号数	ばね論文集 58 号（ 2013 年）
ページ数	pp.9-19
種類	論文
論文名	ショットピーニング後に人工腐食ピット加工を施した懸架ばね用鋼の疲労特性に及ぼす水素の影響
Title	Influence of hydrogen on fatigue property of suspension spring steel with artificial corrosion pit after shot peening.
著者	久保田学 1)，平上大輔 1)，潮田浩作 1)
Author	Manabu KUBOTA 1), Daisuke Hirakami 1) and Kohsaku Ushioda 1)
抄録	懸架ばねを高強度化するためには，懸架ばねの腐食疲労特性を向上することが必要である．しかしながら，懸架ばねの腐食疲労特性の支配因子は必ずしも明らかになっていない．懸架ばねの腐食疲労特性の支配因子を明らかにするためには，腐食ピット，ショットピーニング，水素脆化，旧γ粒径などの影響をそれぞれ分離して評価する必要がある．このため，本研究では，ショットピーニング後に人工腐食ピット加工を施した回転曲げ疲労試験片の疲労特性に及ぼす水素の影響を調査し，前報の結果と合わせて腐食疲労特性の支配因子について検討を加えた．その結果，腐食ピットがない場合，あるいは腐食ピットの深さが浅く，ピット底に作用する圧縮残留応力が大きい場合は拡散性水素が疲労強度低下の支配因子であること，一方，腐食ピットの深さが深く，ピット底に作用する圧縮残留応力が小さい場合には，疲労強度に対して最も影響が大きい因子は，腐食ピットの深さと圧縮残留応力分布であること，水素チャージ後の疲労特性に及ぼす旧γ粒径の影響はほとんどないことがわかった．
Abstract	In order to reduce the weight of the suspension springs by increasing the steel strength, it is necessary to improve the corrosion fatigue property. However, the dominant factor governing the corrosion fatigue property of the suspension spring has not been satisfactorily revealed yet. Therefore, the investigation into elucidating the mechanism has been carried out to independently evaluate the influences of corrosion pits, shot peening, hydrogen, prior-austenite grain size, and so forth on the corrosion fatigue property. In this study, the influence of hydrogen on rotary bending fatigue test was investigated using specimens with artificial corrosion pits after shot peening. The dominant factors governing the corrosion fatigue property of the suspension spring were discussed based on the result of the present study in conjunction with the results of the previous study on the influences of shot peening and corrosion pit depth. The conclusions obtained were as follows: (1) In the case of the specimen without corrosion pit or with only shallow corrosion pits having still large compressive residual stress at the bottom of the pits, the fatigue property was fairly good but declined with the increment of charged hydrogen due to the diffusible hydrogen. On the other hand, in the case of the specimen with deep corrosion pits having only small compressive residual stress, the fatigue property was poor regardless of the charged hydrogen content. We inferred from this result that the deep corrosion pit releases the compressive residual stress at the bottom of pits. (2) The effect of prior-austenite grain size on fatigue properties of hydrogen charged specimens turned out to be almost negligible
著者の所属	1) 新日鐵住金株式会社
Belonging	1) Nippon Steel & Sumitomo Metal Corporation
Key Words	Suspension spring, Corrosion fatigue, Shot peening, Residual stress, Corrosion pit，Hydrogen embrittlement