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采用扫描电镜和透射电镜观察Inconel 617B合金焊接接头750℃持久试验前后微观组织,并探讨了微观组织演变对硬度的影响和持久断裂机制。结果表明:Inconel 617B合金焊接接头持久后,主要析出M_(23)C_6相和γ’相。晶界上M_(23)C_6相呈块状,晶内M_(23)C_6相为薄板状或针状;球形γ’相细小,弥散在晶内。随持久时间延长,晶界M_(23)C_6相长大并连接;晶内γ’相也有长大的趋势,但长时间持久尺寸仍十分细小;晶内除析出的M_(23)C_6相继续长大成薄板状外,还析出新的尺寸较小的针状M_(23)C_6相。持久初期,M_(23)C_6和γ’的析出使得焊接接头的硬度明显升高。随着持久时间延长,由于新析出的M_(23)C_6产生的强化增强效果不足以弥补因析出相粗化和固溶度降低造成的弱化效果,硬度有下降趋势。Inconel 617B合金焊接接头持久试样断裂在焊缝区,晶界和枝晶间M_(23)C_6相粗化严重,更易萌生空洞和裂纹,是引起沿晶断裂的主要原因。
Scanning electron microscopy and transmission electron microscopy were used to observe the microstructure of Inconel 617B alloy welded joints before and after the 750 ℃ long-term test, and the effect of microstructure evolution on the hardness and long-term fracture mechanism were also discussed. The results show that M_ (23) C_6 phase and γ ’phase are mainly precipitated after the Inconel 617B alloy welded joints are persisted. The M_ (23) C_6 phase in the grain boundary is massive, and the M_ (23) C_6 phase in the grain is thin plate or needle; the spherical γ ’phase is fine and dispersed in the crystal. With the prolongation of time, the grain boundary M_ (23) C_6 phase grows and connects; the γ ’phase in the crystal also has the tendency to grow up, but the long lasting dimension is still very small; in addition to the precipitated M_ (23) C_6 Grow into a thin plate, but also precipitated a new smaller size acicular M_ (23) C_6 phase. In the long-term, the precipitation of M_ (23) C_6 and γ ’increased the hardness of welded joint obviously. With the extension of the lasting time, the hardness tends to decrease due to the enhanced strengthening effect of newly precipitated M_ (23) C_6 is not enough to compensate for the weakening effect caused by the precipitation of precipitated phase and the decrease of solid solubility. Inconel 617B alloy welded joints lasting specimen fracture In the weld zone, grain boundary and dendritic M_ (23) C_6 phase coarsening serious, more likely to cause voids and cracks, is the main cause of intergranular fracture.