HOLLOW SEAMLESS PIPE FOR HIGH-STRENGTH SPRING

摘要

PROBLEM TO BE SOLVED: To provide a hollow seamless pipe for high-strength spring, in which the generation of decarburizing at the internal surface layer of the pipe is reduced to the utmost, and sufficient fatigue strength can be secured in the spring to be molded by controlling the shape of flaws existing on the internal surface.SOLUTION: A hollow seamless pipe for high-strength spring comprises a steel material whose chemical component composition is properly adjusted. The depth of the whole decarburized layer in an internal surface layer is ≤100 μm, the depth of the flaws existing on the internal surface is ≤40 μm, and the width of the flaw is ≤60 μm. Further, the number density of carbides having a diameter equivalent to circle of ≥500 nm present in the internal surface is ≤1.8×10piece/μm.