Alloy carbide precipitation in tempered 2.25 Cr–Mo steel under high magnetic field

The influence of a high magnetic field on carbide precipitation during the tempering of a 2.25 Cr–Mo steel was investigated by means of transmission electron microscopy. As-quenched specimens were tempered at 200, 550 and 700 °C for various times in the absence and presence of a 12 T magnetic field. Experimental results indicate that the applied high magnetic field effectively promotes the precipitation of M23C6 carbides at low temperature (200 °C) and M7C3 and M23C6 carbides at intermediate temperature (550 °C). The increased Fe content in the M23C6 and M7C3 carbide significantly increases the magnetization. The magnetic Gibbs free energy, which influenced the alloy carbide precipitation behavior, was considered to be mainly determined by the intrinsic magnetization energy for M23C6 and M7C3 carbides. With the increase of the tempering temperature (700 °C), there was no pronounced effect of the high magnetic field on the precipitation sequence and the concentration of substitutional solute atoms in paramagnetic carbides. The investigation of alloy carbide precipitation under high magnetic fields could contribute to a better understanding of phase transformation of alloy carbides and to the heat treatment and fabrication of heat-resistant steels.