| Deep-drawing steel is mostly used in the outer cover of passenger vehicles,and this type of steel has been developed from the first generation of low-carbon ordinary boiling steel to the third generation of ultra-low carbon Interstitial-Free(IF)Steel.However,its tensile strength(< 500MPa)still cannot meet the performance requirements of advanced high-strength steel(AHSS).In recent years,there is a lack of research on the regulation of deep-drawing texture control of dual-phase or multiphase steel and it is still slightly inadequate to optimize texture by second phase particle carbon sequestration technology in IF steel.Therefore it is necessary to further explore the technology and mechanism of recrystallization texture strengthening of ferrite matrix under the condition of carburization.Whether the deep-drawing texture of the matrix can be optimized under the premise of dual-phase or multiphase has certain theoretical value and practical significance for further reducing the weight of the vehicle body and promoting the lightweight process of the automobile.In this subject,Cr-Nb composite microalloying was utilized under the condition of microcarbon,and the process of low temperature deformation technology combined with annealing in critical zone was used to control the recrystallization texture of <111>//ND based on the ferrite intragranular shear band,thus the deep-drawing texture under the condition of dual phase structure characteristics of ferrite matrix and martensite was optimized.The main conclusions of the paper are as follows:(1)The temperature of Ac1 is 780 °C and the temperature of Ac3 is 900°C of the Cr-Nb series micro-carbon dual-phase steel,and the microstructure of micro-carbon dual-phase steel prepared by the conventional process of "hot rolling follow on cold rolling then annealing" process is the hard martensite phase distributed diffusely on the grain boundary of the soft ferrite phase.After annealing in the critical zone,the strength of ? fiber texture of the micro-carbon dual phase steel is weakened,on the contrary,the rotational cubic texture density of {001}<110> which was harmful to the deep drawing performance was significantly increased,and the density of the ? fiber texture was not enhanced after annealing.(2)Dynamic Strain Ageing(DSA)phenomenon was found when the compression deformation is 350 °C through the low temperature deformation thermal simulation study on the micro-carbon dual-phase steel.The generation mechanism of DSA is mainly the interaction between Nb-containing nanoscale precipitated phase particles and high-density movability dislocation.DSA effect was able to hinder the formation of shear deformation band in intracrystalline during the process of deformation,which was not conducive to the formation of ? fiber texture during annealing and recrystallization process.At the same time,it was found that the regulating effect of low temperature compression process on the texture of micro-carbon dualphase steel is mainly reflected in the effect of recrystallization degree of the dual-phase steel,moreover,the low temperature compression below the recrystallization temperature is beneficial to the subsequent formation of annealing texture.(3)The micro-carbon dual-phase steel was prepared by low temperature rolling in laboratory.The results showed that when the rolling temperature increasing,the yield strength decreased gradually and the elongation first increased then decreased.The elongation of annealing plate achieved the optimal when the temperature of low temperature deformation was 450 ?.Comparing with the micro-carbon dual-phase steel prepared by conventional process,the strength of {001} < 110 > rotating cube texture(density value is 1.0)reduced significantly after low temperature rolling at 450 ? and annealing.Thus it can be confirmed that low temperature rolling technology not only promoted the development of the favorable texture {111},but also greatly reduced the density of unfavorable texture {001}. |
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