VARIATION OF PHASE TRANSFORMATION TEMPERATURE IN FE-C ALLOYS IN A HIGH MAGNETIC FIELD

摘要

A magnetic field can affect the transformation temperature and microstructure if a transformed phase has a different susceptibility from the parent phase. Fe-C alloy is an ideal system to show the magnetic field effect since, in this system, austenite (FCC structure) is a paramagnetic phase and ferrite (bcc structure) is a ferromagnetic phase below 770 ℃. In this paper, phase transformation temperature in Fe-C alloys in a magnetic field was measured from a cooling curve. It was found that the transformation temperature for pure Fe from austenite to ferrite has a linear relationship with magnetic field strength, increasing about 0.8 ℃ per tesla. For eutectoid transformation in Fe-0.8C alloy, similar relationship exists; the transformation temperature increases about 1.5 ℃ per tesla. The measured interaction energy between magnetic field and ferrite is larger than that calculated from molecular field theory. An elongated and aligned microstructure by ferrite transformation in a high magnetic field was found in a Fe-0.4C alloy, but was not found in pure Fe and Fe-0.8C alloy.