High-strength spring steel

Abstract

A spring steel contains 0.15-0.40% carbon, 1-3.5% silicon, 0.20-2.0% manganese, 0.05-1.20% chromium, at most 0.030% phosphorus, at most 0.02% sulfur, and at least one of the following: 0.005-0.10% titanium, 0.005-0.05% niobium, and at most 0.25% vanadium. The remainder of said spring steel includes iron and unavoidable impurities. The carbon equivalent (Ceq 1 ) of the provided spring steel, as calculated by formula (1), is at most 0.55. (1) Ceq 1 =[C]+0.108×[Si]−0.067×[Mn]+0.024×[Cr]−0.05×[Ni]+0.074×[V]. In the formula (1), each symbol in brackets represents the content (mass %) of the corresponding element.

1 - 6 . (canceled) 
     
     
         7 . A high-strength spring steel omitting tempering, comprising:
 C: 0.15-0.40% (means mass %, hereinafter the same);   Si: 1-3.5%;   Mn: 0.20-2.0%;   at least one element selected from a group consisting of Ti: 0.005-0.10%, Nb: 0.005-0.05% and V: 0.25% or less;   Cr: 0.05-1.20%;   P: 0.030% or less; and   S: 0.02% or less, wherein   the remainder includes iron and unavoidable impurities, and   a carbon equivalent Ceq 1  of the spring steel according to the following formula is 0.55 or less:
   Ceq 1 =[C]+0.108×[Si]−0.067×[Mn]+0.024×[Cr]−0.05×[Ni]+0.074×[V],
 
   with each symbol in brackets representing the content (mass %) of the corresponding element.   
     
     
         8 . The high-strength spring steel according to  claim 7 , further comprising:
 Ni: 0.05-2%; and   Cu: 0.05-0.50%.   
     
     
         9 . The high-strength spring steel according to  claim 8 , further comprising:
 Ni: 0.15-2%.   
     
     
         10 . The high-strength spring steel according to  claim 7 , further comprising:
 at least one element selected from a group consisting of Ti: 0.035-0.10%, Nb: 0.005-0.05%, and V: 0.05-0.25%,   wherein the grain size number after quenching is 7.5 or above.   
     
     
         11 . The high-strength spring steel according to  claim 7 , further comprising:
 B: 0.005% or less; and/or   Mo: 0.60% or less.   
     
     
         12 . A method for manufacturing a high-strength spring excellent in corrosion fatigue property, comprising:
 hot-coiling the spring steel according to claim  1 ;   quenching; and   setting thereafter while omitting tempering.