Low-energy Ar ion-induced anomalous carbon diffusion in pre-decarburized 45 steel

Carbon diffusion behavior at 850 degree C in No.45 steel under 1 keV high-flux Ar+ ion irradiation was investigated. The steel samples had been pre-decarburized at 850 degree C in H2 + H2O for 2 h to form a columnar ferrite surface layer of 200 μm. Cross-section structure of the samples indicates that, at the dual phase zone, carbon diffuses to the surface, especially in grain boundaries, leading to the movement of phase boundary between the ferrite and austenite phases towards the surface. Under the ion irradiation, however, the carbon diffusion is restrained, as can be seen by comparing the irradiated samples to the non-irradiated. This effect cannot be explained by any established mechanism of radiation-influenced diffusion. An explanation based on nonlinear effect is proposed. (authors)