Rapid hardening of AISI 4340 steel induced by electropulsing treatment

Mechanisms for the rapid hardening induced by electropulsing treatment (EPT) in an AISI 4340 steel were investigated by X-ray-diffraction analysis, transmission electron microscopy observations and Vickers microhardness tests. It is found that the combined strengthening effects induced by solid-solution atoms, dislocations, and nano-twins gradually surpass the dispersion strengthening after EPT. Besides, carbides dissolution and phase transformation were also detected due to the decreasing trend of Gibbs free energy during EPT. Such rapid hardening method may be preferential for manufacturing metallic materials for its time-saving and energy conservation.