WIRE ROD FOR SPRINGS WITH EXCELLENT CORROSION FATIGUE RESISTANCE, STEEL WIRE, AND MANUFACTURING METHOD THEREOF

1 . A wire rod for springs with excellent corrosion fatigue resistance, comprising:

C: 0.40 to 0.70%, Si: 1.30 to 2.30%, Mn: 0.20 to 0.80%, Cr: 0.20 to 0.80%, Cu: 0.01 to 0.40%, Ni: 0.10 to 0.60%, Mo: 0.01 to 0.40%, P: 0.02% or less, S: 0.015% or less, N: 0.01% or less, and a balance of Fe and inevitable impurities by weight %,

wherein the wire rod satisfies equation 1 below:

−0.14≤0.70[Cr]−0.76[Cu]−0.24[Ni]≤0.47   Equation 1

where each element symbol is a value of a content of each element measured by weight %,

wherein a microstructure comprises 50 area % or less of ferrite and a balance of pearlite, and

wherein the wire rod comprises 8.0×10 4 count/mm 2 or higher of Mo-based carbides.

2 . The wire rod for springs of claim 1 , further comprising:

one or more elements selected from among V: 0.01 to 0.20%, Ti: 0.01 to 0.15%, and Nb: 0.01 to 0.10% by weight %.

3 . The wire rod for springs of claim 1 , wherein the Mo-based carbide includes 5 weight % of higher of Mo based on carbide.

4 . A method of manufacturing a wire rod for springs with excellent corrosion fatigue resistance, comprising:

heating a billet to 900 to 1100° C., the billet comprising C: 0.40 to 0.70%, Si: 1.30 to 2.30%, Mn: 0.20 to 0.80%, Cr: 0.20 to 0.80%, Cu: 0.01 to 0.40%, Ni: 0.10 to 0.60%, Mo: 0.01 to 0.40%, P: 0.02% or less, S: 0.015% or less, N: 0.01% or less, and a balance of Fe and inevitable impurities by weight % and satisfying equation 1 below:

−0.14≤0.70[Cr]−0.76[Cu]−0.24[Ni]≤0.47   Equation 1

where each element symbol is a value of a content of each element measured by weight %;

obtaining a wire rod by finishing-hot-rolling the heated billet at 800 to 1000° C.; and

coiling the wire rod and cooling the wire rod such that the time for maintaining the wire rod at a temperature in a range of 600 to 700° C. is to be 31 seconds or longer.

5 . The method of claim 4 , wherein the billet further comprises one or more elements selected from among V: 0.01 to 0.20%, Ti: 0.01 to 0.15%, and Nb: 0.01 to 0.10% by weight %.

6 . A steel wire for springs with excellent corrosion fatigue resistance, comprising:

C: 0.40 to 0.70%, Si: 1.30 to 2.30%, Mn: 0.20 to 0.80%, Cr: 0.20 to 0.80%, Cu: 0.01 to 0.40%, Ni: 0.10 to 0.60%, Mo: 0.01 to 0.40%, P: 0.02% or less, S: 0.015% or less, N: 0.01% or less, and a balance of Fe and inevitable impurities by weight %,

wherein the steel wire satisfies equation 1 below:

−0.14≤0.70[Cr]−0.76[Cu]−0.24[Ni]≤0.47   Equation 1

where each element symbol is a value of a content of each element represented by weight %,

wherein a microstructure is tempered martensite, and

wherein the steel wire comprises 8.0×10 4 count/mm 2 or higher of Mo-based carbides.

7 . The steel wire for springs of claim 6 , further comprising:

one or more elements selected from among V: 0.01 to 0.20%, Ti: 0.01 to 0.15%, and Nb: 0.01 to 0.10% by weight %.

8 . The steel wire for springs of claim 6 , wherein the Mo-based carbide comprises 5 weight % or higher of Mo based on carbide.

9 . The steel wire for springs of claim 6 , wherein a maximum depth of a corrosion pit of the steel wire is 120 μm or less.

10 . The steel wire for springs of claim 6 , wherein tensile strength of the steel wire is 1800 MPa or higher.

11 . A method of manufacturing a steel wire for springs with excellent corrosion fatigue resistance, comprising:

obtaining the steel wire by drawing a wire rod manufactured by the method in claim 4 ;

austenitizing the steel wire by heating the steel wire to 850˜1000° C. and maintaining the heated steel wire for 1 minute or longer; and

oil-cooling the austenitized wire rod to 25˜80° C. and tempering the wire rod at 350˜500° C.