Abstract
We have already reported that the ultra high density and the low dimensional change were realized by means of the developed die wall lubricated warm compaction and the high temperature sintering with controlling the blister. Increasing the sintered density is one of the effective methods to improve the mechanical properties of sintered steels, and the developed highly densified sintered steel had the excellent tensile strength of 2250 MPa. According to the evaluation of fracture surfaces, the crack path transformed from only the areas of inter-particles i.e. the sinter-neck regions to the areas of inter-particles i.e. the sinter-neck regions and trans-particles i.e. the matrix as increasing the sintered density. This transition in the clack path means the necessity of well-balanced strengthening the sinter-neck regions and the matrix to improve the mechanical properties of highly densified sintered steels. In this study, the effect of the strength of the sinter-neck regions and the matrix on the mechanical property was investigated. As the result of this study, the composite structurizing of the ductile martensite for the matrix and the hard martensite for the sinter-neck regions was realized by the combining fine and coarse powders method and was effective to improve the mechanical properties of the highly densified sintered steel.
