700 ℃超超临界锅炉材料GH4700合金铸态组织及 均匀化工艺

Microstructure and Homogenization of As-cast GH4700 Alloy for 700 oC Ultra-supercritical Boilers

摘要:

对经过真空感应熔炼和保护气氛电渣重熔的镍基合金GH4700铸锭进行研究，分析了其枝晶形貌、元素偏析和析出相特点，运用残余偏析指数理论和扩散动力学软件计算了均匀化动力学曲线并提出5种均匀化制度，通过对不同均匀化工艺结果的分析和热压缩模拟实验验证，确定了GH4700的均匀化制度。结果表明：GH4700合金电渣锭主要存在Nb、Ti元素偏析，电渣锭析出相为γ、γ′、Laves相和一次碳化物MC。经过1170 ℃/48 h均匀化热处理后，合金元素偏析基本消失、有害析出相Laves回溶且具有较好的热加工塑性

Abstract:

Nickel-based superalloy GH4700 ingots of vacuum-induction-melting and electroslag-remelting were prepared and their dendrite morphology, segregation and precipitation were investigated. Kinetic homogenizing curves were calculated by Dictra software through a residual segregation parameter model. Based on the theoretical results, five homogenizing treatments were tested and validated by microstructural analysis and thermal compressions. The results show that Nb and Ti are the principal segregated elements of GH4700 ingots. The precipitated phases of casting ingots include γ, γ′, Laves and primary carbide. After homogenization at 1170 oC/48 h, the segregation of elements Nb and Ti are almost eliminated. The phase of Laves, which is detrimental to plasticity, dissolves to the matrix. GH4700 alloy exhibits excellent workability after homogenizing heat treatment