ADVANCED MATERIALS & PROCESSES | MAY 2026 34 Steel rebars are often used to reinforce concrete structures by providing tensile strength and ductility. Typical applications include bridges, tunnels, building foundations, pillars, and other infrastructure projects. The rebars are produced from the raw iron material or by melting steel scraps in electric arc furnaces. Generally, the properties of steel rebars, such as yield and ultimate tensile strength, ductility, bending properties, rib surface, diameter variation to the nominal value, re- sistance to fatigue, and weldability are tested at the production plants, where the parameters may vary within the 5-10% fractile of the total produced rebar’s amount[1-4]. A thermomechanical treatment called Tempcore is used to improve the mechanical properties of the rebars, creating a microstructural gradient across the rebar’s section. Yield strength depends on the volume of the phases formed during the process[2,5]. However, because the production of steel rebars occurs worldwide, the quality, treatments, and microstructure of steels that meet the specified mechanical parameters may differ, depending on the country. REBARS ON SITE The quality of the steel rebars supplied at a construction site may vary slightly from the requirements. Yield strength and ductility are generally achieved, although chemical composition and ductility may vary[6]. The rebar’s treatment during production STEEL REBARS MEET STRENGTH AND DURABILITY DEMANDS A special treatment used in steel rebar production addresses the need for improved mechanical properties and corrosion protection. Christian Paglia,* Institute of Materials Construction, Mendrisio, Switzerland *Member of ASM International affects the border-core microstructure differently. In addition, corrosion sus- ceptibility is influenced by rebar treatments (Fig. 1). Therefore, a quality inspection on site is necessary. During service life, rebars are embedded within the concrete. Nonetheless, exposure to the atmosphere may promote a decrease in pH due to carbonation or a localized chloride attack—particularly along the degra- dation-sensitive zones. MECHANICAL PROPERTIES AND CORROSION A cost-effective Tempcore treatment is often used to attain the desired mechanical properties. The rolled rebars are rapidly quenched with water to obtain a martensitic outer surface layer and a ferrite-perlite core. The heat flux from the core to the outer surface causes a tempering of the martensite to reduce its brittleness[2]. In this manner, steel rebars with a relatively Fig. 1 — Corrosion sensitive zones along the rebar’s ribs (left) and the curvatures (right). Steel rebars with a yield strength limit class of 500 MPa. Fig. 2 — Scanning electron microscope image (backscatter electron mode) of a polished cross-section of a steel rebar tested under tension close to the highly deformed rupture zone and brittle breakage of the MnS inclusions (top). Steel rebar B500C tempered martensite (center); transition zone to the ferritic-perlitic core (bottom)[1].
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