| Surface hardening of carbon steel by electron beam in the atmosphere was carried out using an 1.0∼2.5MeV electron accelerator. The electron beam energy used was 1.4MeV, and the power density of the beam was about 10⁴kW/㎠. The sample piece was rotated and translated during irradiation, so that the point of irridation on the steel surface changed continuously. When the electron beam impinged on the surface, the irradiated area melted very quickly and cooled rapidly owing to the large heat sink provided by the bulk of the steel material. The cooling rate was so fast that the melted area was mostly transformed into martensite phase(or a bainite phase in a limited part) during the self-cooling. The surface hardness of the carbon steel changed from approximately 250Hv to 700Hv, on the Vickers scale. The maximum hardened depth was l.6mm. The melting and cooling times were so fast that oxidation of the steel surface was almost negligible, even though the sample was always in the atmosphere. This method can be applied to heat treatment of steel surfaces for many industrial purposes, owing to its high treatment rate and simplicity. |
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