RAL of Northeastern University: Help large thickness crack stop steel to achieve 100% domestic production
Time: 2022-06-30 Browse: 375
The world's largest 24,000 TEU super large container ship was delivered in Shanghai recently, and several of the same class container ships are under construction in China at the same time, highlighting the new leapfrog created by China. In a milestone breakthrough in China's shipbuilding industry, the State Key Laboratory of Rolling Technology and Continuous Rolling Automation (RAL) of Northeastern University has made its own contribution to the comprehensive domestic production of large thickness and high cracking toughness steel plates (crack cracking steel) for very large container ships.
▲ The world's largest 24,000 TEU super large container ship delivery
The large thickness crack stop steel is mainly used in the middle of the hull, the top hatch roof and the upper deck side plate and other key parts, which can ensure the safety of the hull structure, resist the propagation of large brittle cracks, and prevent the occurrence of catastrophic accidents. However, it is very difficult to produce crack arresting steel for ships with large thickness, high strength and excellent cracking toughness. 1) The production of extra-thick steel plate with continuous casting billet has the restriction of insufficient rolling compression ratio; 2) The deformation penetration and post-rolling cooling are uneven in the thickness direction of the steel plate; 3) Low final rolling temperature greatly tests the rolling force and torque limits of plate mill.
▲ The application of large thickness crack steel position
In 2013, the International Classification of Shipping Society put forward the crack arresting performance index of −10 °C crack arresting toughness ≥6000 N/mm3/2, and required the new container ships to adopt 50~75 mm thick crack arresting steel plate −10 °C crack arresting toughness ≥6000 N/mm3/2. In 2021, 80~100 mm thick steel plate with 10 °C cracking toughness ≥8000 N/mm3/2 was included into the international standard, which greatly raised the technical threshold for the production of extra-thick crack stopping steel plate. Before 2020, only Japan JFE Company can produce 100 mm thick EH47 crack stop steel with crack stopping toughness ≥8000 N/mm3/2, and the production technology is strictly confidential. Domestic only with the level of products production of maximum thickness of 92 mm, and 10 ° C - crack arrest toughness ˂ 8000 N/mm3/2, crack arrest domestic steel products and the international advanced level in obvious gap.
In this context, Northeastern University, in cooperation with Nanjing Iron and Steel Co., LTD., developed EH40 and EH47 crack stop steel plates with thickness of 50~92 mm series in 2018. In 2020, based on the deep understanding of the nature of large-thickness crack stop steel, the new U-Rolling Rolling process with full-thickness microstructure refinement, homogenization and texture control as the core and the fracture mode of crack tip "multi-peak" distribution were proposed, guiding Nanjing Iron and Steel to take the lead in developing 100 mm thick EH47 and EH40 crack stop steel plates in China. −10 °C crack cracking toughness of 9041 and 9951 N/mm3/2, thickness specifications and crack cracking toughness have reached the world's leading level, completely breaking the foreign high crack cracking toughness steel plate technical barriers.
▲ Develop the "multi-peak" distributed fracture mode of steel plate crack tip and the "single-peak" distributed fracture characteristics of traditional process
At present, Nangang 50~95 mm thick EH40, EH47 crack stop steel has been applied to many of the world's largest 24000 TEU container ships, and has realized the world's only supply of 100 mm thick crack stop steel.
▲ The development of 100 mm thick crack steel national debut
The ongoing COVID-19 pandemic has reduced the efficiency of global shipping, resulting in tight shipping capacity and soaring freight costs. The pandemic pressure has led to a global "ship buying fever". In 2021, China's shipbuilding completions, new orders and orders in hand accounted for 47.2%, 53.8% and 47.6% of the world's total in terms of deadweight tons respectively, continuing to lead the world and further enhancing its international competitiveness. According to statistics, the rapid growth of domestic shipbuilding industry will continue. With the rapid development of shipbuilding industry, there will be a great demand for high technology crack stop steel plate with thickness above 90 mm. At the same time, the ongoing global coronavirus pandemic has disrupted global supply chains and disrupted shipments of imported goods. In this context, relying on independent innovation and accelerating research on core and key technologies has become an opportunity to gradually improve the domestic industrial chain and support the sustainable development of China's shipbuilding industry. China's super large container Marine crack steel to achieve 100% domestic production in the crisis is the best proof, indicating that China's super thick crack steel technology has realized the role of "follow, run, and then lead", among the international advanced ranks, reflects China's first-mover advantage in creating a new height.
▲ The continuous rapid growth of domestic shipbuilding industry in the next five years
RAL creatively developed the NEU-Rolling rolling process, which refines the effective grain of the full thickness of ultra-thick steel plate and breaks through the constraint of low compression ratio between continuous casting billet and plate thickness. Related technologies can be applied to other products that have requirements on cracking performance, such as water and electricity, containers, etc., to solve the key common problems that restrict the development of high strength toughness extra thick steel plate in China's iron and steel industry.
In recent years, RAL has carried out research on high quality and low cost green rolling technology and high quality iron and steel materials for the development of the metallurgical industry, providing a large number of original theories and key technology reserves for technical innovation in the field of rolling, and is the core force for China to realize the "follow up" to "lead" in the field of rolling.
