Effects Of Electropulsing On The Microstructure And Properties Of The ZG25SiMn2CrB Steel

High-strength steels are utilized widely in the modern industrial society.The traditional heat treatment process of high-strength low-alloy steel is complex,consumes large energy and is unable to make full use of material potential.In order to alleviate energy and resource crisis,developments of new technologies is imperative to improve the utilization of energy and resources and shorten iron and steel production process.Electroplusing treatment is a novel technology aiming at improving both mechanical properties of metal materials and the energy efficiency,and some remarkable progresses have been achieved by this promising technique in various research fields.In this paper,electropulsing technology was applied to solid phase transformation and tempering processes of ZG25 Si Mn2Cr B steel.mechanical properties of the steel after electropulsing treatment were tested.The influence of electric pulsed current on the solid phase transition process of ZG25 Si Mn2Cr B steel with different initial states was studied systematically.The reverse martensite to austenite transformation mechanism during electropulsing treatment was investigated comparing with other initial states.Combining experimental results with theoretical analysis,phase transformation mechanisms of ZG25 Si Mn2Cr B steel during the electropulsing treatment were analyzed.The optimum pulse current processing parameters of ZG25 Si Mn2Cr B steel with different initial conditions were obtained.(1)The austenite transformation process in the annealed sample was a diffusion type transition,ferrite/pearlite structures gradually transformed into lath martensite.Microstructure and mechanical properties of the specimen after 500 ms electropulsing treatment were the best.The austenite transformation process with the normalized sample had both diffusion-type and non-diffusion transition,and steel structure gradually changed from bainite/ferrite and martensite into lath martensite and cryptocrystalline martensite,the best quenching process parameters were 480 ms electropulsing treatment.The reverse ???? transformation of the sample with quenched state as its initial structure was dominated by displacive manner.After 380 ms pulse current treatment,the grain size was the smallest,and comprehensive mechanical properties were the best.Compared with initial microstructures of both annealing state and the normalizing state,the starting martensite structure of quenching state was more favorable for the pulsed current treatment process to realize the fine grain refinement of austenite grains.(2)The evolution process and mechanical properties of ZG25 Si Mn2Cr B steel were studied by pulsed current and conventional heat treatment respectively.It was found that instantaneous pulse current tempering could avoid the appearance of temper brittleness.(3)Under the optimal parameters,microstructure of the quenched and tempered samples that were heated by electropulsing was finer than that were heated by traditional furnace.The phase transformation of electropulsing in ZG25 Si Mn2CrB steel was attributed to the coupling of thermal and non-thermal effects of high density pulse current.Due to the non-thermal effect of electropulsing,the thermodynamic energy barrier for the formation of neonatal ? phase nucleus in ? matrix decreased.The thermal effect could improve the austenite nucleation rate,inhibit the austenite gains from growing up,and ultimately refine the microstructure.