The steel plates used for polar icebreaker and polar transport ships have been developed sufficiently in HBIS Steel group. The steel is designed to be micro-alloyed only by Nb and Ti, low carbon equivalent. Oxide metallurgy is applied. The microstructure of the steel plate is controlled to be a mixed microstructure of low carbon bainite and ferrite. The toughness of WM and HAZ are excellent after welded with a large heat input of 300 kJ/cm. The developed steel plate could meet the requirements of large heat input welding during the building process.
The Yamal liquefied natural gas (LNG) project energy base is located in cold Russian Arctic Yamal peninsula, a large cold area covered by snow and ice. The base has been proven rich of natural gas up to 955 trillion cubic meters. The development of the Yamal project requires a large number of polar icebreaker and polar transport ships. In China, there is very little manufacture experience with polar icebreaker and polar transport ships. The steels used on the polar ships requires excellent mechanical properties, especially excellent low temperature toughness.
On the other hand, Welding is the longest step in the manufacture of polar icebreaker and polar transport ships and consumes most of the time in the ship construction. The efficiency level of welding not only affects the construction costs, but also directly determines the delivery cycle of the ship. In recent years, large heat input welding method has been used widely in shipbuilding industry (Wang et al., 2000; Katsuyuki et al., 2005; Katsuyuki et al., 2004), which can improve the Welding efficiency extremely. The heat input of welding can reach a high value of 300kJ/cm, and the welding efficiency can be increased more than 10 times. The large heat input welding methods include FCB (Flux Copper Backing) multi-wire submerged arc welding, gas-electric vertical welding, electroslag welding, etc.
