The Quest for Better Structural Steels

Structural steel grades are widely used in civil engineering applications in various product forms (bar or plates). Through the years focus is laid on how to obtain higher strength in combination with improved impact properties. In parallel, properties such as bendability and weldability are also considered. In this way, constructions comply with raising demands on improved performance under extreme conditions. A good way to achieve this is through the modification of phase transformations. This was achieved either via the Tempcore process, by which a martensitic and/or bainitic microstructure is obtained in the outer surface of the reinforcing bar. This high strength microstructure increases yield strength but reduces albeit ductility. Thus, its volume fraction has to be controlled. The ferritic/pearlitic core of the rebar is responsible for obtaining satisfactory elongation values. Moreover, microalloying elements such as vanadium (V), niobium (Nb), titanium (Ti) are added in steels to produce finer-grained microstructure, which increases the yield strength obeying the Hall – Petch equation while preserving higher elongation values. Nowadays, the need for tailored, more homogeneous microstructures with improved mechanical and technological properties, pave the way for the utilization of micro-alloyed steel bar and plate products.