Journal of Powder Metallurgy & Mining
Open Access

Owing to the loss of the delicate equilibrium between the component phases due to thermal and mechanical working effects, duplex stainless steels are classified as difficult-to-machine. With these steels, selective laser melting is gaining traction as an additive technique for obtaining near-net form manufacturing solutions. However, post-printing machining is required to variable degrees, and the machinability responses of the laser melted duplex stainless steels must be taken into account [1]. This research fills that need by examining the mechanics of machining using laser melted duplex stainless steels in an experimental setting. The machinability of specimens printed using the most promising laser melting process conditions is assessed by comparing them to their wrought equivalents and determining the differences in responsiveness between the as-built and solution annealed stages. Cutting forces and thermal measurements show that the results are better.

The bi-phase austeo-ferritic microstructure of duplex stainless steel has acquired a lot of momentum recently due to its suitability for applications requiring strong corrosion resistance and mechanical strength. Due to their high toughness, work hardening rate, and limited heat conductivity, duplex stainless steels have poor machinability [2-4]. Work hardening is often regarded as the most damaging property of these alloys, with deformation increasing the austenite phase's hardness and strength. The production of micro cracks along machined surfaces as a result of the difference in deformability of the -ferrite and -austenite phases, as seen by Jiang et al. when grinding hot isostatically treated duplex stainless-steel, is a result of this work hardening tendency. Another factor that contributes to duplex stainless steels' poor machinability is their high carbon content.’ Additive manufacturing allows for near net-shape fabrication, which saves time and money by lowering the number of machining processes needed for a finished component. In addition, point-by-point consolidation of metal powders using procedures like selective laser melting may affect microstructures and machining reactions. The majority of research has focused on alloy design and a fundamental knowledge of the laser melting process, with little emphasis paid to the machinability of laser produced components. This is beginning to change as researchers look at the machinability of laser melted alloys, analysing the effects of both process conditions and machining settings on cutting forces, surface quality, and other critical reactions.

However, SLM showed a stronger work hardening tendency than wrought alloy, resulting in a 22 percent increase in axial force. Aziz et al. investigated cutting temperatures and cutting pressures during ball end milling on chromium molybdenum and maraging alloys with a composition similar to duplex stainless steel. With lower cutting temperatures and machined residual stress, the tougher maraging steel showed improved machinability. Because Davidson and Saeidi. state that laser melted duplex stainless steel contains primarily ferrite with trace austenitic grains as a result of the quick cooling process, machinability characteristics might be understood to be more aligned with a ferritic stainless steel. Stainless steels that are ferritic are often easier to process than stainless steels that are austenitic. This supports better machining in laser-melted components, as well as the capacity to re-establish microstructure equilibrium following a solution annealing heat treatment. The authors recently published their findings on the mechanism machining of laser melted duplex stainless steels, which specifically emphasised the probable relevance of metallographic reactions to cutting pressures. The goal of this work is to expand on this research by examining the mechanics of machining laser melted duplex stainless steels in greater detail, as well as to clearly demonstrate the machinability of laser melted duplex stainless steels in comparison to wrought duplex stainless steels [5]. The increased machinability expected from the metallographic studies will be tested using laser melted samples in both as-built and solution annealed settings.

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2.  Dolinšek S (2001) Work-hardening in the drilling of austenitic stainless steels. J Mater Process Technol. 133 (1): 63-70.

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3.  Jiang L, ParoJ , Hänninen H,  (1996) Comparison of grindability of HIPped austenitic 316L, duplex 2205 and super duplex 2507 DSS and as-cast 304 stainless steels using alumina wheels. J Mater Process Technol 62 (1–3): 1-9.

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4. GM Krolczyk, Legutko S (2004) Experimental analysis by measurement of surface roughness variations in turning process of duplex stainless steel. Metrol Meas Syst 21 (4):759-770.

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5.  BaiY,  Zhao C,  Yang J (2021)  Microstructure and machinability of selective laser melted high-strength maraging steel with heat treatment .J Mater Process Technol 288 :11690.

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