SURFACE HARDENING OF A DUCTILE-CAST IRON ROLL USING HIGH-ENERGY ELECTRON-BEAMS

The effects of high-energy electron beam irradiation on surface harden ing and microstructural modification in a ductile cast iron (DCI) roll are investigated in this study. The DCI roll samples were irradiated by using an electron accelerator (1.4 MeV), and then their microstruct ures and hardnesses were examined. Upon irradiation, the unirradiated microstructure containing graphites and the tempered bainite matrix wa s changed to martensite, ledeburite, and retained austenite, together with the complete or partial dissolution of graphites. This microstruc tural modification improved greatly the surface hardness due to transf ormation of martensite whose amount and type were determined by heat i nput during irradiation. In order to investigate these complex microst ructures, a simulation test including thermal cycles of abrupt heating and quenching was carried out. The simulation results indicated that the irradiated surface was heated up to about 1100 degrees C to 1200 d egrees C and then quenched to room temperature, which was enough to ob tain surface hardening through martensitic transformation. Thermal ana lysis of the irradiated surface layer was also carried out using a fin ite difference method to understand the surface hardening of the DCI r oll and to compare with the simulation test results.