(1) Multi-functional varieties: steel plates for offshore platforms can be supplied in series, such as high-strength steel plates, large-line energy welding steel plates, low-temperature and seawater corrosion resistant steel plates and other series of varieties, to achieve a full range of supply.
(2) Welding heat affected zone toughening technology: Foreign steel enterprises have developed their own unique welding heat affected zone toughening technology, such as JFE Company's JFE-EWEL technology and Nippon Steel Company's HTUFF technology.
(3) The formation of unique standards for enterprises: In addition to foreign steel enterprises can produce steel plates for offshore platforms according to common standards, they have also formed enterprise standards with more stringent performance requirements and more special application environment.
(4) Implementation of patent protection strategy: foreign steel enterprises actively carry out the international patent layout of offshore platform steel, paying special attention to applying for patents in China, with the intention of forming technical barriers to Chinese steel enterprises and achieving the purpose of reducing the competitiveness of China's offshore platform steel.
In addition, the offshore platform structure is a very large welding structure, which has more stringent requirements for the welding performance of steel, so the relevant standards stipulate that the upper limit of Mn content of high-strength and ultra-high-strength offshore steel is generally 1.60% to prevent the danger of cracking during hot rolling and cooling. However, recently, people have a new and deeper understanding of the action mechanism of Mn in steel, and found that Mn has a similar effect on the microstructure and phase transition behavior of steel as Ni. In the early study of using Mn instead of Ni to improve the low temperature toughness of steel, it was found that austenitic steel with Mn content of 18% to 25% has very excellent low temperature toughness, but the strength is relatively low. Later, Niikura and Morris et al. showed that 5Mn steel obtained excellent impact toughness at -196℃ after heat treatment to refine grain size and improve austenite stability. The new Fe-(15-30)%Mn-Al-Si-C high manganese TWIP steel can improve its plasticity (that is, TWIP effect) by adding an appropriate amount of Al or Si to control the stacking fault energy to form deformation twins during cold forming, and its tensile elongation can reach 60%~95%, and the strength can reach 600~1100MPa. In recent years, the addition of 5%-10% Mn in the phase change induced plasticity of TRIP steel has received more and more attention. In the 1970s, Miller conducted research on the low carbon medium manganese TRIP steel of Fe-0.1C-5Mn alloy system, and the stable residual austenite content reached 20% ~ 30% through two-phase zone annealing, and good mechanical properties were obtained.
By "Mn/C" alloying and heat treatment process optimization, the content of stable austenite in steel can be increased, so that the microstructure of steel at room temperature is maintained as "austenite + bainite/martensite", and TRIP or even TWIP effect occurs in residual austenite during subsequent processing. While ensuring strength, It greatly improves the strain hardening ability, tensile strength and low temperature toughness, and also ensures a low yield ratio, which is not possessed by conventional low-alloy steel products. Foreign countries have accelerated the research and development of "Mn/C" alloy steel thick plate products, and some have come out of the laboratory to reach the industrialization level. For example, South Korea PoSCO recently successfully produced 30mm high-manganese TWIP steel plate in the thick plate hot rolling line. It is expected that "Mn/C" alloyed steel can better meet the safety requirements of deep sea and polar ocean platforms because of its unique performance advantages, and is an important development direction of offshore platform steel.
