Continuously increasing demands placed on work loads of constructions and special vehicles or the lifting capacity of high-performance cranes, combined with efforts to limit their weight, have raised the need to develop high-strength steel grades for their construction. In many cases these constructions and cranes are in service under low temperature conditions. For this purpose square and rectangular hollow sections basing on a fine-grain alloying concept have been developed. Due to their microstructure, these hollow sections possess high yield strengths and high impact values even at low temperatures. In addition, they provide superior processability in terms of direct welded joints due to their edge geometry. Therefore, these sections are perfectly qualified for the construction of structures and frames dedicated for high working loads and low temperature services such as arctic operating conditions. Particular attention must be payed on the development of proper weld procedures for fabricating structural components from these alloys. This paper will address the material design, examine the weldability of fine-grained, high-strength hollow sections which possess yield strengths of 690 MPa and 890 MPa (~ 100 and 130 ksi). The focus will be on the manufacturing process, base material properties, weldability and some application examples. As applications an innovative new foundation system for offshore wind turbines (PREON marine), lifeboat systems and subsea oil & gas field development hardware are presented.

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