High Magnetic Field Effects on Cu-precipitation Behavior of Fe-1mass%Cu at 773 K

Tramp elements in steel, such as Cu and Sn, cannot be removed by acid treatment. Since these elements condense by repeating recycling process, leading to deterioration of strength. Therefore, the methods for avoiding condensation or removing tramp elements are required. In this study, in-magnetic-field annealing process was focused on because magnetic field is effective for diffusion, phase transformation, phase diagram and precipitation. In-magnetic-field annealing of Fe-1mass%Cu at 773 K was performed in 5 and 10 T for investigating precipitation behavior of supersaturated Cu. From microstructural observation, precipitation of Cu-rich phase in Fe-matrix, and magnetic field effect on itself were not observed clearly. Increase of the hyperfine field was detected for the samples annealed at 5 T by Mössbauer spectroscopy, indicating the enhancement of the Cu-precipitation. On the contrary, hyperfine field for 10T-annealed sample was slightly smaller than that for 0 T. Therefore, in-field annealing effect on Cu-precipitation became unclear at 10 T. These magnetic field effects were discussed in the viewpoints of the change of Cu–Fe phase diagram and the atomic diffusion under magnetic field. Difference of the magnetic field effects on precipitation between 5 T and 10 T is explained by the competition between the enhancement of the driving force of the precipitation and suppression of the atomic diffusion. The obtained results indicated that there is optimized magnetic field intensity for controlling Cu-precipitation.