Abstract
Alloy carbide M23C6 plays a significant role in the creep strength of reduced activation steels. Experiments have proven that a magnetic field accelerates the precipitation of M23C6 at intermediate temperature. A scheme that combines first-principle calculations, Weiss molecular field theory and equilibrium software MTDATA is proposed to investigate the thermodynamic features of magnetic-field-induced precipitation. The calculated results reveal that the origin of the magnetic moment is the NaCl-like crystal structure. The magnetic field enhances the exchange coupling and stabilizes the ferromagnetic phase region. The external field influences the Curie temperature, thereby changing the magnitude and position of the maximum magnetic heat capacity, magnetic entropy and enthalpy. The strong magnetic field improves the stability of M23C6, and the theoretical results agree well with the previous experiment. The study provides a theoretical basis for the magnetic-field-induced precipitation behaviours in steels.
Highlights
The precipitation behavior of iron or alloy carbides induced by an external magnetic field has aroused great interest
Experimental studies [1,2] were performed to discuss the impact of magnetic field on iron carbides
It was found that the magnetic field stabilizes ferromagnetic iron carbide (χ-Fe5 C2 ), which can be magnetized under a magnetic field
Summary
The precipitation behavior of iron or alloy carbides induced by an external magnetic field has aroused great interest. Experimental studies [1,2] were performed to discuss the impact of magnetic field on iron carbides. Alloy carbides M6 C (M = Fe, Mo) precipitated in advance with a magnetic field [3]. The precipitation behavior of carbide is closely related to its stability. The stability of carbides was ascribed to the reduction of free energy related to magnetization [1,2,5]. The magnetic field influences the morphologies of precipitated carbides [6,7]. Many works have explained the precipitation of carbides from the perspective of magnetic free energy [4,8]. Thermodynamic contributions which derived by magnetization to free energy have been taken into account in many studies [5,9], other thermodynamic properties (e.g., heat capacity, entropy and enthalpy) have yet to be studied at the microscopic level
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