Ultra-high strength hull and offshore platform steel with yield strength of 550 Mpa and production method thereof

The invention relates to ultra-high strength hull and offshore platform steel with the yield strength of 550 Mpa and a production method thereof. The steel provided by the invention is characterized in that its chemical components contain, by weight, 0.04-0.07% of C; 0.3-0.5% of Si; 1.45-1.60% of Mn; P being less than or equal to 0.02%; S being less than or equal to 0.005%; 0.25-0.4% of Cr; 0.6-0.8% of Ni; 0.2-0.3% of Mo; 0.04-0.06% of V; 0.6-0.8% of Cu; 0.015-0.045% of Als; and the balance being Fe and impurities. According to the production method, two phases during the rolling process are adopted to control rolling and cooling so as to obtain lath-shaped bainite and ferrite microstructure. In comparison with the prior art, the invention has the following advantages: on the basis of satisfying correlated component range of national standard FH550 steel, low C content design is adopted so as to enhance microalloy element and endow the steel with good welding performance and corrosion resistance.