Microstructure and mechanical properties of 420-550Mpa grade heavy gauge offshore platform steel

Extra high strength off-shore platform plate steels have been developed in An-steel and obtained the certification of nine country specification institutes. The high performance heavy gauge plate steel was manufactured by ultra low carbon, Nb-bearing microalloying approach and optimized Thermomechanical Control Process (TMCP). It shows that 0.03-0.05% carbon content Mn-Nb system (with low alloy Cr, Ni, Cu, Mo) can meet the strength of 420MPa, 460MPa, 500MPa and 550MPa grade with excellent toughness at -60°C. The low carbon approach can also obtain the homogeneous intermediate transformation structure of acicular ferrite and/or bainite at a wide cooling rate range for the heavy gauge plate during on-line accelerated cooling. (AU)