Effects of a high magnetic field on bainitic transformation in Fe-based alloys

It has been found that magnetic fields affect solid/solid phase transformation behavior and structures since helium-free superconducting magnet has been developed, and magnetic fields are new effective tools for the structural and functional control of materials. Structures of materials are controlled by magnetic field not only due to the difference of magnetic moment between parent and product phases but also magnetocrystalline anisotropy, shape magnetic anisotropy, induced magnetic anisotropy and magnetostriction. However, studies on the effects of magnetic field on bainitic transformation are very few. So the effects of magnetic field of 10 T on transformation temperature, kinetics and transformed structure for bainitic transformation have been investigated for an Fe–3.6Ni–1.5Cr–0.5C (mass%) alloy. Transformation temperature is increased by more than 40 K by applying a magnetic field of 10 T. This increment is larger than that for ferrite transformation in pure iron (9 K), pearlite transformation in Fe–0.8C (15 K) and lath martensite transformation in 18Ni maraging steel (20 K). The isothermal transformation behavior at 360 °C is accelerated by applying 10 T. The elongation or alignment of transformed structure is observed under some conditions for ferrite transformation, but has not been observed for bainitic transformation so far.