High-strength spring steel having excellent wire-rod rolling properties

Abstract

The present invention relates to a high-strength spring steel having excellent wire-rod rolling properties, consisting essentially of, in terms of mass %: C: 0.40% to 0.65%; Si: 1.20% to 2.80%; Mn: 0.30% to 1.20%; P: 0.020% or less; S: 0.020% or less; Cu: 0.40% or less; Ni: 0.80% or less; Cr: 0.70% or less; Ti: 0.060% to 0.140%; Al: 0.10% or less; N: 0.010% or less; and O: 0.0015% or less, and optionally: B: 0.0005% to 0.0050%, with the remainder being Fe and inevitable impurities, in which the contents in terms of mass % of the specified chemical components satisfy the following Expressions (1) to (3): X 1=0.14×[Si]−0.11×[Mn]−0.05×[Cu]−0.11×[Ni]−0.03×[Cr]+0.02≦0.2   Expression (1) X 2=(α−500)/β≧3.0   Expression (2) α=912−231×[C]+32×[Si]−20×[Mn]−40×[Cu]−18×[Ni]−15×[Cr] β=10̂(0.322−0.538×[C]+0.018×[Si]+1.294×[Mn]+0.693×[Cu]+0.609×[Ni]+0.847×[Cr]) X 3=31×[C]+2.3×[Si]+2.3×[Mn]+1.25×[Cu]+2.68×[Ni]+3.57×[Cr]−6×[Ti]≧24.0   Expression (3).

What is claimed is: 
     
         1 . A high-strength spring steel having excellent wire-rod rolling properties, consisting essentially of, in terms of mass %:
 C: 0.40% to 0.65%;   Si: 1.20% to 2.80%;   Mn: 0.30% to 1.20%;   P: 0.020% or less;   S: 0.020% or less;   Cu: 0.40% or less;   Ni: 0.80% or less;   Cr: 0.70% or less;   Ti: 0.060% to 0.140%;   Al: 0.10% or less;   N: 0.010% or less; and   O: 0.0015% or less,   and optionally:   B: 0.0005% to 0.0050%,   with the remainder being Fe and inevitable impurities,   wherein the contents in terms of mass % of the specified chemical components satisfy the following Expressions (1) to (3):
     X 1=0.14×[ Si]−0.11×[Mn]−0.05×[Cu]−0.11×[Ni]−0.03×[Cr]+0.02≦0.2   Expression (1)
 
     X 2=(α−500)/β3.0   Expression (2)
 
   α=912−231×[C]+32×[Si]−20×[Mn]−40×[Cu]−18×[Ni]−15×[Cr]
 
   β=10̂(0.322−0.538×[C]+0.018×[Si]+1.294×[Mn]+0.693×[Cu]+0.609×[Ni]+0.847×[Cr])
 
     X 3=31×[C]+2.3×[Si]+2.3×[Mn]+1.25×[Cu]+2.68×[Ni]+3.57×[Cr]−6×[Ti]≧24.0   Expression (3).
 
   
     
     
         2 . The high-strength spring steel having excellent wire-rod rolling properties according to  claim 1 , having a 400° C.-temper hardness of 53.0 HRC or more. 
     
     
         3 . The high-strength spring steel having excellent wire-rod rolling properties according to  claim 1 , having a grain size number of 9 or more. 
     
     
         4 . The high-strength spring steel having excellent wire-rod rolling properties according to  claim 2 , having a grain size number of 9 or more.