Steel wire for springs having excellent fatigue properties, and spring

Abstract

A steel wire rod for a spring includes: C: 0.2 to 1.2%, Si: 1.0 to 3%, Mn: 0.1 to 2%, Cr: 3% or less (not inclusive of 0%), Al: 0.0002 to 0.005%, Ca: 0.0002 to 0.002%, Ti: 0.0003 to 0.010%, and balance: iron and unavoidable impurities. An average composition of oxide-based inclusions having a minor axis of 1 μm or more which are present in a cross section satisfies CaO: 35% or less, Al 2 O 3 : 40% or less, SiO 2 : 30 to 95%, MgO: 8% or less, MnO: 5% or less, TiO 2 : 3 to 10%, and CaO+Al 2 O 3 +SiO 2 +MgO+MnO+TiO 2 ≧80%. The number of oxide-based inclusions having a minor axis of 2 μm or more which are present in the cross section is more than 0.002 inclusions/mm 2 .

1 . A steel wire rod for a spring excellent in fatigue properties, comprising:
 C: 0.2 to 1.2%, where % means mass %, hereinafter the same, unless otherwise indicated,   Si: 1.0 to 3%,   Mn: 0.1 to 2%,   Cr: 3% or less but not inclusive of 0%,   Al: 0.0002 to 0.005%,   Ca: 0.0002 to 0.002%,   Ti: 0.0003 to 0.010%, and   balance: iron and unavoidable impurities,   wherein an average composition of oxide-based inclusions having a minor axis of 1 μm or more which are present in a cross section parallel to a longitudinal direction of a steel satisfies, by mass %, CaO: 35% or less and inclusive of 0%, Al 2 O 3 : 40% or less and inclusive of 0%, SiO 2 : 30 to 95%, MgO: 8% or less and inclusive of 0%, MnO: 5% or less and inclusive of 0%, TiO 2 : 3 to 10%, and CaO+Al 2 O 3 +SiO 2 +MgO+MnO+TiO 2 ≧80%, and   the number of oxide-based inclusions having a minor axis of 2 μm or more which are present in the cross section is more than 0.002 inclusions/mm 2 .   
     
     
         2 . The steel wire rod for a spring according to  claim 1 , wherein the average composition of the oxide-based inclusions further satisfies, by mass %, ZrO 2 : less than 1% but not inclusive of 0% and Na 2 O: less than 5% and inclusive of 0%. 
     
     
         3 . The steel wire rod for a spring according to  claim 1 , further comprising at least one of Ni: 0.5% or less but not inclusive of 0%, Cu: 0.5% or less but not inclusive of 0% and V: 0.5% or less but not inclusive of 0%. 
     
     
         4 . A spring obtained using the steel wire rod for a spring according to  claim 1 . 
     
     
         5 . The steel wire rod for a spring according to  claim 2 , further comprising at least one of Ni: 0.5% or less but not inclusive of 0%, Cu: 0.5% or less but not inclusive of 0% and V: 0.5% or less but not inclusive of 0%. 
     
     
         6 . A spring obtained using the steel wire rod for a spring according to  claim 2 . 
     
     
         7 . A spring obtained using the steel wire rod for a spring according to  claim 3 . 
     
     
         8 . A spring obtained using the steel wire rod for a spring according to  claim 5 .