Effects of Magnetic Field and Hydrostatic Pressure on the Isothermal Martensitic Transformation in an Fe-25.0Ni-4.0Cr Alloy

Abstract
Effects of magnetic fields and hydrostatic pressures on the isothermal martensitic transformation, whose nose temperature is about 140K, in an Fe-25.0Ni-4.0Cr alloy ( mass% ) has been examined by applying magnetic fields up to 30MA/m and hydrostatic pressures up to 1.5GPa. The obtained results are the following : The martensitic transformation is induced instantaneously (less than 20µsec.) under pulsed magnetic fields higher than a critical field over a wide temperature range between 4.2 and 200K The critical magnetic field increases with increasing temperature, and the relation between critical magnetic field and temperature is in good agreement with the one calculated by the equation previously derived by the authors. The T T T diagram under static magnetic field shows a lower nose temperature and a shorter incubation time than that under no external magnetic field, while the T T T diagram under hydrostatic pressure shows a higher nose temperature and a longer incubation time than that under no external hydrostatic pressure. These results are well explained by the new phenomenological theory, which gives a unified explanation on the isothermal and athermal kinetics of martensitic transformations previously constructed by the authors.