Effect of tempering temperature on carbide precipitation behaviours in high strength low alloy steel under high magnetic field

The influence of high magnetic field on carbide precipitation behaviours during the tempering of a high strength low alloy steel was investigated by means of transmission electron microscopy. TEM analysis results indicated that the applied high field effectively promoted the precipitation of Fe5C2 type carbide at low temperature (200 degrees C) and the precipitation of M6C type carbide at intermediate temperature (530 degrees C). The promotion of specific carbides at low and intermediate temperature was caused by the reduction in magnetic Gibbs free energy. Regarding the magnetic Gibbs free energy of carbides, not only the magnetization but also the internal field induction related to the morphology of carbide was taken into consideration. It was observed that there was no pronounced effect of high magnetic field on the precipitation sequence of alloy carbides when specimens were tempered at 700 degrees C, because they were changed into paramagnetic phases at this temperature.