High strength spring-use heat treated steel
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.