EFFECT OF Nb ON THE MICROSTRUCTURE AND PROPERTIES OF SPRAY FORMED M3 HIGH SPEED STEEL

Spray forming with a short process chains has been proven to be a powerful tool for the production of high-alloyed materials.Niobium,as a strong former for the carbide,will mainly form primary MC carbides,such as NbC,which can be formed via the reaction between Nb and C atoms at the beginning of solidification,and it can act as the inoculants and refine the cast structure of steel which can mainly form primary MC carbides.M3 high speed steel with or without Nb addition were prepared via spray forming.The effect of Nb on the microstructure of spray formed M3 high speed steel was investigated by SEM,EDX and XRD methods;the friction performances of these two steels were studied by SRV high temperature tribometer and 3D white-light interfering profilometer.The results show that the amount of primary MC carbides can increase sharply while the reduction of the amount of primary M_2C due to the substitution of 2%Nb for 1%V(mass fraction) in M3 high speed steel.For the high cooling rate during the spray forming,the primary MC carbides can be refined and dispersed.Large number of primary MC carbides can improve the abrasive wear resistance of M3 high speed steel,but cannot enhance its oxidation resistance;M3 high speed steels containing Nb possess high tempering resistance.