will increase.The increment of tungsten of low cobalt hardmetal is lower than that of high cobalt hardmetal.From the results in Table 4,it can be found that before quenching tungsten content in cobalt binder phase of YG15 and YG20 is 25.72%and 18.34%respectively and after quenching that of YG15 and YG20 is 30.40%and 36.26%respectively.That is why the transformation temperature of hcp cobalt binder phase to fcc cobalt binder phase increases with the increase of cobalt ccntent of hardmetal. Frcn tne experimental results of Table 2,it can be found that the transver- se rupture strength of WC-Co hardmetal can be improved by quenching and tem- pering.The increment of transverse rupture strength was dependent on the coba- It content of hardmetal.After quenching the increments of TRS of YG8,YG15 and YG20 were 32,169 and 287 MPa respectively.The higher the cobalt con- tent of hardmetal is,the more the increment of transverse rupture strength is. The increment of TRS of YG8 after quenching and tempering was up to 67 MPa. The properties of hardmetal depend on their compcsition,WC grain size, industrial process etc..The properties of hardmetals which have same cobalt content mainly depend on the composition and structure of cobalt phase and gra- in size of WC.The improvement of properties of WC-Co hardmetal by heat treatment mainly belonged with the change of composition and structure of cobalt phase,although the grain size and mophology of WC also had a little change. WC-Co hardmetals have higher transverse rupture strength and toughness if co- balt phase has more ductile fcc cobalt.The fcc cobalt phase stabilized at high temperature can completely or partly be kept at room temperature by quenching as shown in Table 3.That is,the reason why the transverse rupture strength and toughness can increase by heat treatment.This was discussed in detail in cur early published papert11. In addition tungsten and carbon dissolve in cobalt phase.The solubility of tungsten in cobalt phase is appreciably greater at hign temperature than that at room temperature so that tungsten content in cobalt phase at high temperature can be frozen by quenching as shown in Table 4.The stacking fault energy of fcc cobalt phase increases with increase of its tungsten content.Tungsten content in fec cobalt phase not only increases the solid solution hardening but also increases the stacking fault energy and decreases the width of the stacking fault.Therefore the martensite transformation of fcc cobalt phase to hep cobalt phase can be depressed by dissolved tungsten.For example cobalt binder phase of as-sintered YG20 was hep structure and after quenching it became fcc and hep structure as shown in Table 3. 4 Conclusion (1)During heating the transformation temperatures of hcp cobalt binder pha- 579、 、 从 。 从 一 · ， 。 住 。 卜 。 ， 一 一 ， ， · ， ， ， 。 · 一 ， 一 · ， · · · 一 · 一 。 认 斤 口， 比甘 ‘