三联熔炼GH4169合金大规格铸锭与棒材元素偏析行为

Element Segregation in GH4169 Superalloy Large-Scale Ingot and Billet Manufactured by Triple-Melting

采用真空感应熔炼+保护气氛电渣重熔+真空自耗重熔三联熔炼方法制备大规格GH4169合金铸锭,利用SEM、TEM、EPMA和EDS分析了大规格GH4169高温合金自耗锭(直径508 mm)与棒材(直径240 mm)不同部位的典型元素含量和析出相特征。结果表明:大规格铸锭中Al元素偏析程度较轻,而Nb、Ti和Mo元素偏析较重,枝晶间凝固时析出较多的MC相、Laves相和δ相等。经过两阶段高温均匀化处理和开坯锻造后,GH4169棒材内无"黑斑"、"白斑"等宏观偏析,元素微观偏析也被基本消除。结合计算仿真,进一步对比分析了三联熔炼GH4169与Inconel 718合金棒材的化学成分均匀性,发现国产GH4169存在元素的区域偏析,其棒材的典型元素样本方差值(能够体现区域元素偏析程度)与Inconel 718棒材相比存在差距。这种区域元素偏析对国产三联熔炼GH4169棒材的力学性能(如硬度等)波动性造成一定程度的影响。通过精细控制熔炼过程参数,优化均匀化热处理和锻造工艺,有助于进一步降低GH4169合金大规格棒材的区域元素偏析。

GH4169 has the advantage of excellent comprehensive mechanical properties,good oxidation and corrosion resistance,etc.,which have been widely used in aero engine with the largest consumption.The GH4169 parts include high pressure compressor disk,turbine disk,shaft,gearbox and forged blade,et al.With the development of technology and the requirement of cost reducing,the size of GH4169 ingot and billet increases gradually at home and abroad.However,element segregation becomes more and more severe as the size of GH4169 ingot and billet increases,which will significantly degrade their mechanical properties.In this work,the large-scale GH4169 superalloy ingot(diameter508 mm)was prepared by triple smelting,vacuum induction melting(VIM)+electro sag remelting(ESR)+vacuum arc remelting(VAR).Then,large-scale GH4169 billet(diameter 240 mm)was obtained from this prepared ingot via two-step high temperature homogenization heat treatment and cogging-forging.The element composition and microstructure at different positions of these large-scale ingot and billet were analyzed by SEM,TEM,EPMA and EDS.The results show that the segregation degree of element Al in GH4169 ingot is small,while those of elements Nb,Ti and Mo are large.Moreover,a lot of secondary phases were precipitated at the interdendritic regions of GH4169 ingot,including MC,Laves andδphase.In the GH4169 billet prepared in our work,no"freckle"or"white spot"macro segregation was recognized,and the micro-element segregation was eliminated.Furthermore,combined with computational simulation,the chemical composition uniformity and main mechanical properties of GH4169 and Inconel 718 billets were compared.The statistical analysis using sample variance of macro chemical composition shows that the uniformity of chemical composition in GH4169 billet produced by different manufactures is different.The regional element segregation results in some vacillation on the mechanical properties of GH4169 billet.It is proposed that this regional element segregation can be further depressed by elaborately controlling the triple melting process and optimizing the homogenization heat treatment and forging process.