Abstract

A high-strength gas soft-nitrided crankshaft steel that does not rely on the addition of rare metals has been developed. High strength is realized in Honda’s conventional high-strength crankshaft steel through the addition of the rare metal molybdenum (Mo). By contrast, a high level of strength was achieved in the developed steel by making effective use of manganese (Mn), a universal component of steel, in the production process. High strength was realized by strengthening the ferrite phase using Mn content of 0.9 wt% or higher. It was determined that the strengthening mechanism was precipitation strengthening by means of Mn nitrides (h-Mn3N2) formed in the surface layer ferrite phase as a result of gas soft nitriding. Straightenability, a characteristic that is antagonistic to high strength, is also demanded from crankshaft steels following gas soft nitriding. This demand was responded to in the developed steel by increasing toughness through the reduction of carbon (C) content in order to increase the area ratio of the ferrite phase. The innovations described above have made it possible to reduce material costs by doing away with Mo while realizing an equivalent level of strength to the conventional high-strength steel. Strength has also been increased by 16% against crankshafts produced using the conventional standard steel, which contains no rare metals.

References

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Author (organization or company)

• Hiromasa TAKAHASHI（Automobile R&D Center）
• Hiroki MASUDA（Automobile R&D Center）
• Shigefumi NISHITANI（Nippon Steel & Sumitomo Metal Corporation）
• Motoki TAKASUGA（Nippon Steel & Sumitomo Metal Corporation）

Publication Information

Article of Honda R&D Technical Review Vol.25 No.2 (145 - 153)

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Citation Information