GH4151合金的凝固偏析行为及均匀化热处理研究

Solidification Segregation Behavior and Homogenization Heat Treatment of GH4151 Alloy

GH4151合金是一种承温能力高达800℃的新型涡轮盘用铸锻变形高温合金,该合金在凝固过程中元素偏析严重,主要偏析元素包括Nb、Mo和Ti等元素,同时合金中包含大量的C元素,在熔炼凝固后期由于残余液相中的元素富集,枝晶间会析出大量有害相,包括(γ-γ′)共晶,Laves相,η相和MC碳化物。实验通过研究C含量对各偏析元素的影响发现,增加C含量可减轻Nb元素在枝晶间的偏析,此外,随C含量的增加枝晶更发达,枝晶间区域减少。随后通过研究在1160~1210℃不同温度下的均匀化热处理对各枝晶间析出相的影响发现,(γ-γ′)共晶和Laves相的熔点约为1180℃,η相的熔点约为1200℃,MC碳化物的熔点超过1300℃;同时,发现1170℃/16 h+1200℃/8 h双步均匀化热处理不仅可以消除铸锭中的偏析,而且避免了低熔点相过烧而产生的孔洞,使坯料更加有利于后续开坯变形。

GH4151 alloy is a new type of casting and deformation superalloy of turbine disk with the temperature bearing capacity up to 800℃.The alloy has severe elemental segregation during solidification,and main segregation elements include Nb,Ti and Mo.Meanwhile,the alloy contains a large amount of element C.In the late stages of solidification,due to the enrichment of elements in the residual liquid phase,a large number of harmful phases,including(γ-γ′)eutectic,Laves phase,ηphase and MC carbides,precipitate between the dendrites.The influence of C content in the GH4151 alloy on the segregation elements was investigated.Result show that increasing C content can reduce the segregation of Nb elements between dendrites.In addition,with the increase in C content,the dendrites become more developed and the interdendrite area decreases.The effects of homogenization heat treatment were studied at different temperatures from 1160℃to 1210℃.The melting points of(γ-γ')eutectic and Laves phases are about 1180℃,that ofηphase is about 1200℃and that of MC carbide is higher than 1300℃.At the same time,it is found that the 1170℃/16 h+1200℃/8 h double step homogenization heat treatment can not only eliminate the segregation in the ingot,but also avoid the holes caused by the overburning of the low melting point phases,which makes the billet more conducive to the subsequent billet deformation.