Effect of magnetic field on the carbide precipitation during tempering of a molybdenum-containing steel

The influence of a high magnetic field on the carbide precipitation during the tempering of an Fe-2.8C-3.0Mo(wt%) steel was investigated. As-quenched steels were tempered at 200 °C for various times with and without the presence of 12-T magnetic field. The applied field effectively promoted the precipitation of the relatively high-temperature monoclinic χ-Fe₅C₂ carbide, compared to the usual ε-Fe₂C and η-Fe₂C carbides precipitated without magnetic field. It is believed that the effect of applying a magnetic field is due to the reduction in the Gibbs free energy of the relatively higher magnetization phase. The denser distributions of the metastable carbides are attributed to the increased nucleation rate due to additional transformation force. The dispersed precipitation strengthening compensated for the decrease of hardness due to the loss of supersaturation of carbon atoms in the matrix.