単一加圧焼結鉄の異常脆性

概要

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Impact strength of iron compacts, prepared from commercial powders by single compacting under the pressure of 2-9 t/cm2 and by sintering in hydrogen at the temperature range of 1100-1300°C for less than 1 hr, did not simply increase with densification at room temperature, but decreased in the density range around 7 g/cm3. Three different mechanisms for the observed phenomena of abnormal brittleness were considered. First, a shear crack could propagate through large flaky pores formed by the removal of pressed powder lubricants between iron particles. This type of brittleness disappeared after the elimination of flaky pores by sintering at higher temperatures for longer periods. Second, an abnormal growth of ferritic grains could cause an increase of ductile-brittle transition temperature, together with the increase of porosity on grain boundary. This type of brittleness was the same as previously observed by the authors on double pressed materials, and it became remarkable with the progress of sintering. Third, when the ductile-brittle transition occurred above room temperature, the impact strength of high density (above 7 g/cm3) sintered irons could become lower than that of lower density ones at room temperature, because the transition appeared more evidently with densification.
社団法人粉体粉末冶金協会の論文