Study on the differences in microstructure, mechanical properties, and deformation mechanism between DH and DP steels
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摘要: 采用高速拉伸试验、综合成形试验、场发射扫描电镜（SEM）、X射线衍射（XRD）、电子背散射衍射（EBSD）等表征方法研究了DH780与DP780冷轧双相钢组织性能差异。研究表明，DH780与DP780显微组织差异关键在于是否存在残余奥氏体，前者存在约5.1%残余奥氏体，呈块状、薄膜状、链状与细小粒状位于相界面与铁素体晶界处，在变形过程中具有显著TRIP效应，同时残余奥氏体具有更多滑移系可有效减缓位错塞积、延缓应力集中与裂纹源的形成，使得DH780较DP780具有更优良的强塑积及扩孔性能。高速拉伸试验表明，DH780较DP780具有更高的应变速率敏感性特征；随着应变速率的提升，DH780强塑积增加至38.83 GPa·%，吸能性能显著增强。Abstract: High speed tensile test, comprehensive forming test, field emission scanning electron microscope (SEM), X-ray diffraction (XRD), electron backscatter diffraction (EBSD) and other characterization methods were used to study the differences of microstructure and properties between DH780 and DP780 cold-rolled dual phase steels. The research shows that the main differences between the microstructures of DH780 and DP780 steels depend on the occurrence of retained austenite. The former has about 5.1% retained austenite, which is located at the phase interfaces and ferrite grain boundary in the blocks, thin films, chains and fine particles appearances. It has a significant TRIP effect during deformation. At the same time, the retained austenite has more slip systems, which can effectively retard the dislocation accumulation, stress concentration and crack initiation. DH780 has better strength-ductility balance (TS × EL) and hole expanding performance than DP780. High speed tensile test shows that DH780 has higher strain rate sensitivity than DP780; With the increase of strain rate, the strength-ductility balance (TS × EL) of DH780 increases to 38.83 GPa·%, and the energy absorption performance is significantly enhanced.
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图 1 高速拉伸试样示意（单位：mm）
Figure 1. Schematic diagram of the sample for high-speed stretching tests
图 7 强塑性指标与应变速率的关系
Figure 7. Relationship between strength ＆ plasticity index and strain rate
表 1 试验钢主要化学成分
Table 1. Main chemical compositions of experimental steels
% 牌号 C Mn Si P S Cr Al Nb Ti DH780 0.17～0.19 2.1～2.3 0.4～0.5 ≤0.010 ≤0.005 0.18～0.21 0.7～0.9 0.02～0.04 - DP780 0.09～0.12 2.0～2.4 0.5～0.6 ≤0.010 ≤0.005 0.28～0.30 - 0.02～0.03 0.02～0.04 
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表 2 准静态力学性能（ε=0.01 s−1）
Table 2. Quasi-static mechanical properties（ε=0.01 s−1）
牌号 方向 屈服强度/MPa 抗拉强度/MPa 断后伸长率/% 强塑积/(GPa·%) DH780 0° 501 823 31.3 25.76 45° 487 804 31.6 25.41 90° 522 831 30.8 25.59 DP780 0° 511 818 19.5 18.41 45° 529 821 24.7 17.82 90° 541 843 18.3 16.27
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