高強度懸架ばね用鋼の開発 (自動車用材料<特集>)

概要

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Automobile industries have searched for more reliable steel with higher strength. In case of spring steel, much efforts have been made to develop the high strength steel to endure the applied stress of 130kgf/mm2.For this purpose, at first a fundamental study on the alloy designing of ultra-high strength steel was made.ND 250S (0.4C-2.5Si-0.8Mn-2Ni-0.85Cr-0.4Mo-0.2V) was confirmed to show the great possibility to be applicable to high strength coil spring. Furthermore, the coil spring made of this steel was evaluated in terms of the fatigue properties, sag resistance and delayed fracture property.The following results are obtained.(1) The mechanical properties of ND 250S are superior to those of SUP 7 especially in toughness.(2) The threshold stress intencity factor range of ND 250S is larger than that of SUP 7, which indicate the greater notch toughness.(3) ND 250S is proved to exhibit superior properties necessary for coil spring to conventional spring steels and to show the potential as the 130kgf/mm2 grade high strength coil spring.
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