Rolled steel rebars, also known as deformed bars, are some of the most common steel construction products. They are used in masonry and concrete applications, and are the standard reinforcement material employed in concrete. Generally, the cold-rolled steel bars, also known as ribbed steel bars, are obtained from hot-rolled, heat-treated round bars which develop a slightly textured and ribbed pattern along their length, providing superior grip and shear resistance for superior bond strength to concrete.
The process of cold-rolling steel is also known as work hardening, which makes the steel harder and possesses higher tensile strength. In the process of cold-rolling, the steel bar passes through two consecutive forms of rollers - a pre-shaping roller and a finishing roller. Cold rolled bars present an only slightly less ductile steel that meets the requirements of Hot-Rolled bars.
Various International standards are implemented to ensure that the cold-rolled steel bars throughout the world are of the highest quality and certified for industrial applications. Mostly, Asia uses the Japanese Industrial Standard and European countries usually adhere to the British Standard, BS 4449. Other European countries including the United Kingdom have adopted Eurocode 4 specifications, which covers the steel rebars with deformed profiles.
Generally, rolled steel rebars are available in several grades, such as Fe 415, Fe 500, Fe 550, and Fe 690. Fe 415 is a mild-grade that mostly comes in 8-mm diameter and is suitable for lighter duties, while Fe 500 is a mid-level grade which is made available in 10 and 12-mm diameter and are mostly suitable for medium and heavier duties. The Fe 550 and Fe 690 grades are available in 12-mm and 20-mm diameter, respectively, and are ideal for the heavy-duty constructions.
Rebar steel is also classified based on their origin. China has a classification of HRB400, Russia has a classification of A-III, and UK classifies them as BS 4449. Usually, the rebar steel can be of low carbon steel, high-yield steel, and high-durability steel. Low carbon steel is the most commonly used material for constructing reinforcement applications with a small stress. High-yield steel is often used in compression applications with high stresses and easily burst. The durability steel is used in applications that require high-strength assets and possess low shrinkage potential.
In terms of thermal treatments, cold-rolled steel bars are also typically heat-treated with a hot-rolled type of process. It is a process of annealing, which is performed at a temperature below the solidification point, with the aim to recrystallize and adjust the mechanical properties of the steel. Stress-relief annealing helps to reduce the internal tension and improves the dimensional stability of products. Also, after the deformed steel bars are produced they must be cut to length. Generally, this is done using shearing machines, hydraulic cutting tools and other automated methods.
In conclusion, cold-rolled steel rebars are a common product deployed in concrete and masonry applications as reinforcement materials. These versatile materials are available in various grades, depending upon the application needs and certifications. Furthermore, most cold-rolled steel bars are heat-treated after production, with specific thermal treatments imparting strength and stability to the bars. By following the steel quality standards and industry guidelines, manufacturers have been able to produce high-quality rolled steel bars for many years.
