Liquid phase sintering of ferrous powder by carbon and phosphorus control

Abstract

proper quantities must be monitored. This is conventionally achieved by having a mixture of base powder and liquid Powder mixtures composed of liquid forming master forming master alloy powder constituents. The liquid formalloy powder and coarse iron powder were sintered to ing constituent can be a mixture of additives instead of a near full density by having a high amount (20 wt-%) of homogeneous master alloy powder. During liquid phase liquid phase during sintering. This was made possible sintering, a microstructure gradient will be created, as the by the use of the Fe-P-C system with or without particle boundaries may have a composition similar to Cu. Without post-sintering treatment, a brittle microthe liquid phase and the interior of the particles will have structure was obtained. By means of altered C and P the composition of the base powder. In choosing the control and decarburisation heat treatment of the as composition of the liquid phase, a low melting composition sintered material, the nal non-brittle microstructure is required and good wetting properties are needed to was achieved. Using the open porosity and liquid achieve high densi cation. The amount of liquid must be phase as a diVusion path, rapid decarburisation is just enough to ll the pores without leading to slumping created and the local combination of carbon and and the melt must also be able to penetrate easily by phosphorus in the microstructure is avoided. In this capillary action throughout the sintered body. Some well way, iron phosphide is not formed on grain and/or known binary systems are Fe-Cu, Fe-P, Fe-B.2 However, particle boundaries. Presence of pores is con rmed to these binary systems do not permit the necessary amount be bene cial for grain growth control.PM/1063 of liquid phase for high volume shrinkage when starting from loose packed or moderately pressed coarse powder.

Study of high temperature wetting and infiltration for optimising liquid phase sintering in low alloy steels

“…For this reason, many authors have studied different master alloy systems with such a composition that it fully or partially melts at the common sintering temperatures. [1][2][3][4][5][6] Such master alloys are designed to be mixed with a base powder which remains solid during the process. In addition to enhancing densification, the liquid phase can act as a vehicle to homogeneously distribute the alloying elements and promote their diffusion.…”

New Opportunities for Low Alloy Steels—Master Alloys for Liquid Phase Sintering

“…Nevertheless, this idea was abandoned in the 1990s, mainly due to the two reasons: (1) the high sintering temperature required (near 1280 • C) to fully dissolve the carbides present in the master alloy particles and (2) the high level of wear in the pressing tools, due to the high hardness of the master alloy particles (produced at that time by casting and crushing). Since that period, different compositions have been developed trying to pursue two objectives: the introduction of alloying elements with high oxygen affinity [21][22][23][24][25][26], the formation of a liquid phase during sintering [27][28][29][30] or the two objectives simultaneously [31][32][33][34][35][36][37][38] (Figure 2). But the main impetus for this research area took place in the late 1990s when two parallel developments became available.…”

New masteralloys for sintered high strength steels – the attractive route between mixing and prealloying

“…However, the idea was eventually abandoned in the 90's for two reasons: 1) the need of high sintering temperatures (around 1280 °C) to dissolve the carbide phases present in the masteralloy particles, and 2) the excessive tool wear caused by the very hard and angular MA powder particles (at that time produced by casting and then milling the ingots). Since then, different masteralloy compositions have been developed pursuing the introduction of oxygen-sensitive elements [2][3][4][5][6], or the formation of a liquid phase [7][8][9][10], or both aspects at the same time [11][12][13][14][15][16][17][18][19][20][21][22] (see schematic in Fig. 2).…”