| 摘要 |
PURPOSE:To provide the spring steel capable of securing high toughness in spite of its high hardness by reducing C content in a spring steel with a specific composition and adding specific amounts of Ni and Cr and also adding N by a specific quantity larger than conventional one, respectively. CONSTITUTION:This spring steel has a composition consisting of, by weight, 0.35-0.55% C, 1.80-3.00% Si, 0.50-1.50% Mn, 0.50-3.00% Ni, 0.10-1.50% Cr, 0.01-0.05% Al, 0.010-0.025% N, and the balance Fe and containing, if necessary, one or more kinds among 0.05-0.50% each of V, Nb, and Mo and/or <=0.0015% O. In the above composition, when C content is below the lower limit, sufficient strength cannot be obtained by hardening and tempering, and, when it exceeds the upper limit, toughness is deteriorated and a risk of quenching crack is brought about at the time of water quenching. Although Ni has a function of improving toughness, effect is insufficient when Ni content is below the lower limit, and, when it exceeds the upper limit, the effect is saturated and the possibility of forming retained austenitic is brought about. Cr has effects of improving hardenability and preventing decarburization due to Si, but the effects are insufficient when Cr content is below the lower limit, while a possibility of deteriorating settling resistance is brought about. N has a function of improving settling resistance and durability.
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