High-strength and high-toughness oil casing and manufacturing method thereof

The invention discloses a high-strength and high-toughness oil casing and a manufacturing method thereof. A 'HFW(High Frequency Welding)+welding line on-line thermal treatment+hot tension reducing+whole casing thermal treatment' technology is used for manufacturing a Q125 steel grade oil casing, and the weight percentage of chemical components are as follows: C: 0.18-0.30; Sh: 0.10-0.35; Mn: 1.00-1.30; P: not more than 0.018; S: not more than 0.008; Cr: 0.20-1.20; Mo: 0.20-0.55; Nh: 0.10-0.56; B: 0.0010-0.0015; Nb+V+Ti: not more than 0.08; and the balance of Fe and unavoidable impurities. For the Q125 oil casing produced by the manufacturing method, the yield strength is not less than 865MPa, the tensile strength is not less than 940MPa, the specific elongation is not less than 23.2%, at 0 DEG C, the full-scale transverse impact energy is not less than 105J and the longitudinal impact energy is not less than 110J. The Q125 steel grade oil casing produced by the technology is excellent in comprehensive performance, and has excellent high toughness and high plasticity.