热老化对316LN不锈钢焊缝微观组织和冲击性能的影响

为研究核电站主管道316LN不锈钢焊缝的热老化,开展了316LN不锈钢在400℃下15000h的加速热老化实验。采用TEM和HREM研究热老化后焊缝微观组织演变,利用冲击实验测定不同热老化时间下焊缝夏比冲击性能;以夏比冲击功作为热老化脆化参量,通过拟合法获得了焊缝热老化脆化动力学公式,利用热老化动力学公式预测焊缝在实际运行温度下服役60年内的夏比冲击功变化。结果表明:经1000h热老化后焊缝中的铁素体已经发生了调幅分解,形成了富Fe的α相和富Cr的α′相,同时在铁素体内析出了G相;焊缝中铁素体调幅分解和G相析出导致焊缝冲击功随时间延长而不断下降;夏比冲击功预测结果显示在运行25年内冲击功下降较快,随后的运行过程中下降过程趋缓。

Effects of T hermal Aging on Microstructure and Impact Properties of 316LN Stainless Steel Weld

To study the thermal aging of nuclear primary pipe material 316LN stainless steel weld ,ac-celerated thermal aging experiment was performed at 400℃ for 15000h .Microstructure evolution of weld after aging was investigated by TEM and HREM .Impact properties of weld thermally aged at different time was measured by Charpy impact test .Meanwhile ,taking Charpy impact energy as the standard of thermal aging embrittlement ,the thermal kinetics formula was obtained by the fitting method .Finally ,the Charpy impact properties of the w eld during 60 years of service at the actual op-eration temperature were estimated by the thermal kinetics formula .The results indicate that the spi-nodal decomposition occurs in the ferrite of the weld after thermal aging at 400℃ for 1000h ,results inα (Fe-rich) andα′(Cr-rich) phases ,and meanw hile ,the G-phase is precipitated in the ferrite;the spi-nodal decomposition and the G-phase precipitation lead to the decrease in the impact energy of weld as time prolongs ;the prediction results show that the Charpy impact energy of weld decreases quickly in the early 25 years ,and then undergoes a slow decrease during the subsequent operation process .