1. US20160122844 - HT550 steel plate with ultrahigh toughness and excellent weldability and manufacturing method of the same

An HT550 steel plate with ultrahigh toughness and excellent weldability and a manufacturing method thereof are disclosed. Based on a component system with ultralow-C, high-Mn, Nb-microalloying, ultramicro Ti treatment, Mn/C is controlled in the range of 15˜30, (% Si)×(% Ceq) is less than or equal to 0.050, (% C)×(% Si) is less than or equal to 0.010, (% Mo)×[(% C)+0.13(% Si)] is in the range of 0.003˜0.020, the ratio Ti/N is in the range of 2.0˜4.0, the steel plate is alloyed with (Cu+Ni+Mo), Ni/Cu is greater than or equal to 1.0, Ca treatment is performed, and Ca/S is in the range of 0.80˜3.00; by optimizing TMCP process, the steel plate has microstructures of fine ferrite plus self-tempered bainite with an average grain size being less than or equal to 15 μm, yield strength being 460 MPa or more, tensile strength being 550˜700 MPa, yield ratio being 0.85 or less, and −60° C. Charpy impact energy (single value) being 60 J or more; therefore, the steel plate is capable of bearing large thermal input welding while obtaining uniform and excellent strength, toughness, and strong plasticity matching, and is especially suitable for sea bridge structures, ocean wind tower structures, ocean platform structures and hydroelectric structures.