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| Study on Forming Process and Mechanical Properties of GH4068 Alloy Pipe |
| CUI Chuanyong, BAI Yingbo, ZHANG Rui, ZHOU Zijian, ZHOU Yizhou, SUN Xiaofeng |
| Shi-changxu Innovation Center for Advanced Materials, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China |
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Abstract GH4068 alloy pipes were prepared by casting directly canned hot extrusion and blooming+extrusion. The forming and service properties of the alloy pipes under two kinds of preparation conditions were studied by thermal compression simulation test and mechanical property test. The results show that GH4068 alloy has great thermal deformation ability when processed below γ′ complete solution temperature. After high-temperature annealing, the grain structure of as-cast alloy is coarse and the deformation coordination is poor. The optimum deformation temperature is higher (1130℃ ) during direct extrusion; The fine grain structure obtained after blooming is helpful to improve the deformation ability and reduce the hot extrusion temperature. The dynamic recrystallization volume fraction of the bloom alloy after deformation at 1090℃ and 0.1–1s–1 strain rate is more than 95%. The grain size of the tube obtained by blooming+extrusion is about 6.8μm. Fine grain structure and primary γ′ phase at grain boundary contribute to the improvement of the tensile properties of the alloy, and its yield strength at 750℃ reaches 1088MPa. The existence of a large number of grain boundaries in the fine grain structure of the bloomed + extruded pipe affects the high temperature stress-rupture property of the alloy, and its endurance life is lower than that of the as-cast extruded pipe with coarse grain (about 35μm).
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2022, 
