Magnetic Field-Induced Precipitation Behaviors of Alloy Carbides M 2 C, M 3 C, and M 6 C in a Molybdenum-Containing Stee
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tic fields have become available on a laboratory scale with the development of superconducting magnets. The application of high magnetic fields to phase transformations of metallic materials has thus drawn increasing attention in the last 30 years, as it introduces a new approach for microstructure modification as well as property optimization. If the parent and product phases have different saturation magnetization and are open to transformation under high magnetic fields, the temperature and extent of transformation can be considerably affected. This is because the Gibbs free energy of a phase can be lowered by an amount corresponding to its magnetization.[1,2] Magnetic field effects on microstructure transformation in metallic materials were first reported in the middle of the last century.[3] More recently, the effects of high magnetic fields on martensite,[4–8] bainite,[9] ferrite,[10] and pearlite[11,12] transformations have been studied more vigorously. It has been reported that magnetocrystalline anisotropy, induced magnetic anisotropy, and magneT.P. HOU, Lecturer, Y. LI, Associate Professor, and K.M. WU, Professor, are with the Hubei Collaborative Innovation Center for Advanced Steels, International Research Institute for Steel Technology, Wuhan University of Science and Technology, Wuhan 430081, China. Contact e-mail: [email protected] Y.D. ZHANG, Research Engineer, is with the LEM3, CNRS UMR 7239, Universite´ de Lorraine, 57045 Metz, France, and also with the Laboratory of Excellence on Design of Alloy Metals for low-mAss Structures (DAMAS), Universit´ de Lorraine, 57045 Metz, France. Manuscript submitted January 29, 2013. Article published online January 28, 2014 METALLURGICAL AND MATERIALS TRANSACTIONS A
tostriction can affect the nucleation and growth rate, the transformation kinetics, as well as the microstructures of the product phases.[13,14] Carbides play an important role in the development of high-strength heat-resistant steels, for example, in the strengthening and toughening of micro-alloyed steels and in the exploitation of secondary hardened steels for service at elevated temperatures.[15] As most iron carbides are ferromagnetic with various magnetization degrees, the introduction of a magnetic field can effectively change their stability, by altering their Gibbs free energy, and thus affect their precipitating behaviors. Consequently, the final material properties can be changed and controlled. It has been reported that the precipitation and growth behavior of iron carbide can be influenced by a high magnetic field.[14,16] The investigation of alloy carbide precipitation under high magnetic fields could contribute to a better understanding of alloy carbide formation mechanism. Low alloy Mocontaining steel was selected and treated with and without a 12-T magnetic field to investigate the effects of high magnetic field on molybdenum carbide precipitation during the tempering process at an intermediate temperature of 803 K (530 C).
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EXPERIMENTAL PROCEDURES
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