temperature of ccbalt binder phase must be sludied. The temperature of allotrepic transformaticn of crbalt depends criticaily on purity and the rate cf temperature change.The cebalt binder phase of hardme- tal usually dissves tungsten and carbon by which the transformation temperature of ccbalt binder phase will be changed.It hes already found that carbon does not successfully stabilize fcc cobalt binder phese at all temperatures as tungsten which is usually in cobalt solid solution counteracts the effect of dissolved carben by stabilizing hcp cobalt binder phaset3l.According to cobalt-tungsten phase diagram,the more the tungsten content in cobalt solid solutien is,the higher the transformation temperature ist1. Tungsten content of cobalt binder phase of as-sintered hardmetal depends on the follow ing two factors:sintering temperature and cooling rate.In terms of WC-Co phase diagram the solubility of WC depends on the sintering temperature. The liquid cobalt phase dissolves more WC at highsi ntering temperature than that at low sintering temperature.Tungsten content in cobait binder phase can be hept mcre by quick cooling to room temperature than tht by slow cooling.If the cooling rate is the same,cobalt binder phase of 'as-sintered YG8 has more tungsten than that of YG15 and YG20 because the sintering temperature of YG8 is the highest.This was approved by present study.The composition of cobalt phase cf YG15 and YG20 was analyzed by energy spectrum and the results were given in Table 4. Table 4.Composition of cobalt binder phase cf YG15 and YG20 Composition,wt% Grade Conditions Co W YG15 as-sintered 74.28 25.72 YG15 quenched in oil from 1250C 69.60 30.40 YG20 as-sintered 81.86 18.34 YG20 quenched in oil from 1250C 63.71 36.26 It should be very reasonable to justify that the transformation of cobalt bi- nder phase of YG15 should be higher than that of YG20.The present experim- ental resuits in Fig.I was contrary t)above inference.What is the reason? It is wellknow n that there are many f:.ctors w hich influence on the transforma- tion temperature of cobalt phase for example:impurities in hardmetal,grain size of cobalt phase etc..In parlicular,the grain size affects the stability of two allotropes of cobalt and fine grain size is favourable for fcc cobaltt31.In pre- sent study it w as f.und that during rebealing the tungsten content in cobalt phase 578引 、 · ， 、 一 手 · 、 一 。 、 、 卜 卜 、、 · 手 ， · 一 ， ， 盯 ‘ 一 一 认 一 一 。 一 · 卜 、 了 ” 。 一 卜 〕 ， 一 。 一 引 、 卜 环 · 丁 。 场 ， 手 ， 。 口洲 己 卜 ， 矛夕 左︼甲盖 日亮甘‘任内哆月 … ﹃己︺叮‘ 只匕八恨 ，‘ 汽己丹 … ︵又︺︸︹匕甲八‘ 峥门月 一 “ 一 ， 手 ， 。 ， ， 、 · 、 · 少 · 一 、 、 · 、 认 手 ， ‘ 、 、 。 、 ， 二 ， 隽 铸 ， ， ‘ 凭 、 ‘ 飞 、 、。 ” ， ， 、、 、 ， 、 。 ， 、 。 卜。 卜 一 ， 丫