Effect of Magnetic Field on Successive γ→ε′→α′ Martensitic Transformations in an Fe–Mn–C Alloy

Abstract

The effect of magnetic fields on successive γ→ε′→α′ martensitic transformations in an Fe-13.0Mn-2.1C (at%) alloy, whose transformation start temperatures for the γ→ε′ (Msε′) and ε′→α′ (Msα′) transformations are 223 and 213 K, respectively, has been examined by measuring magnetic field susceptibility and magnetization and by observing optical microstructure, applying a static and/or a pulsed ultra high magnetic field up to about 31 MA/m. As a result, the ε′→α′ transformation was found to be induced under magnetic fields higher than a certain critical one even at extremely higher temperatures than Msα′, while the γ→ε′ and direct γ→α′ transformations were not at any temperatures higher than Msε′ and Msα′. Morphology of the magnetic field-induced α′ martensites in pre-existed ε′ martensite plates was the same as that of thermally-induced ones in the alloy. A thermodynamic analysis suggested that the transformation behavior for the above three different types of transformations under magnetic fields could be systematically explained by the equation previously proposed to estimate the critical field vs transformation temperature, considering that the γ phase of this alloy system near Msα′ temperature exhibits a paramagnetic to antiferromagnetic transition.