利用代表性体积元(RVE)模型以及EBSD技术，研究了变形量为5%时X80管线钢中铁素体和贝氏体在不同应变速率(10^-4~10^-1 s^-1)下的应变分配行为和微结构演变机制。结果表明，应变速率较低时，铁素体有充足的时间来完成几何必需位错(GNDs)向低角度晶界(LAGBs)演变以及LAGBs向高角度晶界(HAGBs)的转变，使得应变畸变能得以释放，应变局域化程度较弱。随着应变速率增加，应变响应时间减少，使得LAGBs向HAGBs的转变过程受阻，导致铁素体内部积累了高密度的GNDs和LAGBs，从而加剧了应变局域化。同时，高应变速率时，铁素体和贝氏体间的应变分配系数降低，容易在其界面附近产生应变梯度，由此形成的GNDs堆积及界面背应力，使得铁素体和贝氏体分别呈现压应力和拉应力状态，极大地限制了两相间的应变协调性，增大了界面间应力集中，从而导致应变硬化能力降低。

X80 pipeline steel, which is mainly composed of ferrite/bainite, is an important structural steel for pipeline transportation. The plastic deformation of X80 pipeline steel at different strain rates caused by geological and human factors deteriorates its strength. Microstructural transformation and strain localization during deformation are the fundamental factors that deteriorate the mechanical properties of steel. Therefore, in this study, the strain partitioning behavior and microstructure evolution mechanism of ferrite and bainite in X80 pipeline steel at different strain rates (10^-4 s^-1 to 10^-1 s^-1) under 5% deformation were revealed using representative volume element models and electron backscatter diffraction technology. The results show that when the strain rate is low (10^-4 s^-1 to 10^-3 s^-1), ferrite has sufficient time to complete the evolution of geometrically necessary dislocations (GNDs) to low-angle grain boundaries (LAGBs) and the transformation of LAGBs to high-angle grain boundaries (HAGBs). Ferrite can release strain distortion energy, which can weaken the strain localization behavior of X80 steel. As the strain rate increases, the strain response time decreases, hindering the transition from LAGBs to HAGBs. This results in the accumulation of high-density GNDs and LAGBs in ferrite, thereby intensifying strain localization. Additionally, when the strain rate is high (10^-2 s^-1 to 10^-1 s^-1), the strain partitioning coefficient between ferrite and bainite could be reduced, thereby producing the strain gradient in the vicinity of the interface and resulting in GNDs accumulation and back stress formation. Furthermore, ferrite and bainite could show compressive and tensile stresses, respectively, thus limiting the strain coordination between the two phases significantly, increasing the stress concentration near the interface, and reducing the strain hardening ability. The strain partitioning behavior between ferrite and bainite was further revealed to better understand the plastic deformation of X80 pipeline steel.