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Abstract

Disclosed is a steel pipe for oil cylinder and a manufacturing method therefor. In addition to 90 wt % or more of Fe and inevitable impurities, the steel pipe for oil cylinder further comprises the following chemical elements in wt %: C: 0.16-0.3%, Si: 0.15-0.5%, Mn: 1.2-1.8%, Nb: 0.02-0.04%, Mo: 0.1-0.2%, and optionally Ti: 0.015-0.03% and B: 0.0015-0.0035%. According to the present invention, after tension reduction and quenching of the steel pipe, different stepped cooling processes are adopted respectively, the distribution of phase change and thermal stress in the whole wall thickness of the steel pipe for oil cylinder is controlled by increasing the rigidity and straightness level of the steel pipe, the distribution of ferrite in the microstructure of the steel pipe for oil cylinder is controlled, the residual stress of the steel pipe for oil cylinder is effectively reduced, cracking of the inner wall is avoided, and therefore the steel pipe for oil cylinder with high strength and low residual stress is obtained. The steel pipe for oil cylinder has a yield strength of greater than or equal to 600 MPa, a tensile strength of greater than or equal to 730 MPa, and a residual stress of less than or equal to 50 MPa.

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First Claim