| The human society urgent need for automobile safety,environmental protection and low-discharge which has made the research on lightweight technology of automobile body have made great progress in recent years.In order to reduce the energy consumption of the car and ensure the safety of the carat the same time,the development and application of the third-generation advanced high-strength steel with high comprehensive strength and good plasticity are expected in time.In this paper,the alloy was designed composition of Fe-0.11C-5.23Mn-1.11 Al and a little Si.The experimental equipment of metallographic microscope,scanning electron microscope and XRD was used to study the ART heat treatment process of experimental steel under different process parameters.The microstructure evolution and mechanical properties of experimental steels with different rolling processes were studied.The comparison between ART and QT processes was studied.The characteristics of microstructure and mechanical properties of the experimental steels under different heat treatment methods were analyzed.The characteristics and superiority of ART heat treatment process were established.The main conclusions are summarized as follows:(1)The hot-rolled experimental steel adopts the austenite reverse transformation(ART)heat treatment process,and the composite phase of ferrite,retained austenite and a small amount of martensite can be obtained at room temperature.The optimum annealing temperature of thecritical region is 625℃。The optimum holding time is 4h.The best cooling method is water quenching.The optimum mechanical properties of the experimental steel are tensile strength reached 817 MPa,elongation reached 70.3%,and product of strength and elongation up to 57.14 GPa·%.(2)When the experimental steel adopts the warm rolling method,the original grain can be remarkably refined,and a more stable long austenite can be obtained,and the retained austenite content can reach 56.8%,and the comprehensive performance of the experimental steel is obviously improved.At this time,the product of strength and elongation up to 57.56GPa·%.(3)The test steel is subjected to QT heat treatment,and a multiphase structure of martensite,ferrite and retained austenite can be obtained at room temperature.Compared with the ART process,the QT process experimental steel has less residual austenite.Therefore,a large amount of martensite in the structure can improve the strength of the experimental steel,but a small amount of retained austenite is not conducive to exerting the deformation-induced plastic effect to enhance plasticity.(4)The tensile strength of the QT process test steel is generally higher than that of the ART process,and the elongation is lower than the ART process.The warm-rolled QT process test steel has good comprehensive performance.The tensile strength of the experimental steel is 1359.7MPa and the elongation reached 31.9%.But the product of strength and elongation is obviously lower than the warm-rolled ART process test steel.(5)Analysis of the work hardening behavior of different process test steels shows that the strain hardening process of ART steel can be divided into four stages,the first stage work hardening rate decreases rapidly(S1);the second stage work hardening rate decreases slowly(S2);The three-stage work hardening rate fluctuates and increases slowly(S3),and the fourth stage work hardening rate decreases with the serrated behavior(S4);the S3 phase lasts longer,which indicates that the ART process steel is more fully TRIP in the middle and late strain,and the coordination deformation ability is better,which is more favorable for obtaining better mechanical properties.The QT process test steel strain hardening process can be divided into three stages,the first stage work hardening rate decreases rapidly(S1);the second stage work hardening rate decreases slowly(S2);the third stage work hardening rate decreases with serrated behavior.Butthe short strain scope of S2 is slightly contributed to the mechanicalproperties. |
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