Effect Of High Magnetic Field On Diffusion Behavior Of Carbon In Pure Iron

In this work high purity iron (99.99%) was selected to exclude the effect of impurities. A series of contrast experiments with different treatment conditions were done with and without a magnetic field. The carburized samples were investigated by means of X-ray diffraction, scanning electron microscope analysis and metallographic analysis. Compared with the non-field carburized samples, the effects of the magnetic field strength, magnetic field direction and magnetic field gradient on the diffusion behavior of carbon in pure iron were studied, and the corresponding affecting mechanism was analyzed theoretically.Samples were carburized at930℃and750℃respectively with different magnetic field strength. The results showed that high magnetic field can significantly affect the carbon diffusion in pure iron. Compared with the non-field carburized samples, with the increasing of the magnetic field strength, the average thickness of the carbon diffusion layer decreased continually, no matter that the carbon diffusion direction parallel or perpendicular to the magnetic field direction. When the magnetic field strength is higher than IT, with the increasing of the magnetic field strength, the carbon diffusion distance decreases obviously, but the diffusion distance of carbon in field carburized samples is lower than that of the non-field carburized samples. The above results indicate that the high magnetic field can significantly affect the carbon diffusion behavior in pure iron. This may attribute that the forced magnetostriction yields a lattice contraction, the activation barrier to carbon diffusion by the interstitial mechanism could be increased. Besides the self-diffusion coefficient of a-Fe decreases obviously below the cuire temperature, leading to the increase of the carbon diffusion activation energy.Samples were carburized at930℃,850℃and750℃respectively with different magnetic field direction. The results showed that the average thickness of the carbon diffusion layer has no obvious change when varying the magnetic field direction. This indicates that high magnetic field direction didn’t affect the carburization in pure iron remarkably. Although the carbon diffusion direction would slightly change along the magnetic-field direction owing to the magnetostriction, a change in carbon diffusion direction is assumed to be negligible because the jump length along each crystallographic direction in the iron lattice would be averaged out.Samples were carburized at930℃and850℃respectively under a magnetic field gradient of-282T2/m. The results showed that the average thickness of the carbon diffusion layer under the negative magnetic field gradient is higher than that under the uniform magnetic field. This indicates that a negative magnetic-field gradient could improve the carbon diffusion behavior in pure iron. This is due to the negative magnetic field can give rise driving force to an increase in solute atoms located at the sites.