ばね鋼の曲げ疲れ強さに及ぼす超清浄化の影響 (自動車用鋼<特集>)

概要

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There is a recent tendency to develop a motorcars suspension coil spring that can be used under higher-stressed condition and to develop a valve spring having a higher-level of strength therefore creating better engine performance. Since there is a difference between the required fatigue strength level of suspension coil spring and valve spring steel, improvement of fatigue property is a common destination. In order to achieve this purpose, ultra clean steel is considered to be one of the effective methods.The degassing process for producing ultra clean steel satisfies the needs for low cost and mass production. Ultra clean steel is examined and tested as to the properties required for valve spring and suspension coil spring steel. The following results are obtained.(1) Ultra-Low-Oxygen steel (ULO steel) with oxygen content less than 15ppm is confirmed one of the effective means to realize a suspension coil spring satisfying 200kgf/mm2 high stress level.(2) ULO+UL·TiN steel produced by ultra low oxygen and ultra low TiN process exhibits almost the same endurance limit as the Vacuum Arc-furnace Remelted steel. Therefore, this steel is found to be applicable to high strength valve spring.