Koji Hayashi1 and Tai-Whan Lim2
1Institute of Industrial Science, The University of Tokyo, Tokyo
The densification behavior of carbonyl iron powder (5.3 μm;oxygen, 0.40 mass%;carbon, 0.03 mass%) in vacuum-sintering and the effects of added elements such as Al, Cr, Mn, Mo, Nb, Si, Ti, V and W on the behavior were investigated.
It was found that the densification of iron compact saturated near 94% of the theoretical density; the densification was incomplete. The addition of Al, Nb, Ti and V, or the use of special iron powder with very low carbon content resulted in the complete densification. These results could not be explained by well-known theories such as pore isolation from grain boundaries and liquid phase sintering. Taking into consideration the relation between the densification and the standard free energy for the formation of oxide of each added element, the incomplete densification of the carbonyl iron powder was attributed to the high value of the equilibrium pressure of CO gas which was formed by the reduction reaction of the iron oxide with carbon and was trapped in the closed pores in the sintered compact.
densification, injection molding, iron powder, sintering, pore, gas pressure, equilibrium, added element
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