| The present article aims at investigating the effects of high-energy electron beam irradiation on surface hardening and improvement of fatigue properties in an AISI 4140 steel currently used for automotive crankshaft. The 4140 steel samples were irradiated at atmosphere by using an electron accelerator and, then the microstructure, hardness, and fatigue property were examined. The beam power was varied in the range of 53-70㎾ by changing the beam current. Upon irradiation, the unirradiated microstructure containing band structure was changed to martensite, bainite in the carbon-rich zone or ferrite, bainite, and martensite in the carbon-depleted zone. This microstructural modification improved greatly the surface hardness and fatigue properties due to transformation of martensite whose amount and type were determined by the heat input during irradiation. Thus, the high-energy electron beam irradiation can be effectively applied to the surface hardening process of automotive parts. |
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