Low-yield-ratio ultrahigh-strength coiled tubing steel and manufacturing method thereof

The invention discloses low-yield-ratio ultrahigh-strength coiled tubing steel and a manufacturing method thereof, and relates to the technical field of coiled tubing steel. The invention relates to low-yield-ratio ultrahigh-strength coiled tubing steel and a manufacturing method thereof,. The steel comprises the following chemical components in percentage by weight: 0.1-0.15% of C, 0.3-0.4% of Si, 1.5-2% of Mn, less than or equal to 0.015% of P, less than or equal to 0.002% of S, 0.5-0.7% of Cr, 0.2-0.5% of Mo, 0.05-0.07% of Nb, 0.05-0.08% of V, 0.01-0.02% of Ti, less than or equal to 0.70% of Ni + Cu, 0.02-0.04% of Als and the balance of Fe and inevitable impurities. According to the chemical components, molten iron pretreatment, converter smelting, external refining, continuous casting, slab cleaning, slab heating, controlled rolling, controlled cooling and coiling are conducted, deformation, temperature and cooling speed are controlled, then a uniform and fine F + M double-phase structure is formed, and l