Ferrite Transformation Microstructure in Low Carbon Iron Alloys in Strong Magnetic Fields

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1.An Fe-0.006mass% C alloy was isothermally held at 850, 950 and 1050℃ for 20 min in a magnetic field of 30 Tesla. After cooling the grain size of ferrite microstructure was measured. At 850℃ the ferrite grain size was somewhat smaller in specimens held in magnetic fields than that held without magnetic fields. The difference in grain size was considerably large at 950℃ which was in the ferrite-single phase region in the magnetic field (the α/γ phase boundary was raised). On the other hand, the γ→α_m (massive) transformation occurred in the specimens held without a magnetic field. At 1050℃ no significant differences in ferrite grain size were observed. These results were essentially the same when the specimens were cooled very slowly through the transformation temperature.2.The influence of magnetic fields on α/γ equilibrium phase boundaries was calculated in Fe-C-X alloys (X=Mn, Si, Ni, Mo and Cr etc.) by means of Weiss molecular field theory. Not only the magnetic moment, but also the Curie temperature of iron solid solution is affected by the presence of these elements. The results indicate that Co stabilizes the ferrite phase while Mn has the opposite effect to the largest extent of all the elements studied. However, the effects are small compared to that on Fe atoms because of (usually) smaller X concentrations in Fe-C-X alloys.