Defects such as abnormal grain growth and cracking are easy to occur in the process of loose tooling forging of large-size molybdenum rods prepared by powder metallurgy. In this work, the forging process of molybdenum rods was simulated, which were heated to 1350 °C, and one end of them was subjected to loose tooling forging with deformation of 20%, 30% and 40%, and then they were subjected to secondary heating at 1200 °C, 1250 °C, 1300 °C and 1350 °C for 60 min. The microstructure of the molybdenum rods was characterized by optical microscope (OM), and the equivalent stress, equivalent strain and damage distribution characteristics of during the forging process were calculated by Deform-3D finite element software. The microstructure evolution law and crack formation mechanism during deformation were analyzed. The results show that when the two ends of the molybdenum rods were separately forged and heated, incomplete static recrystallization was easy to occur in the middle gradient deformation zone due to the uneven distribution of stress and strain, resulting in the abnormal growth of local grains. In the subsequent forging process, the surface of the molybdenum rods was cracked due to the excessive stress at the grain boundary of the coarse grains in the transition zone. The initial temperature and softening temperature of static recrystallization in tempering process were different with the deformation of molybdenum rods. Finally, the process optimization of molybdenum rods forging was put forward.

粉末冶金制备的大尺寸钼棒在松模锻造过程中容易出现晶粒异常长大、开裂等缺陷。本工作模拟钼棒的锻造过程，将钼棒加热到 1350 ℃，对一端进行 20%、30% 和 40% 变形的松动工装锻造，然后对其进行在 1200°C、1250°C、1300°C 和 1350°C 下二次加热 60 分钟。利用光学显微镜(OM)对钼棒的显微组织进行表征，利用Deform-3D有限元软件计算锻造过程中的等效应力、等效应变和损伤分布特征。分析了变形过程中的显微组织演化规律和裂纹形成机制。结果表明，钼棒两端分别锻造加热时，由于应力应变分布不均匀，中间梯度变形区易发生不完全静态再结晶，导致局部晶粒异常长大。在随后的锻造过程中，由于过渡区粗晶粒晶界处应力过大，钼棒表面出现裂纹。回火过程中静态再结晶的起始温度和软化温度随钼棒变形的不同而不同。最后提出了钼棒锻造的工艺优化。由于应力应变分布不均匀，中间梯度变形区易发生静态不完全再结晶，导致局部晶粒异常长大。在随后的锻造过程中，由于过渡区粗晶粒晶界处应力过大，钼棒表面出现裂纹。回火过程中静态再结晶的起始温度和软化温度随钼棒变形的不同而不同。最后提出了钼棒锻造的工艺优化。由于应力应变分布不均匀，中间梯度变形区易发生静态不完全再结晶，导致局部晶粒异常长大。在随后的锻造过程中，由于过渡区粗晶粒晶界处应力过大，钼棒表面出现裂纹。回火过程中静态再结晶的起始温度和软化温度随钼棒变形的不同而不同。最后提出了钼棒锻造的工艺优化。由于过渡区粗晶粒晶界处应力过大，钼棒表面出现裂纹。回火过程中静态再结晶的起始温度和软化温度随钼棒变形的不同而不同。最后提出了钼棒锻造的工艺优化。由于过渡区粗晶粒晶界处应力过大，钼棒表面出现裂纹。回火过程中静态再结晶的起始温度和软化温度随钼棒变形的不同而不同。最后提出了钼棒锻造的工艺优化。