Influence of magnetic property for workpiece on thickness of removal and modified layers in large-area EB irradiation

Abstract

In a large-area electron beam (EB) irradiation method developed recently, the large-area EB with high energy density can be obtained without focusing the beam. It can be used for melting and evaporating metal surface instantly. Therefore, highly efficient surface finishing for mold steels can be done by the EB irradiation. It was also clarified that surface functions such as wear resistance and corrosion resistance of mold steels were improved by formation of modified layer on the surface after melting and resolidification of workpiece surface. On the other hand, the workpiece surface was slightly removed by evaporating the surface. Then, control and prediction of modified layer and removal thickness are effective to maintain the surface function. In this study, influence of magnetic property for workpiece on thickness of removal and modified layers in large-area EB irradiation is investigated. Experimental results show that the thickness of removal and modified layers on workpiece with high relative permeability is larger than that with low one. These results suggest that high energy density of EB is irradiated to the workpiece with high relative permeability. Therefore, the analyzed energy density on workpiece surface is calculated by using an electron track analysis. The energy density on workpiece with high relative permeability is larger than that with low one since EB more concentrates on the surface of workpiece with high relative permeability. Variations of removal and modified layer thickness for workpiece with different magnetic property can be precisely predicted by using an unsteady heat conduction analysis with considering EB concentration.