对比分析DP980高强钢在应变速率10-3～103s-1范围内的动态拉伸实验结果,研究其力学行为以及断裂模式特点.结果表明:应变速率从准静态(10-3s-1)增加至100S-1过程中,强度基本保持不变,塑性下降了7.5％;应变速率从100 s-1增加至103s-1过程中,强度不断增大,而塑性在100～102s-1范围内上升14％,随后在102～103s-1范围内下降了24.7％;应变速率敏感系数m始终随应变速率的增加而升高.变形过程中,位错增殖强化和加速阻力是强度上升的主要原因.塑性变形集中在铁素体中,微孔裂纹主要沿马氏体/铁素体交界扩展.试样沿厚度方向上的宏观断口,在应变速率小于101 s-1时呈“V”形杯锥状,在应变速率高于101 s-1时则是与拉伸方向成约45°的纯剪切型.
The mechanical behavior and fracture modes of DP980 high strength steels were studied by comparing the results of dynamic tensile tests at strain rates from 10-3s-1 to 103S-1.The results show that the strength of DP980 steel remains almost unchanged and the plasticity decreases by 7.5 ％ as the strain rate increasing from quasi-static(10-3s-1) to 100s-1.When the strain rate increases from 100s-1 to 103s-1,the strength keeps increasing,while the plasticity increases by 14％ at the strain rate ranging from 100s-1 to 102s-1,but then follows by a decrease of 24.7％ in the range of 102s-1 to 103s-1.The strain rate sensitivity coefficient m increases with the increasing of the strain rate.During the plastic deformation,the multiplication reinforcement of dislocation and the motion resistance due to the acceleration of dislocation in ferrite matrix are the main reasons for the strength enhancement.The plastic deformation concentrates in the ferrite,and the microvoids and cracks propagate along the martensite-ferrite interface.In the thickness direction of specimen,the macrographs of fracture are "V" shape cups when strain rate is lower than 101s-1,but the pure sheer shape with 45° to the tensile direction when strain rate is over 101s-1.
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