| The quantitative effects of iron in the electro-boronizing treatment, the mechanism of deterioration by iron, and the process of recovery by adding aluminium into the deteriorated molten borax, have been studied. Using iron anode, to promote the deterioration of the molten borax electrolyte, the approximate diffusivity of boron into the mild steel specimen has been decreased rapidly as the iron content in the molten salt increased up to about 3.3% iron and above this content of iron the boronized depth into the specimen was not detected. And when iron oxide (Fe₂O₃) were added into the molten salt, similar effects were founded. This deterioration by iron were thought to be the formation of a porous metallic iron (which was detected by X-ray technique) surrounding the specimen, and the formation of this porous iron film were thought to be effects to reduce the reduction of a active boron in the molten salt. Adding 2% aluminium into the deteriorated molten borax, the extensive recovery of the diffusivity of boron into the specimen were detected. This phenomena were thought to be the reduction of the amount of iron content in the molten salt by the formation of Fe₃Al (which was detected by X-ray technique) which was combined with iron in the deteriorated molten salt and was floated up onto the surface slag layer. The distribution of the micro-vickers-hardness of the boronized layer, the weight gain and the length change of the specimen, the structure of the boronized layer by X-ray Debye-Scherrer method, and also the approximate activation energy of the boron to diffuse into the mild steel, which were 1.3×10⁴ ㎈/㏖ and 3.5×10⁴ ㎈/㏖ in the range of temperature above and below 860℃, respectively, were detected. |
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