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.
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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