High-strength spring steel

Abstract

Provided is a spring steel that 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 comprises iron and unavoidable impurities. The carbon equivalent (Ceq 1 ) of the provided spring steel, as calculated by formula (1), is at most 0.55. Ceq 1 =[C]+0.108×[Si]−0.067×[Mn]+0.024×[Cr]−0.05×[Ni]+0.074×[V]  (1) (In the formula (1), each symbol in brackets represents the content (mass %) of the corresponding element.)

1 . A spring steel wire rod omitting tempering, the spring steel wire rod comprising:
 C: 0.15-0.33% (means mass %, hereinafter the same);   Si: 1.9-3.5%;   Mn: 0.20-1.5%   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;   S: 0.02% or less; and   iron and unavoidable impurities,   
       wherein:
 the spring steel wire rod comprises no Mo; and 
 a carbon equivalent Ceq 1  of the spring steel wire rod expressed by formula (1) below is 0.55 or less:
   Ceq 1 =[C]+0.108×[Si]−0.067×[Mn]+0.024×[Cr]−0.05×[Ni]+0.074×[V]  (1)
 
 
 
       with each symbol in brackets representing the content (mass %) of the corresponding element. 
     
     
         2 . The spring steel wire rod according to  claim 1 , further comprising:
 Ni: 0.05-2% and   Cu: 0.05-0.50%.   
     
     
         3 . The spring steel wire rod according to  claim 2 , further comprising:
 Ni: 0.15-2%.   
     
     
         4 . The spring steel wire rod according to  claim 1 , 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 a grain size number of the spring steel wire rod after quenching is 7.5 or above. 
     
     
         5 . The spring steel wire rod according to  claim 1 , further comprising:
 B: 0.005% or less.   
     
     
         6 . A method for manufacturing a spring excellent in corrosion fatigue property, the method comprising:
 hot-coiling the spring steel wire rod of  claim 1 ;   quenching; and   setting thereafter while omitting tempering.   
     
     
         7 . The spring steel wire rod according to  claim 1 , comprising:
 Si: 2.01-3.55%.   
     
     
         8 . The spring steel wire rod according to  claim 1 , consisting of:
 C: 0.15-0.33% (means mass %, hereinafter the same)   Si: 1.90-3.5%;   Mn: 0.20-1.5%;   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;   S: 0.02% or less;   iron and unavoidable impurities; and   optionally at least one of
 Ni: 2% or less, 
 Cu: 0.50% or less, and 
 B: 0.005% or less, 
   wherein a carbon equivalent Ceqx of the spring steel wire rod according to the following formula is 0.55 or less:
   Ceq1=[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. 
     
     
         9 . The spring steel wire rod according to  claim 8 , consisting of:
 C: 0.15-0.33% (means mass %, hereinafter the same);   Si: 1.90-3.5%;   Mn: 0.20-1.5%;   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;   S: 0.02% or less;   Ni: 0.15-2%;   iron and unavoidable impurities; and   optionally at least one of
 Cu: 0.50 or less, and 
 B: 0.005% or less, 
   
     
     
         10 . The spring steel wire rod according to  claim 8 , consisting of
 C: 0.15-0.33% (means mass %, hereinafter the same)   Si: 1.90-3.5%;   Mn: 0.20-1.5%;   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%; 
   Cr: 0.05-1.20%;   P: 0.030% or less;   S: 0.02% or less;   iron and unavoidable impurities; and   optionally at least one of
 Ni: 2% or less, 
 Cu: 0.50 or less, and 
 B: 0.005% or less, 
   wherein a grain size number of the spring steel wire rod after quenching is 7.5 or above.   
     
     
         11 . The spring steel wire rod according to  claim 1 , comprising:
 Si: 2.01-3.5%,   
     
     
         12 . A method for manufacturing a spring excellent in corrosion fatigue property, the method comprising:
 hot-coiling the spring steel wire rod of  claim 8 :   quenching; and   setting thereafter while omitting tempering.