The void evolution of large-section plastic mold steel during multi-directional forging (MDF) was investigated using multi-scale analysis. To simulate the forging process of the plastic mold steel (SDP1 steel) and realize micro-void reconstruction in a representative volume element (RVE), MDF experiment and void-characteristic evaluation of the SDP1 steel were carried out. Traditional upsetting and stretching forging (TUSF) and MDF were simulated to comparatively analyze the evolution of temperature, effective stress, and effective strain. By embedding RVE with a micro-void and using boundary condition by point tracking into the forging process, the single-void evolution in TUSF and MDF was studied. The effect of void orientation on single-void evolution was also investigated. The multi-scale analysis revealed the following results. (1) Compared with TUSF, MDF achieved a higher efficiency in void closure. (2) The closing efficiency of the void increased with the increase in angle θ (the angle between the Z and long axes of the void). (3) The closing efficiency increased with the increase in the orientation angle during the forging process. On the basis of the important role of the main stress in each forging step on the void closure, an integral formula of the main stress was proposed. When main compressive-stress integration reached − 0.4, the closed state of the void could be accurately determined.

采用多尺度分析研究了大截面塑料模具钢在多向锻造 (MDF) 过程中的空隙演变。为模拟塑料模具钢（SDP1钢）的锻造过程，实现代表性体积元（RVE）中的微孔洞重建，对SDP1钢进行MDF实验和孔洞特性评价。模拟传统的镦粗和拉伸锻造（TUSF）和MDF，对比分析温度、有效应力和有效应变的演变。通过在锻造过程中嵌入带有微孔洞的RVE，并在锻造过程中使用点跟踪边界条件，研究了TUSF和MDF中的单孔洞演化。还研究了空隙取向对单空隙演化的影响。多尺度分析揭示了以下结果。(1) 与 TUSF 相比，MDF 实现了更高的空隙闭合效率。(2)空隙的封闭效率随着角度的增加而增加θ（空隙的Z轴和长轴之间的角度）。(3) 锻造过程中闭合效率随着定向角的增加而提高。根据各锻造步骤中主应力对空隙闭合的重要作用，提出了主应力积分公式。当主压应力积分达到 − 0.4 时，可以准确确定空隙的闭合状态。