Study On Microstructure Control And Properties Of Pearlitic Steel Based On Electric Pulse Treatment

Because of its high strength and good toughness,cold drawn pearlitic steel wire is widely used in long-span bridges,automobile tires,aviation,marine engineering and other fields.In the large strain cold drawn pearlitic steel wires,the cementite is amorphized and partially decomposed,releasing a large number of carbon atoms,and these carbon atoms are dissolved into ferrite sheets.In the subsequent heat treatment,the cold drawn steel wires show a series of unique phenomena.In this paper,the cold drawn pearlitic steel wires are taken as the research object,the effects of electric pulse treatment on the microstructure of pearlite steel wires are studied,the change law of mechanical properties is explored,and the mechanism of electric pulse treatment on the microstructure of steel wire is analyzed.The results showed that short-time(6s)high-energy-density electrical pulse treatment promoted the precipitation of nano-cementite particles and the crystallization of amorphous cementite,which improved its dislocation pinning ability.Due to the short-time electric pulse treatment,the nanosheet structure of the cold drawn pearlitic steel remains,avoiding the deterioration of the strength of cold drawn pearlitic steel wires.The electric pulse treatment promotes the recovery and rearrangement of dislocations in the ferrite sheet,reduces the dislocation density,increases the free path of dislocation motion,and improves the plasticity of the steel wire.Using electric pulse treatment with a current density of 35.7 A/mm~2 and treating the drawn steel wire withε=2.14 for 6 s,the tensile strength can be increased by 10%,but the plasticity is obviously deteriorated;the current density increased to 42.8 A/mm~2,after the same treatment for 6 s,the uniform elongation ofε=2.14～3.08 cold drawn steel wires can be increased by more than 120%,and its tensile strength has no significant decrease compared with cold drawn steel wires.Electric pulse treatment can promote the crystallization of cementite and restore its stability.It can also exert additional force on dislocations,improve dislocation mobility,and promote dislocation de-pinning and disentanglement,thus pair elimination and annihilation occur.Thereby,the dislocation density in the cold drawn pearlite ferrite layer is reduced,and the free path of dislocation movement is increased.Therefore,a composite cold drawing process with electric pulse treatment added to the cold drawing pass gap was designed,and the pearlitic steel wires with tensile strength comparable to the conventional process but higher uniform elongation were prepared.The lamellar structure of the pearlite steel wire is parallel to the drawing axis,showing a highly fibrous structure,and the dislocation density in the ferrite is lower than that of the conventional cold drawn steel wire.Furthermore,the number of solid solution carbon atoms in the ferrite gap is reduced,and the crystalline cementite phase content is higher.The plasticity of the cold drawn steel wire can be further improved by post-treatment of electric pulse withρ=42.8 A/mm~2.