| 摘要 |
<p>A spring steel having excellent fatigue properties by setting critical standards on a ratio of inclusions having an effect on fatigue properties in steel and on a number of the inclusions per sizes is provided, and an apparatus of manufacturing the spring steel having excellent fatigue properties is provided to prevent Al2O3 inclusions from being added into molten steel by limiting a composition for refractories of a portion of the spring steel casting apparatus contacting the molten steel. In a spring steel in which the content of aluminum is suppressed, a spring steel having excellent fatigue properties is characterized in that a ratio of single or composite inclusions containing at least 30 wt.% of Al2O3 to all inclusions with a size of at least 10 mum in inclusions of the spring steel is less than 50%. The number of inclusions with a size of at least 10 mum in the single or composite inclusions containing at least 30 wt.% of Al2O3 is less than 2 per kg of the steel, the number of inclusions with a size of at least 20 mum is less than 1 per kg of the steel, and the number of inclusions with a size of at least 40 mum is less than 0.5 per kg of the steel. The inclusions of the spring steel are anorthite-based inclusions, SiO2-based inclusions, Al2O3-based inclusions, oxidative inclusions, or mixtures thereof. The spring steel comprises 0.53 to 0.67 wt.% of C, 1.3 to 2.6 wt.% of Si, 0.6 to 0.8 wt.% of Mn, 0.6 to 1.3 wt.% of Cr, 0 to 0.21 wt.% of V, 0.25 to 0.55 wt.% of Ni, 0.05 to 0.15 wt.% of Mo, 0.01 wt.% or less of S, 0.02 wt.% or less of P, and 0.007 wt.% or less of N with the balance being Fe and other inevitable impurities.</p> |
