燃气轮机退役转子焊接接头微区冲击韧性研究

Investigation on Impact Toughness of Micro-Zones in Welded Joint for Retired Gas Turbine Rotor

为了探究长期高温服役后焊接转子冲击韧性变化规律,以某退役的燃气轮机透平端CrMoV钢焊接接头为研究对象,对接头各微区显微组织演变特征进行了系统表征,基于此,阐明了接头各特征微区冲击韧性变化规律与显微组织的内在关联。在组织表征中发现焊缝中出现了大量的析出相,尺寸为0.5~1μm,粗大的块状或杆状析出相主要沿原奥氏体晶界分布,而尺寸为100~200 nm的大量细小杆状析出相主要在晶内分布,这说明焊缝组织在长期高温服役过程中发生了时效演变。接头各特征微区冲击试验表明,冲击韧性最低值出现在焊缝柱状晶区(7.1 J),其次为焊缝中心等轴晶区(15.6 J),这是由于焊缝中大量杆状析出相易诱发应力集中,导致裂纹萌生与扩展,且沿晶分布的粗大块状析出相易导致沿晶开裂,从而严重降低了焊缝的冲击韧性。而在热影响区内,粗晶区的高强马氏体以及粗大晶粒导致冲击功较低(25.7 J),细晶区内高强高韧的细小马氏体板条以及更多晶界使其拥有最好的冲击性能(188.6 J),回火区由于存在粗大块状析出相和少量细小杆状析出相,导致冲击功在过回火区出现了局部低值(48.5 J)。该研究结果可为发电机组的延寿设计提供参考借鉴。

To investigate the change rule of impact toughness of welded rotor after long term high temperature service,the CrMoV welded joint of turbine part in a retired gas turbine rotor was taken as research object,and evolution feature of microstructure in each micro-zone of the joint was characterized systematically.Based on this,the internal relation between the impact toughness variation and microstructure in each micro-zone was clarified.Microstructure characterization revealed that large amounts of precipitates occurred in the weld metal(WM).Coarse block-or rod-shaped precipitates with size of 0.5~1μm mainly distributed along prior austenite grain boundaries,while large amounts of fine rod-shaped precipitates with length of 100~200 nm mainly distributed within grains,which indicated aging evolution of the WM during long term service at high temperature.Regarding the impact testing for each micro-zone of the joint,the lowest value of impact energy occurred in the columnar grain zone in WM(7.1 J),followed by the middle equiaxed grain zone of WM(15.6 J).The large amounts of rod-shaped precipitates could induce stress concentration and cause crack nucleation and propagation.Additionally,the coarse block-shaped precipitates at grain boundaries could lead to intergranular cracking,which seriously deteriorated the impact toughness of WM.In the heat affected zone(HAZ),the coarse grain zone possessed lower impact energy(25.7 J)due to the high strength martensite structure and large-sized grains.The impact property was the best in the fine grain zone(188.6 J),benefitting from the high-strength and high toughness fine martensite laths,as well as more grain boundaries.However,due to the coarse block-shaped precipitates and a few fine rod-shaped precipitates in the over tempered zone,a local low impact energy value was reached in the over tempered zone(48.5 J).The research findings are deemed to provide reference for life extension design of generating units.