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Green machining (machining green/un-sintered powder compacts) has prospects in dealing with poor machinability of sinter-hardened powder metallurgy (PM) steels. However, it has the limitation of resulting in a poor-quality machined surface and exit-edge (the edge from where the cutting tool leaves the workpiece) than that of counterparts machined post-sinter-hardening. The feasibility of overcoming the limitation using machining parameters is a scarcely explored area. Investigating this area through understanding the material removal mechanism constitutes the motivation of the present study. The study analyses the turning of green and sinter-hardened compacts prepared from FLC-4608 (Metal Powder Industries Federation denomination, Standard 35) steel powder-premix. Results indicated that, in green machining, a lower feed rate regulates the attribute of powder particles' plucking in the material removal mechanism and improves machined surface quality. Increased cutting velocity and feed rate were found to reduce the size of exit-edge damage (exit-edge-breakout) and improve edge quality. It was determined that these quality improvements could not feasibly achieve the machined surface and exit-edge quality comparable to a compact machined post-sinter-hardening. Nevertheless, green machining has significance in producing sinter-hardened PM components due to its advantages over machining sinter-hardened compacts, i.e., lower F c (cutting force component in the cutting velocity direction) and favourable chip morphology, as identified in this investigation. The present study is potentially helpful to PM industries for green machining considerations in the manufacturing process flow. • The attributes of the material removal mechanism, and their correlation with machining parameters and machinability. • Improved accuracy in the evaluation of exit-edge quality. • Comparison of machining green compacts with machining sinter-hardened compacts, to investigate the feasibility of controlling the green machining process with the help of machining parameters to overcome the process limitations and produce outcomes comparable to the machining of sinter-hardened compacts. [ABSTRACT FROM AUTHOR]

Liquid phase sintering (LPS) of powder metallurgy (PM) components is a well-recognised strategy to enhance the densification of pressed-and-sintered compacts. This work reports the investigation on the liquid phase formation when a Fe–Ni–Mn–C–B master alloy (MA) is used as a boron carrier in combination with two iron base powders pre-alloyed with Mo. Through differential scanning calorimetry tests, quantitation of the microstructure with the help of artificial intelligence, as well as measurement of sintered density and strength as a function of sintering temperature, it was possible to unravel the mechanisms that take place before and during LPS. It was confirmed that a cascade of events takes place in the solid state prior to reaching the temperature necessary for a eutectic reaction to form a liquid. Additionally, the pre-alloyed Mo content was identified as a factor that modifies the initiation of LPS but not the LPS mechanisms per se. [ABSTRACT FROM AUTHOR]

The green machining process is an interesting approach for solving the mediocre machining behavior of high-performance powder metallurgy (PM) steels. This process appears as a promising method for extending tool life and reducing machining costs. Recent improvements in binder/lubricant technologies have led to high green strength systems that enable green machining. So far, tool wear has been considered negligible when characterizing the machinability of green PM specimens. This inaccurate assumption may lead to the selection of sub-optimum cutting conditions. The first part of this study involves the optimization of the machining parameters to minimize the effects of tool wear on the machinability in turning of green PM components. The second part of our work compares the sintered mechanical properties of components machined in green state with other machined after sintering. [ABSTRACT FROM AUTHOR]

This study was undertaken to thoroughly characterize the relationship that exists between microstructure, strength and fracture mechanisms of Fe-Mn-C powder metallurgy steels. Indeed, up to now the peculiar fracture behaviour of PM components made from this metallurgical system was not clearly understood by the PM community. A design of experiments (DOE) approach was used to determine the effect of chemical composition on tensile properties of Fe-Mn-C PM steels components and therefore on the fracture mechanisms leading to failure. Quantitative data describing fracture mechanisms as a function of sintered microstructure were obtained and compared against tensile strength measurements. Results led to the identification of microstructural conditions for which Fe-Mn-C PM steels are susceptible to the detrimental effect of Mn-oxide inclusions. It was found that the presence of martensite having a hardness higher than 661 HV exacerbates the detrimental effect of inclusions present in sinter necks, which explains the decreasing tensile strength observed with increasing carbon concentration. The beneficial effect of the divorced eutectoid phase as a secondary microstructural constituent is also discussed. Knowledge generated regarding the fracture behaviour of components made from this family of PM alloys allowed for the optimization of the volume fraction of microstructural constituents to maximize tensile properties. This work provides information that was missing up to now regarding the capabilities and limitations of admixed Mn PM steels in terms of tensile properties and allows the formulation of design guidelines to alleviate the adverse effects of Mn oxidation. [ABSTRACT FROM AUTHOR]