Effect Of Pulse Current On The Microstructure And Properties Of Different Initial State40Cr Steels

The main target of this thesis is to study the effect of pulse current on themicrostructure and properties of different initial state40Cr steels. Then makecontrast of pulse current and traditional heat dealing. The excitation andresponse concept was introduced to different initial microstructure on theelectrical pulse and make contrast of robust effect. The thesis is to provideexperimental support to improve the comprehensive performance of highstrength bolts.Experiment raw materials are different initial state40Cr bolt steels, thetensile strength of the annealing state of40Cr is551.9MPa, the elongationrate is29.5%, strong plastic product is16281(unit: MPa%，the following unitis the same). The tensile strength is lower and the elongation rate is high.Using different electric pulse parameter, the hardness of materials increasesand the plasticity decreases. The best electric pulse parameter is460ms underthe conditions of the experiment. The tensile strength of the material reachesthe maximum-2155.5MPa, the elongation rate7.5%and strong plasticproduct16163. To have better comprehensive properties, electric pulsetempering and traditional tempering was used. The best parameter-two100ms pulse current. The tensile strength is2058.5MPa, the elongation rate is17%, strong plastic product is34995, the tensile strength decreased slightly,but the plasticity improved greatly, the experimental results are desired. Thetensile strength of quenched and tempered state of40Cr is1253.7MPa, theelongation is18.3%, strong plastic product is25325. The experiment containselectric pulse quenching, traditional oil quenching and electric pulse quenchingtreatment after oil quenching treatment. The best mechanical properties isquenched and tempered40Cr steel after460ms pulse quenching, the tensilestrength is2273.3MPa, extension rate is9.0%, strong plastic product is 43193.Test shows that comprehensive mechanical properties of different initialstates of40Cr are better than those of traditional heat treatment properties andelectric pulse current treatment is short and efficient.Materials before pulse current treatment is incentives for the initial state ofzero response. Organization evolution of annealing of cold drawing electricpulse quenching process is from iron element body, granular pearlite andcarbides to markov body with granular carbides. Electric pulse treatment ofaustenite reverse transformation belongs to diffusion transformation toaustenite, interfacial diffusion and bulk diffusion form grow up. Reverseaustenite does not have sufficient time to growth and homogenization, afterrapid cooling from water, its organization is certain residual granular carbides.For the evolution of the traditional quenching electric pulse treatment: frommartensite to martensite. Martensite inverse process is longer in traditionalheat treatment, for electric pulse treatment, martensite inverter variable forstress elimination austenite grain growth and composition uniformity, andaustenite growth time is short. The size of the quenched martensite is betterthan the initial final grain, but less than quenched and tempered electric pulsetreatment. This process is diffusion phase transition, there is displacementtype shear through recrystallization, grain refinement. For the evolution of thetraditional electric pulse treatment of quenched and tempered sorbiteorganization: from tempered martensite to martensite. Tempered martensitebelongs to the category of pearlite, original pearlite is fine, the higher theaustenite nucleation rate, the faster austenite formation.Austenite grew up inbody diffusion form. Finally, the original tempering of quenched and temperedsorbite transferred to full martensite after electric pulse treatment. Theconclusion is that pulse electric current on metal material strength andtoughening mechanism is mainly fine grain strengthening, dislocationstrengthening, solid solution strengthening and phase transformationstrengthening.