采用光学显微镜(OM)、扫描电镜(SEM)、透射电镜(TEM)、显微硬度仪和冲击试验等研究了 IN 740H焊接接头750 ℃时效后的显微组织、硬度和冲击韧性.结果表明:母材和焊缝的硬度随时效时间的延长先增大后减小.焊缝的冲击韧性在时效初期快速下降,之后下降速率减缓,最终趋于稳定.时效过程中,γ'相的长大与M23C6相的析出不仅会降低γ'相的体积分数,还会导致晶界附近形成γ'贫化区.晶内颗粒状γ'相是影响IN 740H焊接接头硬度变化的关键因素.焊缝冲击韧性的快速下降主要由晶界M23C6相的析出和粗化导致.焊缝晶界γ'贫化区的形成会加速晶界裂纹的扩展,也有害于其冲击韧性.
Microstructure and properties of Inconel 740H welded joint after aging at 750℃
Microstructure,hardness and impact toughness of IN 740H welded joint aged at 750 ℃ were studied by means of optical microscope(OM),scanning electron microscopy(SEM),transmission electron microscopy(TEM),microhardness tester and impact testing.The results show that the hardness of the base metal and weld increases first and then decreases with the increase of aging time.The impact toughness of the weld rapidly decreases in the early stage of aging,and then the rate of decline slows down and eventually stabilizes.During the aging,the growth of the γ'phase and the precipitation of M23C6 phase not only decrease the volume fraction of theγ'phase,but also lead to the formation of γ'-depleted zone near grain boundaries.Intragranular γ'phase is a key factor affecting the hardness change of the IN 740H welded joint.The rapid decrease in impact toughness of the weld is mainly caused by the precipitation and coarsening of grain boundary M23C6 phase.The formation of γ'-depleted zone at the weld grain boundary will accelerate the propagation of grain boundary cracks and also be detrimental to their impact toughness.
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