High strength spring-use heat treated steel

Abstract

The present invention provides spring-use heat treated steel which is cold coiled, can achieve both sufficient atmospheric strength and coiling workability, has a tensile strength of 2000 MPa or more, and can improve the performance as a spring by heat treatment after shaping the spring, that is, heat treated steel for high strength spring containing, by mass %, C: 0.45 to 0.9%, Si: 1.0 to 3.0%, Mn: 0.1 to 2.0%, V: over 0.1 to 1.0%, N: limited to 0.007% or less, and a balance of Fe and unavoidable impurities, and satisfying, in terms of the analyzed value of the extracted residue after heat treatment, [amount of V in filtrate filtered by 0.2 μm filter (mass %)]≧[amount of V in steel (mass %)]×0.4.

1 . Spring steel characterized by
 containing, by mass %,   C, 0.45 to 0.9%,   Si: 1.0 to 3.0%,   Mn: 0.1 to 2.0%,   V: over 0.1 to 1.0%,   N: limited to 0.007% or less, and   a balance of Fe and unavoidable impurities, and   satisfying, in terms of the analyzed value of the extracted residue after heat treatment,
   [amount of  V  in filtrate filtered by 0.2 μm filter(mass %)]≧[amount of  V  in steel(mass %)]×0.4. 
   
   
   
       2 . Spring-use heat treated steel wire as set forth in  claim 1  characterized by further containing, by mass %, one or more of
 Cr: 0.5 to 2.5%,   Nb: 0.001 to less than 0.05%,   Ti: 0.001 to less than 0.05%,   W: 0.05 to 0.5%,   Mo: 0.05 to 0.5%,   Ta: 0.001 to 0.5%,   Ni: 0.05 to 3.0%,   Cu: 0.05 to 0.5%,   Co: 0.05 to 3.0%,   B: 0.0005 to 0.006%,   Te: 0.0002 to 0.01%,   Sb: 0.0002 to 0.01%,   Mg: 0.0001 to 0.0005%,   Zr: 0.0001 to 0.0005%,   Ca: 0.0002 to 0.01%, and   Hf: 0.0002 to 0.01%.   
   
   
       3 . Spring-use heat treated steel wire as set forth in  claim 1  characterized further by restricting, by mass %, Al to 0.005% or less. 
   
   
       4 . Heat treated steel for a high strength spring said characterized by having the steel ingredients as set forth in any one of  claim 1 , having a prior austenite grain size number after quenching and tempering of #10 or more, and having residual austenite in an amount of 15 mass % or less.