中文摘要：

利用电液伺服高速试验机对DP780钢进行不同应变速率下的拉伸变形，结合SEM和TEM等手段，研究了应变速率对DP780钢拉伸性能及变形行为的影响规律及机制．结果表明，在较低应变速率（〈10^0S^-1）条件下，随应变速率增加，DP780钢的强度、塑性等力学性能均未见显著变化．当应变速率超过10^1S^-1后，DP780钢的强度和应变硬化指数n明显提高；塑性在3×10^1-5×10^28-1“范围内出现大幅度增加的现象．高应变速率的变形过程中，铁素体基体中位错运动速度加快，导致“近程阻力”增大，使DP780钢的变形抗力随应变速率的增加而增大．在应变速率达到3X10^1 S^-1之后，铁素体中可动位错数量的大幅度提高，是DP780钢均匀伸长率和断后伸长率在3×10^1-5×10^2S-1范围内得以明显增加的主要原因．DP780钢中的铁索体／马氏体界面是塑性变形过程中位错塞积、微裂纹形核及扩展的主要位置，而随应变速率的增加，铁索体基体中的形变强化程度增大，可降低铁索体基体与铁索体／马氏体界面之间塑性应变能差异，延缓铁索体／马氏体界面处微裂纹的形成和扩展，一定程度上提高了DP780钢非均匀塑性变形能力．

英文摘要：

Tensile properties and deformation behavior of DP780 steel were studied using servo-hydraulic high-speed material testing machine, SEM and TEM. The effects of strain rate and the mechanism were investigated. The results showed that the strength and ductility of DP780 steel remained almost unchanged as the strain rate increased at strain rates lower than 100 s-1. When the strain rate was over 10^1 s-1, the strength and the strain-hardening coefficient increased remarkably. Ductility of DP780 steel increased significantly at the strain rates ranging from 3x10^1 to 5x10^2 s-1. The deformation resistance increased with increasing the strain rate due to the stronger short range resistance induced by the acceleration of dislocation motion in the ferrite matrix. Increasing strain rate up to 3x10^1 s-1 resulted in a considerable increase of the amount of mobile dislocation, which was the main reason for the increasing uniform elongation and fracture elongation of DP780 steel at the strain rate ranging from 3x10^- to 5x10^2 s-1. Interface of ferrite-martensite in DP780 steel was the main location for pile-up of dislocation, crack initiation and propagation.The ability of inhomogeneous plastic deformation of DP780 steel increased due to the decreasing plastic strain energy difference between the ferrite matrix and fei＇rite-martensite interface and the consequent delaying initiation and propagation of microvoids at ferrite martensite interface induced by tile increasing work hardening degree of ferrite matrix with the increasing strain rate.