SUP11A の衝撃値に及ぼす合金元素と焼入れ条件の影響

近年，建設機械用のコイルばねは高強度化が望まれている．このニーズを満たすためにはコイルばねに使用される鋼の高硬度化と高靭性化が必要となる．新たに開発されたばね鋼はC添加とV添加によりSUP11Aよりも高い衝撃値を有する．建設機械用のコイルばねは自動車用のコイルばねと比べて太い．今回の研究で焼入れ時の形状が大きくなると冷却速度が遅くなるために衝撃値が低下することが確認された．しかし，新たに開発された鋼は冷却速度が遅くなってもSUP11Aよりも高い衝撃値を有している．

In these days, high-strength coil springs for construction machines are very much in demand. It is necessary for the coil spring steel to have high hardness and high toughness to meet this needs. Newly developed spring steel has higher Charpy impact value than SUP11A due to the addition of V and the reduction of C. Generally speaking, springs for construction machines are bigger than those for automobiles. This study supported the theory that when the parts size becomes bigger, Charpy impact value decreases since cooling rate becomes slow in the quenching operation. However, newly developed steel has higher Charpy impact value than SUP11A even if the cooling rate is slow.

Charpy impact value, Quenching conditions, SUP11A, Grain refinement