How to Improve the performance of anti-fracture of the shipbuilding steel ?

Posted: 9/4/2011 11:28:21 PM

In order to meet reliability requirements to improve resistance to fracture, the steel takes a long time to develop a high strength and toughness of steel, and has improved its manufacturing process, especially from the 1960s began to develop a controlled rolling method . By 1980, Japan with practical opportunity for the world to promote the use of accelerated cooling (the rolling method of control combined with accelerated cooling method referred to as TMCP), so that the strength of the matrix plate, a substantial increase in toughness. In addition, according to the TMCP process, the same level of intensity of the plate, due to the reduction of carbon equivalent, can be free warm-up welding to improve the weldability of steel, the ship manufacturing productivity greatly improved. Reduction in carbon equivalent, but also heat affected zone (HAZ) toughness greatly improved.
Because most of brittle cracks in welded joints, so to prevent the outward expansion of cracks along the welded joint is very important. In the past, thickness 40 mm below the shipbuilding steel welded joints on large-scale crack performance test, by the welding residual stress and other factors, can extend along the welded joints of brittle crack extension to the base metal side of the stop . However, the situation is different with the thin steel plate for thickness exceeding 40 mm thick steel plate, the same large-scale trial found that cracks along the welded parts of the body to the base expansion, the crack propagation did not stop. In addition, there is no welding on the part of the Department of the matrix test, also found that crack propagation occurred. In order to prevent brittle crack propagation, the greater the thickness, the higher the required steel with Charpy impact energy.
According to the study of crack for the high performance of shipbuilding steel, the surface grain size of 2 microns of fine-grained plate (HIAREST steel) has been achieved commercially. This steel has a temperature of -10 �� over 10000N/mm1.5 (thickness 25mm) high Charpy impact energy of the crack performance. Using a special manufacturing process, can produce the maximum thickness of 50mm shipbuilding plate. For the manufacture of very large container ships, it is necessary to develop high-strength high-thickness crack of steel. To meet this demand, the yield strength (YP) to 460N/mm2, high performance crack shipbuilding steel EH47 realized commercially. Thus, the use of TMCP technology to achieve organizational refinement, while the base metal, HAZ organizations control the use of technology, more than 50mm thickness of steel plate for a one-time large heat welding. This plate is in the iron and steel and shipbuilding enterprises on the basis of development cooperation.