Laves相对GH3625合金管材热挤压过程中爆裂行为的影响

Effects of Laves Phase on Burst Behavior of GH3625 Superalloy Pipe During Hot Extrusion

采用GH3625合金铸态管坯及均匀化态管坯进行相同工艺热挤压管材制备实验,均匀化态管坯能成功挤出,而铸态管坯出现管爆裂现象。通过OM、SEM等手段观察了GH3625合金铸态及均匀化态组织、热挤压成形管材组织、爆裂管材组织及断口形貌,结合EDS分析,研究了GH3625合金管爆裂行为。结果表明,铸态管坯中存在较多的Laves相,经均匀化处理后Laves相和微观偏析基本消除;铸态管坯在热挤压过程中绝热升温导致Laves相回熔是造成管爆裂的主要原因;管爆裂的开裂方式为脆性断裂和韧性断裂相结合的准解理断裂,其中脆性断裂占主导地位。

GH3625 superalloy is a type of solid-solution strengthened nickel-based wrought superalloy having Mo and Nb as the main strengthening elements. Because of its excellent high-temperature mechanical properties and oxidation resistance below 650 ℃, it can be used in harsh stress and atmosphere environments. It is mainly used as a pipe material for aeroengine fuel main pipe, nuclear power steam generator heat transfer pipe, and pressure pipe, etc. Owing to the high alloying degree of nickel-based superalloys, large deformation resistance, and narrow thermal processing temperature range, the pipe preparation process is complicated. In this study, the as-cast and homogenized pipe billets were used for a short-flow hot extrusion pipe preparation test using the same process. The homogenized pipe billet was extruded successfully, and the pipe burst occurred during the extrusion of the as-cast billet. The pipe burst behavior was studied by OM, SEM, and EBSD, with an EDS analysis. The results showed a considerable amount of Laves phases in the as-cast pipe billet, and the Laves phases and micro-segregation were essentially eliminated after homogenization. Adiabatic heating of the as-cast pipe billet leads to the Laves phase remelting during the hot extrusion process, which is the main reason for pipe bursting during a hot extrusion process. The cracking mode of the pipe burst is a quasi-cleavage fracture, combining brittle fracture and ductile fracture with the predominance of the brittle fracture.