Abstract: Based on investigation on macro- and microstructures, failure mechanism of bainite-nodular iron composite rollers is revealed to be related with their low content of bainite, improper distribution of carbide and irregular graphite nodules within the material. Optimization on nickel, copper and niobium contents of the material is conducted, resulting in great improvement in microstructures as well as in mechanical properties of the rollers. After the improvement, the microstructure of the rollers becomes finer, and the morphology of the carbide phase is more regular. Also the addition of the alloying elements results in not only an increase in strength of the material, but also an improvement in roughness as well as ductility of the bainite-nodular iron. The improvement can effectively extend the lifetime of the rollers, and therefore production cost of steels can be decreased.

Key words: Ni-Mo bainite　Mechanical property, Roller