号数	ばね論文集４５号（２０００年）
ページ数	pp.15-18
種類	論文
論文名	疲労特性に優れた高強度弁ばね用鋼の開発
Title	Development of High Strength Valve Spring Steel with Excellent Fatigue Life Performance
著者	吉原 直・黒田 武司・佐藤 仁資・茨木 信彦
Author	Nao YOSHIHARA・Takashi KURODA・Hitoshi SATOH・Nobuhiko IBARAKI
抄録	近年のエンジン弁ばねの高応力設計に応えるべく、高負荷応力下にて優れた疲労特性、耐へたり特性を有し、なおかつ加工性にも優れた弁ばね用鋼を開発した。本論文では下記項目を紹介する。 1)焼戻し軟化抵抗性に優れ、窒化想定の熱処理で引張強さが SAE9254に対して200MPa以上高い。 2)オイルテンパー処理後のγGS-NOがSAE9254に対して#2程度高く、またNi添加の効果、高い焼戻し温度の効果により、SAE9254と同じ硬さにおいて、破壊靭性値が約5MPa 以上高い。 3)SAE9254と同じ工程で弁ばねまでの製造が可能である。 4)疲労特性に関し欠陥(介在物)感受性に優れ、同一介在物レベルでは負荷応力が1.16倍増加できる。 5)高Si鋼に適した製造技術により高清浄化が達成でき、安定して高い疲労特性を得ることができる。
Abstract	In order to respond to the needs for high stress design in valve spring, we developed a new valve spring steel which has superior fatigue property and sag resistance without sacrificing the cold-coiling performance of wire. This paper describes the following results: 1) The tensile strength of newly developed steel was 200MPa higher than that of conventional SAE9254 after heat treatment which simulates the nitriding process.  2) Austenite grain size number of the developed steel was 2 point higher than that of SAE9254 after oil tempering process. 3) Fracture toughness of the developed steel was 5MPa√m higher than that of SAE9254 compared at the same hardness level. This is thought to be the effect of Ni addition and higher tempering temperature. 4) It was confirmed that conventional cold coiling process being adopted to SAE9254 is applicable to this newly developed steel. 5) The developed steel is less sensitive against inclusions during fatigue test. If the inclusion size is same level, 16% higher cyclic stress can be applied for the developed steel than for SAE9254. 6) We have also developed the inclusion control technique for high Si steel, and high fatigue performance are being stably obtained.
著者の所属	(株)神戸製鋼所
Belonging	KOBE STEEL, LTD.
Key Words	valve spring, fatigue, sag resistance, cold coiling, nitriding, fracture toughness, inclusion