Structural elongation and alignment in an Fe-0.4C alloy by isothermal ferrite tansformation in high magnetic fields

Abstract

Structural elongation and alignment in an Fe-0.4C alloy isothermally transformed in high magnetic fields has been studied by quantitative microscopy analysis. It has been already reported by the authors that an elongated and aligned structure is obtained during continuous cooling as far as some conditions are satisfied. It is shown in this paper that an elongated and aligned two-phase structure is formed in high magnetic fields by isothermal ferrite transformation both below and above Curie temperature. To clarify if the elongated structure is formed in the nucleation stage or growth stage, transformation behavior in magnetic fields has been investigated and it was found that equiaxed ferrite grains nucleate randomly at austenite grain boundaries and they become elongated by preferred growth along the direction of applied magnetic field. Effects of isothermal transformation temperature on the degree of elongation has been studied. Below Curie temperature, the degree of elongation increases with increasing transformation temperature, whereas it decreases above Curie temperature. Small chemical driving force for ferrite precipitation and large magnetization of ferrite in high magnetic fields favor the formation of elongated structure. © 2005 The Japan Institute of Metals.