The effect of varying microstructural parameters on the cyclic behaviour of dual-phase steels was studied on the basis of experimental and micromechanical finite-element simulated results. The initial bainitic morphology of as-received 20MnMoNi55 steel was transformed into ferrite and martensite through proper inter-critical heat treatment procedures. Strain-controlled low cycle fatigue tests were conducted at room temperature with different strain amplitudes at a specific strain rate of 10⁻³/s. The cyclic stress–strain curve, obtained through joining the peak stresses of hysteresis loops corresponding to different strain amplitude, shows an increase in strain hardening with an increase in volume fraction of martensite. Whereas the rate of cyclic softening, considering the decrease in stress amplitude with respect to elapsed cycles, increases with increasing strain amplitude. Inclusive of all affecting microstructural parameters, an original microstructure-based representative volume element associated with a crystal plasticity-based material model was adopted for conducting micromechanical finite-element simulation. In addition to several parameters associated with a crystal plasticity model, consideration of initial geometrically necessary dislocation density in constituent phases resulted in the accurate prediction of a hysteresis loop at low strain amplitude as compared with the experimental results. A variation of stress triaxiality built up in ferrite matrix with martensite fraction along with deformation inhomogeneity between ferrite and martensite was also observed through a strain partitioning phenomenon obtained from finite-element simulated results.

在实验和微机械有限元模拟结果的基础上，研究了不同微观结构参数对双相钢循环行为的影响。通过适当的临界间热处理程序，20MnMoNi55 钢的初始贝氏体形貌转变为铁素体和马氏体。应变控制低周疲劳试验在室温下以不同的应变幅值在 10 ^-3的特定应变率下进行/秒。通过连接不同应变幅对应的滞后回线的峰值应力得到的循环应力-应变曲线显示应变硬化随着马氏体体积分数的增加而增加。而循环软化的速率，考虑到应力幅度随循环周期的减少，随着应变幅度的增加而增加。包括所有影响微观结构的参数，采用原始的基于微观结构的代表性体积元素与基于晶体塑性的材料模型相关联，用于进行微观机械有限元模拟。除了与晶体塑性模型相关的几个参数外，与实验结果相比，对组成相中初始几何必要位错密度的考虑导致了在低应变幅度下的磁滞回线的准确预测。通过从有限元模拟结果获得的应变分配现象，还观察到在铁素体基体中建立的应力三轴度随马氏体分数的变化以及铁素体和马氏体之间的变形不均匀性。