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Development of Non-normalized Nitrocarburized High Strength Crankshaft

Article of Honda R&D Technical Review Vol.19 No.1

Summary

A non heat-treated nitrocarburized crankshaft was developed by designing the material composition so as to maximize the effectiveness of the strength increase due to nitrocarburization. This crankshaft has a fatigue strength that is approximately 16% higher than that of a conventional crankshaft of the same material hardness, while possessing the same workability and straightening ability. Strengthening ferrite by adding a relatively small quantity of molybdenum (Mo) gave the developed material both high fatigue strength and excellent straightenability. The mechanism of strengthening by the addition of Mo is thought not to be the secondary hardening due to the precipitation of molybdenum carbonitride, but the formation of a Mo cluster consisting of several atoms during the nitrocarburizing process. This results in a greater strengthening effect compared to solid solution strengthening, thus contributing to higher yield strength. It was found that compared to the conventional high strength crankshaft, the elimination of the normalization process and so on reduced CO2 emission during and after the hot forging process by approximately 22%, and costs by approximately 8%.

Reference

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Author (organization or company)

Tetsuya ASAI(Automobile R&D Center)、Yoshihiro TAKITANI(Automobile R&D Center)、Naoyuki SANO(Sumitomo Metal Industries, Ltd.)、Hitoshi MATSUMOTO(Sumitomo Metals (Kokura), Ltd.)

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