Papers by Author: Ming Long Gong

Abstract: The present studies are to investigate the microstructure features and macroscopical hardness during transformation from austenite to pearlite without and with 12T magnetic field on Fe-1.1%C alloy. It is found that 12T magnetic field can increase the area fraction of abnormal microstructure and the average width of secondary cementite in Fe-1.1%C alloy by remarkably decreasing the Gibbs energy needed for the ferrite transformation. The macroscopical hardness of the specimens heated with 12Tmagnetic field is lower than the specimens without magnetic field. The reason is that the magnetric field increase the lamellar spacing of pearlite

Abstract: The present studies are to investigate the microstructure features during transformation from austenite to ferrite without and with magnetic field on Fe-0.76%C alloy. It is found that the area fraction and numbers of proeutectoid ferrite grain as well as the lamellar spacing of pearlite in Fe-0.76%C alloy increased considerably with the increase of magnetic field intensity. The reason is that, the magnetic field increases the driving force of proeutectoid ferrite nuclei and shifts the eutectoid point to the side of high carbon content and high temperature, which increases the starting-temperature of the transformation from austenite to ferrite. The proeutectoid ferrite grains are elongated along the magnetic field direction, which can be explained as follows: the proeutectoid ferrite becomes the magnetic dipolar under high magnetic field, and then the polarized austenite atoms are much easier to diffuse into ferrite grains along the magnetic field direction. Key words: high magnetic field; Fe-0.76%C alloy; microstructure

Abstract: The effects of the 12T magnetic field on transformed morphology and crystallographic characteristics of high purity Fe-1.1C (wt.%) alloy during diffusional decomposition of austenite are studied by SEM/EBSD. With the applied field, the lamellar spacing of pearlite is greatly enlarged and the spheroidization tendency of the pearlitic cementite is enhanced. This can be attributed to the thermodynamic effect of the field on phase equilibrium by elevating the eutectoid temperature; hence the eutectoid transformation happens at higher temperature that favors carbon diffusion. As a consequence, the eutectoid cementite that is usually in lamellar shape spheroidizes to reduce its specific surface area. In addition, three orientation relationships between ferrite and cementite in pearlite, namely Isaichev ORs and two near Pitsch-Petch ORs (P-P1 and P-P2), are found both in non-field and field treated specimens. The magnetic field favors the occurrence of P-P2 OR due to the promotion of nucleation of the pearlitic ferrite. However, there is no obvious effect of the field on the crystallographic orientation of pearlitic ferrite, and that is probably related to the quick saturation of magnetization that results in the disappearance of magnetization anisotropy.