浸炭により鉄系焼結合金を高速度鋼化する方法

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For the purpose of production of the sintered material having the properties of high-speed steel, the following two methods were investigated : 1) sintering the mixed powder of 1%C-18%W-4%Cr-12%Co.2) carburizing the sintered compact of the same composition excluding carbon.<BR>In the case of method 1), adequate hardness was not obtained, because large carbide grains were formed during the sintering process and they were not dispersed in the subsequent heat-treatments. In the case of method 2), the microstructures of the carburized layer after quenching and tempering were the same with that of high-speed steel and the hardness of its portion was RC 65. In tempering, secondary hardening was apparently observed at 500-550°C and double tempering was more effective to increase the hardness. These phenomena are also closely similar to those of high-speed steel.<BR>The effects of the treating factors were as follows : density of metal compact is important to obtain high hardness ; it shoud be higher than 94% of theoretical density at least. Therefore, the compacting pressure as high as possible is suitable and sintering at higher temperature and for longer time is desirable. Practically, optimum conditions were 10t/cm<SUP>2</SUP>, 1430°C and 3 hrs, respectively. For carburization, ordinary technique is applied and one example of the depth of crburized layer was about 1mm at 950°C and for 8hrs. Quenching from 1280°C was optimum for high hardness.
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浸炭により鉄系焼結合金を高速度鋼化する方法

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