Numerical simulation and mechanical properties of spray-assisted friction stir welding RAFM steel
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摘要: 低活化铁素体/马氏体(reduced activation ferritic/martensitic，RAFM)钢搅拌摩擦焊(friction stir welding，FSW)接头中的高温δ铁素体是影响其冲击韧性的主要因素. 通过喷雾冷却，降低焊接峰值温度并对接头进行快速降温，从而达到抑制δ铁素体生成的目的. 采用Fluent流体软件对RAFM钢FSW在不同喷雾冷却工况下的温度场进行模拟研究，综合模拟结果进行试验验证. 结果表明，液氮辅助FSW(FSW + LN2)可有效降低焊接接头的峰值温度并加速焊后的降温速率. FSW + LN2焊接接头冲击韧性由常规FSW接头的冲击吸收能量23 J提升至33 J，达到与母材等韧匹配，硬度变化趋势与常规FSW接头基本一致，焊接接头硬度远高于母材.
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关键词:
- 低活化铁素体/马氏体钢 /
- 搅拌摩擦焊 /
- 喷雾冷却 /
- 数值模拟 /
- 力学性能
Abstract: High temperature δ ferrite in the friction stir welding (FSW) joint of reduced activation ferrite/martensitic (RAFM) steel is the main factor affecting its impact toughness. This paper combined spray cooling to decreases the peak temperature of welding thermal cycles and provide rapid cooling of the joint to inhibit δ-ferrite formation. Fluid simulation software Fluent was used to simulate the temperature field for FSW of RAFM steel under different working conditions of spray cooling, and the integrated simulation results were verified experimentally. The results show that liquid nitrogen-assisted friction stir welding (FSW + LN2) reduce the peak temperature of the welded joint effectively and accelerate the cooling rate of welding temperature reduction. The impact toughness of FSW + LN2 joint improves from 23 J to 33 J, which matches equal toughness of the base material. Besides this, the change tendency of hardness is basically consistent with that of conventional FSW joints, the microhardness of the welded joint is much higher than that of the base material. -
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图 1 喷雾辅助FSW示意图
Figure 1. Schematic diagram of friction stir welding assisted by spray. (a) 3D diagram; (b) 2D diagram
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图 4 试验与模拟温度曲线对比
Figure 4. Comparison of experimental and simulated temperature curves. (a) advancing side; (b) retreating side
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图 5 焊缝形状与模拟温度场分布的对比(mm)
Figure 5. Comparison of the weld shape and simulated temperature field distribution
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图 7 以水为冷却介质时喷射流量对温度场的影响
Figure 7. Effect of injection flow rate on the temperature field with water as the cooling medium
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图 8 以LN2为冷却介质时喷射流量对温度场的影响
Figure 8. Effect of injection flow rate on the temperature field with the liquid nitrogen as the cooling medium
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图 9 FSW + LN2下模拟与试验温度曲线对比
Figure 9. Comparison of simulated and experimental temperature curves with FSW + LN2. (a) advancing side; (b) retreating side
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图 10 焊接接头形貌(mm)
Figure 10. Morphology of welded joint. (a) FSW joints; (b) FSW + LN2 joints
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图 12 FSW接头的EDS结果
Figure 12. EDS results of the FSW joint. (a) EDS position; (b) EDS results of A and B points
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图 13 液氮辅助FSW焊接接头微观组织
Figure 13. Microstructure of the liquid nitrogen-assisted friction stir welding joint. (a) SZ; (b) HAZ; (c) RS; (d) AS
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图 14 不同工艺下RAFM钢接头与母材断口形貌
Figure 14. Fracture morphology of RAFM steel joints and base metal in different processes. (a) BM; (b) FSW joint; (c) FSW + LN2 joint
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图 15 不同工艺下RAFM钢接头的断口截面硬度分布
Figure 15. Fracture section hardness distribution of RAFM steel joints in different processes
表 1 仿真中使用的参数[19]
Table 1 Parameters used in the simulation
密度
ρ/(kg·m−3)有效应变
速率ε环境温度
T/K材料常数
A/s−1温度相关常数
a/Pa−1温度相关净
应力指数n气体常数
R/(J·mol−1·K−1)活化能
Q/(J·mol−1)7 800 0.35 298 3.1014 × 107 1.07 + 1.70 × 10−4T −
2.81 × 10−7T0.2 + 3.966 × 10−4T 8.314 471205 
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表 2 RAFM钢的热物理性能参数[20]
Table 2 Thermo-physical properties parameters for the RAFM steel
温度T/K 热导率λ/(W·m−1·K−1) 比热容cρ/(J·kg−1·K−1) 373 26.7 446 473 26.3 469 573 25.9 493 673 26.5 542 773 25.8 623 873 23.7 669 973 22.9 765 1073 24.9 699 1173 24.9 587 1273 26.2 590
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表 3 不同工艺下RAFM钢接头与母材冲击吸收能量(J)
Table 3 Impact toughness of base metals and RAFM steel joints in different welding processes
试样 实测值 平均值 BM 35，35，38 36 FSW 21，26，22 23 FSW + LN2 32，32，35 33
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