Microstructure and properties of C69 gear steel for aviation after high temperature carburizing

doi:10.13251/j.issn.0254-6051.2022.04.038

Abstract

Abstract: Effect of different carburizing processes at 1050 ℃ on microstructure and properties of gear steel C69 for aviation was studied by using OM, SEM, TEM and Vickers hardness tester. The results show that after carburizing, cryogenic and tempering, the surface hardness of the carburized layer can reach about 950 HV0.3, and the microstructure is acicular martensite where the M₃C and M₂C carbides precipitate, and the M₇C₃carbides precipitate at grain boundary. At the sub-layer of the carburized surface, microstructure is composed of acicular martensite and lath martensite. At the core, the microstructure is lath martensite and the hardness is about 630 HV0.3. The cyclic carburizing has higher carburizing efficiency. With the increase of carburizing cycle, the thickness of carburized layer and surface carbon concentration increase continuously, and the size and quantity of the M₇C₃ at the grain boundary also increase. After four cycles carburizing, the surface carbon concentration is 1.14%, and the thickness of carburized layer is about 3.0 mm.

Key words: aviation gear steel, C69 steel, carburizing process, carburized layer hardness, carbide

CLC Number:

TG142.1

Dai Jianke, Han Shun, Li Yong, Liu Xianmin, Wang Chunxu, Pang Xuedong, Li Jianxin. Microstructure and properties of C69 gear steel for aviation after high temperature carburizing[J]. Heat Treatment of Metals, 2022, 47(4): 219-225.

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