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Development of Nitrocarburized High-strength Crankshaft with No Rare Metals Added

Article of Honda R&D Technical Review Vol.23 No.2


Conventional nitrocarburized high-strength crankshafts secure high fatigue strength through a strengthening mechanism using the rare metal molybdenum (Mo). In contrast, a crankshaft with high fatigue strength equal to that of the conventional material was developed without the addition of rare metals by using copper (Cu) and chromium (Cr) and optimizing the material design.
Cr increases the hardness near the surface layers during nitrocarburization, which effectively increases the strength. However, in this case cracking easily occurs when plastic deformation is applied to straighten crankshaft bending that occurs in the nitrocarburization process, which has made it a challenge to actively use Cr. The developed material combines hardening by Cr with ferrite solid solution strengthening by Cu, and enhances straightenability by suppressing the Cr content required for strengthening. This simultaneously achieved both high fatigue strength and good straightenability without the addition of rare metals.


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Author (organization or company)

Yoshihiro TAKITANI(Automobile R&D Center)、Isamu SAITO(Automobile R&D Center)、Takahiro MIYAZAKI(Daido Steel Co., Ltd.)、Keiichiro KAMIYA(Daido Steel Co., Ltd.)

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