Weldability of cold-formed high strength and ultra-high strength steels

Hollow sections and cold-formed steels have a key role in modem structures and machinery. In addition, to benefit from full potentials of cold-formed steels, it is usually required to weld them to other steel parts of structures. However, data provided by relevant standards, such as Eurocode 3, do not cover newly developed high strength and ultra-high strength grades of this material. Thus, further study is critical to complete available data in literature and standards. Regarding this matter, having a good weldability for cold-formed high and ultra-high strength steels is vital for development of contemporary steel structures. Thus, newly developed steels S700MC and S1100 were selected to be investigated in this study. To do so, bended base metals with different degrees of cold-forming were welded to their straight (virgin) counterparts. Next, welded joints were investigated via microstructural analysis, hardness measurement, tensile test, and Charpy impact test to assess the weldabilities of the cold-formed base metals. Results show that the final joints had acceptable characteristics, and the cold-formed base metals showed good weldability. However, bending and pre-straining criteria recommended by the manufacturer must be satisfied to have an acceptable joint after welding. Beyond that criteria, fracture elongation and notch toughness of the welded joints decreased, and some welded samples failed from their cold-formed base metals. (C) 2019 Elsevier Ltd. All rights reserved.