引張り試験に現れる焼結鉄の粒界破壊について

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The intergranular fracture appeared on the tensile fractured surfaces of vacuum-sintered irons has been studied. Specimens were prepared from electrolytic, atomized and reduced ore iron powders, followed by single compacting under the pressure of 2-7 t/cm2, and by sintering for 1 hr in the temperature range of 800-1150°C in vacuum (2-4×10-5 mmHg). Results obtained were summarized as follows: The intergranular fracture behavior was, particularly, remarkable in higher density of iron powder compacts, sintered at higher temperature of γ-iron region in vacuum, and depended on the strain rate, but not very on the type and the particle size distribution of iron powders. When the vacuum-sintered irons were reheated for 1 hr at 1150°C in dry hydrogen, the fracture features of them were changed from an intergranular mode, into a transgranular one, these coarsed ferrite grains became again finer, and the tensile properties of them were improved remarkably. It was suggested that this behavior was caused by the impurities (e.g. oxygen and carbon) in the iron powder and the sintering atmosphere, and by the abnormal ferrite grain growth of the vacuum-sintered irons with passing through Ar3 point of iron.
社団法人粉体粉末冶金協会の論文