Another effect of electric current is to change the free energy sequence
between phases. For a system with electric current passing
through, the system free energy consists of chemical free energy, interface
energy, strain-stress energy and electric current free energy
[38–39]. The electric current free energy is different for different phases
due to their different electrical conductivities and magnetic permeabilities.
This causes the different change of the total free energy for different
phases when current is passing through. The original free energy
sequence is hence changed due to the extra electric current free energy.
It has been proved that electric current helps to dissolve low conductive
phase embedded in a high conductive matrix [27–28,38]. The observed
reduction of κ-carbides is alongside with this prediction. κ-α interface
provides the major crack nucleation sites in the steel. The reduction of
κ-α volume fraction leads to less crack nucleation sites. The formability
is hence improved.