| 摘要 |
PURPOSE:To provide a titled steel for a spring having remarkably improved sag resistance and fatigue strength by consisting the steel of specifically composed C, Si, Mn, Cr, Al, V, Nb and Fe, etc. and subjecting the steel to controlled rolling to >=#9 crystal grain size. CONSTITUTION:A steel contg. 0.40-0.75wt% C, 1.0-2.5% Si, 0.5-1.0% Mn, 0.1- 1.0% Cr, and >=1 kind among 0.01-0.1% Al, 0.03-0.3% V and 0.01-0.3% Nb, further contg. S and O regulated to <=0.010% S and <=0.0015% O according to need, further contains 0.005-0.01% B and consisting of the balance Fe and impurities is subjected to controlled rolling to >=#9 crystal grain size, by which a steel for a high-strength and high-toughness spring is obtd. The above-mentioned controlled rolling is preferably accomplished under the conditions of about 930- 980 deg.C billet heating temp., about <=900 deg.C rolling temp. with the final rolling roll, about >=5% draft, and about >=30 deg.C/min cooling rate down to the Ar1 transformation point after the rolling.
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