Continuous hot rolled coil for high collapse-resistant sew petroleum casing and manufacturing method thereof

A method of manufacturing a continuous hot rolled coil for a high collapse-resistant SEW petroleum casing, said method comprising:

• providing a continuous cast slab for use as an initial billet;
• subjecting the continuous cast slab to rough rolling by refined grains for 5-7 passes under a temperature-controlled heating condition to form an intermediate billet;
• subjecting the intermediate billet to finish rolling for at least 4 passes, and
• cooling and coiling the intermediate billet after the finish rolling to provide the continuos hot rolled coil,
• wherein;
• a deformation of the initial billet must be not less than 18% in each pass where the initial billet is subjected to the rough rolling by the refined grains;
• the intermediate billet subjected to the finish rolling is 3.8-4.2 times thicker than the continuous hot rolled coil;
• the cooling of the intermediate billet before coiling is air cooling;
• the continuous hot rolled coil comprises the following chemical components in parts by weight:
• 0.22-0.32% of C, 0.10-0.30% of Si, 1.10-1.40% of Mn, 0.30-0.60% of Cr, ≤0.020% of P, ≤0.010% of S, 0.008-0.019% of Ti, Fe and inevitable impurities;
• an initial yield strength of the continuous hot rolled coil is 340-360 MPa;
• an initial tensile strength of the continuous hot rolled coil is 620-640 MPa;
• a yield strength of the continuous hot rolled coil after quenching and tempering is 840 Mpa-910 MPa;
• and
• a tensile strength of the continuous hot rolled coil after quenching and tempering is 940-1030 MPa.