Liquid phase sintering is commonly used in powder metallurgy to improve physical properties through densification enhancement. With the aim of combining the advantages of liquid phase sintering and the use of promising alloying elements such as Mn and Si, liquid promoters with complex compositions were designed to provide a low melting point to form a liquid phase below the common sintering temperatures. The properties of these liquid phases were characterised in terms of contact angle, spreading evolution and infiltration. Using a Kru ¨ss drop shape analysis system, both wetting angle experiments and infiltration experiments were performed by changing the substrate characteristics from sintered to green iron specimens respectively. The discussion is based on the different features found for these liquids compared with copper, which is a well known liquid phase former used for improving the properties of low alloy steels. Simulations of the thermodynamic and kinetic processes taking place were performed by combining ThermoCalc and DICTRA software analysis.

Low alloy sintered steels with an optimized content of alloying elements require the use of promising candidates such as Mn and Si which can provide improved properties with minimum contents at a lower and less volatile price. The introduction of these alloying elements in the form of a master alloy powder prevents, to some extent, the oxidation and allows a proper "tailoring" of its composition to accomplish particular goals. In this sense, low melting point alloys are especially interesting since they provide the formation of a liquid phase which enhances sintering and promotes the homogeneous distribution of the alloying elements within the compact. In this work, the "product developing" process of master alloys containing Fe-Mn-Si is described, from the theoretical design to the sintering performance. Low melting point compositions were calculated by using ThermoCalc® software and successively manufactured by gas atomization. Liquid phase features are described in terms of melting temperatures and wetting behavior. The effects of the liquid phase (produced by the added master alloys) are studied by differential thermal analysis and dilatometry. Besides, to depict the behavior of liquid phase during heating, interrupted sintering experiments under high cooling rates were carried out, and the results have been discussed through the microstructure examination.

Oxygen-sensitive alloying elements such as Mn, Si, and Cr have a high potential for improving the properties of low alloyed sintered steels while reducing the alloying cost. However, it is necessary to find a way for avoiding, or at least minimizing, the oxidation of these elements especially during the early stages of the sintering cycle. In this study Mn, Si, and Cr were introduced in the form of a master alloy powder designed to be mixed with the iron base powder and provide the final composition of the steel during the sintering process. The reduction/oxidation phenomena taking place during the heating stage were studied by thermogravimetry, dilatometry, and mass spectroscopy, using either reducing (H 2 ) or inert (Ar) atmospheres. The results show how the difference in chemical activity between base iron powder and master alloy causes the so called ''internal-getter'' effect, by which the reduction of less stable iron oxides leads to oxidation of the elements with higher affinity for oxygen. This effect can be somehow minimized when sintering in H 2 , since the iron oxides are reduced at lower temperatures at which the reactivity of the elements in the master alloy is lower. However, H 2 concentration in the processing atmosphere needs to be carefully adapted to the specific composition of the materials being processed in order to minimize decarburization by methane formation during sintering.

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