Microstructural Heterogeneity and Mechanical Performance of Reinforcing Steels from Liberia and Côte d’Ivoire: A Comparative Multi-Scale Investigation

Abstract

The quality of reinforcing steel bars is a major concern in developing countries where structural failures and building collapses continue to occur. This study presents a comparative investigation of reinforcing steels commercialized in Liberia and Côte d'Ivoire, focusing on the relationships between chemical composition, microstructural features and mechanical performance. Twenty-four steel samples obtained from SETHI Ferro Fabrik (Liberia) and SOTACI (Côte d'Ivoire) were characterized using Optical Emission Spectroscopy (OES), tensile testing, optical microscopy, scanning electron microscopy (SEM) and microhardness measurements. Results revealed heterogeneous layered microstructures composed of case, intermediate and core regions. The case regions were characterized by martensitic and bainitic structures, while the core regions consisted mainly of ferrite and pearlite. Liberian steels exhibited higher yield strength (533–600 MPa) than Ivorian steels (431–509 MPa). Hardness profiles showed maximum values near the surface and decreasing values toward the core. Grain refinement, martensite formation and higher dislocation densities contributed significantly to the superior mechanical performance observed in Liberian steels. The study demonstrates that reinforcing bars marketed in West Africa exhibit significant cross-sectional heterogeneity that cannot be detected through conventional bulk mechanical testing alone. These findings provide valuable information for quality control, steel certification and the development of construction standards aimed at reducing structural failures in the West African region.