Wire rod and steel wire for spring, spring with improved strength and fatigue limit, and method for manufacturing same
AssigneePosco
InventorsJunmo LEE, Seokhwan CHOI, Myungsoo CHOI
Life of this patent
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Abstract
Disclosed are a wire rod and a steel wire for a spring, a spring with improved strength and fatigue limit, and a method for manufacturing the same. The disclosed wire rod for a spring with improved strength and fatigue limit according to an embodiment includes, in percent by weight (wt %): 0.6 to 0.7% of C, 2.0 to 2.5% of Si, 0.2 to 0.7% of Mn, 0.9 to 1.5% of Cr, 0.015% or less of P, 0.01% or less of S, 0.01% or less of Al, 0.01% or less of N, 0.25% or less of Mo, 0.25% or less of W, 0.05% to 0.2% of V, 0.05% or less of Nb, and the balance of Fe and unavoidable impurities, wherein Mn+Cr≤1.8% and 0.05 at %≤Mo+W≤0.15 at % may be satisfied.
Claims15
A wire rod for a spring with improved strength and fatigue limit, the wire rod comprising, in percent by weight (wt %), 0.6 to 0.7% of C, 2.0 to 2.5% of Si, 0.2 to 0.7% of Mn, 0.9 to 1.5% of Cr, 0.015% or less of P, 0.01% or less of S, 0.01% or less of Al, 0.01% or less of N, 0.25% or less of Mo, 0.25% or less of W, 0.05% to 0.2% of V, 0.05% or less of Nb, and the balance of Fe and unavoidable impurities,
- wherein Mn+Cr≤1.8% is satisfied,
- 0.05 at %≤Mo+W≤0.15 at % is satisfied,
- a proportion (wt %) of an area satisfying one or more of C>0.85%, Si>3.0%, Mn>0.8%, and Cr>2.0% is 10% or less within an area of 1 mm2 of a central region of a cross-section perpendicular to a lengthwise direction.
A method for manufacturing a wire rod for a spring with improved strength and fatigue limit, the method comprising:
- preparing a bloom by continuously casting a molten steel including, in percent by weight (wt %), 0.6 to 0.7% of C, 2.0 to 2.5% of Si, 0.2 to 0.7% of Mn, 0.9 to 1.5% of Cr, 0.015% or less of P, 0.01% or less of S, 0.01% or less of Al, 0.01% or less of N, 0.25% or less of Mo, 0.25% or less of W, 0.05% to 0.2% of V, 0.05% or less of Nb, and the balance of Fe and unavoidable impurities;
- heating the bloom at a temperature of 1,200° ° C. or above and rolling the bloom to prepare a billet;
- heating the billet at a temperature of 1,030° ° C. or above and rolling the billet at a temperature of 1,000° ° C. below to prepare a wire rod;
- coiling the rolled wire rod at a temperature of 800 to 900° C.;
- and
- cooling the coiled wire rod at a seed of 0.5 to 2ºC/sec.
A steel wire for a spring with improved strength and fatigue limit, the steel wire comprising, in percent by weight (wt %), 0.6 to 0.7% of C, 2.0 to 2.5% of Si, 0.2 to 0.7% of Mn, 0.9 to 1.5% of Cr, 0.015% or less of P, 0.01% or less of S, 0.01% or less of Al, 0.01% or less of N, 0.25% or less of Mo, 0.25% or less of W, 0.05% to 0.2% of V, 0.05% or less of Nb, and the balance of Fe and unavoidable impurities,
- wherein Mn+Cr≤1.8% is satisfied,
- 0.05 at %≤Mo+W≤0.15 at % is satisfied, and
- the steel wire comprises, in an area fraction, 85% or more of a tempered martensite structure and the balance of an austenite structure.
Dependencies are inferred from the claim text.