Numerical simulation and experimental investigation on multi-directional forging of pure molybdenum
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摘要: 采用DEFORM–3D有限元模拟软件对纯钼坯体多向锻造大塑性变形过程进行数值模拟，结合锻造实验，研究了变形温度、锻造压下量及锻造工步等对锻件等效应变及其均匀性分布的影响，优选出了反复拔长–镦粗的锻造工艺。研究发现，随着锻造的进行，等效应变分布趋于均匀，在第三次拔长过后，锻件心部等效应变值可达到3.75以上，锻件整体相对密度接近于100%。初始平均晶粒尺寸约55 μm的纯钼烧结坯经多向锻造后，烧结孔洞明显减少，相对密度增加，晶粒尺寸减小至2～3 μm。Abstract: The multi-directional forging process of pure molybdenum was numerically simulated by using DEFORM-3D finite element simulation software. Based on the forging experiment, the effects of deformation temperature, forging reduction, and forging steps on the equivalent strain and uniform distribution of the forgings were studied, and the forging process of repeatedly drawing and upsetting was optimized. It is found that, with the forging process, the equivalent strain distribution tends to be uniform. After the third drawing, the equivalent strain value at the core of the forging can reach more than 3.75, and the overall relative density of the forging is close to 100%. After the multi-direction forging, the sintered pores of the pure sintered molybdenum billets with the initial average grain size of about 55 μm are reduced obviously, the relative density is increased, and the grain size is reduced to 2~3 μm.
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Key words:
- pure molybdenum /
- numerical simulation /
- multi-directional forging /
- grain refinement
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图 1 拔长弧形砧模具设计图：（a）3D；（b）2D
Figure 1. Mold design of the arc-shaped anvil for drawing: (a) 3D; (b) 2D
图 2 不同单锤压下量条件下进行6锤次锻打后等效应变：（a）12 mm；（b）17 mm；（c）23 mm；（d）28 mm
Figure 2. Equivalent strain after forging for six times in the different single hammer reduction: (a) 12 mm; (b) 17 mm; (c) 23 mm; (d) 28 mm
图 3 不同单锤压下量的锻件中心区域横截面径向等效应变分布
Figure 3. Radial equivalent strain distribution of forging in the cross section of central zone by the different single hammer reduction
图 4 不同变形温度锻造后等效应变分布：（a）1100 ℃；（b）1200 ℃；（c）1300 ℃；（d）1400 ℃
Figure 4. Equivalent strain distribution after forging at different deformation temperatures: (a) 1100 ℃; (b) 1200 ℃; (c) 1300 ℃; (d) 1400 ℃
图 5 多向锻造后圆柱型纯钼坯体形状变化：（a）烧结坯；（b）一次拔长；（c）一次镦粗；（d）二次拔长；（e）二次镦粗；（f）三次拔长
Figure 5. Shape change of the cylindrical pure molybdenum body after the multi-directional forging: (a) sintering body; (b) first step, drawing; (c) second step, upsetting; (d) third step, drawing; (e) fourth step, upsetting; (f) fifth step, drawing
图 6 多向锻造后锻件轴切面等效应变分布：（a）一次拔长；（b）一次镦粗；（c）二次拔长；（d）二次镦粗；（e）三次拔长
Figure 6. Equivalent strain distribution of forging in the axial section after the multi-directional forging: (a) first step, drawing; (b) second step, upsetting; (c) third step, drawing; (d) fourth step, upsetting; (e) fifth step, drawing
图 7 变形均匀性系数和平均等效应变在锻造过程中的变化
Figure 7. Variation of the uniformity coefficient and the average equivalent strain during forging
图 8 多向锻造过程中纯钼的相对密度分布：（a）一次拔长；（b）一次镦粗；（c）二次拔长；（d）二次镦粗；（e）三次拔长
Figure 8. Relative density distribution of pure molybdenum in multi-directional forging process: (a) first step, drawing; (b) second step, upsetting; (c) third step, drawing; (d) fourth step, upsetting; (e) fifth step, drawing
图 9 多向锻造变形过程中各工步纵截面显微组织：（a）烧结坯；（b）一次拔长；（c）一次镦粗；（d）二次拔长；（e）二次镦粗；（f）三次拔长
Figure 9. Longitudinal section microstructure of forging in the multi-directional forging and deformation: (a) sintering body; (b) first step, drawing; (c) second step, upsetting; (d) third step, drawing; (e) fourth step, upsetting; (f) fifth step, drawing
类别 参数 塑流应力方程 $\dot{\bar{\varepsilon}} $=6.19×108[sinh(0.0038σ)]7.7175
exp[−282479/(RT)]热膨胀系数 5×10−6 K‒1 杨氏模量 2.79×1011 MPa 泊松比 0.324 导热系数 98.8 W·m−1·K−1 塑性功至热变换率 0.9 密度 10.2 g·cm−3 初始相对密度 0.95 
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表 2 多向锻造过程各工步试样的变形参数
Table 2. Deformation parameters of the multi-directional forging process in each step
工步数 变形方向 变形温度 / ℃ 变形量 / % 1 一次拔长 1300 56 2 一次镦粗 1100 70 3 二次拔长 1100 50 4 二次镦粗 1100 70 5 三次拔长 1100 50
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