Abstract

The project discussed in this paper developed a nitrocarburizing steel that balances strength, wear resistance, and workability. The hardness of the steel is controlled as low as possible for machining after forging, and the heat applied in the nitrocarburizing process is then used to achieve high hardness in both the surface layer and the base material. As a result, the developed steel achieves at least 40% higher bending fatigue strength than a conventional nitrocarburized steel. The balance between high fatigue strength and workability in the developed steel is realized through the exploitation of Mo-V carbonitride precipitate strengthening. When the material is machined, the Mo and V are in a state of solid solution, but during the nitrocarburization process following machining, fine complex Mo and V carbonitrides are precipitated in lattices coherent with the base material, resulting in high hardness. The fact that the compound layer that formed during nitrocarburization was brittle and lacked ductility represented a disadvantage in terms of abrasive wear, and it was necessary to increase the toughness of the compound layer in order to increase wear resistance. The crystal grains in the compound layer were therefore refined by promoting the precipitation of Mo and V carbonitrides in the compound layer also, resulting in the realization of greater toughness and increased wear resistance.

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Author (organization or company)

• Hiroki MASUDA（Automobile R&D Center）
• Hideki MATSUDA（Automobile R&D Center）
• Ayumi YAMAZAKI（Daido Steel Co., Ltd.）

Publication Information

Article of Honda R&D Technical Review Vol.24 No.2 (117 - 125)

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