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Solidification process of sintered AISI 316L austenitic stainless steel powder modified with boron-containing master alloy


  Wrought stainless steels have wide range of applications as consequence of their corrosion resistance in aggressive environments. Powder metallurgy (P/M) technology can increase range of application of stainless steel through significant reduction of manufacturing costs by simplifying production process. Unfortunately, manufacturing by P/M process created, in structure component, undesired porosity which greatly reduces corrosive resistance of sintered steel. A reduced open porosity can be usually attained by forging or other mechanical treatment. Of course such an operations increase costs. In order to keep manufacturing costs on reasonable level, it is desired to eliminate porosity during already existing manufacturing process. One of the possibilities is proper chemical modification of base alloy to induce appearance of liquid phase during sintering in order to achieve high density sinter. Many researchers indicated boron as an excellent activator for sintering ferrous alloys. Boron added to iron creates lowmelting eutectic liquid (1177°C) which activates densification mechanisms: (i) particles rearrangement by decreasing friction forces among the particles, (ii) fragmentation of particles by liquid penetrating grain boundaries. Moreover, presence of eutectic liquid in some cases under specific conditions during sintering process may lead to appearance of non-porous superficial layer. Such a layer is characterized by the lack of solidified eutectic liquid what greatly improves corrosive resistance of sinter by eliminating electrochemical corrosion cells. The creation of nonporous superficial layer usually requires addition of the high amounts of boron (higher or equal to 0.4 wt %) which during cooling solidifies as a brittle eutectic on grain boundaries drastically lowering mechanical properties of sinter [1]. Loss occurs especially when solidified liquid creates the continuous network surrounding grains [2]. Dispersing of [...]

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