冷鍛・高周波焼入用鋼の開発

概要

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Induction hardening of cold forged parts have become more popular in automotive industries to simplify the production line. However, carbon steel whose carbon content is higher than 0.4% gives rise to the difficulty in cold forgeability even in spheroidizing annealing condition. When alloy contents are decreased to improve cold forgeability, on the other hand, induction hardenability is deteriorated conversely.On these backgrounds, the new steel named HAC steel, Hardenability Assured steel for Cold Forging, has been developed to be compatible these two characteristics each other. Ferrite strengthening elements, Si and Mn, are decreased to reduce the flow stress in cold forging and B is added to maintain induction hardenability. HAC steel, the fundamental composition is 0.48∼0.53C-0.05Si-0.25Mn-0.15Cr-B, shows superior cold forgeability to that of conventional JIS carbon steels keeping the same case depth in induction hardening.HAC steel has been in practical use for constant velocity joint components such as outer race and shaft, and expected to apply to the wide variety of automotive parts.
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