| 摘要 |
PROBLEM TO BE SOLVED: To provide a high strength steel used for spring steel that has excellent hydrogen embrittlement resistance. SOLUTION: The high strength steel which spring steel having excellent hydrogen embrittlement resistance comprises 0.20 to 0.60% of C, 1.0 to 3.0% of Si, 1.0 to 3.5% of Mn, higher than 0% and not higher than 1.5% of Al, 0.15% or less P, 0.02% or less S, and balance of iron and inevitable impurities and the structure includes: 1% or more residual austenite; 80% or more of the total of bainitic ferrite and martensite; and 10% or less (including 0%) of the total content of ferrite and pearlite in the proportion of area to the entire structure, and also the mean axis ratio (major axis/minor axis) of the residual austenite grains is 5 or higher and the steel tensile strength is 1,860 MPa or higher. COPYRIGHT: (C)2007,JPO&INPIT
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