Effect Of High Magnetic Field Annealing On Carbon Diffusion Coefficient In Pure Iron

In this work, the high purity iron and the solid carburizing agent were selected as the experiment materials. A series of carburized experiments with different processing conditions and magnetic field were done. The carburized samples were investigated by means of electron microprobe, scanning electron microscope analysis and metallographic analysis to study the change of microstructure and carburizing depth. According to the experiment result the carbon diffusion coefficient was calculated. The effect of magnetic field strength and magnetic field gradient on the carbon diffusion coefficient in pure iron was systematically studied, and the corresponding mechanism was briefly analyzed.When the samples were carburized at930℃for25min with different magnetic field strength, the results showed that no matter the carbon diffusion direction was perpendicular or parallel to the magnetic field direction, the carbon diffusion coefficient of field annealed samples were all less than that of the non-field annealed samples. For the field annealed samples, the carbon diffusion coefficient decreased gradually with the increasing of the magnetic field strength, which indicated that the magnetic field annealing suppressed the carbon diffusion in pure iron. The main reason is that the magnetic field causes the lattice distortion in iron which is not conductive to the carbon diffusion.When the samples were carburized at850℃for60min with different magnetic field strength, The results showed that no matter the carbon diffusion direction was perpendicular or parallel to the magnetic field direction, the carbon diffusion coefficient of field annealed samples were all greater than that of the non-field annealed sample. For the field annealed samples, with the increasing of the magnetic field strength, the carbon diffusion coefficient increased gradually. The results indicated that in paramagnetic ferrite region above the Curie temperature, the magnetic field annealing promoted the carbon diffusion in pure iron. The main reason is that the structure defects made by the magnetic field cause the increasing of carbon diffusion flux. When the samples were carburized at750℃for4h with different magnetic field strength, the results showed that no matter the carbon diffusion direction was perpendicular or parallel to the magnetic field direction, the carbon diffusion coefficient of field annealed samples were all less than that of the non-field annealed sample. For the field annealed samples, when applying a magnetic field above1T, the carbon diffusion coefficient decreased with the increasing of the magnetic field strength obviously. The results showed that in ferromagnetic field region below the Curie temperature, the magnetic field suppressed the carbon diffusion in pure iron. The main reason is that the magnetostrictive effect causes the lattice distortion in iron which suppresses the carbon diffusion.When the samples were respectively carburized at930℃for25min and850℃for60min with the gradient magnetic field (-282T2/m). The results showed that the negative gradient magnetic field could enhance the carbon diffusion in pure iron compared to the static magnetic field. The main reason is that the negative gradient magnetic field causes an additional carbon diffusion streams along the magnetic field gradient direction.