부산대학교 도서관

A novel technology which was characterized by the vacuum solid state sintering was developed for powder metallurgyhigh speed steels production. During sintering, both the WC and Mo2C reacted with Fe and transformed toW and Mo rich M6C carbides which were the common hard phases in high speed steels. Also, a high number of W,Mo and Fe were dissolved in VC, forming the MC carbides. The densification of the material mainly relied on thesolubility effect during the M6C and MC carbides formation. By alloying with a 0.1 wt% of LaB6 to the steel, thebending strength and the fracture toughness were improved from 3290 MPa and 25.6 MPam1/2to 4018 MPa and29.4 MPam1/2, respectively. The TEM analysis demonstrated three types of reaction products by the LaB6 addition:the amorphous phase, the core-shell structure and the La2O3 phase. The impurity elements such as the Mg, Al,Si, S, Ca, and O were absorbed following the LaB6 addition. Moreover, the deoxidization effect caused by the LaB6addition promoted the sintering at a high-temperature period which contributed to the bending strength and fracturetoughness improvement.