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短流程冷轧深冲钢动态再结晶规律研究及应用

Research on the dynamic recrystallization behavior of short-process cold-rolled deep-drawing steel and its application

  • 摘要: 近年低能耗、低成本的CSP短流程技术在我国钢铁行业得到快速发展,但与传统热轧工艺相比,CSP产品屈服强度偏高,对冲压用钢的成形性能极为不利。为此,通过热模拟实验分析了DC04冷轧深冲钢奥氏体动态再结晶和冷却相变规律,建立了动态再结晶模型,并用于指导CSP产线生产实践,成功试制生产出富有111织构的冷轧深冲钢板。实验结果表明:CSP产线DC04冷轧深冲钢的动态再结晶模型为Z=ε·exp295.21/(RT),动态再结晶判断条件为Z=1.94×1010exp(61.34εc)、Z=2.57×108exp(24.99εs),基于三维动态再结晶图判断出实际生产中带钢在F3机架热变形处于奥氏体部分再结晶区域;采用F3机架空过的方案进行试生产,得到的带钢组织多为等轴晶粒,带钢强度偏低,而F3未空过的常规轧制工艺生产的带钢组织晶粒之间以尖角或直角接触,带钢强度较F3机架空过方案所生产带钢高约30 MPa。在CSP产线F1和F2机架采用高温、大压下率、低变形速率轧制,使带钢组织发生完全动态再结晶,完成柱状晶到等轴晶的转变,避免了混晶的产生。对采用70%的冷轧累积压下率、710 ℃罩式退火,以及F3机架空过和未空过方案生产的冷轧板性能进行了比较,F3机架空过方案生产的冷轧板较F3机架未空过常规方案生产的冷轧板强度差异不大,但伸长率A80r值均较高,分别达到45%和2.1,且有利织构111的组分较高,具有良好的深冲性能。

     

    Abstract: In recent years, low energy consumption and low cost CSP short-process technology has been rapidly developed in Chinese iron and steel industry. However, compared with the traditional hot rolling process, the yield strength of CSP products is higher, which is extremely unfavorable for the formability of steel used in stamping.Therefore, the dynamic recrystalization behavior and cooling phase transformation of austenite of DC04 cold-rolled deep-drawing steel were analized through thermal simulation experiments, and the dynamic recrystalization model was established, which was used to guide the production practice of CSP production line, and the cold-rolled deep-drawing steel sheet with rich 111texture was successfully trial-produced. The experimental results show that the dynamic recrystallization model of DC04 cold-rolled deep-drawing steel in CSP production line isZ=ε·exp295.21/(RT). The judgment conditions of dynamic recrystallization are Z=1.94×1010exp(61.34εc) and Z=2.57×108exp(24.99εs).Based on the 3D dynamic recrystallization diagram, it is determined that the thermal deformation of the strip at F3 stand in actual production is in the austenite part recrystallization region. In the trial production using F3 stand bypassing scheme, the microstructure of the obtained strip is mostly equiaxed grain with low strength. However, the grains of the strips produced by the conventional rolling process of F3 stand non-bypassing scheme,the grains contact with each other at sharp or right angles, and the strength is about 30 MPa higher than former. The F1and F2 stands of CSP production line adopt high temperature, high reduction rate and low deformation rate rolling, which can make the strip microstructure undergo complete dynamic recrystallization, complete the transformation of columnar crystal to equiaxed crystal, and avoid the generation of mixed crystal. The performance of cold-rolled sheets produced using a 70% cold rolling cumulative reduction, bell annealing at 710 ℃, and the F3 stand by passing and non-bypassing schemes were compared. The cold-rolled sheets produced with the F3 stand bypassing scheme showed little difference in strength compared to those produced with the conventional non-bypassing scheme, but exhibited higher elongation A80 and r values reaching 45% and 2.1. Additionally, the proportion of the favorable texture component 111 was higher, resulting in excellent deep-drawing performance.

     

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