Microstructure Evolution During Cemented Carbides Vacuum Sintered With Steel

The The connection between cemented carbides and steel make workpieces with high abrasive resistance and antifatigue.The composite workpieces would not only have high toughness but lower the cost and reduce the processing difficulty for the workpieces.It was applied to workpieces required for high accuracy and strength,such as cutting tool?drills for printing plate of electric circuit and composite roller.The development of nanosize cemented carbides advanced its properties for use.However the preparation of nanosize cemented carbides and the connection of it with steel is becoming the difficulties to be solved in this field for now.In this dissertation,The vacuum sintering was proposed to bond the nanosized WC-20 Co power with the nanosized Fe-36Ni(Invar alloy)power and well bonded interfaces were obtained.The microstructure of its interfaces?grain size distribution and the mechanism of abnormal grain growth of WC in the three sintering condition were systematically analyzed in this study.The detailed contents were shown as follows:First,The vacuum sintering was used to bond the nanosized WC-20 Co power with the nanosized Fe-36 Ni power.The sintering temperature was 1300 ? and the heat preservation was 2h?8h and 16 h.Well formed sintered compact of Invar alloy layer with cemented carbides were obtained in the three sintering condition.Second,The interfaces bonding of cemented carbides with steel was researched.The observation of the interface microstructure indicated that metallurgical bonding can be obtained between Invar layer and cemented carbides in vacuum sintering condition.The existence of interface without crack indicated that the bonding practicable with the two kinds of power.Third,A “two-step” image processing method was used to compute the tungsten carbide(WC)grain size distribution in three different conditions.The results indicate that the grain size of WC getting larger with longer time to preserve.Compared to long heat preservation,WC grain size increasing faster for short heat preservation.Fourth,The mechanism of the abnormal grain growth of WC was researched.The observation of the microstructure of the WC grain growth indicated that the micron WC grains were obtained by the coalescence from initial power of the nanosized WC.Fifth,The mechanical property of the cemented carbides was analyzed.The interfaces of the cemented carbides and the microstructure of the WC grain were observed.The results indicate that good cohesiveness can be obtained,what's more,the existence of step and intercross dislocation within the WC grains make its comprehensive mechanics performance higher.