Boronizing Treatment of spheroidal graphite cast iron has been investigated by means of electrolysis in molten salt mainly consisted of B
2O
3, K
2O and Na
2O at various temperatures and times. The microhardness and the thickness of boride layers were measured and the distributions of B, Si and C on the surface of specimens were observed by X-ray microanalyser.
Microscopic examination and the results of X-ray microanalysis showed that the boride layer consisted of two layer and outer layer was FeB and inner was Fe
2B. The microhardness of these boride layers were about HVN 1500 1800.
Thickness of the boride layer was increased with an increase of square root of time for treatment at constant temperature. The activation energv for diffusion of boron in the specimen obtained from the slope of Arrhenius plots was 19.5 kcal/mol.
Si rich layer was formed at the position out of boride layer in specimens after boronizing. Moreover the graphite formation was observed in Si rich layer in the specimens boronized at austenitizing temperature on prolonged time.
The graphite formation in Si rich layer can be consider as a consequence of the precipitation of carbon during cooling process after boronizing which diffused from spheroidal graphite to austenite matrix at boronizing temperature. Large amount of graphite formation in Si rich layer resulted in the crack passed through these graphites.
抄録全体を表示