPS). In addition, tribological performance was evaluated by studying chip characteristics such as thickness, compression ratio, shear angle, and undersurface morphology. Finally, surface integrity of the machined surface was investigated using the Alicona microscope to measure surface roughness and SEM to reveal the surface distortions created during the cutting process, combined with cutting force analyses. The results obtained showed that the predominant wear mechanisms are adhesion and chipping for all tools investigated and that the AlTiN coating system exhibited better performance in all aspects when compared with CVD TiCN + Al2O3 coated cutting insert and uncoated carbide insert; in particular, built-up edge formation was significantly reduced.
Highlights
Super duplex stainless steel (SDSS) is a specific type of stainless steel alloys that has a biphasic microstructure, consisting of approximately 50% ferrite and 50% austenite by volume
For applications where the cutting process is characterized by high temperatures in the cutting zone, for instance, in machining of materials with low thermal conductivity, the use of cemented carbide tools coated with self-adaptive PVD coatings is strongly recommended
The authors reported that attrition was the principal wear mechanism at lower speed conditions, while abrasion and diffusion wear mechanisms were the failure modes at higher speed conditions
Summary
Super duplex stainless steel (SDSS) is a specific type of stainless steel alloys that has a biphasic microstructure, consisting of approximately 50% ferrite and 50% austenite by volume. SDSS has a favorable combination of chromium, nickel and molybdenum [1], which provides an attractive combination of mechanical and corrosion properties and is widely applied in aggressive corrosion environments such as gas and oil, petrochemical and chemical, industries. These materials are considered difficult to machine because they have low thermal conductivity combined with high tensile strength and high shear strength and during machining they show a high tendency toward work-hardening [2,3,4]. Another point found during machining of these alloys is the work hardening tendency
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