| 摘要 |
PROBLEM TO BE SOLVED: To provide a hollow seamless steel pipe for high strength spring which allows a spring molded therefrom to stably secure sufficient fatigue strength.SOLUTION: The hollow seamless steel pipe for spring contains, by mass%, C:0.2 to 0.7%, Si:0.5 to 3%, Mn:0.1 to 2%, Cr:over 0% and 3% or less, Al:over 0% and 0.1% or less, P:over 0% and 0.02% or less, S:over 0% and 0.02% or less, N:over 0% and 0.02% or less and the balance iron with inevitable impurities and has a maximum value of a thickness deviation rate calculated by the following formula (1), an inner surface flaw depth and an inner total decarbonization depth of 7.0% or less, 50 μm or less and 100 μm or less respectively over a total length of the steel pipe. Thickness deviation rate=(maximum thickness-minimum thickness)/[(maximum thickness+minimum thickness)/2]/2×100 (1).SELECTED DRAWING: Figure 5 |
