Mechanism Of Microstructure Evolution In Fe-C Alloy Under Gradient High Magnetic Field

With the rapid development of high magnetic field technology,solid state phase transformation of Fe-C alloy under the high magnetic field has gradually attracted the attention of material researchers.In particular,the mechanism of microstructure evolution of the diffusion-type solid-state phase transformation of Fe-C alloys under high magnetic field has become one of the heat topics.Therefore,Fe-0.155%C alloy and Fe-0.494%C alloy were selected as the research materials in this paper.By changing the austenitic temperature,the time of the magnetic field,the magnetic induction intensity and the magnetic field gradient parameter study on heat treatment annealing in magnetic field was carried out under without magnetic field,uniform high magnetic field and gradient high magnetic field.Relationships between microstructure and orientation of proeutectoid ferrite was investigated by means of metallographic observation,EBSD and tensile test.Relationships between different microstructures and mechanical properties was discussed.The microstructure evolution and formation mechanism of Fe-C alloy were studied systematically under different heat treatment conditions and different magnetic field conditions.This is of great significance to enrich the theory of material science of strong magnetic field.Different annealing treatment process and different magnetic field conditions can promote the formation of proeutectoid ferrite grains in Fe-0.155%C alloy and Fe-0.494%C alloy,which are elongated in the direction of magnetic field and arranged in chain arrangement orngaization.Although in the strong magnetic field proeutectoid ferrite appeared in the microstructure of the preferential distribution,proeutectoid ferrite did not show the preferred orientation in the direction of the magnetic field in the grain orientation.Under uniform high magnetic field,with the austenitizing temperature is increased,proeutectoid ferrite grains in Fe-0.155%C alloy and Fe-0.494%C alloy extend along the magnetic field and decrease in chain arrangement degree,preeutectoid ferrite content reduced.While increasing the magnetic field strength and prolonging the magnetic field holding time below the Curie point temperature,the proeutectoid ferrite grains in the Fe-0.155%C alloy and the Fe-0.494%C alloy extend along the magnetic field direction and form a chain arrangement orngaization.The degree of arrangement increases,and the proeutectoid ferrite content increases.In addition,the extent of proeutectoid ferrite grains along the direction of the magnetic field and the degree of chain alignment decrease with the increase of carbon content.Under uniform magnetic field,the cause of the formation of proeutectoid ferrite grains in the magnetic field is elongated and grown in a magnetic field.The reason is that magnetic dipole interaction and demagnetization field energy by the demagnetizing field affect them.The interaction of magnetic dipoles in the factors that affect the degree of chain arrangement is greater than the effect of the demagnetization field energy.Compared with uniform high magnetic field,the proeutectoid ferrit grains in the Fe-0.155%C alloy and the Fe-0.494%C alloy under gradient magnetic field extend along the magnetic field and are further increased in the chain arrangement and proeutectoid ferrit content increased slightly.Under gradient high magnetic field due to the role of magnetic force generated by the torque,with more proeutectoid ferrit grains occur along the direction of the magnetic field,with the interaction between the magnetic dipole enhanced,proeutectoid ferrite grains along the magnetic field direction and arranged in a chain elongation increased further.Under gradient high magnetic field,the reason for the elongation of proeutectoid ferrite grains along the magnetic field direction and the more significant chain alignment is the result of the mutual promotion between the magnetic dipole interaction,the magnetization force and the demagnetizing field energy between the three.After both uniform high magnetic field and gradient high magnetic field annealed,the yield strength and tensile strength of Fe-0.155%C alloy and Fe-0.494%C alloy decreased slightly,the elongation ratio increased,and the largest elongation ratio was obtained under gradient magnetic field.