As reported in the previous paper, the authors found the abnormal brittleness in high density sintered iron. It appeared at the density range just above 7g/cc, and was different from usual brittleness of low density iron. The present paper is devoted to report the characteristics of this brittleness.
Specimens, 8×8×40mm, were prepared mainly from reduced ore iron powder and partly from others, followed by compacting under 4t/cm
2, presintering for 30 min at 800°C, repressing under 2-9t/cm
2 and sintering for 1hr at 1050-1350°C in hydrogen. Impact tests were carried out by the Charpy machine with the supports span of 30mm.
Results were summarized as follows.
Except for carbonyl iron, commercial iron powders showed some abnormal brittleness at the density range of 6.8-7.3g/cc. The brittleness increased accelerated with the rise of sintering temperature.
According to microfractographic observations, this brittleness was presumed mainly as to the grainboundary rupture and partly to the cleavage, while the usual brittleness of lowdensity sintered iron results from transgranular shear rupture through the pores.
It was suggested that the shape of pores and their distribution with respect to grainboundaries are responsible for the mode of rupture.
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