From Fig.1,it has been found that the transformation temperatures of hep cobalt binder phase to fcc cobalt binder phase during heating are as follows:YG8- 742°C,YG15-770°C and YG20-821°C. 2.2 The Influence of Heat Treatment on the Properties of WC-Co Hardmetals The mechanical properties and density of WC-Co hardmetals after sintering and heat treatment are shown in Table 2. Table 2 Properties of WC-Co hardmetals Grade Conditions TRS(MPa)HRA D(g/cm3)ATRS(MPa) YG8 as-sintered 1985 89.8 14.64 YG8 quenched in oil from 1000C 2017 89.6 14.65 32 YG8 quenched and tempered at 2052 89.7 14.67 67 600°Cfor2h YG15 as-sintered 2923 85.6 14.03 YG15 quenched in oil from 1250C 3092 85.5 14.07 169 YG20 as-sintered 2951 83.5 13.45 YG20 quenched in oil from 1250C 3238 83.7 13.50 287 2.3 The Phases of WC-Co Hardmetals X-ray diffraction analysis was carried out on the specimens of as-sintered and quenched hardmetals.The results are shown in Table 3. Table 3 The phases of WC-Co hardmetals Grade Conditions Phases Found YG8 as-sintered WC,WC1-x,e-Co YG8 quenched in oil from 1000C WC,Coe WeC,Co3W YG15 as-sintered WC1_x,Co:W,e-Co YG15 quenched in oil from 1250C WC1_x,Co3 Wa C,Coe WeC,e-Co,a-Co YG20 as-sintered WC,WC1_x,CosW,8-Co YG20 quenched in oil from 1250C WC,WC1-x,Coe WeC,a-Co,e-Co a-Co=fcc Co,:-Co=hcp Co, 3 Discussion From Fig.1,it was found that the transformation temperatute of hcp co- balt binder phase to fcc cobalt binder phase increases with the increase of cobalt content of hardmetal and is much higher than the transformation temperature (421C)of pure cobalt.The factors which have influence on the transformation 577一 ， “ ， 。 卜 一 “ 一 。 ， 犷 。 一 一 一 么 卜﹃ 厅自，才 一 … 一 八只︶︶ 一 往 “ 一 。 。 。 ︻比︶了 左尸︸主 … ︸ 斗 日 ︻八了 土，一，工工 … 汽︹只口尸 卜 一 一 从了 一 、 、 。 卜 一 卜 一 “ 一 “ 一 “ 二 ， ￡一 ， ， ， ， ￡ 一 。 ， ， 。 一 ， 一 、 、 ， ， ， ， ， ￡一 ， 一 ， ￡一 一 ， 卜 、 ， 一 元。 三 林