Abstract: Electropulsing treatment was used to treat welding heat-affected zone of FH690 steel, and effect of electropulsing on toughness of heat-affected zone was analyzed by microscopic observation and mechanical properties test.The results of notch impact test showed that toughness of heat affected zone was enhanced after electropulsing treatment, fracture morphology was plastic under microscopic observation, and the plastic phase was austenite by electron back scattered diffraction test.Under the action of electropulsing, the large resistance of brittle element produced concentrated joule heat and current density.According to the Boltzmann distribution law, the formation mechanism of thin-film austenite was revealed under the comprehensive action of voltage gradient, temperature gradient and the generated compressive stress gradient.The spot affected by electropulsing was not more than 0.2 mm, compared with the classical post-weld heat treatment toughening technology, it showed the local characteristics of electric pulse toughening.Highlights:(1)The thin-film austenite was formed after electropulsing.(2)The electropulsing treatment toughened a weld heat-affected region less than 0.2 mm wide.