Abstract
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.
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.
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/cm2, 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.
