Fracture, deformation route, and mechanical performance of welded cold-formed ultra-high strength steel S1100

Abstract

This study investigates the influence of cold-forming on the weldability and fracture behavior of ultra-high strength steel S1100. The mechanical performance and fracture of such steels while simultaneously subjected to cold-forming and welding still require further research, although cold-forming and welding have crucial roles in fabricating economical structures with relatively acceptable strength-to-weight ratios. Hence, S1100, as a thermomechanically processed ultra-high strength carbon steel, was subjected to bending with different radii (representing various levels of cold-forming) and welded with gas-metal arc welding. Next, the strength, ductility, and toughness of the welded samples were evaluated using tensile tests. In addition, digital image correlation was used with the tensile tests to study the plasticity and final failure. Further, macrographs by optical microscopy and fractography by scanning electron microscopy were utilized to investigate the fracture locations and mechanisms of the welded joints. The results confirmed the reliability of the welded joints in steel structures, and the fracture of the welded material was identified as ductile, regardless of its cold-forming degree. Heat-affected zone softening, as a common drawback associated with welded ultra-high strength steel, did not adversely affect the fracture mechanism of welded S1100, even in its cold-formed state.