Steel and steel wire, which are for spring, and manufacturing methods therefor

Abstract

Disclosed in the present specification are steel and a steel wire, which are for a spring, and manufacturing methods therefor, the steel and the steel wire having excellent resistance to permanent deformation by having increased in-material dislocation density or reduced average grain diameter. The steel wire for a spring, having excellent resistance to permanent deformation, according to one embodiment of the present invention, comprises, by wt %, 0.4-0.7% of C, 1.2-2.3% of Si, 0.2-0.8% of Mn, 0.2-0.8% of Cr, and the balance of Fe (iron) and other inevitable impurities, wherein the dislocation density thereof can be 1.16×1015/m2 or more, and the average grain diameter thereof can be 8.4 μm or less.

1 . A steel wire for spring having excellent permanent deformation resistance, comprising:
 C: 0.4 to 0.7%, Si: 1.2 to 2.3%, Mn: 0.2 to 0.8%, Cr: 0.2 to 0.8%, a balance of Fe, and other inevitable impurities, based on weight percent,   wherein a dislocation density is 1.16×10 15 /m 2  or more, and   an average grain diameter is 8.4 μm or less.   
     
     
         2 . The steel wire for spring of  claim 1 , further comprising one or more selected from the group consisting of V: 0.01 to 0.3%, Nb: 0.005 to 0.05%, Ti: 0.001 to 0.15%, and Mo: 0.01 to 0.4%, based on weight percent. 
     
     
         3 . The steel wire for spring of  claim 1 , wherein a hysteresis loop area obtained by a Bauschinger torsion test is 206 mm 2  or more. 
     
     
         4 . A method of manufacturing a steel wire for spring having excellent permanent deformation resistance, the method comprising:
 manufacturing a steel wire by drawing steel comprising C: 0.4 to 0.7%, Si: 1.2 to 2.3%, Mn: 0.2 to 0.8%, Cr: 0.2 to 0.8%, a balance of Fe, and other inevitable impurities, based on weight percent,   heating the drawn steel wire to 850 to 1000° C. and then maintaining the steel wire for 1 second or more to austenitize; and   after austenitization, quenching the steel wire at 25 to 80° C. and then tempering the steel wire at 350 to 500° C.   
     
     
         5 . The method of  claim 4 , wherein the steel further comprises one or more selected from the group consisting of V: 0.01 to 0.3%, Nb: 0.005 to 0.05%, Ti: 0.001 to 0.15%, and Mo: 0.01 to 0.4%, based on weight percent. 
     
     
         6 . Steel for spring having excellent permanent deformation resistance, comprising:
 C: 0.4 to 0.7%, Si: 1.2 to 2.3%, Mn: 0.2 to 0.8%, Cr: 0.2 to 0.8%, a balance of Fe, and other inevitable impurities, based on weight percent,   wherein a dislocation density is 0.11×10 15 /m 2  or more, and   an average grain diameter is 9.6 μm or less.   
     
     
         7 . The steel for spring of  claim 6 , further comprising one or more selected from the group consisting of V: 0.01 to 0.3%, Nb: 0.005 to 0.05%, Ti: 0.001 to 0.15%, and Mo: 0.01 to 0.4%, based on weight percent. 
     
     
         8 . A method of manufacturing steel for spring having excellent permanent deformation resistance, the method comprising:
 manufacturing a billet comprising C: 0.4 to 0.7%, Si: 1.2 to 2.3%, Mn: 0.2 to 0.8%, Cr: 0.2 to 0.8%, a balance of Fe, and other inevitable impurities, based on weight percent,   heating the billet to 960 to 1100° C.; and   finish rolling the billet at 855 to 920° C.   
     
     
         9 . The method of  claim 8 , wherein the billet further comprises one or more selected from the group consisting of V: 0.01 to 0.3%, Nb: 0.005 to 0.05%, Ti: 0.001 to 0.15%, and Mo: 0.01 to 0.4%, based on weight percent.