Abstract
The average grain size of the ultra-fine cemented carbides is less than 0.5μm.Compared with the conventional cemented carbide, ultrafine cemented carbide with high toughness, high wear resistance and good high temperature strength, are widely used in cutting tools, corrosion-resistant tools, metalworking tools and wear-resistant parts etc. Ultrafine W and WC powders are the important raw materials for ultrafine cemented carbides. Their properties have an important impact on the performance of ultra-fine grain cemented carbide. In this thesis, the preparation of ultrafine powder of W, WC, and ultra-fine cemented carbide was studied. The phase was examined by XRD. The uniformity and microstructure of W and WC powders and the alloy were investigated by SEM and BET. Mechanaical properties were tested by material testing machine and hardness machine. The following results are obtained:
1. WC powder affected the performance of both raw materials and impurities, but also factor in process. The particle size, composition, carbonization temperature and carbonization time of W powder were the major factor influencing the properties of W powder. Through the test, the best reduction processing parameters of tungsten powder are determined to be reduction temperature of 700-800 ℃, 30 min, loading boat 800 g/boat, hydrogen flow rate 40 m3/h. The best carbonization processing parameters are determined to be carbonization temperature of the first stage of of 1100～1200 ℃, insulation time 30 min; carbonization temperature of the second phase 1300～1400 ℃, insulation time 90 min.
2. The most proper processing parameters to obtain the best performance of the ultra-fine cemented carbides are 5.2 % carbon, use of grain inhibitors with the composition of 0.4 wt % VC - 0.4 wt % Cr3C2, sintering in 1360 ℃ under low vacuum condition.
3. After sintering at 1360 ℃ under low vacuum for 120 min, when grain inhibitors with the composition of 0.4 %wt VC-0.4 wt % Cr3C2 was used, the grain size of the ultra-fine carbides is 0.4μm and their mechanical properties are HRA 93 and TRS 3320 MPa.
Keywords: Ultrafine WC Cemented carbide Sintering of low pressure vacuum Preparatio
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